How to remove ink from discarded caps

Abstract

To provide a method for removing ink from waste caps that can remove the printing ink on the waste caps and, in turn, improve the quality of the recycled resin.SOLUTION: The ink removal method for waste caps involves contacting the waste caps with an alkaline aqueous solution L. Here, the alkaline aqueous solution L that is brought into contact with the waste cap may be heated, and the alkaline aqueous solution L may be alkaline electrolytic water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for removing ink for printing applied to the outer surface of a waste cap (such as a market-returned cap), for example, which is suitable for use in removing the ink. Here, the "waste cap" includes those corresponding to only a part of the cap before disposal. For example, a pilfer-proof cap with a tamper-evidence band provided on the lower side of the cap body includes at least (1) the case where the cap is discarded with the tamper-evidence band attached to the cap body, (2) the case where the cap is discarded in a state separated into the cap body and (3) the tamper-evidence band. It is considered that there are these two cases. However, not only the entire cap in the state of (1), but also any of (2) the single cap body and (3) the single tamper-evidence band corresponds to the "waste cap".

Background Art

[0002] Conventionally, waste caps (such as synthetic resin caps for plastic bottles) have been collected in dedicated collection boxes and recycled (reprocessed).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, some waste caps have printing on their outer surfaces. If the printing ink mixes into the recycled resin, there is a problem that the quality of the recycled resin deteriorates.

[0005] In addition, the applicant has previously proposed a technique related to a method for cleaning a content-filled container in a state where the container mouth is sealed with a cap (Patent Document 1). However, it can be said that it is difficult to use this technique for cleaning a waste cap removed from a bottle.

[0006] The present invention has been made with the above-mentioned matters in mind, and its purpose is to provide a method for removing ink from discarded caps that can remove the printing ink applied to the discarded caps, and thereby improve the quality of the recycled resin. [Means for solving the problem]

[0007] To achieve the above objective, the method for removing ink from a discarded cap according to the present invention involves contacting the discarded cap with an alkaline aqueous solution. The alkaline aqueous solution is alkaline electrolyzed water, and the contact is performed by immersing the waste cap in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the waste cap from above as a high-pressure shower of 3.0 MPa or higher. (Claim 1). Here, "alkaline aqueous solution" includes both alkaline drug aqueous solutions, which are made alkaline by dissolving an alkaline agent in water, such as an aqueous solution of sodium hydroxide or an aqueous solution of sodium carbonate, and alkaline electrolyzed water, which is made alkaline by electrolysis.

[0008] In the above method for removing ink from a discarded cap, the alkaline aqueous solution that is brought into contact with the discarded cap is Over 90℃ The process may be carried out by heating (Claim 2).

[0009] In the above method for removing ink from discarded caps, the alkaline aqueous solution is pH 13 or higher This is also acceptable (Claim 3).

[0010] In the above method for removing ink from discarded caps, The waste caps are placed in a tank containing the aforementioned alkaline aqueous solution, and while stirring the waste caps in the tank with a stirring rod, a high-pressure shower of the alkaline aqueous solution is applied to the waste caps using a shower device. The alkaline aqueous solution that has entered the tank from the shower device is discharged from the bottom of the tank and sent back to the shower device, where it is sprayed again onto the waste caps in the tank, and this process is repeated in a circulating manner. (Claim 4) [Effects of the Invention]

[0011] The present invention provides a method for removing ink from discarded caps that can remove the printing ink applied to the caps, thereby improving the quality of the recycled resin.

[0012] In other words, after much trial and error, the inventors discovered that the printing ink applied to discarded caps can be removed by bringing them into contact with an alkaline aqueous solution. The method for removing ink from discarded caps according to the claims of this application removes the printing ink applied to the discarded caps and, consequently, improves the quality of the recycled resin. Furthermore, as a ripple effect of removing the printing ink, dirt is also washed away, reducing the contamination of the recycled material with foreign matter and the persistence of unpleasant odors, thereby improving the value of the discarded caps as a recycled material and their suitability for use in food containers and packaging.

[0013] In the method for removing ink from a discarded cap according to claim 2, the effectiveness of removing the printing ink applied to the discarded cap can be enhanced by heating the alkaline aqueous solution that is brought into contact with the discarded cap.

[0014] Claim Item 1 In the method for removing ink from discarded caps according to the invention, by using alkaline electrolyzed water as the alkaline aqueous solution that comes into contact with the discarded cap, subsequent treatment (waste liquid treatment) can be facilitated.

[0015] Claim Item 1 In the method for removing ink from discarded caps according to the invention, the effectiveness of removing the printing ink applied to the discarded caps can be enhanced by spraying alkaline electrolyzed water onto the discarded caps. [Brief explanation of the drawing]

[0016] [Figure 1] (A) and (B) are explanatory diagrams of an apparatus used in a method for removing ink from discarded caps according to one embodiment of the present invention. [Modes for carrying out the invention]

[0017] Embodiments of the present invention are described below.

[0018] The ink removal method for the discarded cap in this example (hereinafter abbreviated as "this method") is for removing the printing ink applied to the outer surface of the discarded cap. For example, when the discarded cap is the cap of a beverage PET bottle, the printing for product display applied to the top surface of the discarded cap (such as by gravure printing or offset printing, etc.) and the printing of expiration date, etc. applied to the outer peripheral surface of the tamper evidence band (such as by inkjet printing, etc.) are the main targets for removal.

[0019] Except for special ones such as factory-discarded caps that are managed, the discarded caps vary in size and shape, including differences in deformation and the presence or absence of a tamper evidence band (there are cases where the tamper evidence band remains attached and cases where it doesn't, and there are also cases where the tamper evidence band separated from the cap body is recycled separately). Therefore, in this method, one aim is to dissolve and remove the printing ink applied to the discarded cap by bringing the alkaline aqueous solution, which is a chemical solution, into contact with the discarded cap so as not to be affected by the differences in the size and shape of the discarded cap.

[0020] Examples of the discarded caps targeted by this method include caps made of synthetic resin (polypropylene) used for beverage PET bottles.

[0021] As methods for bringing the alkaline aqueous solution into contact with the discarded cap, there are (1) a method of immersing the discarded cap in the alkaline aqueous solution, (2) a method of stirring the discarded cap or the alkaline aqueous solution while the discarded cap is immersed in the alkaline aqueous solution, (3) a method of spraying the alkaline aqueous solution onto the discarded cap (applying a high-pressure shower of the alkaline aqueous solution), etc. For example, method (3) may be carried out simultaneously with or after method (1) or method (2). Also, when stirring, in addition to the discarded cap and the alkaline aqueous solution, for example, a plurality of solid foreign substances insoluble in the alkaline aqueous solution may be added to apply frictional force to the discarded cap.

[0022] Here, when the alkaline aqueous solution is the sodium hydroxide aqueous solution, sodium carbonate aqueous solution, or alkaline electrolyzed water described above, its specific gravity is 1 or more. On the other hand, the specific gravity of a waste cap made of polypropylene used for beverage PET bottles, etc. is about 0.9. Thus, when the specific gravity of the waste cap is smaller than that of the alkaline aqueous solution, the waste cap immersed in the alkaline aqueous solution floats. Particularly in the above method (1), a portion of the waste cap that does not contact the alkaline aqueous solution is formed, raising a concern that the removal of printing ink may be insufficient. Therefore, when implementing method (1), it is preferable to configure it so that the waste cap can be held in a state of being submerged in the alkaline aqueous solution. As an example, with the alkaline aqueous solution and the waste cap housed in a water tank, a lid with a large number of holes through which the alkaline aqueous solution passes but the waste cap does not is inserted downward from above into the water tank, and the lower surface of the lid is held so as to be positioned below the liquid level by applying the weight of the lid or downward pressure to the lid. Such a configuration can also be adopted when implementing the above method (2). However, in method (2), if appropriate stirring is carried out (for example, stirring vigorously so that the waste caps rub against each other) so that the waste cap does not continue to float in the same orientation in the alkaline aqueous solution, the adoption of such a configuration is unnecessary.

[0023] Instead of using the above-mentioned lid configuration, the alkaline aqueous solution may be sprayed in a shower-like manner from above onto the discarded cap immersed in the alkaline aqueous solution (preferably at a high pressure of 3.0 MPa or higher) (i.e., method (1) or (2) and method (3) are performed simultaneously). In this case, the discarded cap floating on the surface of the alkaline aqueous solution will sink into the alkaline aqueous solution due to the spraying of the alkaline aqueous solution from above, and then, even if it floats up due to buoyancy, it will sink again due to the spraying, repeating this motion. As a result, the entire cap will be in complete contact with the alkaline aqueous solution, and the repeated sinking and floating of the discarded cap will also have an agitating effect. Furthermore, if the alkaline aqueous solution sprayed from above comes into contact with the printing ink on the outer surface of the discarded cap, it can be expected that the ink will be removed by the physical agitation, making this method extremely effective for removing printing ink.

[0024] Furthermore, the alkaline aqueous solution brought into contact with the discarded cap may be heated, and heating it to a high temperature of 90°C or higher is particularly effective in removing printing ink. For example, the alkaline aqueous solution used in methods (1) and (2) above may be heated to a high temperature, while the alkaline aqueous solution used in method (3) may be at room temperature or a high temperature.

[0025] Examples of alkaline aqueous solutions used in this example include alkaline chemical aqueous solutions (e.g., sodium hydroxide aqueous solution, sodium carbonate aqueous solution), alkaline electrolyzed water, etc., which are strongly alkaline (pH 10 or higher, and pH 13 or higher is particularly preferred from the viewpoint of ink removal).

[0026] In this case, for example, in the case of alkaline electrolyzed water produced by electrolysis using potassium carbonate, only a very small amount of potassium carbonate (about 0.1% by weight) is present in the alkaline electrolyzed water. Therefore, when the alkaline aqueous solution is alkaline electrolyzed water, it becomes possible to simplify (or eliminate the need to) rinsing the discarded caps after washing and removing printing ink using alkaline electrolyzed water, and to simplify (or eliminate the need to remove) the alkaline chemicals from the wastewater. In other words, the overall configuration (process) can be simplified compared to the case where the above-mentioned alkaline chemical aqueous solution is used.

[0027] Therefore, the specific details of this method will be explained below, divided into two cases: when the alkaline aqueous solution is an alkaline chemical aqueous solution such as sodium hydroxide aqueous solution (when rinsing with rinse water is necessary) and when it is alkaline electrolyzed water (when rinsing with rinse water is unnecessary).

[0028] If the alkaline aqueous solution is an alkaline chemical aqueous solution such as a sodium hydroxide aqueous solution, the alkaline aqueous solution L (alkaline chemical aqueous solution) and the waste caps are placed in the first tank 1 shown in Figure 1(A), and the waste caps are immersed in the alkaline aqueous solution L and stirred with a stirring rod 1a (an example of a stirring means). After that, the waste caps are removed from the first tank 1 and transferred to the second tank 2 shown in Figure 1(B), and while stirring the waste caps in the second tank 2 with a stirring rod 2a (an example of a stirring means), a high-pressure shower of rinsing water W (e.g., clean water) is applied to the waste caps using a shower device 2b (an example of a spraying means). In other words, stirring the waste caps with the stirring rod 2a is done to ensure that the high-pressure shower is applied evenly to all the waste caps. The rinsing water W is discharged from the bottom of the second tank 2 and subjected to appropriate treatment such as removal of alkaline chemicals. At this time, the rinsing water W may be kept in the second tank 2 to a certain extent, or it may not be kept in the second tank 2.

[0029] In the example above, two tanks, the first tank 1 and the second tank 2, are used, but the method is not limited to this, and only one tank may be used. Specifically, for example, an alkaline aqueous solution L (alkaline chemical aqueous solution) and a waste cap are placed in the second tank 2, and the waste cap is immersed in the alkaline aqueous solution L and stirred with a stirring rod 2a. After that, the waste cap is left in the second tank 2, the alkaline aqueous solution L is drained, and a high-pressure shower of rinsing water W is applied to the waste cap in this state using a shower device 2b.

[0030] On the other hand, if the alkaline aqueous solution is alkaline electrolyzed water, the alkaline aqueous solution L (alkaline electrolyzed water) and the waste caps are placed in the first tank 1 shown in Figure 1(A), and the waste caps are immersed in the alkaline aqueous solution L and stirred with a stirring rod 1a. Then, the waste caps are removed from the first tank 1 and transferred to the second tank 2 shown in Figure 1(B), and while stirring the waste caps in the second tank 2 with a stirring rod 2a, a high-pressure shower of the alkaline aqueous solution L is applied to the waste caps using a shower device 2b. In other words, stirring the waste caps with the stirring rod 2a is done to ensure that the high-pressure shower is applied evenly to all the waste caps. The alkaline aqueous solution L that has reached the second tank 2 from the shower device 2b is discharged from the bottom of the second tank 2 and sent back to the shower device 2b, and is sprayed again onto the waste caps in the second tank 2, and this series of flow is repeated to circulate the solution. At this time, the alkaline aqueous solution L may be maintained to some extent in the second tank 2, or it may not be maintained to some extent.

[0031] In the example above, two tanks, the first tank 1 and the second tank 2, are used, but the method is not limited to this, and only one tank may be used. Specifically, for example, an alkaline aqueous solution L (alkaline electrolyzed water) and a waste cap could be placed in the second tank 2, and with the waste cap immersed in the alkaline aqueous solution L, a high-pressure shower of the alkaline aqueous solution L could be applied using a shower device 2b while stirring with a stirring rod 2a.

[0032] The inventors tested several types of discarded caps used on commercially available beverage PET bottles by placing them in a magnetic stirrer. They confirmed that when the discarded caps were immersed in a 5% sodium hydroxide aqueous solution heated to 90°C and stirred for 15 minutes, the printing (ink) for product labeling on the top surface of the discarded caps was removed. The same removal was also achieved when the concentration of the sodium hydroxide aqueous solution was increased to 10%, while all other conditions remained the same.

[0033] Furthermore, when a similar test was conducted using alkaline electrolyzed water instead of sodium hydroxide solution, it was confirmed that when a discarded cap was immersed in alkaline electrolyzed water with a pH of 13.2 heated to 90°C and stirred for 50 minutes, and then the discarded cap was removed from the alkaline electrolyzed water and sprayed with room temperature alkaline electrolyzed water at a pressure of 3.0 MPa, the printing (ink) for the product label on the top surface of the discarded cap was removed. The same removal was also achieved when the stirring time was increased to 60 minutes and all other conditions were kept the same.

[0034] As explained above, this method can remove the printing ink applied to discarded caps, thereby improving the quality of the recycled resin. Specifically, by removing the printing ink from discarded caps, it becomes possible to meet the standards of the Food Sanitation Act in mechanical recycling (physical regeneration method), and the uses of recycled resin derived from caps can be expanded. Furthermore, in chemical recycling (chemical regeneration method), it is expected that the amount of impurities will be reduced, and the recycling process and residue disposal will be lessened.

[0035] Furthermore, the printing residue on discarded caps creates a pattern of black dots, which detracts from the aesthetic appeal of recycled products. However, this method eliminates this problem, and when sorting discarded caps by color in a separate process, it reduces the likelihood of misdetecting the color of the cap body due to the printing surface, making it possible to apply this method to products such as white ones.

[0036] Furthermore, as a ripple effect of removing printing ink using this method, dirt is also washed away, reducing the contamination of recycled materials with foreign matter and the persistence of unpleasant odors, thereby improving the value of discarded caps as recycled materials and their suitability for use in food containers and packaging.

[0037] Furthermore, since this method does not involve scraping off the printing ink from discarded caps using only physical force, it generates almost no resin powder (microplastics), and dust collection becomes unnecessary.

[0038] It should be noted that the present invention is not limited in any way to the embodiments described above, and can be implemented in various ways without departing from the spirit of the invention, and it goes without saying that the modifications described herein can be combined as appropriate. [Explanation of symbols]

[0039] 1. First Tank 1a Stirring rod 2. Second Tank 2a Stirring bar 2b Shower device L Alkaline aqueous solution W Rinse water

Claims

1. Contact the discarded cap with an alkaline solution, The aforementioned alkaline aqueous solution is alkaline electrolyzed water, The aforementioned contact is a method for removing ink from a discarded cap, which involves immersing the discarded cap in the alkaline aqueous solution and spraying the alkaline aqueous solution onto the discarded cap from above as a high-pressure shower of 3.0 MPa or more.

2. The method for removing ink from a discarded cap according to claim 1, wherein the alkaline aqueous solution brought into contact with the discarded cap is heated to 90°C or higher.

3. The method for removing ink from a discarded cap according to claim 1 or 2, wherein the alkaline aqueous solution has a pH of 13 or higher.

4. The method for removing ink from a discarded cap according to Claim 3, wherein the discarded cap is placed in a tank containing the alkaline aqueous solution, the discarded cap in the tank is stirred with a stirring rod, and a high-pressure shower of the alkaline aqueous solution is applied to the discarded cap using a shower device, and the alkaline aqueous solution that has reached the tank from the shower device is discharged from the bottom of the tank and sent back to the shower device, where it is sprayed again onto the discarded cap in the tank, and this series of steps is repeated in a circulating manner.

Images