Direct printing type plastic bottle

Abstract

To provide a direct printing type plastic bottle that can ensure recyclability.SOLUTION: In a plastic bottle 1 according to the present invention in which a printing layer 3 is formed on the surface of a bottle body 2 molded from a PET resin material, the weight of ink used for forming the printing layer 3 is 2.5% or less relative to the weight of the bottle body 2, the plastic bottle 1 containing the printing layer 3 is crushed with a 8 mm mesh, the obtained crushed product is stirred in a sodium hydroxide solution having a concentration of 1.5% at 85°C to 95°C, and then the crushed product is subjected to alkali washing of washing with fresh water while stirring to remove an alkali component, and when a plate-like molded product having a thickness of 3 mm is molded using the crushed product after washing, the haze of the molded product is 5% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a so-called direct-printed PET bottle in which a display such as a label is printed on the surface of the bottle body. [Background technology]

[0002] Known technologies relating to so-called direct printing type PET bottles, in which designs, letters, and other display materials are printed on the surface of PET bottles molded from polyethylene terephthalate resin (hereinafter referred to as PET resin), include a technology in which a peelable label support layer is formed on the surface of the bottle body by treatment with heated water or an alkaline aqueous solution, and the designs, letters, and the like are printed on the label support layer using radiation-curable ink (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4505875 Summary of the Invention [Problem to be solved by the invention]

[0004] In direct-printed PET bottles, the bottle body and the printed layer are integrated, so removing the ink components during the recycling process becomes an issue. This becomes an issue when the recycling process is carried out by mechanical recycling, which is currently the mainstream. In particular, in bottle-to-bottle recycling of PET bottles, maintaining the transparency of the PET bottle is important in terms of product characteristics. As a result of extensive research by the inventors, it was found that even if a peelable printed layer is formed by treatment with an alkaline aqueous solution, when the PET bottle is flaked during the mechanical recycling process, if the flakes are bent, the printed layer cannot be completely removed, and the resin after the recycling process lacks transparency.

[0005] Therefore, an object of the present invention is to provide a direct-printed PET bottle that can ensure recyclability. [Means for solving the problem]

[0006] According to the inventors' research, it was found that by adjusting the contents of the printed layer (position, amount of ink, etc.), it is possible to obtain a PET bottle that ensures transparency after mechanical recycling. Specifically, by adjusting the contents of the printed layer of the PET bottle so that the haze when the recycled PET resin is molded into a plate is 5% or less, problems in recycling can be prevented.

[0007] In light of this knowledge, one embodiment of the direct printing type PET bottle of the present invention is a PET bottle having a printed layer formed on the surface of a bottle body molded from PET resin, wherein the weight of the ink used to form the printed layer is 2.5% or less of the weight of the bottle body, the PET bottle containing the printed layer is crushed using an 8 mm mesh, the resulting crushed product is stirred in a 1.5% sodium hydroxide solution at 85°C to 95°C, and then washed with clean water while stirring to remove the alkaline components, and when the washed crushed product is used to mold a 3 mm thick plate-shaped molded product, the haze of the molded product is 5% or less.

[0008] The efficiency of ink component separation during the recycling process is related to the weight of the ink used to form the printed layer, and the higher the weight of the bottle body or the ratio of the ink weight to the body of the bottle body, the more likely the ink components will remain without being separated. On the other hand, if the weight of the ink is set to the above range relative to the weight of the bottle body, it is advantageous to ensure recyclability and transparency. And by using haze as an index for the PET resin of the above embodiment, it is possible to provide a PET bottle that ensures transparency and recyclability.

[0009] In the PET bottle of the above embodiment, the color differences of the 3 mm-thick plate-like molded product compared with a comparative material made of virgin PET resin may be ΔL 5 or less, Δa 2 or less, and Δb 3 or less, thereby further improving recyclability.

[0010] In the PET bottle of the above embodiment, the printed layer may be formed of a radiation curable ink. This allows the ink to be instantly fixed when the printed layer is formed, and printing efficiency can be improved. Furthermore, since the components of the printed layer do not dissolve in the alkaline solution during the above-mentioned alkaline cleaning, the peeled printed layer is easily physically removed, and even considering the difficulty of completely removing the printed layer, the food safety of the recycled PET resin is easily ensured in terms of elution.

[0011] In the PET bottle of the above embodiment, the weight of the ink used to form the printed layer may be 5.0% or less of the weight of the body of the bottle body. Here, the body of the PET bottle refers to a region that is below the mouth, particularly the support ring, and above the bottom where the body diameter decreases or is bent toward the ground surface. The inventors have found that, in the body of the PET bottle or when the bottle wall is less than 0.5 mm thick, bending of the flakes that cannot completely remove the peeling layer of the ink component described above is likely to occur when the flakes are made in the recycling process, whereas such bending hardly occurs in the mouth or bottom of the PET bottle, or in the part of the bottle wall that is 0.5 mm thick or more. [Brief description of the drawings]

[0012] [Figure 1] 1 is a front view of a PET bottle according to one embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] 5A to 5C are diagrams showing an example of a process for printing a primer layer and an indication layer. [Figure 4] FIG. 2 is a diagram showing an example of a recycling process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1 shows a PET bottle according to one embodiment of the present invention. The PET bottle 1 in FIG. 1 is used as a beverage container as an example. The PET bottle 1 includes a bottle body 2 formed into a predetermined shape using PET resin as a material, and a printed layer 3 printed at an appropriate position on the surface of the bottle body 2. By printing the printed layer 3 on the surface of the bottle body 2, the PET bottle 1 is positioned as a direct printing type PET bottle. The bottle body 2 is typically formed by a blow molding method. However, the bottle body 2 may be formed by other molding methods. As shown in FIG. 2, the printed layer 3 includes a primer layer 4 and an indication layer 5 laminated on the primer layer 4. Note that FIG. 2 shows the layer structure of the printed layer 3, and the thickness ratio of the bottle body 2 and each layer 4, 5 does not necessarily indicate the ratio in the actual PET bottle 1.

[0014] In FIG. 1, the printed layer 3 is formed as an approximately elliptical label on a part of the body 2a of the bottle body 2, for example. The body 2a may be understood as, for example, a region located below the mouth 2b of the bottle body 2, particularly a position P1 directly below the support ring 2c, and above a position P2 directly above the bottom 2d that shrinks or bends toward the ground surface, or a region of the bottle body 2 where the wall thickness is 0.5 mm or less. The position and shape of the printed layer 3 may be appropriate. The printed layer 3 may be formed at multiple locations on the bottle body 2. For example, a printed layer 3 for displaying designs and symbols such as a product name and a logo mark, and a printed layer 3 for displaying information required to be displayed on the product, such as product ingredient information and manufacturer information, may be formed in different locations on the bottle body 2.

[0015] The primer layer 4 is printed as a base for the display layer 5. The primer layer 4 is printed directly on the surface of the bottle body 2 using the first ink. "Direct" means that the primer layer 4 is adhered to the surface of the bottle body 2 without any other layer being interposed between the primer layer 4 and the bottle body 2. The primer layer 4 is colorless and transparent, for example. For the first ink, an ink is used that has a necessary level of adhesion to the printing base, which is the PET resin constituting the bottle body 2, and has a property that allows it to be peeled off from the PET resin of the printing base when treated with a predetermined treatment liquid. For example, a radiation-curable ink that contains a polymerizable monomer and a polymerizable surfactant and is thus given curability against radiation such as ultraviolet light and peelability against a treatment liquid such as an alkaline aqueous solution is used as the first ink. For example, the first ink is prepared as an ink suitable for inkjet printing. The radiation is not necessarily limited to ultraviolet light, and gamma rays, beta rays, electron beams, visible light, or the like may be used as long as it exerts the action of applying active energy to the ink to cure the ink. The treatment liquid is, for example, an alkaline aqueous solution, which is preferably heated to 85°C or higher, more preferably 90°C or higher. The alkaline aqueous solution is, for example, a sodium hydroxide aqueous solution, and the sodium hydroxide concentration is preferably 1% or higher, more preferably 1.5% or higher, and even more preferably 2.0% or higher. The concentration here is a weight ratio, and the same applies below. Heated water and alkaline aqueous solution may each be used stepwise as the treatment liquid.

[0016] The display layer 5 is a layer printed by laminating it on the primer layer 4 using the second ink in order to form a label expressing a design, character, symbol, etc. to be attached to the PET bottle 1 as a display. The second ink contains a colorant such as a pigment or dye required to form the label. The second ink is prepared in a plurality of colors required to form the label, for example, in four colors of CMYK. The second ink is a radiation-curable ink that contains a polymerizable monomer and is thus given curability against radiation such as ultraviolet light. As an example, the second ink is prepared as an ink suitable for inkjet printing. The radiation used to cure the ink may be the same as that of the first ink. The second ink may also be given peelability from the bottle body 2.

[0017] As is clear from Fig. 1, the display layer 5 is laminated on the primer layer 4 within a limited range of the primer layer 4. In the example of Fig. 1, the display layer 5 is formed to be somewhat smaller than the primer layer 4, and the outer peripheral portion of the primer layer 4 is exposed outside the display layer 5. However, as long as the positional accuracy of the printing can be ensured, the display layer 5 may be formed to be the same size as the primer layer 4. By limiting the range of the display layer 5 as described above, the display layer 5 can be reliably separated from the bottle main body 2 as the primer layer 4 is peeled off from the bottle main body 2.

[0018] Fig. 3 shows an example of a process for forming the printed layer 3 using ultraviolet-curable inkjet inks as the first ink and the second ink. In the example of Fig. 3, first, in step S11, the first ink is applied to a target position on the surface of the bottle body 2, and the applied ink is irradiated with ultraviolet light to temporarily cure it, thereby printing the primer layer 4. Note that the temporary curing process may be omitted.

[0019] In the next step S12, second inks for forming the display layer 5 are applied on the primer layer 4 in order by color, and each time an ink is applied, the ink is temporarily cured by irradiating it with ultraviolet light, thereby printing the display layer 5. Furthermore, in step S13, a full curing process is performed in which the entire printed layer 3 is irradiated with ultraviolet light to completely cure it. The ultraviolet light used in the full curing process has, for example, a peak wavelength in the range of 365 to 395 nm, and the exposure amount per unit area is 0.5 mJ / cm. 2 That is all. As an example, the light source of the ultraviolet light is a UV-LED that emits light with a peak wavelength in the ultraviolet range. Other light sources such as a mercury lamp and an ultraviolet fluorescent lamp may be used for irradiating the ultraviolet light. After the main curing process, a water washing process or the like may be appropriately performed to remove residual monomers. The temporary curing process may be omitted. When irradiating the ultraviolet light, an inert gas such as nitrogen gas may be supplied to the printing area to reduce the oxygen concentration, thereby suppressing the oxygen polymerization inhibition effect and improving the quality of the printing layer 3.

[0020] In the above PET bottle 1, the weight of the ink used to print the printed layer 3, i.e., the total weight of the first ink used to print the primer layer 4 and the second ink used to print the display layer 5, is set to 2.5% or less of the weight of the bottle body 2. Hereinafter, this ratio may be referred to as the ink weight ratio. When the first ink used to form the primer layer 4 is transparent, the weight of only the second ink, i.e., the weight of only the ink used to form the display layer 5, relative to the weight of the bottle body 2 may be specified as the ink weight ratio, and the ink weight ratio may be set to 2.5% or less. According to the study by the inventors, it has been confirmed that setting the ink weight ratio to 2.5% or less is advantageous in ensuring the recyclability of the PET bottle 1. In addition, considering that the weight of the body 2a of the bottle body 2 accounts for 50% of the weight of the bottle body 2, the weight of the ink used to form the printed layer 3 may be set to 5.0% or less of the weight of the body 2a of the bottle body 2. In this case, similarly to the above, if the first ink used to form the primer layer 4 is transparent, the weight of only the second ink used to form the display layer 5 may be treated as the ink weight.

[0021] The primer layer 4 is formed with a hardness of at least 4B or more, preferably 3B or more, and more preferably 2B or more, when evaluated by pencil hardness. The primer layer 4 imparts peelability to the printed layer 3 from the PET resin, but if its hardness is excessively low, that is, if the primer layer 4 is softer than necessary, the printed layer 3 may partially peel off during distribution or use of the PET bottle 1, which may impair the print quality. According to the inventors' study, it has been confirmed that if the hardness of the primer layer 4 is 4B or more, peeling of the printed layer 3 can be suppressed to a practically acceptable level, if the hardness is 3B or more, peeling of the printed layer 3 can be suppressed more effectively, and if the hardness is 2B or more, peeling can be suppressed even more effectively. The evaluation by pencil hardness is an evaluation method in which the hardness is judged by the presence or absence of scraping marks on the primer layer 4 when the primer layer 4 is rubbed with pencils of different hardness, and the pencil hardness at which no scraping marks are generated is evaluated as the hardness of the primer layer 4. The hardness of the primer layer 4 may be evaluated according to a pencil scratch test specified in the former JIS K 5400 of the Japanese Industrial Standards.

[0022] Next, the recycling process of the PET bottle 1 will be described. Figure 4 shows an example of the process of recycling the PET bottle by the so-called mechanical recycling method. The mechanical recycling method is a method that is widely used in the recycling process of the PET bottle. In the mechanical recycling, first, a pre-processing such as removing foreign matter is carried out, and then, in step S21, the PET bottle 1 is crushed to obtain flakes 11 as an example of a crushed product.

[0023] In the next step S22, the flakes 11 are immersed in a predetermined treatment liquid 12 and the treatment liquid 12 is stirred to wash the flakes 11. The treatment liquid 12 is, for example, an alkaline aqueous solution (aqueous sodium hydroxide solution) heated to 85°C to 90°C and adjusted to a concentration of 1.5%. At this stage, the primer layer 4 attached to the flakes 11 peels off from the flakes 11 together with the display layer 5, and the peeled ink components 13 rise in the treatment liquid and are separated from the flakes 11. The washing and separation process may be performed stepwise using heated water and an alkaline aqueous solution in that order. In the washing and separation process using an alkaline aqueous solution, a rinsing process is also performed in which the washed flakes are washed with clean water while being stirred to remove the alkali.

[0024] In the next step S23, the flakes 11 from which the ink components 13 have been separated are granulated to obtain pellets 14. Hereinafter, the obtained pellets may be referred to as re-pellets to distinguish them from pellets made from virgin raw materials that are not recycled products. Hereinafter, pellets made from virgin raw materials may be referred to as virgin pellets. Thereafter, in step S24, recycled products such as plates 15 are formed using the pellets 14 as a raw material. The recycled products are not limited to plates 15, and may be formed into various forms such as fibers, sheets, bottles, etc. When forming the recycled products, virgin pellets may be mixed into the pellets 14 obtained by the recycling process.

[0025] Next, a description will be given of an example of a method for evaluating the recyclability of the PET bottle 1. In the following example, the recyclability is evaluated by dividing it into a basic physical property evaluation and a reuse suitability evaluation.

[0026] 1. Fundamental physical property evaluation (1) Preparation of samples The PET bottles to be evaluated were crushed to produce flakes with an 8 mm mesh. These were vigorously stirred for 15 minutes in a 1.5% sodium hydroxide aqueous solution heated to 85-90°C, and then the flakes were washed with clean water while stirring to remove the alkaline components, thus performing alkaline washing. Here, 8 mm mesh refers to the particle size of the flakes obtained when sieving through a screen mesh with a pore size set to a diameter of 8 mm. Re-pellets were made from the washed flakes to use as samples. PET resin alone was prepared as a comparison material. When a PET bottle with a printed label is to be evaluated, virgin raw material of PET resin, which is used as a material for molding the bottle body, can be used as a comparison material.

[0027] (2) Basic physical property evaluation criteria The main items in the basic physical property evaluation criteria are as follows: The amount of powder generated during flake production is 120% or less compared to the comparison material. When the sample is re-pelletized from the flakes, the IV retention is 90% or more compared to the control material. Regarding the color difference of the sample compared to the comparison material, the difference in L value is 5 or less, the difference in a value is 2 or less, and the difference in b value is 3 or less. The color was measured using a Nippon Denshoku Kogyo ZE6000. The haze in the 3 mm thick section of the stepped plate made from the sample is 5% or less. The haze was measured using a haze meter (NDH8000 manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with the Japanese Industrial Standard JIS K7136. When drying the sample pellets, there should be no fusion between the pellets.

[0028] 2.Reuse suitability evaluation The assessment of reusability varies depending on the use of the recycled product molded from the re-pellets, but the assessment method specifically for recycling PET bottles from other PET bottles, known as bottle-to-bottle, is as follows:

[0029] · In the same manner as in the evaluation of basic physical properties, crushing, washing and separation processes are carried out to produce flakes, which are then exposed to 50°C hot air for 3 hours to remove any adhering water and produce test flakes. Dry the test flakes at 140°C for 4 hours to crystallize them. Mix the crystallized test flakes with the same weight of virgin pellets and re-pelletize them to prepare test re-pellets. Prepare comparative flakes from virgin raw materials using the same procedure as for the test flakes, crystallize them in the same manner as above, and mix them with the same weight of virgin pellets to prepare comparative pellets. The test pellets are produced under conditions where the IV increase ratio is 90% or more and 120% or less compared to the control pellets. The color value of the test repellet is 12 or less. The haze of the 3mm thick part of the recycled stepped plate molded from the test pellets is 5% or less.

[0030] According to the study by the inventors, when a PET bottle having a printed layer formed on the surface of the bottle body is crushed with an 8 mm mesh, the above-mentioned alkaline washing, that is, a treatment using a sodium hydroxide aqueous solution with a concentration of 1.5% at 85°C to 90°C and a washing treatment with clean water are performed, and then a plate-shaped molded product having a thickness of 3 mm is molded. If the haze of the molded product is 5% or less, sufficient transparency suitable for bottle-to-bottle reuse of PET bottles is maintained, and recyclability is ensured. In addition, it was confirmed that, with respect to the color difference when the above-mentioned molded product is compared with a comparative material made of virgin PET resin, if the difference in L value ΔL is 5 or less, the difference in a value Δa is 2 or less, and the difference in b value Δb is 3 or less, recyclability can be more reliably ensured. Furthermore, it was confirmed that if the above-mentioned ink weight ratio is 2.5% or less, transparency is ensured in terms of the residual rate of ink components during the washing and separation process, and the haze and color difference physical property values ​​of the molded product molded using the recycled material, and an evaluation that can be judged to be recyclable can be obtained. EXAMPLES

[0031] Example 1 PET bottles for testing were prepared according to the following test conditions. Ink used: Radiation curable ink (the ink disclosed in WO 2022 / 225018 was used.) Bottle weight: 28g (500ml capacity) Bottle body weight: 14g Weight of first ink (primer layer ink): 0.35g Weight of second ink (display layer ink): 0.35g - Second ink color scheme: C, Y, M, K, W, 5 colors, evenly distributed Example 2 Weight of first ink (primer layer ink): 0.08g Weight of second ink (display layer ink): 0.09g A PET bottle was produced in the same manner as in Example 1, except for the above. Example 3 Weight of the first ink (primer layer ink): 0.05g Weight of second ink (display layer ink): 0.05g A PET bottle was produced in the same manner as in Example 1, except for the above.

[0032] Test PET bottles were crushed with an 8 mm mesh to prepare test flakes, and the above-mentioned alkaline cleaning was applied to the obtained test flakes. As a result, the residual ratio of ink components was 10 ppm or less in all examples. In addition, the test flakes were re-pelletized, and a sheet-like molded product was molded using the re-pelletized product, and the evaluation was performed following the above-mentioned evaluation of recyclability, with the results shown in Table 1. In all examples, the molded products had a haze of 5% or less, and the color difference ΔL5 when compared with a comparative material made of virgin raw materials was Δa or less, and Δb was 3 or less, confirming that the molded products were suitable for recycling.

[0033] [Table 1] [Explanation of symbols]

[0034] 1 PET bottle 2 Bottle body 3 printing layer 4 Primer layer 5 Display layer

Claims

1. A PET bottle having a print layer formed on the surface of a bottle body molded from PET resin, The weight of the ink used to form the printed layer is 2.5% or less of the weight of the bottle body; A PET bottle including the printed layer is crushed using an 8 mm mesh, the crushed product obtained is stirred in a 1.5% sodium hydroxide solution at 85°C to 95°C, and then washed with clean water while stirring to remove the alkaline components, and when the washed crushed product is used to mold a plate-shaped product having a thickness of 3 mm, the molded product has a haze of 5% or less. This is a direct printing type PET bottle.

2. 2. The PET bottle according to claim 1, wherein the color difference between the molded product and a comparative material made of virgin PET resin is ΔL of 5 or less, Δa of 2 or less, and Δb of 3 or less.

3. 3. The PET bottle according to claim 1, wherein the printed layer is formed of a radiation curable ink.

4. 3. The direct printing type PET bottle according to claim 1, wherein the weight of the ink used to form the printed layer is 5.0% or less of the weight of the barrel of the bottle body.

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