JP6783368B1 - Sheet for metal processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal processing sheet capable of producing a metal processing sheet excellent in storage stability without causing deterioration of the metal layer with time. The metal processing sheet of the present invention can be used as the base sheet when manufacturing a metal processing sheet in which a metal layer is provided on the surface of the base sheet. The sheet for metal processing of the present invention includes a fiber sheet and a specific anion. The specific anion is one or more selected from the group consisting of nitrate ion, acetate ion, sulfate ion, phosphate ion, monohydrogen phosphate ion and dihydrogen phosphate ion. The specific anion measured according to the ion chromatograph method JIS K-0127: 2013, which elutes when the metal processing sheet having an absolute dry weight of 5 g is immersed in distilled water at a liquid temperature of 20 ° C. for 24 hours. The total concentration of the metal processing sheet is 1600 ppm or more with respect to the absolute dry weight of the metal processing sheet. [Selection diagram] None

Description

The present invention relates to a metal processing sheet that is useful as a raw material for a metal processing sheet.

The metal processed sheet is a sheet-like material having a metal layer on the sheet surface, and is typically manufactured by subjecting a base sheet such as paper to metal processing such as foil stamping printing of metal foil or gold ink printing. To. The metal processed sheet is widely used for posters, calendars, catalogs, labels, packages, etc. because it has a unique luster due to the metal layer and is excellent in cosmetics. In particular, black metal-processed sheets have both beauty and luxury and can create a high-class image, so they are mainly used for applications that require beauty and luxury, such as pasting box paper and card paper. ing.

Patent Document 1 discloses a black multilayer paper using carbon black as a colorant as a black metal processed sheet. The black multilayer paper described in Patent Document 1 has inconveniences caused by carbon black and residual chlorine ions, for example, poor transferability of thermal transfer foil, deterioration of adhesiveness during foil stamping printing, dust generated at a manufacturing site, and the like. From the viewpoint of preventing fouling due to the adhesion of fine particles, the carbon black content, surface electrical resistance value, residual chlorine ion concentration, etc. are set in specific ranges.

JP-A-2019-127671

The conventional metal processed sheet has room for improvement in terms of cosmeticity. Further, according to the knowledge of the present inventor, the metal processed sheet has a problem of storage stability due to deterioration of the metal layer with time, as will be described later. The technology that can solve these problems has not yet been provided.

An object of the present invention is to provide a metal processing sheet capable of producing a metal processing sheet which is less likely to deteriorate with time and has excellent storage stability.

Aluminum is widely used as a material for a metal layer in a metal processed sheet. As a result of various studies on this general-purpose metal processed sheet by the present inventor, the metal layer (aluminum) deteriorates over time due to chloride ions (Cl ⁻ ) contained in the sheet, and pitting corrosion occurs in the metal layer. There was found. It was also found that when carbon black is contained in the metal processed sheet, carbon black can cause pitting corrosion of the metal layer. Pitting corrosion significantly reduces the cosmeticity of the metal processed sheet, and its prevention is desired.

As a method of preventing pitting corrosion of the metal layer in the metal processed sheet, a method of reducing the content of chloride ions and carbon black, which are causative substances, can be considered. However, since the chloride ions contained in the metal processed sheet are typically derived from chlorine bleached pulp commonly used in this type of sheet, when it comes to reducing chloride ions, the metal processed sheet As a result, inconveniences such as deterioration of whiteness of the sheet and yellowing of the sheet with time may occur, which may lead to deterioration of cosmetics. In addition, chloride ions are abundant in the environment and are also contained in, for example, the bonding glue of the pasting box used when the metal processing sheet is used as the pasting paper, so before and after the metal processing. Since chloride ions may be mixed into the sheet to be processed, it is not sufficient as a countermeasure against pitting corrosion of the metal layer only by devising measures to reduce chloride ions in the sheet to be processed. Further, in this type of sheet, chloride such as sodium chloride may be added as an antistatic agent in order to prevent contamination due to adhesion of fine particles such as dust generated at the manufacturing site. Chloride ion If the amount of chloride is reduced, the use of chloride as an antistatic agent will be restricted, and there is a concern about contamination due to adhesion of fine particles at the manufacturing site. Further, when the content of carbon black in the metal processed sheet is reduced, the degree of blackness is lowered, and it becomes difficult to express a glossy and luxurious black color such as lacquer black, which is called jet black, and metal. There is a risk of degrading the beauty of the processed sheet.

As a result of various studies to solve the problems peculiar to such a metal processed sheet, the present inventor sets the total concentration of a specific anion such as a sulfate ion in the sheet within a specific range to obtain chloride ion. It was found that pitting corrosion of the metal layer can be effectively suppressed and the storage stability of the metal processed sheet can be improved without reducing the content of or carbon black.

The present invention has been made based on the above findings, and is a metal processing sheet that can be used as the base sheet when manufacturing a metal processing sheet in which a metal layer is provided on the surface of the base sheet, and is a fiber. The sheet contains one or more specific anions selected from the group consisting of nitrate ion, acetate ion, sulfate ion, phosphate ion, monohydrogen phosphate ion and dihydrogen phosphate ion, and 5 g by absolute dry weight. The total concentration of the specific anions measured in accordance with the ion chromatograph method JIS K-0127: 2013, which elutes when the metal processing sheet is immersed in distilled water at a liquid temperature of 20 ° C. for 24 hours, is determined. It is a metal processing sheet having a dry weight of 1600 ppm or more with respect to the absolute dry weight of the metal processing sheet.

According to the metal processing sheet of the present invention, it is possible to produce a metal processing sheet that is less likely to deteriorate over time and has excellent storage stability and can maintain high cosmeticity for a long period of time.

FIG. 1 is an optical micrograph (magnification of 100 times) of a metal layer in an example of a metal processed sheet, and shows a state in which pitting corrosion has occurred in the metal layer. 2 (a) and 2 (c) are diagrams schematically showing an example of the state of pitting corrosion in the metal layer of the metal processed sheet, and are images of evaluation criteria for the storage stability of the metal processed sheet. is there.

The sheet for metal processing of the present invention includes a fiber sheet. The fiber sheet is mainly composed of fibers, that is, a sheet-like material having a fiber content of 50% by mass or more. Typically, the fiber sheet is the main component of the metal processing sheet of the present invention, and it is preferable that the specific anion described later is contained in the fiber sheet.

The fiber contained in the fiber sheet may be a natural fiber or a synthetic fiber. Examples of the constituent fibers of the fiber sheet include coniferous bleached kraft pulp (NBKP), broadleaf bleached kraft pulp (LBKP), coniferous unbleached kraft pulp (NUKP), broadleaf bleached kraft pulp (LUKP), and coniferous bleached sulfite pulp (LBKP). NBSP), wood pulp such as thermomechanical pulp (TMP); other non-wood pulp such as hemp, bamboo, straw, kenaf, sansho, 楮, cotton; modified pulp such as cationized pulp and marcelled pulp; rayon, cupra Regenerated cellulose fibers such as; hydrophilic synthetic fibers such as polyvinyl alcohol fiber and polyacrylonitrile fiber; synthetic fibers made of resin such as polyethylene, polypropylene and polyethylene terephthalate, and one of these may be used alone or in combination of two or more. It can be used in combination.

The form of the fiber sheet is not particularly limited. The fiber sheet may be, for example, a paper, a woven fabric, a non-woven fabric or a resin film, or a composite sheet formed by laminating two or more of these.

A preferred example of a fiber sheet is paper containing wood pulp. The content of wood pulp in the fiber sheet is preferably 50% by mass or more, more preferably 75% by mass or more, based on the total mass of the fiber sheet. The fiber sheet of paper can be produced according to a conventional method using a known paper machine such as a long net type paper machine, a gap former type paper machine, a circular net type paper machine, and a short net type paper machine.

The freeness (CSF) of wood pulp contained in the fiber sheet is not particularly limited, but is preferably 200 to 500 mL, more preferably 300 to 400 mL. Freeness is a value obtained by the Canadian standard form among the drainage test methods for pulp specified in JIS P8121. The freeness can be adjusted by appropriately adjusting the degree of beating of the pulp.

The basis weight of the fiber sheet is not particularly limited, and may be appropriately adjusted according to the intended use of the metal processing sheet. Considering the typical use of the metal processing sheet, the basis weight of the fiber sheet (when the fiber sheet has a multi-layer structure, the basis weight of the multi-layer structure) is preferably 20 to 500 g / m ² , more preferably 50 to 50. It is 300 g / m ² .

The sheet for metal processing of the present invention contains one or more "specific anions" selected from the group consisting of nitrate ion, acetate ion, sulfate ion, phosphate ion, monohydrogen phosphate ion and dihydrogen phosphate ion. It is characterized in that the total concentration of specific anions contained and measured by the following method is 1600 ppm or more with respect to the absolute dry weight of the metal processing sheet. Due to such characteristics, pitting corrosion of the metal layer due to other components contained in the metal processing sheet, typically chloride ions and carbon black, can be effectively suppressed, and the storage stability of the metal processing sheet can be improved. ..

<Measurement method of total concentration of specific anions>
Various ions including specific anions are extracted with cold water from the metal processing sheet to be measured, and the total elution amount of the specific anions contained in the cold water extract is quantitatively analyzed. Specifically, 5 g of a sheet to be measured is prepared by absolute dry weight and used as a sample. Further, as an extraction solvent, 100 mL of distilled water having a liquid temperature of 20 ° C. is prepared. Immerse the entire sample in 100 mL of extraction solvent and allow it to stand for 24 hours. After that, the elution amount of the specific anion eluted in the extraction solvent is quantitatively analyzed by a method based on the ion chromatograph method JIS K-0127: 2013, and the total value of the elution amount of each specific anion is calculated as that of the specific anion. Let it be the total concentration. The measurement conditions of the ion chromatograph method can be set as follows, for example.

<Measurement conditions for ion chromatography>
-Analyzer: Thermo Fisher Scientific, ICS-1100
-Separation column: Thermo Fisher Scientific, AS12A
-Separation column temperature: 35 ° C
-Guard column: Made by Thermo Fisher Scientific, AG12A
-Detector: Electrical conductivity detector-Eluent: 2.7 mM Na ₂ CO ₃ , 0.3 mM NaHCO ₃
・ Eluent flow rate: 1.5 mL / min ・ Sample injection amount: 20 μL

The total concentration of specific anions in the metal processing sheet (total elution amount of specific anions contained in the cold water extract of the metal processing sheet) is at least 1600 ppm or more with respect to the absolute dry weight of the metal processing sheet. Yes, preferably 2900 ppm or more, more preferably 3100 ppm or more. The upper limit of the concentration of specific anions in the metal processing sheet is preferably 10,000 ppm or less, more preferably 10,000 ppm or less, based on the absolute dry weight of the metal processing sheet from the viewpoint of storage stability of the metal processing sheet itself. It is 7500 ppm or less, more preferably 5000 ppm or less.

In the metal processing sheet of the present invention, on the premise that the total concentration of the specific anion is 1600 ppm or more, the specific anion, that is, "nitrate ion, acetate ion, sulfate ion, phosphate ion, monohydrogen phosphate ion" , At least one of "dihydrogen phosphate ion" may be contained, and all of them may not be contained. According to the findings of the present inventor, among the specific anions, sulfate ion, acetate ion and nitrate ion are particularly effective, and sulfate ion is particularly effective. Therefore, it is preferable that the metal processing sheet contains at least sulfate ion as a specific anion.

As a method of adjusting the total concentration of the specific anion in the metal processing sheet to the specific range, the specific anion or a salt thereof is added to the fiber sheet constituting the metal processing sheet, and the total concentration of the specific anion is the specific. There is a method of adding so as to be in the range. The type of cation that forms a salt with a specific anion is not particularly limited, and examples thereof include cations such as zinc, aluminum, calcium, sodium, and magnesium. The method of adding the specific anion or its salt includes a method of adding the specific anion or its salt during the production of the fiber sheet (for example, during the wet papermaking process) (internal addition method) and the produced fiber sheet (for example, wet papermaking). There is a method of adding a specific anion or a salt thereof (external addition method) to the fiber sheet obtained in (1), and any of them can be adopted. Considering that the main purpose of adding the specific anion is to prevent pitting corrosion of the metal layer provided on the surface of the fiber sheet, an external addition method in which the specific anion easily stays on the surface layer of the fiber sheet is more preferable. In the external addition method, the method of adding the specific anion or a salt thereof to the fiber sheet is not particularly limited. For example, a method of preparing a treatment liquid containing the specific anion and applying or spraying the treatment liquid on the fiber sheet. Alternatively, a method of immersing the fiber sheet in the treatment liquid can be mentioned.

In the metal processing sheet of the present invention, it is preferably 0 to 50%, more preferably 0 to 20%, still more preferably 0.1 to 15% with respect to the total concentration of the specific anion. The concentration of chloride ions in the metal processing sheet is measured by the same method as the method for measuring the total concentration of the specific anions. As described above, chloride ion is a causative substance of pitting corrosion of the metal layer (aluminum) in the metal processing sheet, and it is preferable that it does not exist in the metal processing sheet in consideration of prevention of pitting corrosion. Considering the preferable effects of chloride ions, for example, prevention of adhesion of fine particles such as dust by antistatic action, improvement of whiteness of sheet, prevention of yellowing of sheet over time, etc., a certain amount is present in the sheet for metal processing. It is preferable to do so. Further, in the present invention, by adjusting the total concentration of specific anions in the metal processing sheet to the specific range, the deterioration of the metal layer due to chloride ions with time is effectively suppressed, so that chloride is contained in the sheet. Even if a certain amount of ions are present, it is unlikely that any inconvenience will occur. Considering the above comprehensively, it is preferable to set the chloride ion concentration in the metal processing sheet within the above range.

The concentration of chloride ions in the processed metal sheet is determined by using the white water used in the papermaking process as the chloride ion when using wet papermaking paper using chlorine bleached pulp such as NBKP or LBKP as the fiber sheet constituting the sheet. It can be adjusted by changing to water having a relatively low content of chlorine, or adjusting the amount of a chemical containing chloride ion or a salt thereof in the papermaking process. However, when the concentration of chloride ions is surely adjusted to the above-mentioned specific range, it is preferable to intentionally add chloride ions or a salt thereof to the processed metal sheet (fiber sheet). Then, as a method of adjusting the concentration of chloride ions in the processed metal sheet to the specific range, the amount of chloride ions added or a salt thereof at the time of manufacturing the processed metal sheet (fiber sheet) is set to the amount of chloride ions. It can be said that a method of adjusting the concentration so as to be within the specific range is preferable.

The metalworking sheet of the present invention has a volume resistivity (value measured by the four-probe method) measured in accordance with JIS K-7194: 1994, preferably 1 × 10 ¹¹ Ω · cm or less, more preferably. Is 5 × 10 ¹⁰ Ω · cm or less. At least, it is preferable that the volume resistivity of the surface to be metal-processed in the metal processing sheet is within the above-mentioned specific range. When the volume resistivity of the metal processing sheet is within the above-mentioned specific range, the inconvenience of attracting and adhering fine particles such as dust due to static electricity is effectively suppressed. Adjusting the volume resistivity of the metal processing sheet to the specific range can be achieved by adjusting the concentration of chloride ions in the sheet to the specific range. The lower limit of the volume resistivity of the metal processing sheet is not particularly limited, but particularly when the sheet contains carbon black, the carbon black and the metal layer provided on the sheet by metal processing are locally formed. From the viewpoint of suppressing the formation of a battery and further improving the storage stability of the metal layer, it is preferably 1 × 10 ³ Ω · cm or more, more preferably 1 × 10 ⁵ Ω · cm or more, and further preferably 1 × a 10 ⁷ Ω · cm.

The metal processing sheet of the present invention may further contain a colorant in addition to the above-mentioned essential components (fiber sheet, specific anion). By containing the colorant, the fiber sheet is colored in the color of the colorant, and the design of the metal processing sheet can be further enhanced. As the colorant, known colorants such as dyes, pigments and natural dyes can be used without particular limitation. Examples of the coloring method include a method of adding a colorant during the production of the fiber sheet (for example, during the wet papermaking process) (internal addition method), or a fiber sheet obtained after the production (for example, wet papermaking). There is a method of adding a colorant (external addition method) to the fiber sheet), and any of them can be adopted. The content of the colorant in the metal processing sheet may be appropriately adjusted so as to obtain a desired color.

Preferred examples of colorants include carbon black or iron oxide. By containing carbon black or iron oxide in the metal processing sheet (fiber sheet), the color of the sheet can be changed to black or brown. If a black metal-processed sheet is desired, carbon black is used as the colorant, and if a brown metal-processed sheet is desired, iron oxide is used as the colorant. It is also possible to use both colorants in combination to obtain a metal processed sheet having a neutral color between black and brown. Black or brown metal processing sheets, especially metal processing sheets obtained by metal processing a glossy black metal processing sheet called jet black, have both beauty and luxury, and create a high-class image. Therefore, it is suitable for applications that require beauty and luxury, such as pasting box paper and card paper. As described above, carbon black can be a causative substance of pitting corrosion of the metal layer (aluminum) in the metal processing sheet, but in the present invention, the total concentration of specific anions in the metal processing sheet is set within the specific range. By adjusting, the inconvenience caused by carbon black is effectively suppressed, so that carbon black can be positively contained in the sheet.

The content of carbon black in the metal processing sheet of the present invention is preferably 1 to 10% by mass, more preferably 2 to 5% by mass, based on the total mass of the sheet. It is preferable to set the iron oxide content in the same manner as the carbon black content.

The metal processing sheet of the present invention may contain elements other than the above-mentioned components (fiber sheet, specific anion, colorant). Other factors include, for example, various agents commonly blended in paper. Specifically, for example, fillers such as heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin, clay, talc, silica, titanium oxide, white carbon, aluminum oxide, mica, plastic pigments, or composites thereof; starch, Paper strength enhancer or fixing agent or water resistant agent such as polyacrylamide, polyamine polyamide epichlorohydrin; sizing agent such as rosin, alkylketen dimer, alkenyl anhydride succinic acid, styrene acrylic resin; fixing of drainage yield improver, sulfuric acid band, etc. Agents; fluorescent whitening agents; antifoaming agents; slime control agents; adhesives such as vinyl acetate resin, acrylic copolymer resin, styrene, polyvinyl alcohol, processed starch, dextrin and the like can be exemplified. The metal processing sheet of the present invention may contain one or more of these other elements.

The metal processing sheet of the present invention can be used as the base sheet when manufacturing a metal processing sheet in which a metal layer is provided on the surface of the base sheet. The metal processing sheet has a form in which the metal layer covers the entire area of one side or both sides of the base sheet (metal processing sheet), and the metal layer covers only a part of one side or both sides of the base sheet (metal processing sheet). The metal processing sheet of the present invention can be used in either form. Further, the metal layer is provided on the surface of the metal processing sheet by performing the metal processing on the sheet. However, as the metal processing, a known method can be used without particular limitation, for example, for example. Examples thereof include foil stamping printing of metal foil and gold ink printing. As the metal foil and gold ink, known ones can be used without particular limitation. A typical metal material contained in the metal layer is aluminum. As described above, there is a concern that aluminum deteriorates with time due to chloride ions and carbon black contained in the sheet, but such a concern has been eliminated in the metal processing sheet of the present invention, and aluminum was used. Suitable for metal processing.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[Examples 1 to 8 and Comparative Examples 1 to 3]
Chlorine-bleached NBKP and LBKP were used as the wood pulp, and a raw material pulp slurry having a beating degree of 370 mL by Canadian Standard Freeness was prepared by the method described in JIS P-8221-1: 1998. In this raw material pulp slurry, carbon black (manufactured by Mitsubishi Carbon Black, # 40) is added to 2.3 parts by mass of pulp, and a paper strength enhancer (manufactured by Arakawa Chemicals, Polystron 117) is added to 0.53 parts by mass of pulp. A raw material slurry was prepared by adding an agent (manufactured by Arakawa Chemical Industries, Size Pine N-771) to 0.3 parts by mass of pulp and a sulfuric acid band (manufactured by Nippon Light Metal Co., Ltd.) to 1.4 parts by mass of pulp. Using this raw material slurry, a wet papermaking method was carried out by the method described in JIS P-8222: 1998 to obtain a fiber sheet made of paper having a basis weight of 81.4 g / m ² . At the time of this wet papermaking, a predetermined amount of the coating liquid prepared by the following method was applied by a size press in terms of solid amount to obtain a sheet for metal processing.

[Preparation method of coating liquid]
After dispersing 5 parts by mass of processed chloride (manufactured by Nippon Corn Starch, SK-20) in 94.3 parts by mass of water heated to 90 ° C., the dispersion liquid was cooled and a surface paper strength enhancer (manufactured by Arakawa Chemical Industries) , Polymasset 305) by 0.2 parts by mass, surface sizing agent (manufactured by Starlight PMC, sizing agent SE2016) by 0.5 parts by mass, sodium sulfate (specific anion salt) and sodium chloride (chloride ion salt) A predetermined amount of either one or both of the above was added to obtain a coating liquid.

〔Evaluation test〕
Using the metal processing sheets of each Example and Comparative Example, a metal processing sheet was produced by the following method, and the storage stability of the metal processing sheet was evaluated by the following method. The results are shown in Table 1 below.

<Manufacturing method of metal processed sheet>
An aluminum foil (standard metallic foil made of Murata gold foil) was stamped and printed on one surface of the metal processing sheets of each Example and Comparative Example by a hot stamping method to obtain a metal processing sheet. The hot stamping method was performed under the following conditions.
・ Temperature: 130 ℃
・ Pressurization time: 5 seconds ・ Pressure: 30 kgf / cm ²

<Evaluation method of storage stability>
The metal processing sheet to be evaluated was allowed to stand in a constant temperature and humidity chamber having an atmospheric temperature of 70 ° C. and a humidity of 90% RH for 144 hours, and then the metal layer (aluminum foil) of the metal processing sheet was visually observed. It was evaluated according to the following evaluation criteria.

(Evaluation criteria for storage stability)
FIG. 1 is an optical micrograph (magnification of 100 times) of a metal layer in an example of a metal processed sheet. In FIG. 1, a plurality of black portions arranged in a scattered pattern are dropout portions (corroded portions). Arrows are attached to some of the missing parts in FIG. It can be evaluated that the smaller and smaller the fallen portion, the better the storage stability of the metal processed sheet.
In this evaluation standard, in the visual observation of the metal layer on the metal processed sheet to be evaluated, among the black parts (dropped parts) as shown in FIG. 1, those having a diameter (maximum transfer length) of 50 μm or more are referred to as “pitting corrosion”. By definition, the degree of corrosion was evaluated in the following three stages according to the frequency of occurrence of the pitting corrosion in a unit region of 30 mm square.
⊚: Almost no pitting corrosion has occurred. Good storage stability.
〇: Although pitting corrosion has occurred slightly, there is no problem in actual use.
X: A large number of pitting corrosion occurs and it cannot be actually used. Poor storage stability.
FIG. 2 schematically shows a typical example of the state of pitting corrosion occurring in the unit region of the metal layer. In the above-mentioned three-stage evaluation, ⊚ is a state as shown in FIG. 2 (a), ◯ is a state as shown in FIG. 2 (b), and × is a state as shown in FIG. 2 (c).

As shown in Table 1, according to the processed metal sheet of each example, the total concentration of specific anions (sulfate ions) is 1600 ppm or more with respect to the absolute dry weight of the sheet, so that the metal layer is corroded. The occurrence of pitting corrosion associated with this was effectively suppressed, and a metal-processed sheet having excellent cosmetic properties and storage stability of the metal layer could be obtained. On the other hand, in the processed metal sheet of each comparative example, since the total concentration of specific anions is less than 1600 ppm with respect to the absolute dry weight of the sheet, a large number of pitting corrosion occurs and the storage stability of the metal layer is inferior. It was.

Claims (6)

A metal processing sheet that can be used as the base sheet when manufacturing a metal processing sheet in which a metal layer made of aluminum is provided on the surface of the base sheet.
With fiber sheet,
It contains one or more specific anions selected from the group consisting of nitrate ion, acetate ion, sulfate ion, phosphate ion, monohydrogen phosphate ion and dihydrogen phosphate ion.
The specific anion measured in accordance with the ion chromatography method JISK-0127: 2013, which elutes when the metal processing sheet having an absolute dry weight of 5 g is immersed in distilled water at a liquid temperature of 20 ° C. for 24 hours. A metal processing sheet having a total concentration of 1600 ppm or more with respect to the absolute dry weight of the metal processing sheet. The metal processing sheet according to claim 1, wherein the concentration of chloride ions is 0 to 50% with respect to the total concentration of the specific anions. The metalworking sheet according to claim 1 or 2, wherein the volume resistivity measured in accordance with JIS K-7194: 1994 is 1 × 10 ¹¹ Ω · cm or less. The metal processing sheet according to any one of claims 1 to 3, further comprising a colorant. The metal processing sheet according to claim 4, wherein the colorant is carbon black or iron oxide. The metal processing sheet according to any one of claims 1 to 5, wherein the fiber sheet is paper containing wood pulp.