Pet bottle manufacturing method and pet bottle

Abstract

To provide a direct printing type PET bottle manufacturing method that can improve recycling suitability.SOLUTION: A manufacturing method is a method for producing a PET bottle in which a printing layer 3 including a white printing layer 6 is formed on a surface of a bottle body 2 molded by using a PET resin as a material, wherein an ink weight of a white exposed portion 6a exposed on a surface of the printing layer 3 in the white printing layer 6 relative to a weight of the bottle body 2 is limited so that a haze of a plate 15 obtained by applying predetermined recycling processing to the PET bottle 1 containing the printing layer 3 is 5% or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a so-called direct-printed PET bottle, in which a printed layer is formed on the surface of a bottle body molded from PET resin. [Background technology]

[0002] There are so-called direct-printed PET bottles in which a printed layer is formed on the surface of a bottle body molded from polyethylene terephthalate resin (hereinafter referred to as PET resin). For example, one known technology related to direct-printed PET bottles is to form a peelable label support layer on the surface of the bottle body by treating it with heated water or an alkaline aqueous solution, and then print designs, letters, etc. 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] Various colors of inks are used for the printing layer, and various layers can be formed, including a white printing layer printed with white ink. On the other hand, impurities such as ink are undesirable when recycling PET bottles as raw materials for PET resin. In particular, in bottle-to-bottle recycling, maintaining the transparency of the PET bottle is important for product characteristics. In the PET bottle of Patent Document 1, text and other elements are printed on the label support layer, but the label support layer is peeled off by hand before recycling. Thus, there is a need for improved recyclability of direct-printed PET bottles.

[0005] Therefore, an object of the present invention is to provide a method for manufacturing a direct-printed PET bottle that can improve the suitability for recycling. [Means for solving the problem]

[0006] The manufacturing method of the present invention is a method for manufacturing a PET bottle in which a printed layer including a white printed layer is formed on the surface of a bottle body molded from PET resin, and the range of the white exposed portion of the white printed layer that is exposed on the surface of the printed layer is limited so that the haze of the molded product obtained by applying a specified recycling process to the PET bottle containing the printed layer is within a specified allowable range.

[0007] The PET bottle of the present invention is a PET bottle having a printed layer including a white printed layer formed on the surface of a bottle body molded from PET resin, and the printed layer has a limited range of white exposed portions that are exposed on the surface of the printed layer so that the haze of a molded product obtained by applying a specified recycling process to a PET bottle containing the printed layer is within a specified allowable range. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing an example of a PET bottle manufactured by a manufacturing method according to one embodiment of the present invention. [Figure 2] FIG. 4 is an explanatory diagram for explaining details of a primer layer and an indication layer. [Figure 3] 1A to 1C are diagrams illustrating an example of a printing process applied to a manufacturing method according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing an example of a recycling process. [Figure 5] FIG. 10 is a table summarizing the results of the examples. [Figure 6] FIG. 6 is a graph plotting some of the measurement results in the table of FIG. 5(b). DETAILED DESCRIPTION OF THE INVENTION

[0009] (PET bottles) FIG. 1 shows an example of a PET bottle manufactured by a manufacturing method according to one embodiment of the present invention. The PET bottle 1 in FIG. 1 is used, for example, as a beverage container. The PET bottle 1 includes a bottle body 2 molded into a predetermined shape using PET resin, 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-printed PET bottle. The bottle body 2 is typically molded by blow molding. However, the bottle body 2 may also be molded by other molding methods.

[0010] In FIG. 1 , the printed layer 3 is formed as a generally elliptical label on a portion of the barrel 2a of the bottle body 2, for example. The barrel 2a may be understood as, for example, the mouth 2b of the bottle body 2, particularly the region below position P1 directly below the support ring 2c, and above position P2 directly above the bottom 2d, which narrows or curves toward the ground, or as 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 in multiple locations on the bottle body 2. For example, a printed layer 3 for displaying designs and symbols such as a product name and logo, 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.

[0011] The printing layer 3 includes a primer layer 4 and a display layer 5 laminated on the primer layer 4. 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 a first ink. "Directly" means that the primer layer 4 is adhered to the surface of the bottle body 2 without any other layer interposed between the primer layer 4 and the bottle body 2. The primer layer 4 is, for example, colorless and transparent. The first ink is an ink that has the necessary level of adhesion to the PET resin constituting the bottle body 2 as the printing substrate, and is releasable from the PET resin printing substrate when treated with a specified processing liquid. For example, a radiation-curable ink containing a polymerizable monomer and a polymerizable surfactant is used as the first ink, imparting curability to radiation such as ultraviolet light and releasability to processing liquids such as alkaline aqueous solutions. The first ink is, for example, prepared as an ink suitable for inkjet printing. The radiation is not necessarily limited to ultraviolet light; gamma rays, beta rays, electron beams, visible light, or other radiation may be used as long as it provides activation energy to the ink and cures it. The treatment liquid is, for example, an alkaline aqueous solution, 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, preferably having a sodium hydroxide concentration of 1% or higher, more preferably 1.5% or higher, and even more preferably 2.0% or higher. The concentration here refers to a weight ratio, and this also applies hereinafter. Heated water and alkaline aqueous solution may each be used stepwise as the treatment liquid.

[0012] The display layer 5 is a layer printed on the primer layer 4 using a second ink to form a label, which displays a design, letters, symbols, etc. to be attached to the PET bottle 1. The second ink contains colorants such as pigments and dyes necessary for forming the label. The second ink is prepared in multiple colors necessary for forming the label, for example, five colors including the four colors CMYK and white. The second ink is a radiation-curable ink that contains a polymerizable monomer and is thereby rendered curable by radiation such as ultraviolet light. For 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 used for the first ink. The second ink may also be rendered releasable from the bottle body 2.

[0013] In the example of Fig. 1, the display layer 5 is laminated on the primer layer 4 within a limited area of ​​the primer layer 4. Specifically, the display layer 5 is formed to be slightly smaller than the primer layer 4, and the outer periphery of the primer layer 4 is exposed outside the display layer 5. However, as long as the printing positional accuracy 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 body 2 as the primer layer 4 is peeled off from the bottle body 2.

[0014] (Printing layer) The printed layer 3 will be further described with reference to Figure 2. Figure 2 is an explanatory diagram for explaining the details of the primer layer 4 and the display layer 5. Figure 2 (a) to (c) all show examples of cross-sectional views of the primer layer 4 and the display layer 5. Specifically, as examples of cross-sectional views of the primer layer 4 and the display layer 5, Figure 2 (a) shows a first pattern, Figure 2 (b) shows a second pattern, and Figure 2 (c) shows a third pattern. Note that Figure 2 shows the layer structure of the printed layer 3, and the thickness ratios of the bottle body 2 and the layers 4 and 5 do not necessarily represent the ratios in the actual PET bottle 1.

[0015] As shown in (a) to (c) of Figure 2, the display layer 5 includes a white printed layer 6 and an other-color printed layer 7. The white printed layer 6 is a display layer 5 formed by printing using white ink. The white printed layer 6 is formed so that the area of ​​the white exposed portion 6a, which is the portion exposed on the surface of the printed layer 3, falls within a predetermined range. In the example of Figure 2, white is indicated by the symbol "W." The other-color printed layer 7 is a display layer 5 formed by printing using ink other than white, i.e., the four colors CMYK. In the example of Figure 2, the other-color printed layer 7 is formed, for example, using a single-color ink corresponding to black, but is not limited to this and may be any appropriate color realized using the four colors CMYK. The first to third patterns are distinguished, for example, by how the white printed layer 6 is exposed in the printed layer 3.

[0016] For example, in the first and second patterns, a white printed layer 6 is formed on the primer layer 4, and an other-color printed layer 7 is formed on the white printed layer 6. The range of the exposed white portion differs between the first and second patterns. In the first pattern, the entire white printed layer 6 is covered by the other-color printed layer 7, and no exposed white portion exists. In other words, the range of the exposed white portion is zero. On the other hand, in the second pattern, only a portion of the white printed layer 6 is covered by the other-color printed layer 7, and an exposed white portion 6a is formed in the portion not covered by the other-color printed layer 7. In other words, the first and second patterns have in common that the white printed layer 6 is provided between the primer layer 4 and the other-color printed layer 7, but differ in the presence or absence of the exposed white portion 6a. In this example, the other-color printed layer 7 functions as the ink layer of the present invention.

[0017] In the third pattern, the white printed layer 6 and the other color printed layer 7 are both formed on the primer layer 4. In other words, in the third pattern, the white printed layer 6 and the other color printed layer 7 are not in a layered relationship in which one is formed on top of the other. In this case, the entire white printed layer 6 is exposed on the surface of the printed layer 3, which corresponds to the exposed white portion 6a. The display layer 5 can be formed as appropriate, and as examples, configurations such as those in the first to third patterns are acceptable.

[0018] The display layer 5 is not limited to the first to third patterns, and may be formed as appropriate as long as the range of the white exposed portion 6a falls within a predetermined range. For example, the other color printed layer 7 may be omitted from the display layer 5. In this case, as with the third pattern, all of the white printed layer 6 corresponds to the white exposed portion 6a. Alternatively, the display layer 5 may have a plurality of white printed layers 6 and a plurality of other color printed layers 7. When a plurality of white printed layers 6 are formed, the display layer 5 is formed so that the combined range of the plurality of white exposed portions 6a falls within a predetermined range.

[0019] (Printing process) Next, an example of a printing step for forming the printed layer 5 will be described with reference to Figure 3. Figure 3 shows an example of a printing step applied to a manufacturing method according to one embodiment of the present invention. The example in Figure 3 shows a case in which the printed layer 3 is formed using ultraviolet-curable inkjet inks as the first and second inks. In addition to the printing step, the manufacturing method for the PET bottle 1 also includes various well-known steps for manufacturing the PET bottle 1, such as a step of forming the bottle body 2 by blow molding, as appropriate, but descriptions of these will be omitted.

[0020] As shown in Figure 3, the printing process includes, in order, three steps S11 to S13, as an example. Specifically, a primer layer forming step is carried out in step S11. The primer layer forming step is a step for forming the primer layer 4. In the primer layer forming step, a 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.

[0021] The primer layer 4 is formed with a pencil hardness of at least 4B, preferably 3B, and more preferably 2B. The primer layer 4 provides peelability for the printed layer 3 from the PET resin. However, if the primer layer 4 is too soft, the printed layer 3 may partially peel off during distribution or use of the PET bottle 1, resulting in impaired print quality. The inventors' studies have confirmed that a primer layer 4 with a hardness of 4B or higher can effectively prevent peeling of the printed layer 3, while a hardness of 3B or higher can more effectively prevent peeling of the printed layer 3, and a hardness of 2B or higher can even more effectively prevent peeling. Pencil hardness evaluation is performed by rubbing the primer layer 4 with pencils of different hardnesses to determine the hardness based on the presence or absence of scraping marks. The pencil hardness at which no scraping marks are observed is evaluated as the hardness of the primer layer 4. The hardness of the primer layer 4 may be evaluated in accordance with the pencil scratch test specified in the former JIS K 5400 of the Japanese Industrial Standards.

[0022] In step S12, a display layer forming process is performed. The display layer forming process is a process for forming the display layer 5. In the display layer forming process, second inks for forming the display layer 5 are sequentially applied onto the primer layer 4 by color, and the ink is temporarily cured by irradiating it with ultraviolet light after each application, thereby printing the display layer 5. For example, when forming the display layer 5 of the first or second pattern in the example of FIG. 2, these processes are performed for each layer, i.e., the white printed layer 6 and the other-color printed layer 7. Specifically, first, the second ink corresponding to white is applied onto the primer layer 4, and the white printed layer 6 is formed by temporary curing. Next, the second ink corresponding to black is applied onto the white printed layer 6, and the other-color printed layer 7 is formed by temporary curing. Furthermore, when forming the display layer of the third pattern in the example of FIG. 2, second inks for realizing the white printed layer 6 and the other-color printed layer 7 are sequentially applied onto the primer layer 4 by color, and the white printed layer 6 and the other-color printed layer 7 are formed by temporary curing.

[0023] In the display layer forming process, the exposed white portion 6a of the white print layer 6 is formed so that it falls within a predetermined range. The predetermined range is a range specified by standards regarding the haze of a molded product obtained by applying a predetermined recycling process to a PET bottle 1. Specifically, the predetermined range is set so that the haze of a molded product obtained by applying a predetermined recycling process to a PET bottle 1 falls within a predetermined allowable range. The allowable range can be set appropriately according to standards determined depending on the use of the molded product after recycling, and is set to 5%, as an example. In other words, when forming the display layer 5 in the display layer forming process, the range of the exposed white portion 6a is limited so that the haze of a molded product obtained by the predetermined recycling process falls within 5%.

[0024] The inventors' studies have confirmed that the ratio of the ink weight in the white exposed portion 6a to the weight of the bottle body 2 affects the haze of the molded product. Therefore, the range of the white exposed portion 6a is determined by the ratio of the ink weight in the white exposed portion 6a to the weight of the bottle body 2. Hereinafter, this ratio may be referred to as the white weight ratio. The inventors' studies have also confirmed that when the white weight ratio is 0.214%, the haze of the molded product obtained through a specified recycling process is 5% or less. Therefore, when the display layer 5 is formed in the display layer forming step, the range of the white exposed portion 6a is limited so that the white weight ratio is 0.214% or less.

[0025] In step S13, a full curing process is performed. In this process, ultraviolet light is irradiated onto the entire printed layer 3 to completely cure it. The ultraviolet light used in this process has a peak wavelength of, for example, 365 to 395 nm, and the exposure dose per unit area is 0.5 mJ / cm2 or more. For example, the ultraviolet light source is a UV-LED that emits ultraviolet light at a peak wavelength. Other light sources, such as a mercury lamp or ultraviolet fluorescent lamp, may also be used for irradiating ultraviolet light. After the full curing process, a water washing process or other process may be performed as appropriate to remove residual monomer. The preliminary curing process may be omitted in the primer layer forming process and the display layer forming process. During ultraviolet irradiation, an inert gas, such as nitrogen gas, may be supplied to the printed area to reduce the oxygen concentration, thereby suppressing oxygen polymerization inhibition and improving the quality of the printed layer 3.

[0026] (Recycling process) Next, an example of a recycling process applied to PET bottles 1 will be described with reference to FIG. 4. FIG. 4 is a diagram showing an example of the steps of a recycling process. The example in FIG. 4 shows the steps of a PET bottle recycling process using a so-called mechanical recycling method. The mechanical recycling method is a method widely used in the recycling of PET bottles. In mechanical recycling, first, 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 crushed products.

[0027] 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. One example of the treatment liquid 12 is an alkaline aqueous solution (sodium hydroxide aqueous 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 float up in the treatment liquid and are separated from the flakes 11. The washing and separation process may be carried out in stages using heated water and an alkaline aqueous solution in that order. In the washing and separation process using an alkaline aqueous solution, a rinse process is also carried out in which the washed flakes are washed with water while being stirred to remove the alkali.

[0028] 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, which are not recycled products. Also, below, pellets made from virgin raw materials may be referred to as "virgin pellets." Then, in step S24, recycled products such as plates 15 are molded from the pellets 14. The recycled products are not limited to plates 15, and may be molded into various forms such as fibers, sheets, and bottles. Virgin pellets may be mixed with the pellets 14 obtained by the recycling process during molding of the recycled products. The plate 15 is used as the molded product to measure recyclability. For example, the plate 15 used for the measurement is formed to a thickness of 3 mm. Note that a bottle body 2 may be molded instead of the plate 15. In this case, the haze may be measured on a portion of the bottle body 2 having a thickness of approximately 3 mm.

[0029] As described above, according to this embodiment, the range of the white exposed portion 6a is limited so that the haze of the plate 15 obtained by applying a predetermined recycling process to the printed layer 3 of the bottle body 2 falls within a predetermined tolerance range. This improves the recyclability of direct-printed PET bottles. For example, in bottle-to-bottle recycling, a haze of 5% or less is often required for recycled PET bottles. Therefore, if 5% is adopted as the predetermined tolerance range and the range of the white exposed portion 6a is limited so that the haze of the plate 15 falls within 5%, the recyclability of bottle-to-bottle recycling can be improved.

[0030] The white printed layer 6, including the white exposed portion 6a, is formed on the primer layer 4. The primer layer 4 uses an ink that has the property of being peelable from the PET resin substrate when treated with a specific treatment liquid. As the primer layer 4 peels, the overlying white printed layer 6 also peels from the PET resin. This facilitates peeling of the white printed layer 6 from the bottle body 2. Furthermore, according to the inventor's findings, when the white printed layer 6 is covered with another ink layer, the underlying white printed layer tends to peel easily along with the other ink layer. Therefore, even when the white printed layer 6 is formed under another ink layer, as in the first or second pattern of the example in Figure 2, peeling of the white printed layer 6 from the bottle body 2 can be facilitated. These features further improve recyclability.

[0031] The present invention is not limited to the above-described embodiments, and may be embodied in embodiments with appropriate modifications or changes. Furthermore, the present invention may be embodied in embodiments obtained by appropriately combining various technical means included in the above-described embodiments and the following modified embodiments. [Example]

[0032] Examples related to the manufacturing method of the PET bottle according to the above-described embodiment will be described below, however, the technical scope of the present invention is not limited to the following examples.

[0033] (Evaluation method) The method for evaluating recyclability applied to the following examples will be described. In the following examples, the recyclability is evaluated by dividing it into a basic physical property evaluation and a reuse suitability evaluation. Details of the basic physical property evaluation and the reuse suitability evaluation are as follows.

[0034] 1. Basic 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 solution heated to 85–90°C. The flakes were then washed with water while stirring to remove the alkaline components. The alkaline washing was performed by rinsing 30 times. Here, 8 mm mesh refers to the particle size of flakes obtained when sieving through a screen mesh with pores set to a diameter of 8 mm. Repelletization of the washed flakes was performed as a sample. PET resin alone was prepared as a comparison material. When evaluating PET bottles with printed labels, virgin PET resin, the raw material used to mold the bottle body, can be used as a comparison material.

[0035] (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. The color difference of the sample compared to the comparison material is 5 or less in L value, 2 or less in a value, and 3 or less in b value. The haze of the 3mm thick part of the stepped plate made from the sample is 5% or less. - When drying the pellets used as samples, there should be no fusion between the pellets.

[0036] 2.Reuse suitability evaluation The evaluation of reusability varies depending on the use of the recycled product molded from re-pellets, but the evaluation method for the so-called bottle-to-bottle process, in which PET bottles are recycled from other PET bottles, is as follows.

[0037] · In the same way 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 pellets. Comparative flakes are prepared from virgin raw materials using the same procedure as for the test flakes, crystallized in the same manner as above, and mixed with the same weight of virgin pellets to prepare comparative pellets. The test pellets are produced under conditions that result in an IV increase ratio of 90% to 120% compared to the control pellets. The color value of the test pellets 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.

[0038] (Example 1: Measurement of the effect of color on haze, etc.) The impact of five CMYKW color inks on recyclability was measured according to the basic physical property evaluation criteria of the evaluation method described above. The impact of each color on color difference and haze became clear, and the results are shown in Figure 5(a). Figure 5(a) is a table showing the results of measuring the impact of five color inks on color difference and haze. In the table of Figure 5(a), figures are shown to three decimal places, with the fourth decimal place rounded off. Errors in the total ink weight, etc., are due to the effect of rounding off. The same applies to the table of Figure 5(b).

[0039] In Example 1, the PET bottles for testing were produced under the following test conditions. Ink used: Radiation curable ink (disclosed in International Publication No. 2022 / 225018) The ink used was Bottle weight: 28g (500ml capacity) Bottle body weight: 14g Weight of the first ink (ink for the primer layer) and the second ink (ink for the display layer): as shown in the table in FIG. 5(a). · RIP (Raster Image Processor) settings are: Amount: 14PL, Image quality: 720 x 720 Dpi. The five colors of CMYKW were measured using a Nippon Denshoku SD6000, and color difference was measured using a Nippon Denshoku ZE6000. Haze was measured using a Nippon Denshoku COH7700 haze meter in accordance with Japanese Industrial Standard JIS K7136.

[0040] As shown in Figure 5(a), the ink weight of the primer layer was measured at 0.104 grams for all colors. The primer layer is indicated by the symbol "P" in the example of Figure 5(a). A single-color display layer was formed on top of the primer layer, and measurements were taken for each color. The ink weight of each color in the display layer was 0.069 grams for white, and 0.064 grams for the other colors. The sum of the ink weight of the primer layer and the ink weight of the display layer is the total ink weight of the printing layer. The total ink weight was 0.173 grams for a display layer with only white, and 0.167 grams for all display layers with only other colors.

[0041] When the display layer was white only, i.e., when only a white printed layer was formed, the haze value was 5.6%, exceeding the recyclability standard of 5% or less. Regarding color difference, the difference in L value was 1.44, the a value was 0.48, and the b value was 1.50, all of which were within the recyclability standard. Similarly, when the display layer was formed in black, cyan, magenta, and yellow, the haze values ​​were 2.38%, 2.72%, 2.52%, and 2.54%, respectively, all of which were within the recyclability standard of 5% or less. Regarding color difference, the a value when the cyan display layer was used and the L value when the yellow display layer was used both exceeded the recyclability standard, but all other values ​​were within the recyclability standard. These measurement results confirmed that white ink had the greatest impact on haze by color. Similarly, regarding the impact on color difference, cyan ink had the greatest impact on the a value, and yellow ink had the greatest impact on the L value.

[0042] (Example 2: Measurement of the effect of white ink weight on haze) Based on the results of Example 1, the effect of white ink weight on haze was measured in more detail. In Example 2, haze was measured in the same manner as in Example 1, according to the basic physical property evaluation criteria of the evaluation method. The results are shown in Figure 5(b). Figure 5(b) is a table showing the haze values ​​measured for different white ink weights. In the table of Figure 5(b), the vertical columns represent measurements using different ink weights, and the horizontal columns represent various conditions such as weight and the haze value measurement results for each measurement. Furthermore, in the measurements of Figure 5(b), black was used uniformly as the color other than white, and a printed layer was used in which a white printed layer was formed on a primer layer using white ink, and a printed layer of another color was formed on top of that using black ink, as in the first pattern in Figure 2(a) or the second pattern in Figure 2(b).

[0043] In Example 2, a PET bottle for testing was produced according to the following test conditions. Ink used: Radiation curable ink (disclosed in International Publication No. 2022 / 225018) The ink used was Bottle weight: 28g (500ml capacity) Bottle body weight: 14g Weight of the first ink (ink for the primer layer) and the second ink (ink for the display layer): as shown in the table in FIG. 5(b). · RIP (Raster Image Processor) settings are: Amount: 14PL, Image quality: 720 x 720 Dpi. Haze was measured using a Suga Test Instruments HZ-V3 haze meter in accordance with Japanese Industrial Standard JIS K7136.

[0044] The table in Figure 5(b) shows five measurement results (1) to (6), but the measurement result in (1) was reused from Example 1. Similarly, the measurement in (2) corresponds to the case where the display layer was formed with black ink in Example 1, so the result from Example 1 was also reused. The measurement result in (6) was also performed separately before the measurements in (3) to (5). Note that the other-color printed layers were formed to cover the white printed layer, and all colors of ink were applied so that the weight per unit area was constant. Therefore, the weight of the exposed white portion was calculated by subtracting the weight of the ink other than white from the weight of the white ink. The table in Figure 5(b) also shows the results of simple subtraction for the weight of the exposed white portion. Although negative weights are seen, these mean that the entire white printed layer was covered by the other-color printed layers, and the ink weight of the exposed white portion can be considered to be zero.

[0045] As shown in Figure 5(b), in measurement (6), the haze was measured using a smaller white ink weight of 0.05 grams than in measurement (1), but the haze value was 3.18, a decrease from 5.60 in measurement (1). From the results of (1) and (6), it was inferred that the haze value increases as the white ink weight or the ratio of white ink weight to bottle weight increases. For this reason, measurements (3) to (5) were carried out. The white ink weights in measurements (3) to (5) were 0.055 grams, 0.060 grams, and 0.066 grams, respectively. Based on the trends seen in the measurement results of (1) and (6), these were ink weights that were assumed to result in a haze value of 5%.

[0046] However, the actual measurement results were different from what was expected, with haze values ​​of 1.99%, 2.07%, and 2.28%, respectively, lower than the trends obtained from the measurement results in (1) and (6). In this measurement, the white printed layer was sandwiched between the primer layer and the other color printed layer, and peeled off together with the upper other color printed layer, i.e., the black ink. This reduced the impact of the remaining white ink on haze, which is thought to be the reason why the actual haze values ​​were lower than the expected trends. Taking this into consideration, it is clear that the white ink affects the haze value, but the main factor is thought to be the extent of the exposed white area in the printed layer, rather than simply the ink weight or the weight of the white ink relative to the bottle weight.

[0047] Figure 6 is a graph plotting some of the measurement results in the table of Figure 5(b). Specifically, in the example of Figure 6, three measurement results (1), (5), and (6) from the measurement results in Figure 5(b) are plotted. In the graph of Figure 6, the vertical axis represents the haze value (%), and the horizontal axis represents the ink weight (grams) of the white exposed portion.

[0048] As shown in Figure 6, a clear linear trend was found among the three measurement results. In other words, it was confirmed that there is a clear relationship between the ink weight of the white exposed portion and the haze value, and that this relationship is linear. Furthermore, the linear trend in the graph in Figure 6 indicates that the haze value is 5% or less when the weight of the white exposed portion is up to 0.06 grams. Therefore, the range of the white exposed portion where the haze value is within 5% is determined, for example, by 0.06 grams or by the bottle weight ratio of 0.214%, calculated by dividing this weight by the bottle weight of 28 grams. Furthermore, for example, when the weight per unit area of ​​the white printed layer is constant, the range of the white exposed portion where the haze value is within 5% may be determined by the area of ​​the white exposed portion, the ratio of the area of ​​the white exposed portion to the area of ​​the printed layer, or the ratio of the area of ​​the white exposed portion to the surface area of ​​the bottle body.

[0049] In the above evaluation method, the haze value standard is set to within 5%, but the range of the white exposed portion may be set according to an appropriate standard. If a different standard is applied to the haze value, the range of the white exposed portion that falls within the different standard may be set based on, for example, the graph in FIG. 6.

[0050] Various aspects of the present invention derived from the above-described embodiments and modifications will be described below. In the following description, corresponding components shown in the accompanying drawings will be written in parentheses to facilitate understanding of each aspect of the present invention, but the present invention is not limited to the illustrated forms.

[0051] The manufacturing method of the present invention is a method for manufacturing a PET bottle (1) having a printed layer (3) including a white printed layer (6) formed on the surface of a bottle body (2) molded from PET resin, and limits the range of the white exposed portion (6a) of the white printed layer that is exposed on the surface of the printed layer so that the haze of a molded product (15) obtained by applying a specified recycling process to the PET bottle containing the printed layer is within a specified allowable range.

[0052] The inventors discovered that there is a correlation between the color of the printed layer and haze when recycling direct-printed PET bottles. In particular, the exposed white portion of the white printed layer formed with white ink, which is exposed on the surface of the printed layer, has a significant impact on haze. It was discovered that limiting the range of the exposed white portion, such as weight, can improve haze during recycling. According to the present invention, the range of the exposed white portion is limited so that the haze of the molded product obtained by applying a specified recycling process to the printed layer of the bottle body falls within a specified allowable range. This improves the recyclability of direct-printed PET bottles.

[0053] The PET bottles may be subjected to an appropriate recycling process as a predetermined recycling process. For example, in one embodiment of the present invention, the predetermined recycling process may include crushing the PET bottles containing the printed layer with an 8 mm mesh (S21), stirring the resulting crushed product (11) in a 1.5% sodium hydroxide solution at 85°C to 90°C, and then washing with water while stirring to perform alkaline washing to remove alkaline components (S22).

[0054] The predetermined allowable range of haze may be set as appropriate depending on the use of the recycled PET resin, its recyclability, and the like. For example, in bottle-to-bottle recycling, a haze of 5% or less is often required for recycled PET bottles. Therefore, for example, in one embodiment of the present invention, 5% may be adopted as the predetermined allowable range, and the range of the exposed white portion may be limited so that the haze of the molded article is 5% or less. In this case, the recyclability of the bottle-to-bottle recycling can be improved.

[0055] The range of the white exposed portion may be determined by various factors related to the predetermined allowable range of haze, such as the weight of the white ink used therein, the ratio of the weight of the white ink to the weight of the bottle body, or the area. According to the inventor's findings, it has been found that the ratio of the ink weight in the white exposed portion to the weight of the bottle body is related to haze. Therefore, for example, in one embodiment of the manufacturing method of the present invention, the range of the white exposed portion may be specified by the ratio of the ink weight in the white exposed portion to the weight of the bottle body.

[0056] The white printed layer may be entirely or partially exposed on the surface of the bottle body. In other words, the entire white printed layer may be a white exposed portion, or only a portion may be a white exposed portion. The printed layer may or may not include layers other than the white printed layer. For example, the printed layer may include a white printed layer and another ink layer. In this case, the white printed layer and the other ink layer may be formed in a laminated manner or as the same layer. Similarly, the printed layer may include a primer layer that is easily peeled from the bottle body by a predetermined treatment, and an indication layer formed on top of the primer layer to include the white printed layer.

[0057] Specifically, for example, in one embodiment of the manufacturing method of the present invention, at least a portion of the white printed layer may be covered with an ink layer (7) of a color other than white. Similarly, for example, in one embodiment of the manufacturing method of the present invention, the printed layer may include a primer layer (4) that has the property of being peeled from the surface of the bottle body by a predetermined treatment liquid, and an indicator layer (5) formed on the primer layer so as to include the white printed layer. According to the inventor's findings, when the white printed layer is covered with another ink layer, the underlying white printed layer tends to peel off easily along with the other ink layer. Therefore, whether at least a portion of the white printed layer is covered with another ink layer or the white printed layer is formed on the primer layer, peeling of the white printed layer from the bottle body can be promoted, thereby further improving recyclability.

[0058] The PET bottle of the present invention is a PET bottle (1) having a printed layer (3) including a white printed layer (6) formed on the surface of a bottle body (2) molded from PET resin, wherein the printed layer has a limited range of white exposed portion (6a) that is exposed on the surface of the printed layer so that the haze of a molded product (15) obtained by applying a specified recycling process to a PET bottle containing the printed layer is within a specified allowable range. [Explanation of symbols]

[0059] 1 PET bottle 2 Bottle body 3 printing layer 4 Primer layer 5 Display layer 6 White printing layer 7 Other color printing layer (ink layer) 11 Flakes (crushed) 15 Plate (molded product) 6a White exposed area

Claims

1. A method for manufacturing a PET bottle in which a printed layer including a white printed layer is formed on the surface of a bottle body molded from a PET resin, comprising: A manufacturing method in which the range of the white exposed portion of the white printed layer that is exposed on the surface of the printed layer is limited so that the haze of a molded product obtained by applying a specified recycling process to a PET bottle containing the printed layer is within a specified allowable range.

2. The manufacturing method according to claim 1, wherein the predetermined recycling process includes crushing the PET bottles containing the printed layer using an 8 mm mesh, stirring the resulting crushed products in a 1.5% sodium hydroxide solution at 85°C to 90°C, and then washing with water while stirring to remove alkaline components.

3. The predetermined tolerance is set to 5%. The method according to claim 2 , wherein the range of the white exposed portion is limited so that the haze of the molded article is 5% or less.

4. The manufacturing method according to claim 1 , wherein the range of the white exposed portion is specified by a ratio of the weight of ink in the white exposed portion to the weight of the bottle body.

5. The manufacturing method according to claim 1 , wherein at least a portion of the white print layer is covered with an ink layer of a color different from white.

6. A manufacturing method described in any one of claims 1 to 5, wherein the printing layer has a primer layer that has the property of being peeled off from the surface of the bottle body by a predetermined processing liquid, and an indication layer that is formed on the primer layer so as to include the white printing layer.

7. A PET bottle having a printed layer including a white printed layer formed on the surface of a bottle body molded from PET resin, The printed layer has a limited range of white exposed portions that are exposed on the surface of the white printed layer so that the haze of a molded product obtained by applying a specified recycling process to a PET bottle containing the printed layer is within a specified allowable range.

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