How to remove ink from shrink labels

Abstract

The present invention provides a method for efficiently removing an ink layer.　This method comprises: a step for immersing a shrink label piece 71, which is provided with an alkali-removable ink layer, into an alkali solution 80; and a step for immersing the shrink label piece 71, which has been immersed into the alkali solution 80, into water 90. In the water immersion step, the ink layer 93 is removed from the shrink label piece 71 by stirring the shrink label piece 71.

Description

Technical Field

[0001] The present disclosure relates to a method for removing an ink layer from a shrink label.

Background Art

[0002] In recent years, plastic products such as polyethylene terephthalate bottles (PET bottles) have been widely used. From the viewpoints of resource conservation and the environment, etc., it is strongly required to reuse plastic products.

[0003] Among plastic products, the reuse of PET bottles has already been established. However, a plastic shrink label having an ink layer printed for displaying product information or the like may be attached to the body of a PET bottle, but the reuse of this shrink label has not yet been achieved.

[0004] One of the factors inhibiting the reuse of shrink labels is that the ink layer cannot be efficiently removed from the shrink label. When the ink layer cannot be efficiently removed from the shrink label, pellets with useful value cannot be produced from the shrink label.

[0005] For example, Patent Document 1 describes a method of heating and shrinking a heat-shrinkable label under non-aqueous immersion conditions and then detaching and removing the ink layer using low-temperature alkaline water.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Although it is possible to remove the ink layer by the method described in Patent Document 1, due to the increasing environmental awareness in recent years, a more efficient method for removing the ink layer is desired.

Means for Solving the Problems

[0008] According to the embodiment disclosed herein, there is provided a method for removing an ink layer from a shrink label, including a step of immersing the shrink label having an alkali-detachable ink layer in an alkali, and a step of immersing the shrink label after the alkali immersion in water. In the step of immersing in water, the ink layer is removed from the shrink label by stirring the shrink label.

Advantages of the Invention

[0009] According to the embodiment disclosed herein, it is possible to provide a method for removing an ink layer more efficiently than before.

Brief Description of the Drawings

[0010]

Figure 1

Mode for Carrying Out the Invention

[0011] Figs. 1(a) to (j) show a diagram illustrating an example of the flow of a method for removing an ink layer from a shrink label according to an embodiment. Hereinafter, with reference to Figs. 1(a) to (j), a method for removing an ink layer from a shrink label according to the embodiment will be described.

[0012] <Recovery Step> First, as shown in Fig. 1(a), the PET bottle 10 is recovered in the recovery box 12. Here, a shrink label 11 having an ink layer is attached to the body portion of the PET bottle 10. The ink layer is a printing layer for product display and the like.

[0013] The shrink label 11 is a shrink label provided with an alkali-detachable ink layer on at least one surface of a heat-shrinkable shrink film (base material). The alkali-detachable ink layer means an ink layer that is detached from the shrink film when stirred at 1500 rpm for 5 minutes in an 80°C to 90°C aqueous alkali solution 80 (described later). For example, when the ink layer itself has alkali solubility or alkali swelling properties and the ink layer is detached from the shrink film, or when the anchor coat layer has alkali solubility or alkali swelling properties and the ink layer on the anchor coat layer is detached from the shrink film. The anchor coat layer is a layer provided between the shrink film and the ink layer to enhance the adhesion between the two layers.

[0014] Examples of the shrink film include polyester films made of polyethylene terephthalate, polyethylene naphthalate, etc.; styrene-based films made of styrene-butadiene block copolymers, etc.; olefin-based films made of olefin resins such as polyethylene and polypropylene; vinyl chloride-based films made of vinyl chloride resins, so-called biomass films made of polylactic acid resins, etc. These may be foamed films. The shrink film may be single-layer or a laminate of two or more layers including the same type or different types of shrink films. The color of the shrink film is not particularly limited and may be, for example, milky white or transparent.

[0015] From the viewpoint of shrinkage adhesion to various containers, etc., the heat shrinkage rate of the shrink film in at least one direction X (main shrinkage direction) is preferably 30% or more, more preferably 50% or more. The thickness of the shrink film can be appropriately selected in consideration of the handleability of the shrink label 11, etc., and can be, for example, about 10 to 100 μm, preferably about 15 to 60 μm. Note that these numerical values of the shrink film are the numerical values of the shrink film used for the production of the shrink label 11 before being attached to a container such as a PET bottle 10.

[0016] The surface of the shrink film may be subjected to a conventionally known surface treatment as necessary. Examples of the surface treatment include corona discharge treatment for enhancing the adhesion to the ink layer.

[0017] The ink layer can be composed of, for example, either an oil-based ink or an aqueous ink. Examples of the method for forming the ink layer on the surface of the shrink film include gravure printing, flexographic printing, screen printing, or inkjet printing. The thickness of the ink layer can be appropriately selected depending on the application and the like, and can be, for example, about 0.1 to 100 μm. Further, an ink layer removable by alkali can be formed by using an ink having alkali solubility or alkali swellability.

[0018] The anchor coat layer can be composed of a resin composition for a conventionally known anchor coat layer. Examples of the method for forming the ink layer on the surface of the shrink film include the same printing methods as those for the ink layer. The thickness of the anchor coat layer can be appropriately selected and can be, for example, about 0.1 to 20 μm. Further, an ink layer removable by alkali can be formed by using a resin composition for an anchor coat layer having alkali solubility or alkali swellability and forming an ink layer thereon.

[0019] <Compression step> Next, as shown in Fig. 1(b), the recovered PET bottle 10 is compressed with the shrink label 11 attached thereto to obtain a labeled bottle 20 with a shrink label.

[0020] <Integration step> Next, as shown in Fig. 1(c), the labeled bottle 20 with a shrink label is sent to a recycling factory 30 and integrated.

[0021] <Separation step> Next, as shown in FIG. 1(d), at the recycling factory 30, the shrink label 11 is removed from the PET bottle 10 with the shrink label 20, and the PET bottle 10 and the shrink label 11 are separated. The objects to be removed from the PET bottle 10 include the normal label 40 other than the shrink label 11. The PET bottle 10 from which the shrink label 11 and / or the normal label 40 is separated is reused in the recycling process of the existing PET bottle. Examples of the normal label 40 include a label having a non-alkali releasable printing layer or a non-shrink label.

[0022] <Sorting process> Next, as shown in FIG. 1(e), by sorting the shrink label 11 and the normal label 40, the shrink label 11 is separated from the normal label 40 and recovered. The recovered normal label 40 is reused, for example, in a thermal recycling process.

[0023] <Preheating process> Next, as shown in FIG. 1(f), the shrink label 11 provided with the ink layer is preheated. The method of preheating the shrink label 11 is not particularly limited as long as it can suppress the amount by which the shrink label piece shrinks and curls in the alkali immersion described later. However, the preheating is performed so that the temperature of the preheating is the same as or higher than the temperature of the alkali immersion. From the viewpoint of efficiently reducing the adhesion between the shrink film and the ink layer in the alkali immersion described later, it is preferable that the temperature of the preheating is 5°C or more higher than the temperature of the alkali immersion in order to sufficiently reduce the above-mentioned curling amount.

[0024] Examples of the method of preheating the shrink label 11 include a method of passing the shrink label 11 through a hot air tunnel 61 or a method of immersing the shrink label 11 in the warm water 60 in a warm water tank 62.

[0025] However, from the following viewpoints 1) to 4), as a method of preheating the shrink label 11, it is preferable to use a method of immersing the shrink label 11 in the warm water 60 in the warm water tank 62 rather than a method of passing the shrink label 11 through the hot air tunnel 61. 1) When using hot air, the shrink label 11 removed from the PET bottle 10 is blown away by the hot air, making control difficult. 2) The method of immersing in warm water is easier to control the temperature. 3) The method of immersing in warm water has a smaller footprint of the device. 4) The method of immersing in warm water is less likely to cause uneven shrinkage of the shrink label 11 and can shrink uniformly.

[0026] For example, when preheating the shrink label 11 by immersing the shrink label 11 in the warm water 60 in the warm water tank 62, it can be performed by immersing the shrink label 11 in warm water at about 80°C to 90°C for about 10 seconds to 20 seconds.

[0027] The preheating temperature means the surface temperature of the shrink label 11 during preheating. Therefore, when preheating the shrink label 11 by immersing the shrink label 11 in the warm water 60 in the warm water tank 62, the preheating temperature can be replaced with the temperature of the warm water. Also, when preheating the shrink label 11 by passing the shrink label 11 through the hot air tunnel 61, the preheating temperature can be replaced with the temperature of the hot air.

[0028] <Crushing process> Next, as shown in FIG. 1(g), the pre-heated shrink label 11 is crushed by a crusher 70 to produce shrink label pieces 71. The method of crushing the pre-heated shrink label 11 is not particularly limited as long as the size of the shrink label pieces 71 generated after the crushing is smaller than the size of the pre-heated shrink label 11. For example, the pre-heated shrink label 11 can be crushed to a size such that in the alkali immersion described below, the adhesion between the shrink film and the ink layer is sufficiently reduced, and in the water immersion described below, the ink layer can be efficiently removed from the shrink label pieces 71.

[0029] <Alkali Immersion Step> Next, as shown in FIG. 1(h), the shrink label pieces 71 are immersed in an alkali. The alkali immersion can be performed, for example, by immersing the shrink label pieces 71 in an aqueous alkali solution 80 at 65°C to 90°C, more preferably 70°C to 90°C, in a hot alkali tank 82 for about 30 seconds to 20 minutes.

[0030] As described above, in the present embodiment, the temperature of the pre-heating is set to be the same as or higher than the temperature of the alkali immersion. The temperature of the alkali immersion means the surface temperature of the shrink label pieces 71 during the alkali immersion. Therefore, the temperature of the alkali immersion can be replaced with the temperature of the aqueous alkali solution 80 in which the shrink label pieces 71 are immersed. From the viewpoint of sufficiently reducing the adhesion between the shrink film and the ink layer in the alkali immersion, the temperature of the alkali immersion is preferably 65°C or higher. The upper limit of the temperature of the alkali immersion is theoretically 100°C, more preferably the temperature of the alkali immersion is 85°C or higher and 95°C or lower, and even more preferably the temperature of the alkali immersion is 80°C or higher and 90°C or lower.

[0031] As the alkaline aqueous solution 80, for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), an aqueous solution of an alkali metal carbonate such as sodium carbonate (Na2CO3), an aqueous solution of an alkali metal hydrogen carbonate such as sodium hydrogen carbonate (NaHCO3), or aqueous ammonia can be used.

[0032] The concentration of the alkaline substance in the alkaline aqueous solution 80 can be appropriately selected within a range that does not impair operability, workability, etc. The concentration of the alkaline substance in the alkaline aqueous solution 80 is, for example, about 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably about 1 to 3% by weight. Also, the alkaline aqueous solution 80 may contain other components such as a surfactant.

[0033] In the alkali immersion, it is preferable to immerse the shrink label piece 71 in the alkaline aqueous solution 80 so that the entire shrink label piece 71 can come into contact with the alkaline aqueous solution �0. Also, in the alkali immersion, it is preferable that the shrink label piece 71 is not stirred. That is, in the alkali immersion, it is preferable that the alkaline aqueous solution 80 is not stirred. However, extremely gentle stirring that does not cause detachment of the ink layer from the shrink label piece 71 may be included in the case where it is not stirred. Thereby, while reducing the adhesion between the alkali-soluble ink layer and / or other layers of the alkali-soluble anchor coat layer provided on the shrink label piece 71, complete separation between the ink layer and the shrink film can be efficiently suppressed.

[0034] <Water immersion and stirring step> Next, as shown in FIG. 1(i), the shrink label piece 71 is immersed in water. The water immersion can be performed, for example, by taking out the shrink label piece 71 immersed in the alkaline aqueous solution 80 from the hot alkaline tank 82 and immersing the shrink label piece 71 in the water 90 in the water tank 91. In the water immersion step, the shrink label piece 71 is stirred. The stirring of the shrink label piece 71 can be performed, for example, by rotating the stirring blade 92 in the water tank 91. Also, in the water immersion step, the shrink label piece 71 only needs to be dispersed in the water 90, and it is not necessarily required to sink the shrink label piece 71 in the water 90.

[0035] Due to the alkali immersion, the adhesion between the shrink film and the ink layer of the shrink label piece 71 is in a sufficiently reduced state. By continuously stirring such a shrink label piece 71 in water, the ink layer is removed from the shrink film. As a result, the shrink film piece 101 and the ink coating film 103 exist in the water 90. The ink coating film 103 is a film in which the ink layer removed from the shrink label piece is finely divided.

[0036] The amount of the shrink label piece 71 in water is preferably 20 g / L or more, and more preferably 40 g / L or more. When the amount of the shrink label piece in water is 20 g / L or more, the shrink label pieces 71 can sufficiently rub against each other in water, whereby the shrink film piece 101 and the ink coating film 103 are well separated. Also, the amount of the shrink label piece 71 in water is preferably 1000 g / L or less, and more preferably 500 g / L or less. In this case, the adhesion of the ink coating film 103 to the surface of the shrink film piece 101 can be suppressed. Note that the amount of the shrink label piece 71 in water is the weight (g) of the shrink label piece with respect to the total amount (L) of the water 90 in the water tank 91.

[0037] The temperature of the water 90 is not particularly limited, and can be, for example, normal temperature (23°C to 27°C). The stirring speed is also not particularly limited, and any speed at which the shrink label piece 71 in the water tank 91 is sufficiently stirred may be used.

[0038] <Separation process> Next, as shown in FIG. 1(j), the shrink film piece 101 and the ink coating film 103 are separated. Specifically, for example, after the ink layer is removed from the shrink label piece by the first net 100 having a relatively large opening, the shrink film piece 101 is collected, and the ink coating film 103 smaller than the shrink film piece 101 is collected by the second net 102 having a relatively small opening.

[0039] Thereafter, the shrink film piece 101 collected by the first net 100 can be reused as a plastic raw material for manufacturing plastic products such as pellets. Also, by mixing the shrink film piece 101 into the raw material of a new shrink label, it can be reused as a shrink label. On the other hand, the ink coating film 103 collected by the second net 102 can be reused, for example, in a thermal recycling process.

[0040] <Function and effect> The method for removing the ink layer from the shrink label of the embodiment includes a step of immersing the shrink label having an ink layer removable by alkali in an alkali (alkali immersion step), and a step of immersing the shrink label piece after being immersed in the alkali solution in water (water immersion and stirring step). In the step of immersing in water, the ink layer is removed from the shrink label by stirring the shrink label. The removal method of the embodiment can remove the ink layer from the shrink label more efficiently than before by including at least these steps.

[0041] For example, as in the prior art, when a shrink label is immersed in an alkaline solution and the alkaline solution is stirred to remove the ink layer from the shrink film in the alkaline solution, there is a risk that the hot alkaline tank will be contaminated with the ink. In a hot alkaline tank contaminated with ink, the effect of reducing the adhesion between the ink layer and the shrink film may become insufficient, and there is also concern that it will be difficult to reuse the alkaline solution. In addition, when disposing of the contaminated alkaline solution, it is considered that the concentration operation for reducing the disposal amount is accompanied by danger. There is also concern that precise control of the stirring speed is required to prevent the alkaline solution from splashing.

[0042] On the other hand, in the removal method of the embodiment, due to the alkali immersion step, the adhesion between the ink layer that can be desorbed by alkali and the shrink film is sufficiently reduced, and then, due to the subsequent water immersion and stirring step, the shrink film and the ink layer are separated. That is, since it is the water tank that is contaminated with the ink, the risk that the effect of reducing the adhesion between the ink layer and the shrink film by the alkaline solution becomes insufficient is low. In addition, the concentration operation of the contaminated water is easy. Also, precise splash prevention like that of the alkaline solution is not required. For the above reasons, according to the removal method of the embodiment, the ink layer can be removed from the shrink label more efficiently than in the prior art.

[0043] Further, the removal method of the embodiment can further include a step of preheating the shrink label (preheating step) and a step of crushing the preheated shrink label (crushing step) before the alkali immersion step. By further providing the preheating step and the crushing step in the removal method of the embodiment, the ink layer can be removed from the shrink label more efficiently.

[0044] Specifically, by providing a crushing step, the shrink label is crushed into shrink label pieces prior to alkali immersion. By crushing the shrink label and subjecting it to alkali immersion and water immersion in the state of smaller shrink label pieces, the ink layer can be efficiently removed from the shrink label.

[0045] Here, when shrink label pieces that have not been preheated are immersed in alkali, the shrink label pieces shrink while curling round and round in the alkali aqueous solution. It is very difficult to remove the ink layer from the curled small pieces of shrink label. The shrink label attached to a PET bottle or the like has been thermally shrunk once at the time of attachment, but the shrinking ability still remains in the shrink label. Therefore, when the temperature of the alkali aqueous solution during alkali immersion is high, the shrink label pieces will further thermally shrink. On the other hand, when the temperature of the alkali aqueous solution is low, the ink layer cannot be efficiently removed from the shrink label pieces.

[0046] Therefore, in the present embodiment, before crushing the shrink label into shrink label pieces, preheating of the shrink label is performed at a temperature equal to or higher than the temperature of alkali immersion to pre-thermally shrink it. Then, the shape of the shrink label can be made, for example, a wavy shape with a small degree of curling. When preheating of the shrink label is performed after crushing the shrink label, the shrink label pieces will curl (be rolled up) as a whole, which is not suitable for removing the ink layer.

[0047] Then, the pre-heated shrink label is crushed into shrink label pieces. The shrink label pieces obtained by crushing a shrink label with a small degree of curling also have a small degree of curling.

[0048] Thereafter, such a shrink label piece is subjected to the above-described alkali immersion at a temperature equal to or lower than the preheating temperature. Thereby, even when the temperature of the alkaline aqueous solution during the alkali immersion is high, it is possible to suppress the shrinkage of the shrink label piece during the alkali immersion, and thereby, the adhesion between the shrink label piece and the ink layer can be uniformly reduced.

[0049] In particular, generally, many of the shrink labels 11 removed from containers such as PET bottles 10 have a side length of 10 cm or more. After heat-shrinking such a large shrink label 11 by preheating, the efficiency of removing the ink layer at several centimeters square, preferably 5 cm square or less, can be significantly improved.

[0050] Examples of the shrink label 11 suitable for the method of the present embodiment include shrink labels having a shrinkage rate of 30% or more, preferably 40% or more, more preferably 50% or more, measured in the radial direction (main shrinkage direction) of the container, after being removed from a container such as a PET bottle 10 and immersed in a warm bath at 95°C for 10 seconds.

Example

[0051] <Experimental Example 1> First, using a raw roll of a PET-based shrink film with a thickness of 20 μm, a tubular shrink film with a thickness of 20 μm × height (width) of 15 cm × circumference of 24 cm was prepared. An ink layer with a thickness of 2 μm was provided on the surface of the tubular shrink film to produce a shrink label. An alkali-soluble ink (manufactured by Dainichi Seika Kogyo Co., Ltd., product name "CycleFine") was used for the ink layer. Next, a PET bottle with a shrink label was produced by shrinking the shrink label while it was attached to a tubular PET bottle with an outer diameter of 54 mm. The shrinkage rate of the shrink label at this time was about 30%, and the area of the shrink label after attachment was about 70% of the area of the shrink label before attachment. Then, the shrink label was peeled off from the PET bottle.

[0052] Next, while gently stirring the warm water, the shrink label peeled from the PET bottle was immersed in warm water at 80°C for 20 seconds for preheating. As a result, the area (length × width) of the shrink label became about 50% of the area of the shrink label before preheating (the area of the shrink label after attachment).

[0053] Next, the shrink label after preheating was crushed to produce shrink label pieces in a substantially square shape with a length of 40 mm × a width of 40 mm.

[0054] Thereafter, 1 kg of the shrink label pieces was immersed in a 1.5 wt% NaOH aqueous solution (50 L) at 70°C for 10 minutes. At this time, while submerging the entire shrink label pieces in the NaOH aqueous solution, the NaOH aqueous solution was not stirred.

[0055] Next, all the shrink label pieces were taken out from the NaOH aqueous solution, put into water (50 L) at 27°C, and stirred at 3500 rpm for 5 minutes.

[0056] After going through the above steps, the shrink label pieces were visually observed and separated into a film (Film A) in which no ink layer was visually observed on the surface of the shrink film and a film (Film B) in which an ink layer was visually observed on the surface of the shrink film. When calculating the weight percentage of Film A with respect to the total of the weight of Film A and the weight of Film B, the value was 73%. The ink layer removed from the shrink film existed as a coating film in water, while no coating film existed in the NaOH aqueous solution.

[0057] <Experimental Example 2> In Experimental Example 2, the same method as in Example 1 was carried out except that 2 kg of shrink label pieces were used. Also in Example 2, when calculating the weight percentage of Film A with respect to the total of the weight of Film A and the weight of Film B, the value was 93%. The ink layer removed from the shrink film existed as a coating film in water, while no coating film existed in the NaOH aqueous solution.

[0058] Although the embodiments and examples have been described as above, it has been planned from the beginning to appropriately combine each configuration of the above-described embodiments and examples.

[0059] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0060] 10 PET bottle, 11 shrink label, 12 collection box, 20 label with shrink label, 30 recycling factory, 40 normal label, 60 warm water, 61 hot air tunnel, 62 warm water tank, 70 crusher, 71 shrink label piece, 80 alkaline aqueous solution, 82 hot alkaline tank, 90 water, 91 water tank, 92 stirring blade, 100 first net, 101 shrink film piece, 102 second net, 103 ink coating film.

Claims

1. A step of immersing a shrink label having an alkali-detachable ink layer in alkali, A step of immersing the shrink label after the alkali immersion in water, and including, In the step of immersing in alkali, the shrink label is not stirred, In the step of immersing in water, the ink layer is removed from the shrink label by stirring the shrink label. A method for removing an ink layer from a shrink label.

2. Before the step of immersing in alkali, A step of preheating the shrink label, A step of crushing the preheated shrink label, and including, In the step of preheating, the temperature of the preheating is the same as or higher than the temperature of the alkali immersion. The method for removing an ink layer from a shrink label according to Claim 1.

3. In the step of immersing in water, the amount of the shrink label in water is 20 g / L or more. The method for removing an ink layer from a shrink label according to Claim 1 or Claim 2.

4. The temperature of the alkali immersion is 65°C or higher. The method for removing an ink layer from a shrink label according to any one of Claims 1 to 3.

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