Method for inspecting paper container

Abstract

To provide a method for inspecting paper containers, the method being capable of accurately evaluating the risk of leakage by a simple procedure.SOLUTION: A method for inspecting a paper container includes the steps of: filling a paper container with a colored liquid; and determining whether or not the colored liquid has penetrated by irradiating light to the bottom portion of the paper container from below the paper container and observing the lower portion of the paper container from the side of the paper container.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting paper containers. [Background technology]

[0002] Paper containers such as paper cups are known. When paper containers are manufactured, they are usually inspected for leakage risks.

[0003] For example, Patent Document 1 (JP 2007-108162 A) describes a method for inspecting air leaks in a cup-shaped container, which is characterized by sending pressurized air into the body space while the body space and the thread bottom space are sealed, measuring the pressure in the thread bottom space, and detecting air leakage mainly from the body space to the thread bottom space, then cutting off the air supply to the body space, and after a predetermined time has passed, measuring the residual pressure in the body space, and detecting air leakage mainly from the body to the outside. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-108162 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires an apparatus for feeding air and an apparatus for measuring pressure. Therefore, a technology that can evaluate the leakage risk in a simple manner is desired. Furthermore, the leakage risk needs to be evaluated with high accuracy.

[0006] That is, an object of the present invention is to provide a paper container inspection method that can accurately evaluate leakage risk in a simple manner. [Means for solving the problem]

[0007] In one aspect, the method for inspecting paper containers according to the present invention comprises the steps of filling a paper container with a coloring liquid, and, after the filling step, observing the lower part of the paper container from the side while irradiating light onto the bottom of the paper container from below the paper container, and determining whether the coloring liquid has penetrated. [Effects of the Invention]

[0008] According to the present invention, a paper container inspection method is provided that can accurately evaluate leakage risk in a simple manner. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating the paper container inspection method according to this embodiment. [Figure 2] FIG. 2 is a perspective view showing a paper cup. [Figure 3] FIG. 3 is a cross-sectional side view of a paper cup, showing a cross section passing through a side seam portion. [Figure 4] FIG. 4 is a graph showing the measurement results of the maximum transmittance difference in Experimental Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] FIG. 1 is a schematic diagram illustrating an inspection method for paper containers according to this embodiment. In the inspection method according to this embodiment, first, as shown in FIG. 1(a), a coloring liquid is filled into a paper container. Next, as shown in FIG. 1(b), the paper container is left to stand. Next, the coloring liquid is removed. Next, as shown in FIG. 1(c), while irradiating the bottom of the paper container with light from below, the lower part of the paper container is observed from the side of the paper container to determine whether the coloring liquid has penetrated.

[0012] According to the above-mentioned method, it is possible to easily evaluate the risk of leakage because it is only necessary to prepare the coloring liquid and a light source for irradiating light. Furthermore, by irradiating light onto the bottom of the paper container during observation, it is possible to identify defects that would not be visible without irradiating light. Therefore, the risk of leakage can be inspected with high accuracy.

[0013] In addition, while it is not possible to identify the location of a leak when using an air leak test such as that described in Patent Document 1, this embodiment makes it possible to identify the location of the leak. By identifying the location of the leak, it is possible to pinpoint the manufacturing equipment and manufacturing conditions, and to manufacture paper containers that do not leak.

[0014] The inspection method according to this embodiment will be described in detail below.

[0015] (1) Paper containers First, the paper container to be inspected will be described. A paper container is a container for holding liquid. There is no particular limitation on the paper container, but a paper cup is preferable. In the following, we will also take the case where the paper container is a paper cup as an example. Figure 2 is a perspective view showing a paper cup 1. The paper cup 1 has a body 2 and a bottom 3.

[0016] The body 2 is cylindrical and formed by a body paper 5. The body 2 is provided with a side seam 4. The side seam 4 is a portion where both ends of the body paper in the circumferential direction are joined together.

[0017] The bottom part 3 is connected to the lower end of the body part 2 and closes the lower end of the body part 2. The bottom part 3 is formed by a bottom paper (6).

[0018] Fig. 3 is a side cross-sectional view of the paper cup 1, showing a cross section passing through the side seam portion 4. The structure of the joining portion between the body paper 5 and the bottom paper 6 will be described with reference to Fig. 3. For convenience, Fig. 3 depicts a gap at the joining portion between the body paper 5 and the bottom paper 6. However, in reality, no gap exists at the joining portion between the two.

[0019] As shown in Figure 3, the bottom paper 6 is sandwiched between the body paper 5 at the joint between the body 2 and the bottom 3. Specifically, the bottom paper 6 has a bottom surface 7 and a folded portion 8. The bottom surface 7 is the portion that forms the bottom of the paper cup 1. The folded portion 8 is a portion provided on the outer periphery of the bottom paper 6 and extends downward. In other words, the bottom paper 6 is folded downward at its outer periphery.

[0020] The folded portion 8 is sandwiched by the lower end of the body paper 5. That is, the lower end of the body paper 5 is folded back so as to sandwich the folded portion 8. As a result, a three-layer laminated structure (five layers at the side seam) is formed at the bottom of the paper cup 1 by the folded portion 8 and the body paper 5 sandwiching the folded portion 8.

[0021] Although not explicitly shown in Figure 3, a resin layer such as polyethylene is provided on the top surface of the bottom paper 6. This resin layer functions as an adhesive, bonding the bottom paper 6 and the body paper 5 at the folded portion 8.

[0022] Here, poor adhesion may occur at the bonded portion between the body paper 5 and the bottom paper 6. If such poor adhesion exists, the contents may leak through the poorly bonded portion. In other words, there is a risk of leakage. The inspection method according to this embodiment is suitable for inspecting for such a leakage risk (poor adhesion). Specifically, if poor adhesion exists at the bonded portion, the coloring liquid will seep in between the bottom paper and body paper at the bonded portion. As a result, the end surface of the bottom paper 6 (the lower end surface at the folded portion 8) will come into contact with the coloring liquid. Because the end surface of the bottom paper is not provided with a resin layer or the like, the coloring liquid will penetrate into the bottom paper 6 through the end surface. In other words, if poor adhesion exists, the coloring liquid will penetrate into the bottom paper at the bonded portion. Therefore, by observing whether or not the coloring liquid has penetrated into the bottom paper, it is possible to determine whether or not there is a risk of leakage.

[0023] The density of the paper (body paper and bottom paper) that constitutes the paper container is not particularly limited. For example, the density of the paper is 0.5 to 1.1 g / cm 3 The basis weight of the paper is, for example, 100 to 400 g / m 2 and preferably 170 to 350 g / m 2 If the paper container is made of paper having such paper quality, the risk of leakage can be evaluated using the inspection method according to this embodiment.

[0024] The thickness of the joint between the bottom paper and the body paper (the part where the folded portion 8 is sandwiched between the folded body paper 5) (the total thickness of the bottom paper 6 and the two body paper 5) is, for example, 0.38 mm to 1.5 mm. The basis weight of the joint is, for example, 170 to 400 g / m 2 For paper cups having such a joint, the risk of leakage can be suitably evaluated using the inspection method according to this embodiment.

[0025] The paper constituting the paper container may be plain white or may be colored. For example, the outer surface of the plain white body paper may be colored by printing. Preferably, the paper constituting the paper container is in accordance with CIE 1976 L * a * b *L of 40 or more in color space * The L value of the paper that makes up the paper container * The higher the value, the easier it is to distinguish between the areas that have been penetrated by the coloring liquid and the areas that have not. * When a paper container is made of paper having a color value (L * a * b * The color values ​​of the paper that makes up the paper container are specified, but the color of the parts other than the outer surface of the lower body is not particularly limited.

[0026] (2) Colored liquid Next, the coloring liquid will be described.

[0027] It is preferable to use a coloring liquid that has a maximum transmittance difference of 0.5% or more. In this specification, the term "maximum transmittance difference" refers to the value indicating the transmittance difference between the permeated and non-permeated areas of paper when the coloring liquid is permeated into the paper under specified conditions. Specifically, the "maximum transmittance difference" is determined by the method described in the Examples section below. Using a coloring liquid that has a maximum transmittance difference of 0.5% or more makes it easier to sufficiently distinguish between the permeated and non-permeated areas of the coloring liquid. As a result, leakage risk can be inspected more accurately.

[0028] The coloring solution is CIE 1976 L * a * b * L below 80 in color space * It is preferable that the coloring liquid has a value of L * The smaller the value, the easier it is to distinguish between the permeated and non-permeated areas of the coloring liquid. * If the value is 80 or less, it becomes easy to distinguish between the permeated portion and the non-permeated portion, and the leakage risk can be evaluated more accurately.* The values ​​are obtained by measurement according to the method described in the Examples below.

[0029] When the paper container is colored, it is preferable to use a coloring liquid of a color different from that of the paper container. Specifically, it is preferable that the color difference ΔE between the paper constituting the paper container and the coloring liquid is 3000 or more. The larger the color difference ΔE, the easier it is to distinguish between the permeated and non-permeated portions of the coloring liquid. If the color difference ΔE is 3000 or more, it becomes sufficiently easy to distinguish between the permeated and non-permeated portions, and the risk of leakage can be evaluated more accurately. Note that the color difference ΔE in this embodiment is calculated based on the CIE 1976 L * a * b * This is the color difference based on the color space, and is calculated using the following formula: (Equation 1) ΔE = [(ΔL * ) 2 +(Δa * ) 2 +(Δb * ) 2 ] 1 / 2

[0030] (3) Other Next, other inspection conditions will be described.

[0031] Although the amount of coloring liquid to be filled into the paper container is not particularly limited, it is preferable that the coloring liquid be filled to a certain depth. For example, the coloring liquid is filled into the paper container to a depth of 0.5 mm or more, preferably 1 cm or more.

[0032] The time for which the coloring liquid is left to stand after being filled into the paper container is, for example, 5 minutes or more, preferably 10 minutes or more, and more preferably 15 to 30 minutes.

[0033] When observing a paper container, as described above, light is irradiated from below the paper container toward the bottom of the paper container. In this case, it is preferable that the light be irradiated onto the bottom of the paper container at an illuminance of 6000 lux or more. The illuminance here refers to the illuminance at the bottom of the paper container. The higher the illuminance, the easier it is to distinguish between the permeated and non-permeated areas of the coloring liquid. Irradiating light at an illuminance of 6000 lux or more makes it easy to sufficiently distinguish between the permeated and non-permeated areas, allowing for more accurate evaluation of the leakage risk.

[0034] The light source used to irradiate the bottom of the paper container with light is not particularly limited. For example, a light built into a mobile phone may be used as the light source. Alternatively, a flashlight may be used as the light source.

[0035] In this embodiment, the paper container is left to stand after being filled with the coloring liquid. However, if a coloring liquid with a high penetration rate is used, the paper container does not necessarily have to be left to stand.

[0036] In this embodiment, the case where "observation" is performed after "removal" of the coloring liquid has been described. However, even if the coloring liquid is filled, it may be possible to determine whether or not the coloring liquid has penetrated. In such cases, it is not necessarily necessary to "remove" the coloring liquid before "observation."

[0037] The inspection method according to this embodiment can be implemented as one step in a paper container manufacturing method. For example, a plurality of paper containers are manufactured under certain manufacturing conditions. Then, a leakage risk is evaluated for certain paper containers through sampling inspection using the inspection method according to this embodiment. The paper containers are selected based on the inspection results. That is, if there is no leakage risk, the paper container manufactured under those manufacturing conditions is distributed as a product. On the other hand, if a leakage risk is confirmed, the paper container manufactured under those manufacturing conditions is discarded. Alternatively, the leakage risk of each paper container is further inspected individually using another inspection method, and then it is determined whether or not to distribute the paper container as a product. This makes it possible to reliably identify paper containers with a leakage risk before distribution. If a leakage risk is discovered after distribution, products manufactured under the same conditions will have to be recalled, which may result in significant recall costs. This embodiment makes it possible to prevent such recall costs from occurring. [Example]

[0038] Next, examples performed by the present inventors will be described in order to explain the present invention in more detail, but the present invention should not be construed as being limited to the examples described below.

[0039] [Experimental Example 1] Examination of the effects of light irradiation A paper cup with adhesive defects was prepared as a paper container. Specifically, a paper cup with the configuration shown in Figures 2 and 3 was prepared, with adhesive defects at the joint between the body paper and the bottom paper. The prepared paper cup was plain white. In addition, a liquid colored red with rouge was prepared as coloring liquid 1. Coloring liquid 1 was filled into the paper cup to a depth of 10 cm. After filling, the paper container was left to stand for 20 minutes. After standing, coloring liquid 1 was removed. Next, while irradiating the bottom of the paper container from below with light, the lower part of the paper container (specifically, the joint between the body paper and the bottom paper) was visually observed from the side of the paper container. The presence or absence of penetration of coloring liquid 1 was observed, and whether or not adhesive defects could be detected was evaluated. The illuminance was changed by changing the light source or the distance between the light source and the paper container, and whether or not adhesive defects could be detected was evaluated at different illuminances. The light irradiation conditions and the results of whether or not they could be detected are shown in Table 1 below. The illuminance at the bottom of the paper container without light irradiation was approximately 2000 lux.

[0040] [Table 1]

[0041] As shown in Table 1, when the illuminance at the bottom of the paper container was 6,000 lux or higher, it was possible to detect poor adhesion. On the other hand, when the illuminance was below 6,000 lux, it was not possible to detect poor adhesion. This shows that by observing a paper container while shining light at a specific illuminance, it is possible to confirm the presence of leakage risks (poor adhesion) that cannot be confirmed without shining light.

[0042] [Experimental Example 2] Examination of coloring liquid In addition to colored liquid 1 (red), colored liquids 2 to 4 were prepared. Colored liquid 2 was a blue liquid, colored liquid 3 was a yellow liquid, and colored liquid 4 was a green liquid. Using each of colored liquids 1 to 4, the feasibility of detecting adhesion defects was evaluated in the same manner as in Experimental Example 1. The illuminance was set to 120,000 lux.

[0043] In addition, the CIE 1976 L of each coloring liquid * a* b * L in color space * value, a * value, and b * The conditions for measuring the color value of the colored liquid were as follows: (Measurement conditions for color value of colored liquid) Measuring equipment: Spectrophotometer Model: CM-3500d Manufacturer: Konica Minolta, Inc. Measurement type: Transmission measurement Glass cell: width (optical path length) 10 mm (model CM-A98) Measurement method: The colored liquid was poured into a 10 mm wide glass cell to fill it to at least 2 / 3, which was then set in a spectrophotometer and irradiated with a pulsed xenon lamp to measure the L*a*b* values.

[0044] The results are shown in Table 2. As shown in Table 2, L * When coloring liquid 3 was used, the value of which exceeded 80, adhesion failure could not be detected. * When colored liquids 1, 2, and 4, which had a value of 80 or less, were used, poor adhesion could be detected. * It can be seen that if a coloring liquid with a value of 80 or less is used, it becomes easier to determine poor adhesion.

[0045] [Table 2]

[0046] [Experimental Example 3] Examination of maximum transmittance difference For each of the colored liquids 1 to 4, the maximum transmittance difference was determined by the following method.

[0047] (Method for measuring maximum transmittance difference) A sample was prepared that mimicked the structure of the joint portion where the coloring liquid had permeated. As mentioned above, if there is a risk of leakage, the coloring liquid will permeate the bottom paper at the joint portion. Therefore, a sample was prepared in which the bottom paper permeated with the coloring liquid was sandwiched between two sheets of body paper. Specifically, two sheets of body paper and one sheet of bottom paper that make up a paper container were prepared. The bottom paper was impregnated with the coloring liquid for 20 minutes. Three sheets of base paper were stacked so that the bottom paper impregnated with the coloring liquid was sandwiched between the two sheets of body paper to create a measurement sample. Meanwhile, a stack of three sheets of base paper that had not been impregnated with the coloring liquid was prepared as a reference sample. The transmittance in the visible light range (380 to 780 nm) was measured for each of the measurement sample and the reference sample. Specifically, the transmittance was measured using an ultraviolet-visible-near-infrared spectrophotometer (model V-750, manufactured by JASCO Corporation) in the measurement mode of %T (transmittance measurement). Based on the measurement results, the maximum value of the difference in transmittance in the visible light region between the measurement sample and the reference sample was calculated as the maximum transmittance difference.

[0048] Figure 4 shows the measurement results of the maximum transmittance difference. Figure 4(a) shows spectra showing the relationship between wavelength and transmittance for the reference sample and each measured sample. Meanwhile, Figure 4(b) shows spectra showing the difference of each measured sample from the reference sample. In Figures 4(a) and 4(b), spectra 1 to 4 are the spectra of colored liquids 1 to 4, respectively. Furthermore, spectrum S in Figure 4(a) is the spectrum of the reference sample.

[0049] As shown in Figure 4(b), the maximum transmittance difference for coloring liquid 1 (red) was 0.67%. The maximum transmittance difference for coloring liquid 2 (blue) was 1.46%. The maximum transmittance difference for coloring liquid 3 (yellow) was 0.26%. The maximum transmittance difference for coloring liquid 4 (green) was 0.95%. As previously described (Table 2), it was impossible to distinguish when coloring liquid 3 (yellow) was used, whereas poor adhesion could be distinguished when coloring liquids 1, 2, and 4 were used. These results confirmed that using coloring liquids that result in a maximum transmittance difference of 0.5% or more between the permeated and non-permeated areas makes it easier to distinguish poor adhesion.

[0050] [Experimental Example 4] Study of paper color and color difference ΔE A paper cup was colored red with an oil-based marker to obtain paper cup 1. Specifically, the outer surface of the lower body of the paper cup (the outer body paper at the joint) was colored. Similarly, a paper cup colored blue was prepared as paper cup 2. A paper cup colored green was prepared as paper cup 3. Furthermore, a plain white paper cup was prepared as paper cup 4. A paper cup colored black was prepared as paper cup 5. Paper cups 1 to 5 were colored in accordance with CIE 1976 L * a * b * L in color space * value, a * value, and b * The measurement results are shown in Table 3.

[0051] [Table 3]

[0052] For each of paper cups 1 to 5, coloring liquids 1 to 4 were used to check whether poor adhesion could be detected using the same method as in Experimental Example 1. The results are shown in Table 4. Table 4 also shows the color difference ΔE between the paper cups and the coloring liquids.

[0053] [Table 4]

[0054] As shown in Tables 3 and 4, L * For paper cup 5 (black) with a value of less than 40, no adhesion failure could be detected regardless of which coloring liquid was used. * For paper cups 1 to 4 with a value of more than 40, it was possible to determine whether the adhesive was defective by using a specific coloring liquid. * It was confirmed that for paper cups with a bond strength of over 40, poor adhesion can be detected by using an appropriate coloring liquid.

[0055] L *For colored liquid 3 (yellow) with a value exceeding 80, no adhesion failure could be detected regardless of the paper cup used. * For coloring liquids 1, 2 and 4, which have a value of less than 80, adhesion failure could be determined for a specific paper cup. * The value is less than 80 (colored liquid 1, 2, 4) and the L of the paper cup * When the color difference ΔE was greater than 40 (paper cups 1 to 4), poor adhesion could be detected if the color difference ΔE was 3000 or greater. On the other hand, poor adhesion could not be detected if the color difference ΔE was less than 3000. This confirmed that poor adhesion can be easily detected if the color difference ΔE is 3000 or greater.

[0056] [Note] Representative configurations of the present invention will be summarized below as appendices.

[0057] (Appendix 1) A method for inspecting paper containers, comprising the steps of: filling a paper container with a coloring liquid; and observing the lower part of the paper container from the side while irradiating light onto the bottom of the paper container from below the paper container, and determining whether the coloring liquid has penetrated. (Appendix 2) An inspection method as described in Appendix 1, wherein the paper container has a cylindrical body formed from body paper and a bottom formed from bottom paper and joined to the lower end of the body, the bottom paper is sandwiched between the body paper at the joint between the body and the bottom, and the coloring liquid is a coloring liquid such that the maximum transmittance difference measured by the method described below is 0.5% or more. (Method for measuring maximum transmittance difference) Two sheets of base paper for the body and one sheet of base paper for the bottom paper that make up the paper container are prepared. The base paper for the bottom is impregnated with a coloring liquid. Three sheets of base paper are stacked so that the base paper for the bottom impregnated with the coloring liquid is sandwiched between the two sheets of base paper for the body, to form a measurement sample. Meanwhile, a stack of three sheets of base paper that have not been impregnated with the coloring liquid is prepared as a reference sample. The transmittance in the visible light range (380 to 780 nm) is measured for each of the measurement sample and the reference sample. Based on the measurement results, the maximum difference in transmittance in the visible light range between the measurement sample and the reference sample is determined as the maximum transmittance difference. (Appendix 3) An inspection method according to claim 1 or 2, wherein the determining step includes a step of irradiating the bottom of the paper container with light at an illuminance of 6000 lux or more. (Appendix 4) In the inspection method according to any one of Supplementary Notes 1 to 3, the coloring liquid is a colorant according to CIE 1976 L * a * b * L below 80 in color space * A test method that has a value. (Appendix 5) 5. The inspection method according to any one of appendices 1 to 4, wherein the paper container is uncolored. (Appendix 6) The inspection method according to any one of Supplementary Notes 1 to 5, wherein the paper constituting the paper container is a paper that satisfies CIE 1976 L * a * b * L of 40 or more in color space * A test method that has a value. (Appendix 7) The inspection method according to any one of Supplementary Notes 1 to 6, * a * b * An inspection method, wherein the color difference ΔE between the paper constituting the paper container and the coloring liquid in color space is 3000 or more. (Appendix 8) A method for manufacturing a paper container, comprising: a step of manufacturing a paper container; after the manufacturing step, a step of inspecting the paper container using an inspection method described in any one of Appendices 1 to 7; and a step of sorting the paper container based on the inspection results in the inspection step. [Explanation of symbols]

[0058] 1...paper cup, 2...body, 3...bottom, 4...seam, 5...body paper, 6...bottom paper, 7...bottom, 8...folded part

Claims

1. Filling a paper container with a coloring liquid; A step of irradiating light onto the bottom of the paper container from below the paper container, while observing the lower part of the paper container from the side of the paper container, and determining whether the coloring liquid has penetrated; Equipped with Inspection methods for paper containers.

2. The inspection method according to claim 1, The paper container is a cylindrical body portion formed by a body paper; a bottom formed of a bottom paper and connected to a lower end of the body; and At the joint between the body and the bottom, the bottom paper is sandwiched by the body paper, The coloring liquid is a coloring liquid that has a maximum transmittance difference of 0.5% or more as measured by the following method: Testing method. (Method for measuring maximum transmittance difference) Two sheets of base paper for the body paper and one sheet of base paper for the bottom paper that make up the paper container are prepared. The base paper for the bottom paper is impregnated with a coloring liquid. Three sheets of base paper are stacked so that the base paper for the bottom paper impregnated with the coloring liquid is sandwiched between the two sheets of base paper for the body paper to form a measurement sample. Meanwhile, a stack of three sheets of paper that have not been impregnated with the coloring liquid is prepared as a reference sample. The transmittance in the visible light region (380 to 780 nm) is measured for each of the measurement sample and the reference sample. Based on the measurement results, the maximum value of the difference in transmittance in the visible light region between the measurement sample and the reference sample is determined as the maximum transmittance difference.

3. The inspection method according to claim 1, The determining step includes a step of irradiating the bottom of the paper container with light at an illuminance of 6000 lux or more. Testing method.

4. The inspection method according to claim 1, The coloring liquid is in accordance with CIE 1976 L ＊ a ＊ b ＊ L below 80 in color space ＊ has a value, Testing method.

5. The inspection method according to claim 1, The outer surface of the lower part of the paper container is plain white. Testing method.

6. The inspection method according to claim 1, The paper constituting the paper container is in accordance with CIE 1976 L ＊ a ＊ b ＊ L of 40 or more in color space ＊ has a value, Testing method.

7. The inspection method according to claim 1, CIE 1976 L ＊ a ＊ b ＊ The color difference ΔE between the paper constituting the paper container and the coloring liquid in the color space is 3000 or more. Testing method.

8. A process of producing a paper container; After the manufacturing step, inspecting the paper container using the inspection method described in claim 1; A step of sorting paper containers based on the inspection results in the inspection step; Equipped with A method for manufacturing paper containers.

Images