Eco-friendly printing ink that can be recycled

Abstract

One embodiment of the present invention provides an ink composition for printing on a plastic container. The ink composition enables the removal of the ink printed on the plastic container during a washing process, and consequently, allows for the recycling of PET bottles. That is, since the plastic bottles can be recycled without damage, the amount of waste can be reduced and the amount of recycling can be increased.

Description

Technology Field

[0001] The present invention relates to an ink composition for printing on plastic containers, and more specifically, to an ink composition for facilitating the recycling of plastic containers. Background Technology

[0003] Plastic is indispensable in modern social life, and if current plastic consumption patterns are maintained, 1.1 billion tons of plastic will be used annually by 2050, consuming 20% ​​of total petroleum for production. It is predicted that the cumulative amount of waste plastic generated by 2050 will be 33 billion tons, of which 12 billion tons will be incinerated, 12 billion tons will be landfilled or dumped, and only 9 billion tons will be recycled.

[0004] However, currently, plastic cups and food containers are printed with logos or text using chemical printing inks, making them difficult to recycle; instead, they are disposed of through incineration or landfill. This is pointed out as a major cause of environmental pollution, as well as a waste of resources.

[0005] Accordingly, the plastic container industry is making efforts to improve and increase recycling. To this end, collaboration is taking place among container manufacturers, brand owners, end users, and government agencies. Current recycling infrastructure and processes must be compatible to adequately respond to changes in the industry. In particular, it is important to utilize current industry standard processes to provide recyclable products. These recycling processes typically involve high-temperature washing and crushing, and labels must be removed during the recycling process.

[0006] In the past, when labeling attachments (ink printing, label stickers, shrink film, etc.) were printed directly on the body, they were classified as materials or structures difficult to recycle, leading to problems such as being unable to recycle or the imposition of heavy recycling fees. However, as of 2022, even if a label is printed directly on the body, classification and grade adjustments are being reviewed based on a verification and determination of whether the ink can be washed and separated during the recycling process. Therefore, it is necessary to use eco-friendly ink to enable the washing and separation of the ink during the recycling process. Consequently, there is a need for eco-friendly ink that complies with the Ministry of Environment's notification regarding the determination of attachment separation. The problem to be solved

[0008] The present invention has been devised to solve the aforementioned problems, and one embodiment of the present invention provides an ink composition for printing on a plastic container.

[0009] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0011] As a technical means for achieving the aforementioned technical problem, one aspect of the present invention is,

[0012] An ink composition for printing on a plastic container is provided, comprising: an oligomer consisting of one or more functionalized ester groups; a pigment comprising BaSO4; a photoinitiator; and an additive; and having a viscosity of 2,000 to 30,000 cps at a temperature of 25°C.

[0013] The above oligomer may be a urethane-based oligomer that performs a saponification reaction, a urethane-based oligomer that does not perform a saponification reaction, an acrylic-based oligomer, an epoxy-based oligomer, a polyester-based oligomer, or a mixture thereof.

[0014] The above oligomer may have a molecular weight of 10,000 to 40,000.

[0015] The above oligomer may be characterized as being in an amount of 10 to 70 parts by weight based on 100 parts by weight of the total ink composition.

[0016] In addition to the pigment containing BaSO4 above, one or more of the following may be included: a pigment containing CaCO3, a pigment containing Mg(OH)2, and a pigment containing TALC.

[0017] The above photoinitiator may be characterized as being one or more of benzophenone, TPO (2,4,6-trimethylbenzoyl-phosphine oxide), Irgacure-1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone), Irgacure-184 (1-hydroxy-cyclohexyl-phenyl-ketone), and Irgacure-907 (2-methyl-1-[4(methylthio)phenyl]-2-(4-mor-pholinyl)-1-propanone).

[0018] The above photoinitiator may be characterized as being in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the total ink composition.

[0019] The above additive may be characterized as being at least one selected from the group consisting of defoaming agents, thickening agents, plasticizers, dispersants, adhesives, and drying agents.

[0020] The above ink composition may further include vinyl-based monomers.

[0021] The above ink composition may further include wax or a wax mixture.

[0022] When the above ink composition is applied to a plastic container, the ink composition has a value of 200 to 500 mJ / cm² 2 It can be characterized by being UV-cured by exposure to UV light with a dose of [amount].

[0023] When the above ink composition is applied to a plastic container, the ink composition can be removed in a washing process performed for 10 minutes under alkaline conditions of 60 to 90°C.

[0024] When the above ink composition is applied to a plastic container, the plastic container may not peel off when detached with tape after being left for 24 hours in a space with a temperature of 30°C to 45°C and a humidity of 80°C to 90°C.

[0025] When the above ink composition is applied to a plastic container, it may not peel off when removed with tape after being left in 90% to 98% ethanol for 2 to 5 hours.

[0026] When the above ink composition is applied to a plastic container, the print may not discolor even if left in an aqueous solution of 2% to 10% NaCl for 24 to 48 hours. Effects of the invention

[0028] According to an embodiment of the present invention, an ink composition for printing on a plastic container can be provided. The ink composition may enable the removal of the ink printed on the plastic container during a washing process, and consequently, the PET bottle can be recycled. That is, since the plastic bottle can be recycled without damage, the amount of waste can be reduced and the amount of recycling can be increased.

[0029] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention. Brief explanation of the drawing

[0031] Figure 1 is the result of confirming the degree of ink peeling in an aqueous NaOH solution when an ink composition according to one embodiment of the present invention is printed on a plastic container by UV curing. Figure 2 is the result of confirming the degree of ink peeling in an aqueous NaOH solution when an ink composition according to one comparative example of the present invention is printed on a plastic container by UV curing. Figure 3 is the result of checking the degree of ink peeling after tape peeling when an ink composition according to one embodiment of the present invention is printed on a plastic container by UV curing. Figure 4 is the result of checking the degree of ink peeling after tape peeling when an ink composition according to one comparative example of the present invention is printed on a plastic container by UV curing. Figure 5 is the result of confirming the degree of ink peeling in ethanol when an ink composition according to one embodiment of the present invention is printed on a plastic container by UV curing. Figure 6 is the result of confirming the degree of ink peeling in NaCl when an ink composition according to one embodiment of the present invention is printed on a plastic container by UV curing. Figure 7 is the result of confirming the degree of printing according to the viscosity of an ink composition according to one embodiment of the present invention. Specific details for implementing the invention

[0032] The present invention will be described in more detail below. However, the present invention may be implemented in various different forms and is not limited by the embodiments described herein, and is defined only by the claims set forth below.

[0033] Additionally, the terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. Throughout the specification of this invention, the term 'comprising' any component means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0034] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0035] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0037] The first aspect of the present invention is,

[0038] An ink composition for printing on a plastic container is provided, comprising: an oligomer consisting of one or more functionalized ester groups; a pigment comprising BaSO4; a photoinitiator; and an additive; and having a viscosity of 2,000 to 30,000 cps at a temperature of 25°C.

[0040] Hereinafter, an ink composition according to the first aspect of the present invention will be described in detail.

[0042] In one embodiment of the present invention, the oligomer may be a urethane-based oligomer that performs a saponification reaction, a urethane-based oligomer that does not perform a saponification reaction, an acrylic-based oligomer, an epoxy-based oligomer, a polyester-based oligomer, or a mixture thereof.

[0043] The oligomers that can be used as ink compositions may be selected from the group consisting of urethane, urethane acrylate, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, pentyl acrylate, isopentyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, nonyl acrylate, isononyl acrylate, dodecyl acrylate, and stearyl acrylate. However, they are not limited thereto, and one or more mixtures selected from the group consisting of those containing ester groups may also be used.

[0044] In one embodiment of the present invention, the ink composition may have a viscosity of 2,000 to 30,000 cps at a temperature of 25°C. The viscosity of the ink composition of the present invention may preferably be 5,000 to 25,000 cps, more preferably 7,000 to 23,000 cps, and even more preferably 10,000 to 20,000 cps.

[0045] In one embodiment of the present invention, the oligomer may have a molecular weight of 10,000 to 40,000. In other examples, the molecular weight of the oligomer of the present invention may be 11,000 or more, 12,000 or more, 13,000 or more, 14,000 or more, 15,000 or more, 16,000 or more, 17,000 or more, 18,000 or more, 19,000 or more, 20,000 or more, or 39,000 or less, 38,000 or less, 37,000 or less, 36,000 or less, 35,000 or less, 34,000 or less, 33,000 or less, 32,000 or less, 31,000 or less, 30,000 or less.

[0046] Generally, for polymerized printing films, inks are designed to increase molecular weight to meet the required reliability. However, to ensure the printing film separates from the cleaning solution, the molecular weight must be reduced, and methods to lower the crosslinking density must be used.

[0047] This is because when the ink of the present invention is used in actual products, it must not separate from the cleaning solution to meet the quality standards required by consumers, whereas conversely, if it is designed to separate from the cleaning solution, it may fail to meet reliability standards. Therefore, designing an appropriate molecular weight is necessary.

[0048] In one embodiment of the present invention, the oligomer may be characterized as being in an amount of 10 to 70 parts by weight based on 100 parts by weight of the total ink composition. In another example, the ink composition of the present invention may be in an amount of 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, or 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, 50 parts by weight or less, or 45 parts by weight or less.

[0049] In one embodiment of the present invention, in addition to the pigment containing BaSO4, one or more of the following may be further included: a pigment containing CaCO3, a pigment containing Mg(OH)2, and a pigment containing TALC.

[0050] Extender pigments are colorless pigments that are mixed with other pigments to increase the volume or dilute the concentration, by crushing natural stone or white clay as is or by processing it through heat treatment. Extender pigments include calcium carbonate, talc, barium sulfate, silicon oxide, and aluminum hydroxide. However, they are not limited to these, and one or more mixtures may also be used to increase the mechanical properties of the ink.

[0051] In one embodiment of the present invention, the photoinitiator may be characterized as being one or more of benzophenone, TPO (2,4,6-trimethylbenzoyl-phosphine oxide), Irgacure-1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone), Irgacure-184 (1-hydroxy-cyclohexyl-phenyl-ketone), and Irgacure-907 (2-methyl-1-[4(methylthio)phenyl]-2-(4-mor-pholinyl)-1-propanone).

[0052] Generally, since short wavelengths may have difficulty penetrating the coating film, it is preferable to use a photoinitiator in the range of 380 to 400 nm, particularly 390 nm, to maximize the characteristics of long wavelengths; however, in the present invention, it is more preferable to use a photoinitiator in the short wavelength range of 360 to 370 nm, which helps with surface curing, by mixing.

[0053] The photoinitiator that can be used in the present invention is not particularly limited as long as it has a wavelength having characteristics of a mixture of the above photoinitiators and is capable of initiating ultraviolet curing.

[0054] In one embodiment of the present invention, the photoinitiator may be characterized as being in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the total ink composition. In other examples, the ink composition of the present invention may contain a photoinitiator in an amount of 0.1 parts by weight or more, 0.2 parts by weight or more, 0.5 parts by weight or more, 0.7 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, or 15 parts by weight or less, 13 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, or 5 parts by weight or less.

[0055] In one embodiment of the present invention, the additive may be characterized as being at least one selected from the group consisting of defoaming agents, thickening agents, plasticizers, dispersants, adhesives, and drying agents.

[0056] Antifoamers serve to collect small particles dispersed within the ink. By stabilizing the ink, they maintain a consistent texture during printing and improve the print quality of the printed surface. Thickeners are used to increase the viscosity of the ink and ensure its even distribution. Plasticizers are used to lower the viscosity of the ink, improve its flowability, and enhance color, brightness, and transparency. Dispersants disperse particles within the ink to maintain consistent color and texture and improve ink quality. Adhesives are used to increase the adhesion between the ink and the printed surface. Drying agents are used to increase the drying speed of the ink; faster drying increases the productivity of printed materials and prevents the ink from fading. In this invention, the ink composition can be modified by appropriately selecting additives that can improve ink quality and productivity.

[0057] In one embodiment of the present invention, the ink composition may further include a vinyl-based monomer. The vinyl-based monomer may include acrylate, vinyl acetate, and methyl methacrylate. This may be used to adjust the viscosity of the ink or to reinforce adhesion.

[0058] In one embodiment of the present invention, the ink composition may further comprise wax or a wax mixture.

[0059] The aforementioned wax is used to enhance ink performance and improve the appearance of printed materials. For example, wax can control the drying speed of the ink. When wax is added, it keeps the ink surface dry quickly, helping to prevent problems during the printing process. Additionally, wax forms a protective layer on the ink surface to protect the printed material from scratches, friction, moisture, and other factors.

[0060] In one embodiment of the present invention, when the ink composition is applied to a plastic container, the ink composition has a pressure of 200 mJ / cm² 2 Up to 500 mJ / cm 2 It may be characterized by UV curing by exposure to UV light at a dose of . Preferably 320 mJ / cm² 2 Up to 450 mJ / cm 2 , more preferably 350 mJ / cm² 2 Up to 400 mJ / cm 2 It can be the dose of.

[0061] UV curing is a process that uses ultraviolet (UV) light to harden materials into a solid state. This process involves the strong energy of UV rays emitted from a UV lamp providing photoinitiator with the energy to initiate a chemical reaction, thereby instantaneously converting monomers—the state before they become the main components of UV-cured paints—or oligomers—the state just before they become the main components—into polymers. Although monomers and oligomers are liquids under normal conditions (1 atmosphere, 25°C), receiving strong energy known as UV—a type of powerful electromagnetic wave—transforms them into polymers. As they appear as solids, they perform their intended functions, such as printing, coating, or adhesion.

[0062] While increasing UV irradiation time can meet light intensity requirements, it directly leads to a decrease in productivity. Therefore, it is necessary to maximize the initiation effect by applying a combination of a wide range of photoinitiators.

[0063] When UV light is irradiated onto a material, the photoinitiator is activated to initiate a reaction, causing monomer molecules to bond with each other to form a polymer network, and the material hardens into a solid. This curing process proceeds very rapidly and can generally be completed within a few seconds to a few minutes. UV curing is widely used in various industrial fields because it offers advantages such as fast curing speed, high productivity, the ability to cure at low temperatures, and environmental friendliness. Furthermore, since UV curing does not use heat, it offers benefits such as the absence of heat-related side effects, the ability to perform precise operations, and the minimization of material waste.

[0064] In one embodiment of the present invention, the UV curing may be characterized as irradiation by a high-pressure mercury lamp, a metal halide lamp, or a UV LED lamp.

[0065] High-pressure mercury lamps are the most commonly used lamps and emit a large amount of ultraviolet light at 365 nm. To emit more ultraviolet light, the gas pressure inside the lamp tube is higher than that of a standard mercury lamp, and it has a wavelength range from 254 nm to 436 nm. Even within this range, a lamp that emits the most light at a wavelength of 365 nm is called a high-pressure ultraviolet lamp.

[0066] Most UV resins are designed to cure better as energy increases, so short-wavelength UV with high energy is used, which has poor transmittance. However, for thick coatings or colored coatings, long-wavelength UV with low energy but good transmittance is often required. UV resins used in industrial settings require UV that is neither too long nor too short.

[0067] However, mercury UV lamps have the disadvantage of emitting a single spectrum of intermediate wavelengths at 365 nm. To improve this, while searching for a discharge material that emits a large amount of intermediate wavelengths, it was discovered that iron (Fe) emits a large amount of ultraviolet light in a range of wavelengths around the intermediate wavelength of 365 nm. Consequently, iron was used as a light-emitting material instead of mercury, and lamps made by adding metal additives such as iron and tin are called metal halide lamps.

[0068] Metal halide lamps emit continuous ultraviolet rays in the ultraviolet range of 240 nm to 420 nm. Compared to high-pressure mercury lamps, they have a higher ultraviolet generation efficiency and a higher UV radiation efficiency per unit length, which improves product quality and shortens the curing time.

[0069] UV LED lamps, which have recently begun to be applied, utilize light-emitting diodes that emit UV light, and there are various UV LED lamps ranging from 240nm to 420nm depending on the product. Depending on the purpose of the ink to be manufactured, an appropriate UV lamp must be selected and used during production.

[0070] In one embodiment of the present invention, when the ink composition is applied to a plastic container, the ink composition can be removed in a washing process performed for 10 minutes under alkaline conditions of 60 to 90°C.

[0071] The sample is placed in a 2% NaOH aqueous solution (1L) and stirred for 10 minutes at a speed of 200 r / min using a stirring device controlled to 80°C. This implements conditions similar to the washing step of plastic in the plastic recycling process.

[0072] In the above process, the ink printed on the surface of the plastic container is separated from the plastic container; that is, all the ink printed on the plastic is removed. Since only the washed PET bottle and the washed label fragments exist in the washing solution, there is also an advantage that the ink of the present invention does not contaminate the washing solution.

[0073] In one embodiment of the present invention, when the ink composition is applied to a plastic container, the plastic container may not peel off when detached with a tape with very strong adhesive strength, such as Evertec OPP, Ichiban OPP, or 3M 610 OPP tape, after being left for 24 hours in a space with a temperature of 30°C to 45°C and a humidity of 80°C to 90°C. Preferably, the temperature may be 32°C to 42°C, more preferably 34°C to 40°C. Preferably, the humidity may be 82°C to 88°C, more preferably 84°C to 86°C.

[0074] The durability of the surface-treated area is verified under high temperature and high humidity conditions. This allows for an evaluation of whether the ink of the present invention maintains the quality level required by consumers when used in actual products.

[0075] A plastic container printed with the ink composition of the present invention is placed in a space at a temperature of 38°C and a humidity of 85% for 24 hours, and then removed from a constant temperature and humidity chamber. Evertec OPP tape is attached to the printed surface with strong pressure and then quickly peeled off to check for peeling of the coating film. There should be no peeling, leaching, pinholes, or changes in the coating film.

[0076] In one embodiment of the present invention, when the ink composition is applied to a plastic container, it may not peel off when removed with tape after being left in 90% to 98% ethanol for 2 to 5 hours. Preferably, the ethanol content may be 92% to 97%.

[0077] Peeling, deformation, discoloration, and cracking of the coating film caused by alcohol are checked. This allows for an evaluation of whether the ink of the present invention maintains the quality level required by consumers when used in actual products.

[0078] In one embodiment of the present invention, a plastic printed with the ink composition of the present invention on the surface of a container is immersed in 95% ethanol and left at 37°C for 2 hours, after which the condition of the coating film is checked. An Evertec OPP tape is attached to the printed surface with strong pressure and then quickly peeled off to check for peeling of the coating film. There should be no peeling, pinholes, corrosion, or changes in the coating film.

[0079] In one embodiment of the present invention, when the ink composition is applied to a plastic container, the print may not discolor even when left in an aqueous solution of 2% to 10% NaCl for 24 to 48 hours. Preferably, the NaCl may be 3% to 8%, and more preferably 4% to 7%.

[0080] It is checked whether it turns into an oxide due to salt water, causing discoloration and corrosion. This allows for an evaluation of whether the ink of the present invention maintains the quality level required by consumers when used in actual products.

[0081] Plastic printed with the ink composition of the present invention on the surface of a container is immersed half in a 5% aqueous solution of Grade 1 NaCl and the other half in the air, stored at 37°C for 24 hours, then removed and checked. There should be no peeling, pinholes, discoloration, or corrosion of the coating film.

[0083] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0085] Example 1: Preparation of an ink composition

[0086] An ink composition according to one embodiment of the present invention is prepared. Based on 100 parts by weight of the total ink composition, it comprises 20 to 60 parts by weight of a urethane-based oligomer that performs a saponification reaction, 5 to 40 parts by weight of an acrylic-based or polyester-based oligomer, 0.1 to 15 parts by weight of TPO, 1 to 10 parts by weight of Irgacure-184, 0 to 30 parts by weight of a extender pigment, 1 to 10 parts by weight of an antifoaming agent, and 0 to 10 parts by weight of a color pigment. The method of preparing the ink composition may be to utilize a method well known in the art.

[0088] Comparative Example 1: Preparation of Ink Composition

[0089] As in Example 1 above, an ink composition was prepared, but an ink composition without adding a urethane-based oligomer that performs a saponification reaction was designated as Comparative Example 1. The other manufacturing methods are the same as those in Example 1.

[0091] Comparative Example 2: Preparation of Ink Composition

[0092] As in Example 1 above, an ink composition was prepared, but an ink composition without adding an acrylic or polyester oligomer was designated as Comparative Example 2. The other manufacturing methods are the same as in Example 1.

[0094] Experimental Example 1: Peeling experiment in NaOH aqueous solution

[0095] After printing an ink composition including one embodiment and a comparative example of the present invention onto a plastic container, a peeling test was performed. Figure 1 shows the results of Example 1 and a general ink, and Figure 2 shows the results of Comparative Example 1.

[0096] The ink compositions of the embodiments and comparative examples of the present invention are printed on a plastic container by UV curing. The printed plastic container is placed in 1 L of a 2% NaOH aqueous solution, and the temperature is maintained at 67.5 ℃. Then, the mixture is stirred for 10 minutes at a speed of 200 r / min using a stirring device.

[0097] FIG. 1(a) is a photograph of a plastic container before stirring and an experimental apparatus for stirring, and FIG. 1(b) is a photograph of a plastic container after stirring is completed. Looking at FIG. 1(a), when printed on a plastic container using the recycled ink of the present invention, all the ink peeled off after stirring for 10 minutes. In contrast, looking at FIG. 1(b), when printed on a plastic container using ordinary ink, it can be seen that the ink still remains on the plastic container even after stirring for 10 minutes.

[0098] Figure 2(a) is a photograph of a plastic container before stirring, and Figure 2(b) is a photograph of a plastic container after stirring is completed. Looking at Figure 2, it can be seen that there is no change in the printed ink before and after stirring in the NaOH aqueous solution. In other words, it can be expected that the urethane-based oligomer performing the saponification reaction affects the washing in the NaOH aqueous solution.

[0099] The peeling experiment in an aqueous NaOH solution of Experimental Example 1 simulated conditions similar to the washing step in an actual plastic recycling process. Therefore, when printed on plastic with the ink of the present invention, the ink is easily separated during the washing step of plastic recycling, so it can be expected that plastic recycling will be easier.

[0101] Experimental Example 2: Tape Peeling Experiment

[0102] After printing an ink composition including one embodiment and a comparative example of the present invention onto a plastic container, a tape peeling test was performed. Figure 3 shows the result of Example 1, and Figure 4 shows the result of Comparative Example 2.

[0103] The ink compositions of the embodiments and comparative examples of the present invention are printed on a plastic container by UV curing. The container is then placed in a constant temperature and humidity chamber at a temperature of 38°C and a humidity of 85%, and the condition of the coating film is checked. Afterward, an Evertec OPP tape is applied with strong pressure and left for several minutes. The OPP tape is then rapidly peeled off to check for peeling of the coating film.

[0104] Figure 3(a) is a photograph of a plastic container before applying tape after a cross cut, and Figure 3(b) is a photograph of a plastic container after removing the tape. Looking at Figure 3, it can be seen that there is no change in the printed ink before and after the tape peeling experiment.

[0105] Figure 4(a) is a photograph of a plastic container before applying tape after a cross cut, and Figure 4(b) is a photograph of a plastic container after removing the tape. Looking at Figure 4, peeling of the print can be observed when the tape is peeled off.

[0106] The tape peeling test of Experimental Example 2 can evaluate whether the ink maintains the quality level required by consumers when used in actual products. In the case of Example 1, since no peeling of the print was observed as a result of the tape peeling test, it can be expected that the ink of one embodiment of the present invention is easily separated during the washing process, but there is no change in the print quality when supplied to consumers. Therefore, through Experimental Example 2, it can be seen that the print adhesion is increased when an acrylic or polyester-based oligomer is added.

[0108] Experimental Example 3: Exfoliation Experiment in Ethanol

[0109] After printing an ink composition containing one embodiment of the present invention onto a plastic container, a peeling test was performed. Figure 5 is the result of Example 1.

[0110] The ink compositions of the embodiments and comparative examples of the present invention are printed on plastic containers by UV curing. The printed plastic containers are placed in 95% ethanol and immersed at 37°C for 2 hours to check the degree of deformation of the ink.

[0111] Figure 5(a) is a photograph of a plastic container before immersion in ethanol, and Figure 5(b) is a photograph of a plastic container after immersion in ethanol. Looking at Figure 5, it can be seen that there is no change in the printed ink when immersed in ethanol.

[0112] The ethanol peeling test of Experimental Example 3 can evaluate whether the ink maintains the quality level required by consumers when used in actual products. Since no peeling of the print was observed as a result of ethanol immersion in the case of Example 1, it can be expected that the ink of one embodiment of the present invention is easily separated during the washing process, but there is no change in the quality of the print when supplied to consumers.

[0114] Experimental Example 4: Exfoliation Experiment in NaCl

[0115] After printing an ink composition containing one embodiment of the present invention onto a plastic container, a peeling test was performed. Figure 6 is the result of Example 1.

[0116] The ink compositions of the embodiments and comparative examples of the present invention are printed on plastic containers by UV curing. The printed plastic containers are placed in 5% NaCl and immersed at 37°C for 24 hours to check the degree of deformation of the ink.

[0117] Figure 6(a) is a photograph of a plastic container before immersion in NaCl, and Figure 6(b) is a photograph of a plastic container after immersion in NaCl. Looking at Figure 6, it can be seen that there is no change in the printed ink when immersed in NaCl.

[0118] The NaCl peeling test of Experimental Example 4 can evaluate whether the ink maintains the quality level required by consumers when used in actual products. Since no peeling of the print was observed as a result of NaCl immersion in Example 1, it can be expected that the ink of one embodiment of the present invention is easily separated during the washing process, but there is no change in the quality of the print when supplied to consumers.

[0120] Experimental Example 5: Printing Experiment According to Viscosity

[0121] In one embodiment of the present invention, to determine the optimal viscosity of the ink composition, the degree of printing was checked while varying the viscosity of the ink composition. The viscosity of the ink composition was measured using a BrookField DV II viscometer (spindle No. 7, 50 rpm).

[0122] Figure 7(a) shows the result of printing on a plastic container with a thin ink composition of 2,000 cps or less at 25 ℃. Looking at Figure 7(a), it can be seen that the printing is not clear and the text is smudged.

[0123] Figure 7(b) shows the result of printing on a plastic container with an ink composition having a viscosity of 30,000 cps or higher at 25°C. Looking at Figure 7(b), it can be seen that the ink is printed unevenly on the plastic container due to the high viscosity. In particular, it can be seen that small text is not printed. Therefore, it can be seen that an ink composition having a viscosity of 2,000 to 30,000 cps at a temperature of 25°C is suitable for printing on plastic containers.

[0125] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0126] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 An ink composition for printing on a plastic container, comprising: an oligomer; a pigment containing BaSO4; a photoinitiator; and an additive; wherein the oligomer comprises, based on 100 parts by weight of the total ink composition, 20 to 60 parts by weight of a urethane-based oligomer that performs a saponification reaction; and 5 to 40 parts by weight of an acrylic-based or polyester-based oligomer; wherein the ink composition has a viscosity of 10,000 to 20,000 cps when measured with a BrookField DV II viscometer (spindle No. 7, 50 rpm) at a temperature of 25 ℃; and wherein, when the ink composition is applied to a plastic container, the ink composition is removable in a washing process performed for 10 minutes under alkaline conditions at 60 to 90 ℃. Claim 2 delete Claim 3 An ink composition according to claim 1, characterized in that the oligomer has a molecular weight of 10,000 to 40,000. Claim 4 delete Claim 5 An ink composition according to claim 1, characterized in that, in addition to the pigment containing BaSO4, it further comprises one or more of a pigment containing CaCO3, a pigment containing Mg(OH)2, and a pigment containing TALC. Claim 6 An ink composition according to claim 1, wherein the photoinitiator is one or more of benzophenone, TPO (2,4,6-trimethylbenzoyl-phosphine oxide), Irgacure-1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone), Irgacure-184 (1-hydroxy-cyclohexyl-phenyl-ketone), and Irgacure-907 (2-methyl-1-[4(methylthio)phenyl]-2-(4-mor-pholinyl)-1-propanone). Claim 7 An ink composition according to claim 1, characterized in that the photoinitiator is in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the total ink composition. Claim 8 An ink composition according to claim 1, characterized in that the additive is at least one selected from the group consisting of defoaming agents, thickening agents, plasticizers, dispersants, adhesives, and drying agents. Claim 9 An ink composition according to claim 1, characterized in that the ink composition further comprises a vinyl-based monomer. Claim 10 An ink composition according to claim 1, characterized in that the ink composition further comprises a wax or a wax mixture. Claim 11 In claim 1, when the ink composition is applied to a plastic container, the ink composition has a value of 200 to 500 mJ / cm² 2 An ink composition characterized by being UV-cured when exposed to UV light at a dose of [a specific amount]. Claim 12 delete Claim 13 An ink composition according to claim 1, characterized in that when the ink composition is applied to a plastic container, the plastic container is left for 24 hours in a space at a temperature of 30°C to 45°C and a humidity of 80°C to 90°C, and then detached with tape, it does not peel off. Claim 14 An ink composition according to claim 1, characterized in that when the ink composition is applied to a plastic container, it does not peel off when detached with tape after being left in 90% to 98% ethanol for 2 to 5 hours. Claim 15 An ink composition according to claim 1, characterized in that when the ink composition is applied to a plastic container, the print does not discolor even when left in an aqueous solution of 2% to 10% NaCl for 24 to 48 hours.

Images