Paper type determination method

Abstract

To provide a method for easily determining the type of paper.SOLUTION: A method for determining a type of paper, the method comprising: performing reflection spectroscopy measurement using a terahertz wave. The step is a step of evaluating a ratio of a peak area based on a reflection spectrum obtained by the reflection spectrometry, or a step of evaluating a ratio of a reflectance at a specific frequency based on the reflection spectrum obtained by the reflection spectrometry, and the ratio of the peak area is based on a peak area of a corrugated cardboard, and the ratio of the reflectance is based on a reflectance of the corrugated cardboard.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for determining the type of paper. [Background technology]

[0002] In the paper and pulp industry, used paper generated from stores, offices, homes, etc. (hereinafter referred to as "community recovered waste paper") is an important raw material for paper production. Paper that is not suitable for recycling may be mixed in with recycled paper. Regarding the quality of recycled paper, the Waste Paper Recycling Promotion Center, a public interest incorporated foundation, has established the Standard Quality Standard for Waste Paper, which states that the mixing of prohibited items, especially Class A, is not permitted (see Non-Patent Document 1). Among the prohibited paper products, waxed cardboard and synthetic paper, which are classified as Class A, are often mixed in with recycled paper in the city. Waxed cardboard, in particular, is difficult to distinguish from regular cardboard that can be recycled.

[0003] The separation of waste paper is left to the waste paper producer, but if the waste paper cannot be separated completely and prohibited items are mixed in with the waste paper collected in the city, the waste paper will be separated by a waste paper collector. Conventionally, waste paper sorting has been done manually, which is time-consuming and increases labor costs. In addition, because the accuracy of sorting depends on the skill of the workers, it is difficult to completely eliminate the inclusion of prohibited items in the papermaking process for waste paper recycling.

[0004] As a method for separating waste paper, for example, a method is known in which the whiteness of the waste paper to be separated is measured and material measurement using a hyperspectral camera is performed to determine whether the waste paper can be recycled or not (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-211208 [Non-patent literature]

[0006] [Non-Patent Document 1] "Recycled Paper Standard Quality Standards" Waste Paper Recycling Promotion Center, Public Interest Incorporated Foundation, revised August 3, 2016 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the sorting method described in Patent Document 1 is based on the whiteness of the surface of the waste paper and the wavelength spectrum in the near-infrared region using a hyperspectral camera, and determines whether or not the paper is a prohibited item based solely on information on the paper surface, making it difficult to identify the type of prohibited item. An object of the present invention is to provide a method for easily determining the type of paper. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors discovered that the type of paper can be easily determined by performing reflection spectroscopy using terahertz waves, and thus completed the present invention.

[0009] That is, the present invention has the following aspects. [1] A method for determining the type of paper, including a step of performing terahertz wave reflection spectroscopy. [2] The method for determining the type of paper described in [1], wherein the step is a step of evaluating the ratio of peak areas based on the reflection spectrum obtained by the reflection spectroscopy measurement, and the ratio of peak areas is based on the peak area of ​​cardboard. [3] The method for determining the type of paper according to [2], wherein the ratio of the peak area in the frequency region of 16.0 THz or more and 19.0 THz or less in the reflection spectrum is evaluated. [4] The method for determining the type of paper according to [3], wherein the ratio of the peak area is evaluated using a threshold value of 3.0 when the peak area of ​​the cardboard is set to 1. [5] The method for determining the type of paper described in [1], wherein the step is a step of evaluating the reflectance ratio at a specific frequency based on the reflectance spectrum obtained by the reflectance spectroscopy measurement, and the reflectance ratio is based on the reflectance of cardboard. [6] The method for determining the type of paper according to [5], wherein the ratio of reflectivity at a specific frequency in the frequency range of 18.2 THz or more and 18.4 THz or less in the reflection spectrum is evaluated. [7] The method for determining the type of paper described in [6], wherein the reflectivity ratio is evaluated using a threshold value of 2.0 when the reflectivity of the cardboard is 1. [8] The method for determining the type of paper according to any one of [1] to [7], which determines whether the paper type is unsuitable for waste paper recycling. [9] The method for determining the type of paper described in [8] above, wherein the type of paper unsuitable for waste paper recycling is one or more types selected from cardboard containing at least one of wax and synthetic paper. [Effects of the Invention]

[0010] According to the present invention, a method for easily determining the type of paper can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] 10 shows an example of the reflection spectrum of each paper obtained by reflection spectroscopy measurement using terahertz waves. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments within the scope of the object. In this specification, a numerical range expressed as "to" means a numerical range that includes the numerical values ​​before and after "to" as the lower and upper limits. The numerical ranges of the contents, various physical property values, and property values ​​disclosed in this specification can be arbitrarily combined with the lower and upper limits to form new numerical ranges.

[0013] [How to determine the type of paper] The paper type determination method according to this embodiment includes a step of performing terahertz wave reflection spectroscopy (hereinafter also referred to as "step (A)"). Step (A) determines the type of paper. That is, step (A) is a step of performing terahertz wave reflection spectroscopy to determine the type of paper.

[0014] The paper to be judged is not particularly limited, but may be, for example, recycled waste paper from the city. The recycled waste paper from the city may be waste paper at the stage of being discharged into the city from stores, offices, homes, etc., or may be waste paper discharged into the city and collected by a waste paper collector, or raw waste paper purchased from a waste paper collector.

[0015] The paper type determination method according to this embodiment is suitable for determining whether a paper type is unsuitable for waste paper recycling. In particular, it is suitable for determining whether the paper to be determined is one or more types selected from cardboard containing wax or at least one of wax, and synthetic paper. Cardboard containing wax or at least one of wax, and synthetic paper, are classified as Class A prohibited items (items that cause serious problems when mixed with waste paper) by the Waste Paper Recycling Promotion Center.

[0016] Corrugated board containing at least one of wax and wax is corrugated board that has been waterproofed with at least one of wax and wax. Corrugated board containing at least one of wax and wax can be obtained, for example, by applying at least one of wax and wax to the surface of the corrugated board or by immersing the corrugated board in at least one of wax and wax. In this specification, corrugated board containing at least one of wax and wax is also collectively referred to as "waxed corrugated board" or "waxed corrugated board." Synthetic paper is a film-like molded product with properties similar to those of paper, made from synthetic resins, such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., polyethylene terephthalate), and polyamides.

[0017] The method for generating and detecting terahertz waves used in reflection spectroscopy is not particularly limited, and commercially available terahertz wave generating and detecting devices can be used. In the present invention, "terahertz waves" refer to electromagnetic waves that exist in a frequency range between radio waves and light waves. For example, terahertz waves are electromagnetic waves in the frequency range of 0.1 THz or more and 30.0 THz or less, and in the wavelength range of 0.01 mm or more and 3.00 mm or less.

[0018] Specific examples of step (A) include step (A1) and step (A2) shown below. Step (A1): A step of evaluating the ratio of peak areas based on the reflectance spectrum obtained by reflectance spectroscopy. Step (A2): A step of evaluating the ratio of reflectance at a specific frequency based on the reflectance spectrum obtained by reflectance spectroscopy measurement.

[0019] <Process (A1)> Step (A1) is a step of evaluating the ratio of peak areas based on the reflection spectrum obtained by reflection spectroscopy. The peak area ratio is based on the peak area of ​​cardboard, which is not waterproofed with wax or wax. An example of step (A1) will be described below. Step (A1) of this embodiment specifically includes the following steps (A1-1) to (A1-3).

[0020] First, the peak area of ​​the cardboard is determined based on the reflection spectrum obtained by reflection spectroscopy (step (A1-1)). The peak area of ​​the cardboard may be determined from the reflection spectrum obtained by irradiating a known cardboard with terahertz waves and performing reflection spectroscopy to obtain a reflection spectrum, or, if terahertz waves have been irradiated onto cardboard in the past and reflection spectroscopy has been performed, from the reflection spectrum obtained from the previous measurement. In the step (A1-1), the peak area may be determined over the entire frequency range of the terahertz waves irradiated onto the cardboard, but it is particularly preferable to determine the peak area in the frequency range of 16.0 THz or more and 19.0 THz or less. The known corrugated board is not particularly limited, and corrugated board selected from recycled paper in the city may be used, or new corrugated board may be used. A method for selecting corrugated board from recycled paper in the city may include, for example, a visual method. In addition, if terahertz waves have been irradiated onto cardboard in the past to perform reflection spectroscopy measurements and the peak area of ​​the cardboard has already been determined from the reflection spectrum, the value of the peak area of ​​the cardboard determined in the past may be used.

[0021] Next, one piece of paper is selected at random from the collected waste paper to be measured, and this is the paper to be evaluated. The paper to be evaluated is irradiated with terahertz waves under the same conditions as in the case of the reflection spectroscopy measurement of cardboard, and reflection spectroscopy measurement is performed to obtain a reflection spectrum, and the peak area of ​​the paper to be evaluated is determined from the obtained reflection spectrum (step (A1-2)). In step (A1-2), the peak area of ​​the paper to be evaluated in the same region as the peak area of ​​the cardboard determined in step (A1-1) is determined.

[0022] Next, the peak area ratio is calculated from the peak area of ​​the cardboard obtained in step (A1-1) and the peak area of ​​the paper to be evaluated obtained in step (A1-2), and the paper to be evaluated is evaluated (step (A1-3)). In step (A1-3), it is preferable to evaluate the ratio of the peak area in the frequency range of 16.0 THz or more and 19.0 THz or less in the reflection spectrum. Specifically, it is preferable to evaluate the peak area ratio using a threshold of 3.0 when the peak area of ​​the cardboard obtained in step (A1-1) is set to 1, and to judge the paper to be judged. More specifically, if the ratio of the peak area, expressed as "peak area of ​​the paper to be judged / peak area of ​​the cardboard" when the peak area of ​​the cardboard is set to 1, is 3.0 or more, the paper to be judged is judged to be unsuitable for waste paper recycling, i.e., a prohibited product for waste paper recycling. On the other hand, if the ratio of the peak area when the peak area of ​​the cardboard is set to 1 is less than 3.0, the paper to be judged is judged to be suitable for waste paper recycling.

[0023] Separately, one paper is randomly selected from among commercially collected waste paper, and the steps (A1-2) and (A1-3) are carried out to determine the type of the selected paper. This operation is repeated to determine the type of commercially collected waste paper.

[0024] <Process (A2)> Step (A2) is a step of evaluating the ratio of reflectance at a specific frequency based on the reflectance spectrum obtained by reflectance spectroscopy. The reflectivity ratio is based on the reflectivity of cardboard, which is not waterproofed with wax or wax. An example of step (A2) will be described below. Step (A2) of this embodiment specifically includes the following steps (A2-1) to (A2-3).

[0025] First, the reflectance of the cardboard at a specific frequency is determined based on the reflection spectrum obtained by reflection spectroscopy measurement (step (A2-1)). The reflectivity of cardboard may be determined by irradiating a known cardboard with terahertz waves, performing reflection spectroscopy to obtain a reflection spectrum, and then determining the reflectivity from the obtained reflection spectrum. Alternatively, if terahertz waves have been irradiated onto cardboard in the past and reflection spectroscopy has been performed, the reflectivity may be determined from the reflection spectrum obtained from the previous measurement. In step (A2-1), a specific frequency may be selected from the entire frequency range of the terahertz waves irradiated onto the cardboard, and the reflectivity at the selected frequency may be determined, but it is particularly preferable to determine the reflectivity at a specific frequency in the frequency range of 18.2 THz or more and 18.4 THz or less. The known corrugated board is not particularly limited, and corrugated board selected from recycled paper in the city may be used, or new corrugated board may be used. A method for selecting corrugated board from recycled paper in the city may include, for example, a visual method. In addition, if terahertz waves have been irradiated onto cardboard in the past to perform reflection spectroscopy measurements and the reflectivity of the cardboard at a specific frequency has already been determined from the reflection spectrum, the previously determined value of the reflectivity of the cardboard may be used.

[0026] Next, one piece of paper is randomly selected from the collected waste paper to be measured, and this is the paper to be evaluated. The paper to be evaluated is irradiated with terahertz waves under the same conditions as in the case of the reflection spectroscopy measurement of cardboard, and reflection spectroscopy measurement is performed to obtain a reflection spectrum, and the reflectance of the paper to be evaluated is determined from the obtained reflection spectrum (step (A2-2)). In step (A2-2), the reflectance of the paper to be evaluated at the same frequency as the reflectance of the cardboard determined in step (A2-1) is determined.

[0027] Next, the reflectance ratio is calculated from the reflectance of the cardboard calculated in step (A2-1) and the reflectance of the paper to be evaluated calculated in step (A2-2), and the paper to be evaluated is evaluated (step (A2-3)). In step (A2-3), it is preferable to evaluate the reflectance ratio at a specific frequency in the frequency range of 18.2 THz or more and 18.4 THz or less in the reflection spectrum. Specifically, it is preferable to evaluate the reflectance ratio using a threshold of 2.0 when the reflectance of the cardboard obtained in step (A2-1) is set to 1, and to judge the paper to be judged. More specifically, if the reflectance ratio, expressed as "reflectance of the paper to be judged / reflectance of the cardboard" when the reflectance of the cardboard is set to 1, is 2.0 or more, the paper to be judged is not suitable for waste paper recycling, i.e., is a prohibited product for waste paper recycling. On the other hand, if the reflectance ratio when the reflectance of the cardboard is set to 1 is less than 2.0, the paper to be judged is suitable for waste paper recycling.

[0028] Separately, one paper is randomly selected from among commercially collected waste paper, and the steps (A2-2) and (A2-3) are carried out to determine the type of the selected paper. This procedure is repeated to determine whether the paper is commercially collected waste paper.

[0029] <Action and effect> According to the paper type determination method of the present embodiment described above, the type of paper can be easily determined by performing reflection spectroscopy using terahertz waves. Therefore, even if paper that falls under the category of prohibited items, particularly Class A paper, specified by the Waste Paper Recycling Promotion Center is mixed in with commercially collected waste paper, the paper can be efficiently separated into waste paper suitable for waste paper recycling (i.e., suitable as papermaking raw material) and waste paper that is not suitable for waste paper recycling (prohibited items), thereby preventing serious impacts on waste paper recycling due to the mixing of prohibited items. [Example]

[0030] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The embodiments of the present invention can be modified in various ways as long as the gist of the present invention is not changed.

[0031] [Example 1] As measurement samples, corrugated cardboard contained in commercially collected waste paper was used as a material suitable for waste paper recycling, and waxed corrugated cardboard and synthetic paper made from polypropylene were used as materials unsuitable for waste paper recycling. Using a terahertz wave spectrometer (manufactured by JASCO Corporation, model number "VIR-F"), the measurement wavenumber range was 40 to 800 cm under a typical indoor environment. -1 , resolution 4cm -1 Terahertz waves were irradiated onto each measurement sample, and reflection spectroscopy measurements were performed with an accumulation count of 512, to obtain the reflection spectra. Taking into account the influence of daily temperature and humidity, the reflection spectra were calculated by averaging the results of measuring each measurement sample three or four times over multiple days in an indoor environment. The results are shown in Figure 1.

[0032] Based on the obtained reflection spectrum, the peak area of ​​each measurement sample in the frequency range of 16.0 THz or more and 19.0 THz or less was calculated. The peak area ratio for the remaining measurement samples was calculated, assuming that the peak area for the cardboard was 1. The results are shown in Table 1. Furthermore, based on the obtained reflection spectrum, the reflectivity of each measurement sample at a frequency of 18.33 THz was calculated. The reflectivity ratio of the remaining measurement samples was calculated, assuming that the reflectivity of cardboard was 1. The results are shown in Table 1.

[0033] [Table 1]

[0034] As is clear from Figure 1, the reflectivity of waxed cardboard and synthetic paper, which are not suitable for waste paper recycling, is higher in the frequency range of 16.0 THz or higher and 19.0 THz or lower than the reflectivity of cardboard, which is suitable for waste paper recycling. Therefore, when separating cardboard, waxed cardboard, and synthetic paper into papers suitable for waste paper recycling and those that are not, if the ratio of the peak area in the frequency range of 16.0 THz or more to 19.0 THz or less is less than 3.0 when the peak area of ​​cardboard is set to 1, the paper can be determined to be suitable for waste paper recycling, and if it is 3.0 or more, the paper can be determined to be unsuitable for waste paper recycling. Also, if the ratio of the reflectivity when the reflectivity of cardboard at a frequency of 18.33 THz is set to 1 is less than 2.0, the paper can be determined to be suitable for waste paper recycling, and if it is 2.0 or more, the paper can be determined to be unsuitable for waste paper recycling.

Claims

1. A method for determining the type of paper, comprising a step of performing reflection spectroscopy measurement using terahertz waves.

2. 2. The paper type determination method according to claim 1, wherein the step is a step of evaluating a peak area ratio based on the reflection spectrum obtained by the reflection spectroscopy measurement, and the peak area ratio is based on the peak area of ​​cardboard.

3. The method for determining the type of paper according to claim 2 , wherein a ratio of the peak area in the frequency region of 16.0 THz or more and 19.0 THz or less in the reflection spectrum is evaluated.

4. The method for determining the type of paper according to claim 3 , wherein the ratio of the peak area is evaluated using a threshold value of 3.0 when the peak area of ​​the cardboard is set to 1.

5. 2. The method for determining the type of paper according to claim 1, wherein the step is a step of evaluating the reflectance ratio at a specific frequency based on the reflection spectrum obtained by the reflection spectroscopy measurement, and the reflectance ratio is based on the reflectance of cardboard.

6. The method for determining the type of paper according to claim 5 , wherein a ratio of reflectance at a specific frequency in the frequency range of 18.2 THz or more and 18.4 THz or less in the reflection spectrum is evaluated.

7. The method for determining the type of paper according to claim 6, wherein the reflectance ratio is evaluated using a threshold value of 2.0 when the reflectance of the cardboard is 1.

8. The method for determining the type of paper according to any one of claims 1 to 7, wherein the method determines whether the type of paper is unsuitable for waste paper recycling.

9. The method for determining the type of paper according to claim 8, wherein the type of paper unsuitable for waste paper recycling is one or more types selected from cardboard containing at least one of wax and synthetic paper.

Images