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 transmission spectroscopy measurement using a terahertz wave. The step is a step of evaluating a ratio of peak areas based on a transmission spectrum obtained by the transmission spectrometry, or a step of evaluating a ratio of transmittances at a specific frequency based on a transmission spectrum obtained by the transmission spectrometry, and the ratio of peak areas is based on a peak area of high-quality paper, and the ratio of transmittances is based on a transmittance of high-quality paper.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 papers classified as prohibited items, heat-sensitive foam paper, sublimation transfer paper, and synthetic paper, which are classified as Class A, are difficult to distinguish from regular paper that can be recycled, such as high-quality paper, and are often mixed in with recycled paper collected in the city.

[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 separation method described in Patent Document 1 separates waste paper based on the whiteness of the paper surface and the wavelength spectrum in the near-infrared region using a hyperspectral camera, and determines whether the paper is a prohibited item based only on the information on the paper surface, and is unable to identify components incorporated into the paper. It is also 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 transmission 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 transmission spectroscopy using terahertz waves. [2] The method for determining the type of paper described in [1] above, wherein the step is a step of evaluating the peak area ratio based on the transmission spectrum obtained by the transmission spectroscopy measurement, and the peak area ratio is based on the peak area of ​​high-quality paper. [3] The method for determining the type of paper according to [2], wherein the ratio of the peak area in the frequency region of 3.0 THz or more and 9.0 THz or less in the transmission 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 0.6 or 5.0 when the peak area of ​​the fine paper 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 transmittance ratio at a specific frequency based on the transmission spectrum obtained by the transmission spectroscopy measurement, and the transmittance ratio is based on the transmittance of high-quality paper. [6] The method for determining the type of paper according to [5], wherein the transmittance ratio at a specific frequency in the frequency range of 5.6 THz or more and less than 5.8 THz in the transmission spectrum is evaluated. [7] The method for determining the type of paper according to [6], wherein the transmittance ratio is evaluated using a threshold value of 0.4 or 3.0 when the transmittance of the high-quality paper 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 according to [8], wherein the type of paper unsuitable for waste paper recycling is one or more types selected from the group consisting of heat-sensitive foam paper, sublimation transfer paper, 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 transmission spectrum of each paper obtained by transmission 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 transmission spectroscopy using terahertz waves (hereinafter also referred to as "step (A)"). Step (A) determines the type of paper. That is, step (A) is a step of performing transmission spectroscopy using terahertz waves 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 type of paper is unsuitable for waste paper recycling. In particular, it is suitable for determining whether the paper being determined is one or more types selected from heat-sensitive foam paper, sublimation transfer paper, and synthetic paper. Heat-sensitive foam paper, sublimation transfer paper, and synthetic paper are all classified as Class A prohibited items (items that cause serious problems when mixed with waste paper) by the Waste Paper Recycling Promotion Center.

[0016] Heat-sensitive foam paper is a paper coated with thermally expandable microcapsules, and has the property of swelling when heated. Examples of heat-sensitive foam paper include braille paper such as 3D copy paper. Sublimation transfer paper is paper on which patterns, letters, etc. are printed using sublimation ink containing dyes such as sublimation dye compounds. It is used when transferring patterns, letters, etc. printed on sublimation transfer paper to textile products by heating. Examples of sublimation transfer paper include textile printing paper and iron-on print paper. 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 transmission 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 transmission spectrum obtained by transmission spectroscopy. Step (A2): A step of evaluating the ratio of transmittance at a specific frequency based on the transmission spectrum obtained by transmission spectroscopy measurement.

[0019] <Process (A1)> Step (A1) is a step of evaluating the ratio of peak areas based on the transmission spectrum obtained by transmission spectrometry. The peak area ratio is based on the peak area of ​​fine paper. 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 fine paper is determined based on the transmission spectrum obtained by transmission spectrometry (step (A1-1)). The peak area of ​​high-quality paper may be determined by irradiating terahertz waves onto a known high-quality paper, performing transmission spectroscopy to obtain a transmission spectrum, and then determining the peak area from the obtained transmission spectrum. Alternatively, if high-quality paper has previously been irradiated with terahertz waves and undergone transmission spectroscopy, the peak area may be determined from the transmission spectrum obtained from the previous measurement. In step (A1-1), the peak area may be determined over the entire frequency range of the terahertz waves irradiated onto the fine paper, but it is particularly preferable to determine the peak area in the frequency range of 3.0 THz or more and 9.0 THz or less. The known fine paper is not particularly limited, and fine paper selected from recycled waste paper in the market may be used, or new fine paper may be used. A method for selecting fine paper from recycled waste paper in the market may include, for example, a visual method. In addition, if terahertz waves have been irradiated onto high-quality paper in the past to perform transmission spectroscopy measurements, and the peak area of ​​the high-quality paper has already been determined from the transmission spectrum, the value of the peak area of ​​the high-quality paper determined in the past may be used.

[0021] 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 transmission spectroscopy measurement of fine paper, and transmission spectroscopy is performed to obtain a transmission spectrum, and the peak area of ​​the paper to be evaluated is determined from the obtained transmission 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 fine paper determined in step (A1-1) is determined.

[0022] Next, the peak area ratio is calculated from the peak area of ​​the fine paper calculated in step (A1-1) and the peak area of ​​the paper to be evaluated calculated 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 peak areas in the frequency range of 3.0 THz or more and 9.0 THz or less in the transmission spectrum. Specifically, it is preferable to evaluate the peak area ratio using a threshold of 0.6 or 5.0 when the peak area of ​​the fine paper obtained in step (A1-1) is set to 1, and to evaluate the paper to be evaluated. More specifically, if the ratio of the peak area, expressed as "peak area of ​​the paper to be evaluated / peak area of ​​the fine paper" when the peak area of ​​the fine paper is set to 1, is 0.6 or less or 5.0 or more, the paper to be evaluated is determined to be unsuitable for waste paper recycling, i.e., a paper that is prohibited from waste paper recycling. On the other hand, if the ratio of the peak area when the peak area of ​​the fine paper is set to 1 is more than 0.6 and less than 5.0, the paper to be evaluated is determined 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 transmittance ratio at a specific frequency based on the transmission spectrum obtained by transmission spectrometry. The transmittance ratio is based on the transmittance of fine paper. 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 transmittance of the fine paper at a specific frequency is determined based on the transmission spectrum obtained by transmission spectrometry (step (A2-1)). The transmittance of high-quality paper may be determined by irradiating terahertz waves onto a known high-quality paper, performing transmission spectroscopy to obtain a transmission spectrum, and then determining the transmittance from the obtained transmission spectrum. Alternatively, if high-quality paper has previously been irradiated with terahertz waves and undergone transmission spectroscopy, the transmittance may be determined from the transmission 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 high-quality paper, and the transmittance at the selected frequency may be measured, but it is particularly preferable to measure the transmittance at a specific frequency in the frequency range of 5.6 THz or more and less than 5.8 THz. The known fine paper is not particularly limited, and fine paper selected from recycled waste paper in the market may be used, or new fine paper may be used. A method for selecting fine paper from recycled waste paper in the market may include, for example, a visual method. In addition, if terahertz waves have been irradiated onto high-quality paper in the past to perform transmission spectroscopy measurements, and the transmittance of the high-quality paper at a specific frequency has already been determined from the transmission spectrum, the transmittance value of the high-quality paper determined in the past may be used. The common logarithm of the reciprocal of the transmittance is the absorbance.

[0026] 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 transmission spectroscopy measurement of fine paper, and transmission spectroscopy measurement is performed to obtain a transmission spectrum, and the transmittance of the paper to be evaluated is determined from the obtained transmission spectrum (step (A2-2)). In step (A2-2), the transmittance of the paper to be evaluated at the same frequency as the transmittance of the fine paper determined in step (A2-1) is determined.

[0027] Next, the transmittance ratio is calculated from the transmittance of the fine paper calculated in step (A2-1) and the transmittance 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 transmittance ratio at a specific frequency in the transmission spectrum, in the frequency range of 5.6 THz or more and less than 5.8 THz. Specifically, it is preferable to evaluate the transmittance ratio using a threshold of 0.4 or 3.0, assuming the transmittance of fine paper obtained in step (A2-1) to be 1, and to determine the paper to be evaluated. More specifically, if the transmittance ratio, expressed as "transmittance of the paper to be evaluated / transmittance of fine paper," where the transmittance of fine paper is 1, is 0.4 or less or 3.0 or more, the paper to be evaluated is determined to be unsuitable for waste paper recycling, i.e., a paper that is prohibited from waste paper recycling. On the other hand, if the transmittance ratio, where the transmittance of fine paper is 1, is more than 0.4 and less than 3.0, the paper to be evaluated is determined to be 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 transmission 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] The measurement samples used were high-quality paper (notebook paper for school use) and newspaper, which were found in collected waste paper from the city and were suitable for paper recycling, and heat-sensitive foam paper, sublimation transfer paper, and synthetic paper made from polypropylene, which were not suitable for 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 transmission spectroscopy measurements were performed with an accumulation of 512 times to obtain the transmission spectra. The transmission spectra were calculated by averaging the results of measuring each measurement sample three or four times over multiple days in an indoor environment, taking into account the influence of daily temperature and humidity. The results are shown in Figure 1.

[0032] Based on the obtained transmission spectrum, the peak area of ​​each measurement sample in the frequency range of 3.0 THz or more and 9.0 THz or less was calculated. The peak area ratio for the remaining measurement samples was calculated, assuming that the peak area for the fine paper was 1. The results are shown in Table 1. Furthermore, based on the obtained transmission spectrum, the transmittance of each measurement sample at a frequency of 5.7 THz was calculated. The transmittance ratio of the remaining measurement samples was calculated, assuming that the transmittance of fine paper was 1. The results are shown in Table 1.

[0033] [Table 1]

[0034] As is clear from Figure 1, the transmittance of synthetic paper, which is not suitable for waste paper recycling, in the frequency range of 3.0 THz or more and 9.0 THz or less is extremely high compared to the transmittance of fine paper and newspaper, which are suitable for waste paper recycling. In addition, the transmittance of fine paper and newspaper in the frequency range of 3.0 THz or more and 9.0 THz or less, especially in the range of 3.0 THz or more and 7.0 THz or less, is higher than that of heat-sensitive foam paper and sublimation transfer paper, which are not suitable for paper recycling. Therefore, when separating fine paper, newspaper, heat-sensitive foam paper, sublimation transfer paper, and synthetic paper into papers suitable for waste paper recycling and those not, if the ratio of the peak area in the frequency range of 3.0 THz or more to 9.0 THz or less, where the peak area of ​​fine paper is taken as 1, is more than 0.6 and less than 5.0, the paper can be determined to be suitable for waste paper recycling, and if it is 0.6 or less or 5.0 or more, the paper can be determined to be unsuitable for waste paper recycling. Also, if the transmittance ratio when the transmittance of fine paper at a frequency of 5.7 THz is taken as 1, is more than 0.4 and less than 3.0, the paper can be determined to be suitable for waste paper recycling, and if it is 0.4 or less or 3.0 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 transmission 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 transmission spectrum obtained by the transmission spectroscopy measurement, and the peak area ratio is based on the peak area of ​​high-quality paper.

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 3.0 THz or more and 9.0 THz or less in the transmission spectrum is evaluated.

4. The method for determining the type of paper according to claim 3 , wherein the peak area ratio is evaluated using a threshold value of 0.6 or 5.0 when the peak area of ​​the fine paper is set to 1.

5. 2. The paper type determination method according to claim 1, wherein the step is a step of evaluating a transmittance ratio at a specific frequency based on the transmission spectrum obtained by the transmission spectroscopy measurement, and the transmittance ratio is based on the transmittance of high-quality paper.

6. The method for determining the type of paper according to claim 5 , wherein a ratio of transmittance at a specific frequency in the frequency range of 5.6 THz or more and less than 5.8 THz in the transmission spectrum is evaluated.

7. The paper type determination method according to claim 6 , wherein the transmittance ratio is evaluated using a threshold value of 0.4 or 3.0 when the transmittance of the fine paper 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. 9. The method for determining the type of paper according to claim 8, wherein the type of paper unsuitable for waste paper recycling is at least one type selected from the group consisting of heat-sensitive foam paper, sublimation transfer paper, and synthetic paper.

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