Ink composition, method for manufacturing printed container, and printed container

Abstract

To provide a printing vessel having good recyclability and adhesion to a printing layer.SOLUTION: An ink composition for directly printing on a transparent polyethylene terephthalate (PET) vessel contains a coloring agent, a binder resin, and a solvent, in which a content of the binder resin in the ink composition is 30 wt.% or less, and the binder resin contains an acrylic resin and a polyester resin in a weight ratio of 95:5 to 20:80. There are provided a printing vessel using the ink composition, and a method for manufacturing the printing vessel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink composition, a method for producing a printed container, and a method for printing a container. [Background technology]

[0002] Containers with an alkali-soluble printed layer on the surface of the container body are known (Patent Document 1). However, when printing is performed directly on the container body, the adhesion between the ink and the container is insufficient, and rubbing and staining are likely to occur. [Patent Document 1] JP 2018-52607 A Summary of the Invention

[0003] In a first aspect of the present invention, there is provided an ink composition for direct printing on transparent polyethylene terephthalate (PET) containers, the ink composition comprising a colorant, a binder resin, and a solvent, wherein the content of the binder resin in the ink composition is 30% by weight or less, and the binder resin comprises an acrylic resin and a polyester resin in a weight ratio ranging from 95:5 to 20:80.

[0004] In addition, in a second aspect, there is provided a printed container comprising a transparent polyethylene terephthalate (PET) container body and a printed layer comprising a colorant and a binder resin provided on at least a portion of the outer surface of the container body, wherein the binder resin comprises an acrylic resin and a polyester resin in a weight ratio ranging from 95:5 to 20:80.

[0005] The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also be inventions. [Brief explanation of the drawings]

[0006] [Figure 1] 1 shows an example of the appearance of a printing container 100 in this embodiment. [Figure 2]1 shows an example of the layer structure of a printed container 100 in this embodiment. [Figure 3] An example of the flow of a method for manufacturing the printed container 100 of this embodiment will be shown. [Figure 4] 10 shows another example of the layer structure of the printed container 100 in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention as claimed. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0008] 1 shows an example of a printed container 100 according to this embodiment. The printed container 100 has a transparent appearance, and is printed on at least a portion thereof. The printed container 100 includes a container body 10 and a print layer 30.

[0009] The container body 10 is a structure capable of holding contents. The container body 10 is molded from a recyclable transparent material such as resin or glass. For example, the container body 10 is molded from transparent polyethylene terephthalate (PET), in which case the printed container 100 becomes a PET container, also known as a PET bottle. The contents held in the container body 10 may be beverages, food, medicines, industrial products, etc.

[0010] The printed layer 30 is a layer containing a colorant and a binder resin, and is provided on at least a portion of the outer surface of the container body 10. The printed layer 30 is formed by printing an ink composition and curing it.

[0011] The printed layer 30 expresses characters, identification codes, symbols, pictures, designs, etc. (hereinafter collectively referred to as "designs, etc.") formed by various printing processes. Examples of characters include the product name and product description (e.g., flavor, ingredients, manufacturer, and expiration date of the contents) of the printed container 100, and a description of the container body 10 (e.g., the material of the container body 10, whether it can be recycled, and how to recycle it). Examples of identification codes include barcodes and two-dimensional codes, which, instead of characters, may display the product name, product description, and description of the container body 10, as well as a link to a website or the like that displays this information.

[0012] Fig. 2 shows an example of the layer structure of the printing container 100 in this embodiment. In Fig. 2, the upper side is the outer surface of the printing container 100 (i.e., the surface in contact with the outside air), and the lower side is the inner surface (i.e., the surface in contact with the contents).

[0013] The printed layer 30 is formed on the outer surface of the container body 10. The printed layer 30 is a cured product of an ink composition formed by printing. The printed layer 30 is dissolved or peeled off by alkaline treatment. This leaves the printed container 100 in a decolorized state, allowing the container body 10 to be recycled smoothly. The printed layer 30 of this embodiment adheres firmly to the container body 10 and is less likely to be rubbed or stained due to friction, etc. Details of the ink composition for forming the printed layer 30 will be described later.

[0014] Fig. 3 shows an example of the flow of a method for manufacturing the container 100 of this embodiment. The container 100 of this embodiment can be manufactured by performing the processes of S100 to S500 in Fig. 3. For convenience of explanation, the processes of S100 to S500 will be explained in order, but at least some of these processes may be performed in parallel, or the steps may be interchanged and performed within the scope of the present invention. Furthermore, some steps may be omitted.

[0015] First, in S100, a preform is molded. For example, a transparent material such as a resin that will be used to form the container body 10 may be melted at high temperature and pressure, injected into a mold, and then cooled and solidified to form a preform in the shape of the mold. The temperature during melting and injection may be any temperature that sufficiently softens the material, and may be in the range of, for example, 200°C to 300°C. The pressure during injection may be set appropriately depending on the shape of the container, and may be in the range of, for example, 10 to 40 MPa.

[0016] A transparent material, such as a resin, can be used as the material for the container body 10. The material for the container body 10 may be one or a combination of two or more selected from polyester resins, polyolefin resins, polystyrene resins, polyamide resins, acrylic resins, polyvinyl chloride resins, polyacrylonitrile resins, polyvinyl alcohol resins, and biodegradable resins.

[0017] Among the above materials, polyester-based resins are particularly preferred as the material for the container body 10 from the viewpoint of adhesion with the printed layer 30 to be formed later. Specific examples of polyester-based resins include thermoplastic polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of polyolefin-based resins that can be used include low-density / high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, and random / block copolymers of any linear or cyclic olefin. Examples of polystyrene-based resins that can be used include polystyrene, acrylonitrile-styrene copolymer, ABS, and α-methylstyrene-styrene copolymer. Examples of polyamide-based resins include nylon 6, nylon 6-6, nylon 6 / 6-6 copolymer, metaxylylenediadipamide, nylon 6-10, nylon 11, nylon 12, and nylon 13. Examples of acrylic-based resins include acrylic esters and methacrylic esters. Examples of polyvinyl chloride-based resins include polyvinyl chloride and polyvinylidene chloride.

[0018] The container body 10 may contain various additives, such as a plasticizer, a UV absorber, a flame retardant, an antistatic agent, an antioxidant, a weather resistance agent, a deodorizer, a matting agent, a release agent, an ion exchange agent, a colorant, and other additives.

[0019] The palate portion of the injection-molded preform may be heat-treated to crystallize it. Crystallization of the palate portion of the preform can impart heat resistance. The heat treatment temperature may be any temperature at which the material crystallizes, and may be, for example, in the range of 140°C to 200°C.

[0020] Next, in S200, the preform is blow-molded. For example, biaxial stretch blow molding may be performed. As an example, the preform may be heated and then inserted into a mold, stretched in the longitudinal direction of the preform with a stretching rod (i.e., vertical stretching) to elongate the preform in the longitudinal direction, and then pressurized air may be blown into the preform to stretch the preform so that its radius increases (i.e., horizontal stretching), thereby molding the container body 10.

[0021] Blow molding may be performed while heating the preform at a temperature equal to or higher than the glass transition point (Tg) of the material and lower than the crystallization temperature. For example, if the material of the container body 10 is PET, it may be heated to 100 to 130°C. Known heating methods such as infrared radiation, high-frequency induction, and hot air may be used. After molding of the container body 10 is complete, the pressurized air may be replaced with cooling air (e.g., air, carbon dioxide, nitrogen gas, or a liquefied form of these) and sent into the container body 10 to cool the container body 10. This results in the formation of a container body 10 such as a transparent polyethylene terephthalate (PET) container.

[0022] After blow molding, at least a portion of the container body 10 or the entire outer surface may be subjected to a surface treatment. For example, the container body 10 may be subjected to plasma treatment, corona treatment, ozone treatment, primer coating treatment, or the like. This can improve adhesion between the container body 10 and the printed layer 30 formed later in S400. The inner surface of the container body 10 may also be surface treated or another layer may be formed thereon. For example, an oxygen barrier film (e.g., an SiOx film) may be formed on the inner surface of the container body 10. The thickness of the container body 10 is optional, but is preferably in the range of 0.1 to 1.0 mm, for example.

[0023] Next, in S400, the ink composition is printed directly onto the outer surface of the container body 10 to form a printed layer 30. The printed layer 30 may be formed on a part of or the entire outer surface of the container body 10.

[0024] The printing method for the printed layer 30 is not particularly limited, but may be inkjet printing, offset printing, gravure printing, electrophotographic printing, or other printing methods, with inkjet methods that enable on-demand printing being particularly preferred. As the inkjet method, on-demand or continuous printing may be used, with the continuous type being preferred due to its printing speed and the ability to use high-viscosity ink. Furthermore, at least a portion of the printed layer 30 may be formed by coating, such as roll coating.

[0025] The printed layer 30 is formed by printing an ink composition, etc. For example, the printed layer 30 is formed by directly printing the ink composition by inkjet printing or the like on the container body 10 formed by steps S100 to S200.

[0026] For example, the ink composition is applied to the container body 10 by printing or the like so that the thickness of the cured product after drying of the coating film is 1 to 50 μm. In particular, when forming a print with the ink composition, the ink composition may be applied to the container body 10 by printing or the like so that the thickness of the cured product after drying of the ink composition is about 1 to 10 μm.

[0027] The ink composition may contain a binder resin, a colorant, and a solvent. The ink composition does not have to be a UV-curable type and may not contain a photopolymerization initiator. The ink composition may be a heat-curable type or a dry-curable type (i.e., a solvent ink).

[0028] The binder resin may be an alkali-soluble resin. For example, the binder resin may contain an acrylic resin and a polyester resin. The binder resin may further contain other resins.

[0029] Examples of acrylic resins include (meth)acrylic esters such as polyacrylic esters and polymethacrylic esters, and copolymers of (meth)acrylic esters and styrene. In particular, styrene-acrylic copolymers and modified styrene-acrylic copolymers are preferably used.

[0030] The weight-average molecular weight of the acrylic resin may be from 1,000 to 30,000, and preferably from 1,000 to 20,000. If the molecular weight is too low, the adhesion between the container body 10 and the printing layer 30 may be insufficient, and if the molecular weight is too high, the alkali treatment may not proceed smoothly.

[0031] The acid value of the acrylic resin may be optimized based on the weight-average molecular weight, thereby ensuring sufficient alkali solubility and allowing the printing layer 30 to be decolorized by alkali treatment. For example, when the weight-average molecular weight of the acrylic resin is 10,000 or less, the acid value may be 50 or more and less than 110 mgKOH / g. When the weight-average molecular weight of the acrylic resin is 10,000 or more, the acid value may be 100 mgKOH / g or more. The acid value may be measured using a method in accordance with JIS K0070.

[0032] With such an acid value, the printed layer 30 has sufficient solubility in an alkaline solution and is sufficiently decolorized by alkaline treatment. That is, an acrylic resin with a relatively large weight-average molecular weight of 10,000 or more has lower solubility than an alkaline resin with a lower molecular weight. For this reason, it is desirable to increase the acid value to 100 mgKOH / g or more for an acrylic resin with a relatively large weight-average molecular weight of 10,000 or more.

[0033] From the viewpoint of solubility in solvents, the weight-average molecular weight of the acrylic resin may be 1,000 to 20,000, and the acid value may be 200 mgKOH / g or more. It is particularly preferable that the weight-average molecular weight is 1,000 to 10,000, and the acid value is 200 to 250 mgKOH / g. Within these ranges, a good balance of solvent solubility, adhesion, and alkali decolorization properties can be maintained.

[0034] Examples of polyester resins include thermoplastic polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, amorphous polyesters, and polyester urethanes.

[0035] The number-average molecular weight of the polyester resin is 1,000 to 40,000. If the molecular weight is too low, the adhesion between the container body 10 and the printed layer 30 will be insufficient, and if the molecular weight is too high, the alkali treatment may not proceed smoothly. Therefore, by setting the molecular weight in this range, the physical strength and alkali solubility of the printed layer 30 can be achieved at the same time.

[0036] The binder resin may contain acrylic resin and polyester resin in a weight ratio ranging from 95:5 to 20:80. By setting the weight ratio of acrylic resin to polyester resin within this range, the printed layer 30 can be easily peeled and dissolved using an alkaline solution, facilitating recycling of the printed container 100 and forming a printed layer 30 that does not cause rubbing or the like. If the amount of either the acrylic resin or the polyester resin is too small, adhesion to the container body 10 formed from a resin such as PET will be insufficient, causing rubbing or the like. On the other hand, by further including at least 20 parts by weight of acrylic resin per 80 parts by weight of polyester resin, development using an alkaline solution will be easier.

[0037] The content of the binder resin in the ink composition may be 30% by weight or less, and preferably 20% by weight or less. If the content of the binder resin is too high, problems such as difficulty in dissolving it in a solvent, clouding of the ink, and increased clogging of nozzles during inkjet printing may occur.

[0038] Although there is no particular lower limit for the binder resin content in the ink composition, it is preferably 0.5 wt % or more, and more preferably 10 wt % or more. If the binder resin content is too low, the adhesion between the printed layer 30 and the container body 10 will deteriorate. Furthermore, if the binder resin content is low relative to the colorant, the colorant may remain undissolved in the alkaline solution. Therefore, the binder resin content may be at least the same (wt %) as the colorant, or preferably at least twice as much (wt %).

[0039] The amount of binder resin to be contained in the ink composition may be determined by weighing the raw materials as described above, but it may be difficult to determine the amount of binder resin from an already prepared ink composition. Therefore, in one example of this embodiment, instead of weighing the raw materials, the property equivalent to "30 wt % or less" may be determined by a solid content measurement method, a viscosity measurement method, an electrical conductivity measurement method, or a combination of two or three of these methods.

[0040] For example, in the solid content measurement method, an ink composition is heated at 120°C using a halogen heating moisture meter until the weight change over 50 seconds is 1 mg, and the remaining solid content is measured. If the measured solid content is 41.0% or less, the binder resin content in the ink composition may be considered to be 30% by weight or less. Furthermore, for example, if the viscosity of the ink composition measured with a B-type viscometer at 20°C is 0.5 to 8.0 mPa·s, the binder resin content in the ink composition may be considered to be 30% by weight or less. Furthermore, for example, if the electrical conductivity of the ink composition measured with an electrical conductivity meter at 20°C is 0.20 mS / cm or more, the binder resin content in the ink composition may be considered to be 30% by weight or less.

[0041] The binder resin may contain one or more types of resin other than the acrylic resins and polyesters listed above, such as vinyl resin, rosin resin, epoxy resin, fluorine-based resin, styrene resin, carbonate resin, amide resin, imide resin, olefin resin, cellulose resin, urethane resin, and phenolic resin, as long as it does not impair adhesion to the container body 10 or alkali solubility.

[0042] The colorant may include a pigment or dye usable for printing, but preferably includes a dye. For example, the dye may include azo compounds such as monoazo and disazo. Examples of dyes that can be used include Solvent Black 3, 22, 27, 28, 29, and 43; Solvent Red 5, 8, 83, 109, 125, 127, and 132; Solvent Blue 47, 48, 70, and 136; Solvent Yellow 21, 88, 89, 90, and 146; Basic Blue 5 and 7; Basic Violet 1 and 3; and Basic Red 1 and 8. Azo compounds having hydrophilic groups are particularly preferred. Hydrophilic groups make the printed layer 30 more easily soluble in alkaline treatment, making it easier to erase the color.

[0043] The content of the colorant such as a dye in the ink composition is not particularly limited, but may be, for example, 3 to 10 wt % of the total ink composition. If the content of the colorant is too low, the color tone in the printed layer 30 will be light and will not be fully expressed, while if the content is too high, the erasability may be reduced or rubbing may occur.

[0044] The solvent is not particularly limited as long as it can sufficiently dissolve or disperse the binder resin and colorant. For example, water; ketones such as acetone, dimethyl ketone, and methyl ethyl ketone; alcohols such as methanol, ethanol, propanol, and isopropyl alcohol; esters such as ethyl acetate and butyl acetate; ethers such as glycol ether; aromatic solvents such as toluene, butylhydroxytoluene, and xylene; and aliphatic solvents such as hexane can be used alone or in combination. The content of the solvent is adjusted depending on the printing method used, etc., so that the ink composition has an appropriate viscosity. For example, when a continuous-type inkjet printing device is used, the solvent may be contained in an amount of 50 to 95 wt % of the total ink composition.

[0045] In addition to these, the ink composition may contain additives or other components as needed. For example, the ink composition may contain a leveling agent to improve wetting during printing. For example, a silicone-based compound or a fluorine-based compound may be used as the leveling agent. In addition, the ink composition may contain a pH adjuster, a release agent, a matting agent, a color inhibitor, a lubricant, an ion exchange agent, a UV absorber, a flame retardant, an antistatic agent, an antioxidant, a weathering agent, or a deodorizer as needed.

[0046] After printing or coating the ink composition, the ink composition is cured. For example, the ink composition may be cured by air drying or heating. Curing may be performed by ultraviolet curing instead of / in addition to thermal curing or the like. The cured ink composition becomes the printed layer 30.

[0047] The cured ink is dissolved and decolorized by alkali treatment. For example, when the cured ink formed using the ink composition has a thickness of 10 μm or less, it is decolorized by immersing it in a sodium hydroxide solution with a pH of 10 or higher at 85°C for 15 minutes.

[0048] The printing layer 30 may be formed as a single layer or multiple layers. Furthermore, if necessary, another layer may be provided on the printing layer 30. For example, a protective layer may be provided on the printing layer 30 to protect the printing layer 30 from physical / chemical damage.

[0049] Next, in S500, the printed container 100 after the formation of the printed layer is inspected. For example, the outer or inner surface of the printed container 100 is inspected for dents, holes, scratches, stains, etc. For example, the printed container 100 is inspected for sufficient clarity of the image, etc. formed on the printed container 100, and for any misalignment, chipping, bleeding, etc. The inspection may be performed using an inspection device or visually by a person.

[0050] The printed container 100 is then filled with a beverage or other content at a bottler or the like, and the product using the printed container 100 is shipped and sold. After the content is consumed, the printed container 100 is collected for recycling. The printed container 100 manufactured according to this embodiment maintains sufficient adhesion between the ink and the container to prevent rubbing, and the printed layer 30 can be easily removed from the container body 10 by alkaline treatment.

[0051] 4 shows another example of the layer structure of the printed container 100 according to this embodiment. As shown, the container body 10 may include multiple layers. For example, the container body 10 may have an intermediate layer 14 and PET layers 12 and 16 made of polyethylene terephthalate, sandwiching the intermediate layer 14.

[0052] The PET layer 12 and the PET layer 16 may have the same configuration as the container body 10 described in Fig. 2. Instead of the PET layer 12 and the PET layer 16, a layer of a resin different from the PET listed as a material for the container body 10 may be provided.

[0053] The intermediate layer 14 imparts various functions and added value to the container 100. For example, the intermediate layer 14 may be a layer having oxygen barrier properties. In this case, the intermediate layer 14 may be a polyamide resin such as nylon (e.g., nylon 6, nylon 6-6, nylon 6 / 6-6 copolymer, metaxylylenediadipamide, nylon 6-10, nylon 11, nylon 12, and nylon 13), or an ethylene-vinyl alcohol copolymer (e.g., ethylene-vinyl acetate copolymer), preferably nylon. Using these materials can improve the shelf life of the contents.

[0054] Furthermore, for example, the intermediate layer 14 may be a layer made of recycled materials. For example, the intermediate layer 14 may be a recycled resin such as recycled PET. As an example, the intermediate layer 14 may be mechanically recycled PET or chemically recycled PET. By using recycled materials, the environmental impact caused by the production of the printed container 100 can be reduced.

[0055] When forming a multilayer printed container 100 as shown in Fig. 4, a multilayer preform may be formed. For example, in S100 of Fig. 3, a multilayer preform may be formed by co-injecting multiple resins into a mold. Instead of or in addition to co-injection, a multilayer preform may be formed by co-compression molding, sequential injection, or the like.

[0056] When forming a multi-layer preform, co-injection may be performed so that a resin with a specific function (e.g., a resin with oxygen barrier properties such as nylon or a recycled resin) is positioned between layers of the base resin (e.g., PET).

[0057] [Example] Examples of this embodiment will be described below, but the present invention is not limited to these examples.

[0058] [Example 1] An ink composition A having the following composition was prepared. Acrylic resin (weight average molecular weight 16500, acid value 240 mg KOH / g) 10.4% by weight Polyester resin (number average molecular weight 15,000) 2.6% by weight ·Complex colorant 5 parts by weight Ether solvents, mainly ether, containing ketones and alcohols, 81.5% by weight Leveling agent 0.5% by weight

[0059] Ink composition A was applied to a 1 mm thick polyethylene terephthalate (PET) transparent plate using a bar coater in a constant temperature and humidity chamber at 20°C and 60%. The transparent plate coated with ink composition A was then left to dry naturally in a constant temperature and humidity chamber at 20°C and 65% for 12 hours, forming a printed layer with a thickness of 10 to 20 μm, and test piece A was obtained.

[0060] [Example 2] Ink composition B and test piece B were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 12.8 wt%, the polyester resin content was changed to 3.2 wt%, and the solvent was changed to an ether-based solvent at 78.5 wt%.

[0061] [Example 3] Ink composition C and test piece C were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 8 wt%, the polyester resin content was changed to 2 wt%, and the solvent was changed to an ether-based solvent at 84.5 wt%.

[0062] [Example 4] Ink composition D and test piece D were obtained by the same procedure as in Example 1, except that the content of the colorant was changed to 7.5% by weight and the solvent was changed to an ether-based solvent at 79% by weight.

[0063] [Example 5] Ink composition E and test piece E were obtained by the same procedure as in Example 1, except that the content of the colorant was changed to 2.5% by weight and the solvent was changed to an ether-based solvent at 84% by weight.

[0064] [Example 6] Ink composition F and test piece F were obtained by the same procedure as in Example 1, except that the content of the acrylic resin was changed to 7.8% by weight and the content of the polyester resin was changed to 5.2% by weight.

[0065] [Example 7] Ink composition G and test piece G were obtained in the same manner as in Example 1, except that the acrylic resin was changed to 10.4% by weight of a resin having a weight average molecular weight of 1700 and an acid value of 238 mgKOH / g.

[0066] [Example 8] Ink composition H and test piece H were obtained in the same manner as in Example 6, except that the acrylic resin was changed to 7.8% by weight of a resin having a weight average molecular weight of 1700 and an acid value of 238 mgKOH / g.

[0067] [Example 9] Ink composition I and test piece I were obtained by the same procedure as in Example 7, except that the content of the acrylic resin was changed to 5.2% by weight and the content of the polyester resin was changed to 7.8% by weight.

[0068] [Example 10] Ink composition J and test piece J were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a polyester resin with a number average molecular weight of 23,000.

[0069] [Example 11] Ink composition K and test piece K were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a polyester resin with a number average molecular weight of 3,000.

[0070] [Example 12] Ink composition L and test piece L were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a polyester resin with a number average molecular weight of 30,000.

[0071] [Example 13] Ink composition M and test piece M were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a resin with a number average molecular weight of 40,000.

[0072] [Example 14] Ink composition N and test piece N were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a resin with a number average molecular weight of 25,000.

[0073] [Example 15] An ink composition O and a test piece O were obtained in the same manner as in Example 1, except that the polyester resin was changed to 2.6% by weight of a polyester resin with a number average molecular weight of 16,000.

[0074] [Example 16] An ink composition P and a test piece P were obtained in the same manner as in Example 1, except that the acrylic resin was changed to 10.4% by weight of a resin having a weight average molecular weight of 4600 and an acid value of 108 mgKOH / g.

[0075] [Example 17] Ink composition Q and test piece Q were obtained in the same manner as in Example 1, except that the acrylic resin was changed to 10.4% by weight of a resin having a weight average molecular weight of 5850 and an acid value of 278 mgKOH / g.

[0076] [Example 18] Ink composition R and test piece R were obtained in the same manner as in Example 1, except that the acrylic resin was changed to 10.4 wt % of a resin having a weight average molecular weight of 8100 and an acid value of 53 mgKOH / g.

[0077] [Example 19] Ink composition S and test piece S were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 0.6 wt%, the polyester resin content was changed to 0.4 wt%, and the solvent was changed to 93.5 wt% of a ketone-based solvent containing ether and alcohol with ketone as the main component.

[0078] [Example 20] Ink composition T and test piece T were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 0.9 wt%, the polyester resin content was changed to 0.6 wt%, and the solvent was changed to 93 wt% ketone solvent.

[0079] [Example 21] Ink composition U and test piece U were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 0.1 wt%, the polyester resin content was changed to 0.2 wt%, and the solvent was changed to 94.2 wt% ketone solvent.

[0080] [Example 22] Ink composition X and test piece X were obtained by the same procedure as in Example 1, except that the acrylic resin was changed to 20.0 wt% of a resin with a weight average molecular weight of 1700 and an acid value of 238 mgKOH / g, the polyester resin content was changed to 5.0 wt%, and the solvent was changed to 69.5 wt% of an ether-based solvent.

[0081] [Example 23] Ink composition Y and test piece Y were obtained by the same procedure as in Example 1, except that the content of the acrylic resin was changed to 12.4% by weight and the content of the polyester resin was changed to 0.6% by weight.

[0082] [Example 24] Ink composition Z and test piece Z were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 0.4 wt%, the polyester resin content was changed to 0.1 wt%, and the solvent was changed to an ether-based solvent at 94 wt%.

[0083] [Example 25] Ink composition α and test piece α were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 4.0 wt %, the polyester resin content was changed to 1.0 wt %, and the solvent was changed to an ether-based solvent at 89.5 wt %.

[0084] [Example 26] Ink composition β and test piece β were obtained by performing the same operations as in Example 1, except that the acrylic resin content was changed to 16.0 wt%, the polyester resin content was changed to 4.0 wt%, and the solvent was changed to an ether-based solvent at 74.5 wt%.

[0085] [Comparative Example 1] Ink composition a and test piece a were obtained by the same procedure as in Example 1, except that the content of the acrylic resin was changed to 13% by weight and no polyester resin was used.

[0086] Comparative Example 2 Ink composition b and test piece b were obtained by the same procedure as in Example 1, except that the content of the polyester resin was changed to 13 wt % and no acrylic resin was used.

[0087] Comparative Example 3 Ink composition c and test piece c were obtained by the same procedure as in Example 7, except that the content of the acrylic resin was changed to 13% by weight and no polyester resin was used.

[0088] Comparative Example 4 Ink composition d and test piece d were obtained by the same procedure as in Example 1, except that the acrylic resin was changed to 13% by weight of a resin with a weight average molecular weight of 17,000 and an acid value of 94 mgKOH / g, and no polyester resin was used.

[0089] Comparative Example 5 An ink composition e and a test piece e were obtained by carrying out the same procedure as in Comparative Example 1, except that the content of the acrylic resin was changed to 35.0% by weight.

[0090] Comparative Example 6 Ink composition f and test piece f were obtained by carrying out the same procedure as in Comparative Example 5, except that the acrylic resin was changed to 35.0 wt % of a resin having a weight average molecular weight of 1700 and an acid value of 238 mgKOH / g.

[0091] The compositions of the ink compositions are shown in Tables 1 to 3 below. [Table 1] [Table 1] [Table 2] [Table 2] [Table 3] [Table 3]

[0092] The test pieces A to f were subjected to a cross-cut peel test, pencil hardness measurement, visual evaluation of alkali-discoloring property, and evaluation of alkali-discoloring property with a color difference meter, which will be described below.

[0093] [Cross-cut peel test (JIS K5600-5-6)] The following work will be carried out in a temperature and humidity controlled room at 20°C and 65% humidity. (1) Using a cross-cutting jig, create a 1 mm grid on the printing layer of the test piece. (2) Cut the cellophane tape (LP24 made by Nichiban) to a length of approximately 75 mm. (3) Stick cellophane tape on the printed layer and rub it with your fingers to make it adhere firmly. (4) Pull the cellophane tape at an angle of approximately 60 degrees from the main surface of the test piece and remove it from the test piece within 1 second. (5) Repeat steps (1) to (4) above twice for each test piece. (6) Items that showed no peeling were rated as "0", items that showed slight discoloration of the cellophane tape were rated as "1", and items that showed discoloration of the cellophane tape but no change to the board were rated as "2".

[0094] [Measurement of pencil hardness (JIS K5600-5-4)] The following work will be carried out in a temperature and humidity controlled room at 20°C and 65% humidity. (1) Place a pencil with hardness F against the main surface of the printed layer of the test piece at an angle of approximately 45 degrees and press it down with all your strength, pushing it out about 1 cm. (2) Check whether the pencil scratches the printed layer. (3) If the printed layer is scratched with the pencil, use a pencil with hardness HB; if not, use a pencil with hardness H and repeat steps (1) to (2). (4) The hardness before the scratch is evaluated as the result (for example, if the scratch is caused by a pencil with hardness H, the result will be "F").

[0095] [Visual evaluation of alkali decolorization] The printed layer of the test piece was tested for ease of recycling by immersing it in a sodium hydroxide solution with a pH of 10 or higher at 85°C for 15 minutes to see if it faded. ◯: The printed layer 30 was almost completely dissolved and completely decolorized. Δ: The printed layer 30 was partially dissolved and partially discolored. ×: No discoloration occurred.

[0096] [Alkaline decolorization color difference meter evaluation] The color difference of the test piece before and after immersion in a sodium hydroxide solution under the same conditions as in the visual evaluation of alkaline decolorization was measured using a color difference meter (microsurface spectrocolor difference meter VSS400 manufactured by Nippon Denshoku Industries Co., Ltd.). After the decolorization test, measurements were taken from the back of the coated surface, and if the L value was 2 or more and the a value was 1 or more, the evaluation was rated as good, and if not, the evaluation was rated as bad.

[0097] The results of each test are shown in Tables 4 to 6 below. [Table 4] [Table 4] [Table 5] [Table 5] [Table 6] [Table 6]

[0098] Furthermore, the ink compositions A to f were subjected to the printing test described below.

[0099] [Print test] In a constant temperature and humidity chamber at 20°C and 60%, characters were printed using each of the ink compositions A to f on the outer surface of a polyethylene terephthalate (PET) container body molded into a 1 mm thick PET bottle container using a continuous inkjet printer. The printed matter was then left to dry naturally for 12 hours in a constant temperature and humidity chamber at 20°C and 65%, forming a printed layer with a thickness of 10 to 20 μm, yielding printed matter A to f.

[0100] Printed matter A to β (corresponding to Examples 1 to 26) and printed matter b and d (corresponding to Comparative Examples 2 and 4) did not peel off when rubbed with a finger. On the other hand, printed matter a, c, e, and f (corresponding to Comparative Examples 1, 3, 5, and 6) had the printed layer peel off relatively easily when rubbed with a finger.

[0101] As described above, good results were obtained in each test in Examples 1 to 26, in which the weight ratio of acrylic resin to polyester resin was in the range of 95:5 to 20:80. On the other hand, in Comparative Examples 1 to 6, in which the weight ratio of acrylic resin to polyester resin was outside the range of 95:5 to 20:80, the alkali decolorization property, peel strength, etc. were poor.

[0102] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0103] It should be noted that the order of execution of each process, such as an operation, procedure, step, or stage, in the ink composition, the manufacturing method for a printed container, and the method of using the ink composition, the printed container, etc., shown in the claims, the specification, and the drawings is not specifically stated as "before," "prior to," etc., and that the processes can be performed in any order unless a previous process is used in a later process. Even if the flow of operations in the claims, the specification, and the drawings is described using "first," "next," etc. for convenience, this does not mean that the operations must be performed in that order. [Explanation of symbols]

[0104] 10 Container body 12 PET layers 14 Middle Class 16 PET layers 30 printing layer 100 Printed Containers

Claims

1. 1. An ink composition for direct printing on clear polyethylene terephthalate (PET) containers, comprising: Contains colorants, binder resins, and solvents. the content of the binder resin in the ink composition is 30% by weight or less, the binder resin contains an acrylic resin and a polyester resin in a weight ratio ranging from 95:5 to 20:80; the colorant is a dye; It is used for directly printing on the PET container by an inkjet printing method, The ink composition is cured to form a cured ink product. Discoloration in a sodium hydroxide solution of pH 10 or higher at 85°C for 15 minutes. Ink composition.

2. The acrylic resin has a weight average molecular weight of 10,000 or less and an acid value of 50 or more and less than 110 mgKOH / g. The ink composition according to claim 1 .

3. The acrylic resin has a weight average molecular weight of 10,000 or more and an acid value of 100 mgKOH / g or more. The ink composition according to claim 1 .

4. The weight average molecular weight of the acrylic resin is 1,000 to 20,000, and the acid value is 200 mgKOH / g or more. The ink composition according to claim 1 .

5. The number average molecular weight of the polyester resin is 1,000 to 40,000. The ink composition according to any one of claims 1 to 4.

6. the content of the binder resin in the ink composition is 0.5 to 20% by weight; The ink composition according to any one of claims 1 to 5.

7. The ink composition according to claim 1 , wherein the dye comprises an azo compound having a hydrophilic group.

8. The content of the dye in the ink composition is 3 to 10% by weight. The ink composition according to any one of claims 1 to 7.

9. The inkjet printing method is a continuous type. The ink composition according to any one of claims 1 to 8.

10. 10. A method for producing a printing method for a printing head comprising the steps of: directly printing the ink composition of claim 1 onto a transparent polyethylene terephthalate (PET) container; A method for manufacturing printed containers.

11. A transparent polyethylene terephthalate (PET) container body; and A printed container including a printed layer provided on at least a portion of the outer surface of the container body, the printed layer including a colorant and a binder resin, the binder resin contains an acrylic resin and a polyester resin in a weight ratio ranging from 95:5 to 20:80; the colorant is a dye; The printing layer is Discoloration in a sodium hydroxide solution of pH 10 or higher at 85°C for 15 minutes. Printing container.

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