Printed film with detachable printed layer

Abstract

The present invention relates to a printed film including forming a detachable printed layer composed of an ink having alkali detachability and a top clear coat layer formed on a base film, the top clear coat layer being formed at least from a curable resin and a curing agent, the curing agent being compounded in an amount of less than 40 parts by mass relative to 100 parts by mass of the curable resin, whereby it is possible to prevent scratch / detachment of the printed layer, and at the time of disposal, the printed layer can be reliably detached by alkali treatment.

Description

Technical Field

[0001] The present invention relates to a printed film having a printed layer using a printing ink that can be detached by alkali treatment, and more specifically, to a printed film that prevents scratching / detachment of the printed layer and can reliably detach the printed layer by alkali treatment upon disposal. Background Technology

[0002] In recent years, from the perspective of reducing environmental impact, there has been a demand for the reuse of resin packaging containers, and for packaging bags made of multi-layer films, there is also a desire to reuse the materials.

[0003] However, in multilayer films used in packaging bags, various plastics are mixed together, necessitating the separation of these plastics for material reuse. Furthermore, because a printed layer is formed on the packaging bag, if the printing ink is not removed, only black resin particles are obtained, limiting its applications.

[0004] To address this problem, Patent Document 1 below proposes a bag container made by laminating unstretched PET and stretched PET, and describes the provision of a printing layer composed of ink that can be desorbed using a solution of strong alkali.

[0005] In the aforementioned bag container, reuse is facilitated by layering layers made of the same type of plastic without the use of adhesives, and the printed layer can be easily removed from the unstretched PET layer before reuse by forming a printed layer on the exposed surface opposite to the unstretched PET layer, which serves as a sealant layer.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-183252 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, with the printed layer exposed on the surface of the packaging bag, its scratch resistance is poor, and the packaging bag has poor slip resistance. Therefore, during the packing and transportation of the filled bags, vibration and collisions can cause the printed layer to be damaged or detached. Furthermore, in cases where packaging bags are stacked and stored before the filling process, efficient supply of bags may be impossible. To solve these problems and to give the packaging bags a beautiful sheen, a protective layer is usually formed on the printed layer.

[0011] However, if a topcoat (top coat) is used to form a protective layer that achieves the above purpose on a printed layer using ink that can be removed by alkali treatment, a new problem arises where the printed layer cannot be completely removed even if alkali treatment is performed.

[0012] Therefore, the object of the present invention is to provide a printing film whose printed layer can be easily removed by alkali treatment, and which has excellent slip properties and gloss, as well as scratch resistance of the printed layer.

[0013] Technical solution

[0014] According to the present invention, a printing film is provided, characterized in that it comprises forming a releasable printing layer and a topcoat varnish layer on a substrate film, the topcoat varnish layer being formed of at least a curable resin and a curing agent, the curing agent being formulated in an amount of less than 40 parts by mass relative to 100 parts by mass of the curable resin, the releasable printing layer being detachable from the substrate film by alkali treatment.

[0015] In the printed film of the present invention, the following are preferred.

[0016] (1) The coating amount of the removable printing layer is 1.2 g / m². 2 above.

[0017] (2) The curing resin is an epoxy resin and the curing agent is an isocyanate curing agent. In the epoxy isocyanate topcoat clear varnish, the curing agent is prepared in an amount with an NCO / OH molar ratio of less than 8.4.

[0018] (3) The curing resin is a urethane resin and the curing agent is an isocyanate curing agent. In the urethane isocyanate topcoat clear varnish, the curing agent is prepared in an amount with an NCO / OH molar ratio of less than 21.3.

[0019] (4) The coating amount of the removable printing layer is 2.6 g / m². 2 The NCO / OH molar ratio in the epoxy isocyanate-based topcoat varnish is less than 1.05.

[0020] (5) The coating amount of the removable printing layer is 2.6 g / m². 2 The NCO / OH molar ratio in the urethane isocyanate-based topcoat varnish is less than 1.07.

[0021] (6) The coefficient of dynamic friction of the surface of the topcoat varnish layer is less than 0.8.

[0022] (7) Other printed layers are formed on the removable printed layer.

[0023] (8) The curable resin is an epoxy resin, the curing agent is an isocyanate-based curing agent, and the coating weight of the release printing layer is 2.6 g / m². 2 The coating amount of the other printed layers mentioned above is 2.2 g / m². 2 The curing agent described above is formulated in an amount where the NCO / OH molar ratio is less than 4.2.

[0024] (9) The curable resin is a urethane resin, the curing agent is an isocyanate curing agent, and the coating amount of the release printing layer is 2.6 g / m². 2 The coating amount of the other printed layers mentioned above is 2.2 g / m². 2 The curing agent described above is formulated in an amount where the NCO / OH molar ratio is less than 3.2.

[0025] (10) A sealant layer is formed on the side of the substrate film opposite to the removable printed layer.

[0026] (11) The substrate film is a stretched film formed of olefin resin or polyester resin, and the sealant layer is an unstretched film or amorphous film formed of the same resin as the laminated substrate film.

[0027] Invention Effects

[0028] Although a topcoat varnish layer is formed on the printing layer (hereinafter sometimes referred to as "alkali-removable printing layer") composed of alkali-removable ink, the printing layer can be easily removed by alkali treatment, resulting in excellent reusability. Furthermore, by using the same olefin-based resin or polyester resin for both the substrate film and the sealant layer, it is not necessary to separate different resins, further improving reusability.

[0029] Furthermore, by forming a clear varnish layer on the surface of the printed film, the operability during the manufacturing of packaging bags and other products can be improved, effectively preventing scratches and detachment from the printed layer. In particular, with a dynamic friction coefficient of less than 0.8 on the surface of the clear varnish layer, the sliding properties and scratch resistance of the clear varnish layer are significantly improved, effectively preventing detachment of the printed layer caused by vibration during transportation. Moreover, by forming a clear varnish layer, a printed film with excellent surface gloss can be provided.

[0030] Furthermore, in the printed film of the present invention, by forming other layers such as a gravure printing layer between the alkali-removable printing layer and the topcoat varnish layer, the transfer of curing agent components to the alkali-removable printing layer can be suppressed. Therefore, the printing layer can be efficiently detached through alkali treatment, and the amount of curing agent in the topcoat varnish layer can be increased, thereby improving the required performance of the topcoat varnish layer (such as the protective effect of the printing layer). In addition, it also has the effect of making the thickness of the alkali-removable printing layer thinner. Attached Figure Description

[0031] Figure 1 This is a cross-sectional view showing an example of the laminated structure of the printed film of the present invention.

[0032] Figure 2 This is a cross-sectional view showing a laminated structure of another example of the printed film of the present invention.

[0033] Figure 3 This is a cross-sectional view showing a laminated structure of another example of the printed film of the present invention. Detailed Implementation

[0034] like Figure 1 As shown, the printing film of the present invention includes a releasable printing layer 2 composed of an alkali-releasable ink and a topcoat varnish layer 3 formed on a substrate film 1. An important feature of the printing film is that the topcoat varnish layer, formed of a curable resin and a curing agent, is formed with the following composition: it can exhibit the properties required by the topcoat varnish layer, such as protection, scratch resistance, and slip resistance of the printing layer, and does not impair the alkali removal performance of the alkali-releasable printing layer.

[0035] In other words, according to the research of the inventors, if a topcoat varnish is applied as a protective layer onto an alkali-removable printing layer, the components of the topcoat varnish, especially the curing agent in the topcoat varnish, diffuse and penetrate into the alkali-removable printing layer, causing the alkali-removable ink to crosslink, or the penetrated topcoat varnish components to cure near the interface between the alkali-removable printing layer and the substrate. As a result, it cannot be easily removed even by alkali treatment. Therefore, in this invention, a composition of topcoat varnish that does not affect the alkali-removable printing layer and can maintain the required performance of the topcoat varnish layer has been discovered.

[0036] (Topcoat clear varnish layer)

[0037] The topcoat varnish layer constituting the printed film of the present invention is formed from a curable resin and a curing agent. It is important that the curing agent is formulated in an amount of less than 40 parts by weight relative to 100 parts by weight of the curable resin. In particular, the amount formulated as described below is appropriate depending on the combination of the curable resin and the curing agent, the thickness of the alkali-detachable printed layer, or whether there are other layers between the topcoat varnish layer and the alkali-detachable printed layer.

[0038] As described above, by incorporating a specific amount of curing agent into the curing resin, the transfer of components of the topcoat varnish, especially the curing agent, to the alkali-detachable printing layer can be suppressed, and the alkali-detachable printing layer can be reliably detached.

[0039] The clear varnish that forms the topcoat layer can be any curing resin that has been used in clear varnishes in the past, and epoxy resins or urethane resins are particularly preferred.

[0040] In addition, as a curing agent, isocyanate-based curing agents, amino-based curing agents, etc., which are known as curing agents for epoxy resins or urethane resins, can be used. However, in this invention, isocyanate-based curing agents that can exhibit excellent curability in small amounts and can form a topcoat clear coat with the above-mentioned properties are particularly preferred.

[0041] In this invention, as described above, by using a specific topcoat varnish with a reduced curing dosage, the transfer of the curing agent to the alkali-detachable printing layer can be suppressed, the cross-linking of the alkali-detachable ink can be suppressed, and the alkali-detachability of the aforementioned alkali-detachable printing layer is not impaired. Furthermore, the coefficient of dynamic friction on the surface of the topcoat varnish layer can be controlled to be less than 0.8, preferably in the range of 0.1 to 0.3, thereby improving abrasion resistance and effectively preventing ink detachment caused by vibrations during transport, etc.

[0042] As an epoxy resin, conventionally known epoxy resins can be used, but are not limited to these. Examples include: bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic varnish type epoxy resin, alicyclic epoxy resin, polyethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc.

[0043] As a urethane resin, conventionally known urethane resins can be used, but are not limited thereto. Examples include polyether urethane resins, polyester urethane resins, and polycarbonate urethane resins.

[0044] Examples of isocyanate-based curing agents that can be used include: aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), and trimethylhexamethylene diisocyanate; aliphatic cyclic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, and 1,2-cyclohexane diisocyanate; aromatic isocyanates such as diphenylmethylene diisocyanate (XDI), 2,4-toluene diisocyanate (TDI), and 2,6-toluene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate (IPDI) and norbornene diisocyanate methyl ester; and their biuret forms, isocyanurate forms, polymers, and mixtures. Two or more of these can also be used in combination.

[0045] When using an epoxy isocyanate-based topcoat clear varnish, which is a combination of an epoxy resin and an isocyanate-based curing agent, the isocyanate-based curing agent is formulated such that the molar ratio (NCO / OH molar ratio) of the hydroxyl groups (OH) of the epoxy resin to the isocyanate groups (NCO) of the isocyanate-based curing agent is less than 8.4. When using a urethane isocyanate-based topcoat clear varnish, which is a combination of a urethane resin and an isocyanate-based curing agent, the isocyanate-based curing agent is formulated such that the molar ratio (NCO / OH molar ratio) of the hydroxyl groups (OH) of the urethane resin to the isocyanate groups (NCO) of the isocyanate-based curing agent is less than 21.3.

[0046] That is, when the NCO / OH molar ratio is above the aforementioned value, the isocyanate-based curing agent is excessive relative to the epoxy or urethane resins. The remaining curing agent, not used for curing the topcoat layer, migrates to the alkali-detachable printing layer, not only hindering the detachment of the alkali-detachable printing layer but also potentially impairing economic efficiency and the performance of the topcoat layer. On the other hand, the lower limit of the NCO / OH molar ratio only needs to be the minimum necessary for the topcoat layer to fully crosslink, and can also be as close to zero as possible depending on the curing conditions.

[0047] Furthermore, the range of the NCO / OH molar ratio used to achieve both the performance required by the topcoat layer and the detachability of the alkali-detachable printing layer varies depending on the coating amount (thickness) of the alkali-detachable printing layer, the presence or absence of other printing layers, and their coating amount (thickness). That is, when the alkali-detachable printing layer is thick, or when other layers are sandwiched between the alkali-detachable printing layer and the topcoat layer, the distance from the topcoat layer to the vicinity of the interface between the substrate and the alkali-detachable printing layer where detachment occurs becomes longer. The curing agent in the topcoat layer has difficulty reaching this vicinity, therefore, compared to the case of a thin alkali-detachable printing layer or the absence of other layers, the amount of curing agent in the topcoat layer can be set higher.

[0048] As a topcoat clear coat, when using an epoxy isocyanate-based topcoat clear coat that employs an epoxy resin and an isocyanate-based curing agent, the coating amount of the alkali-removable printing layer is set to 1.2 g / m², as described above. 2 The NCO / OH molar ratio is set to less than 8.4, and more preferably, the coating amount of the alkali-removable printing layer is set to 2.6 g / m². 2 The NCO / OH molar ratio is set to less than 1.05, and ideally, it is set to 0.21 or more and 0.525 or less. Therefore, it is clear from the results of the embodiments described later that the required properties for a topcoat varnish layer are achieved, and that the alkali-removable printed layer can be reliably removed by alkali-removal treatment.

[0049] Furthermore, when other layers are sandwiched between the topcoat varnish layer and the alkali-removable printing layer, preferably other printing layers described later, the coating amount of the alkali-removable printing layer is preferably set to 2.6 g / m². 2 The coating amount of the above and other printed layers is set to 2.2 g / m². 2 The NCO / OH molar ratio is less than 4.2, and in particular, it is set to be greater than 0.21 and less than 3.15.

[0050] As a topcoat varnish, when using a urethane-isocyanate based topcoat varnish employing urethane-based resins and isocyanate-based curing agents, the coating amount of the alkali-removable printing layer is set to 1.2 g / m², as described above. 2 The NCO / OH molar ratio is set to less than 3.2, and more preferably, the coating amount of the alkali-removable printing layer is set to 2.6 g / m². 2 The NCO / OH molar ratio is set to less than 1.07, and ideally, it is set to 0.27 or more and 0.53 or less. Therefore, it is clear from the results of the embodiments described later that the required properties for a topcoat varnish layer are achieved, and that the alkali-removable printing layer can be reliably removed by alkali removal treatment.

[0051] Furthermore, when other layers are sandwiched between the topcoat varnish layer and the alkali-removable printing layer, preferably other printing layers described later, the coating amount of the alkali-removable printing layer is preferably set to 2.6 g / m². 2 The coating amount of the above and other printed layers is set to 2.2 g / m². 2 The NCO / OH molar ratio is less than 3.2, and in particular, is set to be 0.27 or higher and 1.6 or lower.

[0052] In the topcoat varnish, lubricants such as paraffin wax and polyethylene wax can be added, and conventionally known additives such as anti-blocking agents can be added within the range that does not impair the transparency of the topcoat varnish layer.

[0053] In this invention, it is preferable that each 100 parts by weight of the curable resin contains 0.1 to 1.0 parts by weight of wax. This allows the coefficient of kinetic friction of the clear coat surface to be controlled to less than 0.8, particularly in the range of 0.1 to 0.3, thereby improving the slip resistance and scratch resistance of the clear coat.

[0054] It should be noted that the value of the dynamic friction coefficient of the varnish layer surface is obtained from the results of a vibration test. This vibration test was conducted using a varnish made primarily of epoxy resin, with variations in the type and content of wax, to create flat bags with different dynamic friction coefficients. Except for the bag size (1kg capacity), corrugated cardboard size, and stacking shape (6 bags stacked horizontally in 2 rows of 3 bags each), the test was conducted according to JIS standards under the same conditions as in the examples described later. The results showed that when the dynamic friction coefficient was 0.8 or higher, ink detachment of more than 1 mm was observed. It can be considered that the sliding properties and scratch resistance of the varnish layer depend on the value of the dynamic friction coefficient of the varnish layer surface, not on the composition of the varnish. The preferred range also applies to the varnish layer of this invention.

[0055] The preferred application rate of the topcoat varnish is 0.5–2.5 g / m². 2 The preferred concentration is 1.4–1.7 g / m³. 2 The range of coating amounts is as follows. If the coating amount is less than the range mentioned above, the protective effect of the topcoat layer on the printed layer may not be sufficient. On the other hand, if the coating amount is more than the range mentioned above, not only is it less economical, but it may also impair alkali detachment compared to the case where the coating amount is within the range mentioned above.

[0056] (Alkali-removable printing layer)

[0057] The alkali-removable ink constituting the printing film of the present invention can be any conventionally known alkali-removable ink, provided that the printing layer can be detached from the substrate film by alkali treatment while a topcoat varnish layer is formed on the surface.

[0058] The binder resin used as an alkali-removable ink is not limited thereto, but preferably contains at least one selected from the group consisting of acrylic resin, urethane resin, polyamide resin, polyester resin, amino resin, phenolic resin, epoxy resin, ethylene-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate copolymer resin, vinyl acetate resin, cellulose resin, etc.

[0059] In this invention, the penetration of topcoat varnish components, especially curing agent components, into the alkali-free ink layer is suppressed. Therefore, it is effective when using an alkali-free ink containing one or more urethane resins, epoxy resins, polyamide resins, cellulose resins (nitrocellulose), etc., which are easily affected by these curing agents.

[0060] Furthermore, alkali-free inks can be used with the aforementioned adhesive resins using known organic solvents, and are not limited thereto. Examples include ketone solvents, hydrocarbon solvents, ester solvents, ether solvents, glycol ether solvents, alcohol solvents, etc., which can be used alone or in combination of two or more.

[0061] The thickness of the alkali-removable printing layer, measured by coating weight, is preferably 1.2 g / m. 2 The above is particularly preferred at 2.6 g / m 2 ~6.0g / m 2 The reason why the detachment of the alkali-detachable printing layer using alkali treatment is hindered is believed to be that near the interface between the alkali-detachable printing layer and the substrate film, the varnish component transferred from the varnish layer cures, or the alkali-detachable ink is cross-linked by the curing agent of the varnish, thus making it difficult to detach from the substrate film. However, by keeping the thickness of the alkali-detachable printing layer within the above-mentioned range and using a curing agent with an NCO / OH molar ratio within the above-mentioned range, the varnish component originating from the varnish layer cannot reach the vicinity of the interface with the substrate film, and cross-linking near the interface can be suppressed. As a result, even if the alkali-detachable ink on the varnish layer side is cross-linked by the curing agent, since it is not cross-linked on the substrate film side, the hydrophilicity of the resin in the alkali-detachable ink increases and it swells due to alkali treatment, and the printing layer can easily detach from the surface of the substrate film.

[0062] (Other layers)

[0063] The printing layer in the printing film of the present invention is not limited to a single layer, but can also be multiple layers, as long as it has an alkali-removable printing layer using alkali-removable ink. In the case of multiple layers, the layer that requires the use of alkali-removable ink is located on the substrate film side. Thus, as described above, as the alkali-removable printing layer is removed in a manner that detaches from the interface with the substrate film, the printing layer formed on the layer composed of alkali-removable ink is also removed simultaneously.

[0064] The alkali-removable printing layer in the multilayer structure can be a full-page printing layer formed by roller coating, a transparent printing layer without colorant (a dilution ink layer), or a gravure printing layer made of alkali-removable ink formed on the full-page printing layer or the transparent printing layer, or a pattern layer formed by gravure printing using ordinary ink that is not alkali-removable ink.

[0065] Printing using alkali-free inks can also be carried out using previously known printing methods such as inkjet printing, gravure printing, offset printing, and flexographic printing.

[0066] There is no particular limitation on the amount (thickness) of the other printed layers formed between the alkali-removable printed layer and the topcoat varnish layer on the substrate film. However, as mentioned above, since it can inhibit the penetration of the curing agent from the topcoat varnish into the alkali-removable printed layer, a coating amount of 2.2 g / m² is preferred. 2 above.

[0067] (Substrate film)

[0068] The substrate film constituting the printed film of the present invention can be a thermoplastic resin known to be capable of forming a film. For example, depending on the application, the following substances can be appropriately selected to form: olefin resins such as random or block copolymers of α-olefins such as low-density polyethylene, high-density polyethylene, polypropylene, poly(1-butene), poly(4-methyl-1-pentene), or ethylene, propylene, 1-butene, 4-methyl-1-pentene; olefin resins such as cyclic olefin copolymers; ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl chloride copolymers, etc. Alkenyl copolymer resins; styrene-based resins such as polystyrene, acrylonitrile-styrene copolymer, ABS, and α-methylstyrene-styrene copolymer; vinyl-based resins such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, polymethyl methacrylate, and polymethyl methacrylate; amide resins such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, and nylon 12; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polycarbonate; polyphenylene ether; polylactic acid and other biodegradable resins; etc.

[0069] In this invention, from the viewpoints of mechanical strength and printability, olefin-based resins and polyester resins are preferred among the aforementioned thermoplastic resins. By using a substrate film formed from an olefin-based resin or a polyester resin, as described later, a sealant layer formed from the same resin can be combined, eliminating the need for separating different resins during reuse.

[0070] From the point of view of mechanical strength, the substrate film is preferably a stretch film, and more preferably a biaxial stretch film.

[0071] There are no particular restrictions on the thickness of the substrate film. Depending on the application, it can be appropriately set from 5.0 to 50.0 μm, especially from 10.0 to 30.0 μm.

[0072] In addition, conventionally known resin additives such as lubricants, anti-blocking agents, antistatic agents, and antioxidants can be added to the substrate film according to known formulations.

[0073] (Layer Composition)

[0074] The printed film of the present invention, as long as it has at least the above-described substrate film, alkali-removable printing layer, and topcoat varnish layer, may also have other printing layers, sealant layers, or other layers. For example, such as... Figure 2 As shown, a removable printing layer 2a composed of alkaline removable ink and a printing layer 2b formed by gravure printing are formed on the substrate film 1. A topcoat varnish layer 3 is formed on the gravure printing layer 2b, and a sealant layer 4 is formed on the opposite side of the removable printing layer 2a of the substrate film layer 1.

[0075] In addition to the sealant layer, various functional resin layers may be provided, such as gas barrier resin layer, tear-resistant resin layer, oxygen-absorbing resin layer, UV barrier resin layer, visible light barrier resin layer, rigid resin layer, impact-resistant resin layer, chemical-resistant layer, puncture-resistant layer, heat-resistant layer, etc., or layers formed from resins with excellent environmental adaptability, such as by-product resin, recycled resin, biomass polyester, etc. However, in this invention, in order to improve reusability, it is preferable to use a functional resin layer with the same resin as the substrate film as the base resin and reduce the amount of other components.

[0076] like Figure 2 As shown, the sealant layer formed on the opposite side of the alkali-removable printing layer of the substrate film is preferably formed of an olefin-based resin when the substrate film is formed of an olefin-based resin, and preferably formed of a polyester resin when it is formed of a polyester resin. From the viewpoint of heat-sealing properties, it is preferable to use an unstretched film or an amorphous film formed by extrusion coating.

[0077] Specifically, when using a film formed of an olefin resin such as polyethylene or polypropylene as the substrate film, the sealant layer can be formed by extruding and coating the olefin resin such as polyethylene or polypropylene onto the substrate film. When using a film formed of a polyester resin such as polyethylene terephthalate or polybutylene terephthalate as the substrate film, amorphous polyester such as PETG can preferably be used as the sealant layer.

[0078] The thickness of the sealant layer is not particularly limited, but is preferably in the range of 10.0 to 300.0 μm.

[0079] Furthermore, when the aforementioned functional resin layer is present, such as Figure 3 As shown, a functional resin layer 5 is formed on the other surface of a substrate film 1 on one surface of which an alkali-removable printing layer 2 and a topcoat varnish layer 3 are formed. A sealant layer 4 may also be formed on the functional resin layer 5, although not shown, but may also be formed between the substrate film and the alkali-removable printing layer.

[0080] (Manufacturing of printing film)

[0081] The printing film of the present invention can be manufactured by forming an alkali-removable printing layer on a substrate film using an alkali-removable ink, and then applying a topcoat varnish on the alkali-removable printing layer.

[0082] An alkali-removable printed layer formed on a substrate film is generally formed by heating (drying) at a temperature of 50.0–100.0°C for 0.2–10.0 seconds. Next, a topcoat varnish is applied to the formed printed layer using known methods such as roller coating, doctor blade coating, line coating, or spray coating. As described above, the use of a topcoat varnish in this invention reduces the content of the curing agent; therefore, it is preferable to appropriately adjust the heating temperature and heating time according to the curing agent dosage, but this is not a limitation. In a topcoat varnish composed of an epoxy resin or a urethane resin and an isocyanate curing agent and / or an amino curing agent, the topcoat varnish is formed by heating (drying) at a temperature of 50.0–150.0°C for 0.2–10.0 seconds.

[0083] In addition, when a sealant layer is formed on a substrate film, for example, a resin constituting the sealant layer can be extruded and coated on the substrate film, the sealant layer can be directly laminated on the substrate film, or it can be laminated by dry lamination or solventless lamination using an adhesive.

[0084] (Alkali treatment)

[0085] The printed film of the present invention undergoes alkali treatment, causing the alkali-removable printed layer to detach from the substrate film, thus enabling the separation of only the substrate film. Furthermore, even when a sealant layer is formed on the substrate film, as long as the laminated film is composed of a sealant layer of the same type as the substrate film, it is not necessary to separate them, resulting in excellent reusability.

[0086] Alkali treatment can be carried out according to the formulation of the alkali-removing ink used, such as using alkaline solutions such as sodium hydroxide and sodium carbonate, and immersing at 70-90°C for 10-20 minutes to remove the printed layer.

[0087] Example

[0088] (Experimental Examples 1-5)

[0089] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 1.2 g / m was applied to this substrate film. 2 A transparent, alkali-removable ink was applied and cured at 70°C for 10 seconds. Then, a 1.48 g / m² ink was applied to this transparent printing layer. 2 The coating amount of the epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 1 is applied and cured at 70°C for 10 seconds to form a topcoat varnish layer, which is then used to make a printing film.

[0090] It should be noted that, as an alkali-free ink, a commercially available alkali-free ink containing polyamide resin and nitrocellulose is used.

[0091] (Experimental Examples 6-10)

[0092] The coating weight of the alkali-free ink was set at 2.6 g / m². 2 In addition, similar to Experimental Example 1, an epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 2 was used to form a topcoat varnish layer and to produce a printed film.

[0093] (Experimental Examples 11-15)

[0094] The coating weight of the alkali-free ink was set at 5.1 g / m². 2 In addition, similar to Experimental Example 1, an epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 3 was used to form a topcoat varnish layer and a printed film was made.

[0095] (Experimental Examples 16-20)

[0096] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 1.2 g / m was applied to this substrate film. 2 A transparent, alkali-removable ink was applied and cured at 70°C for 10 seconds. Then, a 1.61 g / m² ink was applied to this transparent printing layer. 2 The coating amount of the urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 4 is applied and cured at 70°C for 10 seconds to form a topcoat varnish layer, which is then used to make a printing film.

[0097] (Experimental Examples 21-25)

[0098] The coating weight of the alkali-free ink was set at 2.6 g / m². 2 In addition, similar to Experimental Example 16, a urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 5 was used to form a topcoat varnish layer and a printed film was made.

[0099] (Experimental Examples 26-30)

[0100] The coating weight of the alkali-free ink was set at 5.1 g / m². 2 In addition, similar to Experimental Example 16, a urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 6 was used to form a topcoat varnish layer and a printed film was made.

[0101] (Experimental Examples 31-40)

[0102] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 2.6 g / m was applied to the substrate film. 2 A transparent, alkali-free ink was applied and cured at 70°C for 10 seconds. Then, a coating of 2.2 g / m² was applied onto this transparent printing layer. 2A printing layer is formed by gravure printing. Then, a 1.61 g / m² layer is applied to this gravure printing layer. 2 The coating amount of the epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 7 is cured at 70°C for 10 seconds to form a topcoat varnish layer and produce a printing film.

[0103] (Experimental Examples 41-50)

[0104] The coating weight of the gravure printing layer was set to 5.9 g / m². 2 In addition, similar to Experimental Example 31, an epoxy isocyanate-based coating composition (topcoat varnish) with an NCO / OH molar ratio as shown in Table 8 was used to form a topcoat varnish layer and a printed film was made.

[0105] (Experimental Examples 51-60)

[0106] The coating weight of the gravure printing layer was set to 11.9 g / m². 2 In addition, similar to Experimental Example 31, an epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 9 was used to form a topcoat varnish layer and a printed film was made.

[0107] (Experimental Examples 61-70)

[0108] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 1.2 g / m was applied to this substrate film. 2 A transparent, alkali-free ink was applied and cured at 70°C for 10 seconds. Then, a coating of 2.2 g / m² was applied onto this transparent printing layer. 2 A printing layer is formed by gravure printing. Then, a 1.48 g / m² layer is applied to this gravure printing layer. 2 The coating amount of the epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 10 is cured at 70°C for 10 seconds to form a topcoat varnish layer and produce a printing film.

[0109] (Experimental Examples 71-80)

[0110] The coating weight of the alkali-free ink was set at 5.1 g / m². 2 In addition, similar to Experimental Example 61, an epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 11 was used to form a topcoat varnish layer and a printed film was made.

[0111] (Experimental Examples 81-90)

[0112] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 2.6 g / m was applied to the substrate film. 2A transparent, alkali-free ink was applied and cured at 70°C for 10 seconds. Then, a coating of 2.2 g / m² was applied onto this transparent printing layer. 2 A printing layer is formed by gravure printing. Then, a 1.61 g / m² layer is applied to this gravure printing layer. 2 The coating amount of the urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 12 is cured at 70°C for 10 seconds to form a topcoat varnish layer and produce a printing film.

[0113] (Experimental Examples 91-100)

[0114] The coating weight of the gravure printing layer was set to 5.9 g / m². 2 In addition, similar to Experimental Example 81, a urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 13 was used to form a topcoat varnish layer and a printed film was made.

[0115] (Experimental Examples 101-110)

[0116] The coating weight of the gravure printing layer was set to 11.9 g / m². 2 In addition, similar to Experimental Example 81, a urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 14 was used to form a topcoat varnish layer and a printed film was made.

[0117] (Experimental Examples 111-120)

[0118] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 1.2 g / m was applied to this substrate film. 2 A transparent, alkali-free ink was applied and cured at 70°C for 10 seconds. Then, a coating of 2.2 g / m² was applied onto this transparent printing layer. 2 A printing layer is formed by gravure printing. Then, a 1.61 g / m² layer is applied to this gravure printing layer. 2 The coating amount of the urethane isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 15 is cured at 70°C for 10 seconds to form a topcoat varnish layer and produce a printing film.

[0119] (Experimental Examples 121-131)

[0120] The coating weight of the alkali-free ink was set at 5.1 g / m². 2 In addition, similar to Experimental Example 111, an epoxy isocyanate-based coating composition (topcoat varnish) with the NCO / OH molar ratio shown in Table 16 was used to form a topcoat varnish layer and a printed film was made.

[0121] (Experimental Example 132)

[0122] A film (25 μm thick) made of low-density polyethylene was used as the substrate film, and a coating amount of 2.6 g / m was applied to the substrate film. 2 Apply a transparent, alkali-free ink and cure at 70°C for 10 seconds.

[0123] (Alkali removal test)

[0124] Samples (1.0 cm × 1.0 cm) were taken from the printed films obtained in Experiments 1–131 and immersed in a 0.5% NaOH aqueous solution heated to 85°C for 20 minutes. The results are shown in the tables. It should be noted that the evaluation criteria are as follows.

[0125] ◎: More than 90% have broken away.

[0126] ○: More than 70% but less than 90% have left.

[0127] Δ: More than 50% but less than 70% detached.

[0128] ×: Less than 50% detachment.

[0129] (Vibration test)

[0130] The printed films from Experiments 6 and 132 were attached to the side of stand-up pouches filled with 400ml of contents. Sixteen pouches were placed in a corrugated cardboard box measuring 30cm x 23cm x 27cm (W x D x H) with the printed film side facing the same direction, and a vibration test was conducted. The vibration test conditions are as follows.

[0131] Types of vibration: random vibration (vertical vibration) 23 30 27.

[0132] Vibration frequency range: 2~200Hz (according to JISZ0232(2020) standard).

[0133] Test duration: 90 minutes (JISZ0200 Level 2 conditions).

[0134] In the bag with the printed film of Experiment 6 attached, no ink detachment occurred. In contrast, ink detachment occurred in the bag with the printed film of Experiment 132 attached. Ink adhered to the inner surface of the corrugated paper containing the printed film, and there was ink scraped off at the bottom.

[0135] (Coefficient of kinetic friction)

[0136] For the printed films of Examples 6 and 132, the coefficient of kinetic friction of the printed film surface was measured. The coefficient of kinetic friction of the printed film surface in Example 6 was 0.16, and the coefficient of kinetic friction of the printed film surface in Example 132 was 0.26. The film surface of Example 6 was a topcoat varnish layer, and the coefficient of kinetic friction was less than the preferred range of 0.8, therefore no ink detachment occurred. On the other hand, in Example 132, there was no topcoat varnish layer, and the alkaline detachable ink layer was exposed, so the coefficient of kinetic friction of the film surface was less than 0.8, but ink detachment was observed. It should be noted that the coefficient of kinetic friction was measured according to JIS K7125.

[0137] [Table 1]

[0138] Experimental Case No. 1 2 3 4 5 Topcoat varnish (epoxy resin / hardener) 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 1.2 1.2 1.2 1.2 1.2 NCO / OH molar ratio 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × × Δ ◎

[0139] [Table 2]

[0140] Experimental Case No. 6 7 8 9 10 Topcoat varnish (epoxy resin / hardener) 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × Δ ○ ◎

[0141] [Table 3]

[0142] Experimental Case No. 11 12 13 14 15 Topcoat varnish (epoxy resin / hardener) 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 5.1 5.1 5.1 5.1 5.1 NCO / OH molar ratio 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × Δ ○ ◎ ◎

[0143] [Table 4]

[0144]

[0145]

[0146] [Table 5]

[0147] Experimental Case No. 21 22 23 24 25 Topcoat varnish (urethane resin / hardener) 100 / 3 100 / 2 100 / 1 100 / 0.5 100 / 0 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 1.6 1.07 0.53 0.27 0 Alkali removal evaluation × × Δ ○ ◎

[0148] [Table 6]

[0149] Experimental Case No. 26 27 28 29 30 Topcoat varnish (urethane resin / hardener) 100 / 3 100 / 2 100 / 1 100 / 0.5 100 / 0 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 5.1 5.1 5.1 5.1 5.1 NCO / OH molar ratio 1.6 1.07 0.53 0.27 0 Alkali removal evaluation × Δ ○ ◎ ◎

[0150] [Table 7]

[0151] Experimental Case No. 31 32 33 34 35 36 37 38 39 40 Topcoat varnish (epoxy resin / hardener) 100 / 40 100 / 30 100 / 25 100 / 20 100 / 15 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 8.4 6.3 5.25 4.2 3.15 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × × × Δ Δ Δ ○ ○ ◎

[0152] [Table 8]

[0153] Experimental Case No. 41 42 43 44 45 46 47 48 49 50 Topcoat varnish (epoxy resin / hardener) 100 / 40 100 / 30 100 / 25 100 / 20 100 / 15 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 <![CDATA[Alkaline removable ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 8.4 6.3 5.25 4.2 3.15 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × × × Δ Δ Δ ○ ○ ◎

[0154] [Table 9]

[0155] Experimental Case No. 51 52 53 54 55 56 57 58 59 60 Topcoat varnish (epoxy resin / hardener) 100 / 40 100 / 30 100 / 25 100 / 20 100 / 15 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 11.9 11.9 11.9 11.9 11.9 11.9 11.9 11.9 11.9 11.9 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 8.4 6.3 5.25 4.2 3.15 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × × Δ Δ Δ Δ ○ ○ ◎

[0156] [Table 10]

[0157] Experimental Case No. 61 62 63 64 65 66 67 68 69 70 Topcoat varnish (epoxy resin / hardener) 100 / 40 100 / 30 100 / 25 100 / 20 100 / 15 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 NCO / OH molar ratio 8.4 6.3 5.25 4.2 3.15 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × × × × × × × Δ Δ ○

[0158] [Table 11]

[0159] Experimental Case No. 71 72 73 74 75 76 77 78 79 80 Topcoat varnish (epoxy resin / hardener) 100 / 40 100 / 30 100 / 25 100 / 20 100 / 15 100 / 10 100 / 5 100 / 2.5 100 / 1 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 NCO / OH molar ratio 8.4 6.3 5.25 4.2 3.15 2.1 1.05 0.525 0.21 0 Alkali removal evaluation × Δ Δ Δ Δ ○ ○ ○ ◎ ◎

[0160] [Table 12]

[0161] Experimental Case No. 81 82 83 84 85 86 87 88 89 90 Topcoat varnish (urethane resin / hardener) 100 / 30 100 / 20 100 / 15 100 / 10 100 / 6 100 / 3 100 / 2 100 / 1 100 / 0.5 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 16 10.7 8 5.33 3.2 1.6 1.07 0.53 0.27 0 Alkali removal evaluation × × × × × Δ Δ ○ ○ ◎

[0162] [Table 13]

[0163] Experimental Case No. 91 92 93 94 95 96 97 98 99 100 Topcoat varnish (urethane resin / hardener) 100 / 30 100 / 20 100 / 15 100 / 10 100 / 6 100 / 3 100 / 2 100 / 1 100 / 0.5 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 5.9 <![CDATA[Alkaline detachment ink coating amount (g / m 2 )]]> 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 NCO / OH molar ratio 16 10.7 8 5.33 3.2 1.6 1.07 0.53 0.27 0 Alkali removal evaluation × × × × × Δ Δ ○ ○ ◎

[0164] [Table 14]

[0165]

[0166]

[0167] [Table 15]

[0168] Experimental Case No. 111 112 113 114 115 116 117 118 119 120 Topcoat varnish (urethane resin / hardener) 100 / 30 100 / 20 100 / 15 100 / 10 100 / 6 100 / 3 100 / 2 100 / 1 100 / 0.5 100 / 0 <![CDATA[Gravure ink coating amount (g / m 2 )]]> 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 <![CDATA[Alkaline Separation Ink Application Amount (g / m 2 )]]> 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 NCO / OH molar ratio 16 10.7 8 5.33 3.2 1.6 1.07 0.53 0.27 0 Alkali removal evaluation × × × × × × × Δ Δ ○

[0169] [Table 16]

[0170]

[0171] Industrial availability

[0172] The printing film of the present invention can prevent the printing layer from being scratched or detached during use, and the printing layer can be reliably detached by alkali treatment when discarded. Therefore, it is preferably used for packaging bags and the like that require reuse.

[0173] Explanation of reference numerals in the attached figures

[0174] 1: Substrate film; 2: Alkali-removable printing layer; 3: Topcoat varnish layer; 4: Sealant layer.

Claims

1. A printing film, characterized in that, The process involves forming a release varnish layer and a topcoat varnish layer on a substrate film. The release varnish layer is formed from an ink with alkaline release properties. The topcoat clear coat is formed of at least a curable resin and a curing agent, the curing agent being formulated in an amount of less than 40 parts by weight relative to 100 parts by weight of the curable resin. The release varnish layer can be detached from the substrate film by alkali treatment. The curable resin is an epoxy resin or a urethane resin, and the curing agent is an isocyanate-based curing agent. The coating weight of the removable printed layer is 1.2 g / m². 2 Above and 5.1g / m 2 the following, Where the curable resin is an epoxy resin, When no other printed layers are formed on the release printed layer and the coating amount of the release printed layer is 1.2 g / m² 2 Above and less than 2.6 g / m 2 When the curing agent is prepared, the amount of NCO / OH molar ratio is less than 0.525; When no other printed layers are formed on the release printed layer and the coating amount of the release printed layer is 2.6 g / m² 2 Above and 5.1g / m 2 In the following cases, the curing agent is formulated in an amount where the NCO / OH molar ratio is less than 1.05; When other printed layers are formed on the removable printed layer, the coating amount of the other printed layers is 2.2 g / m². 2 Above and 11.9g / m 2 The coating amount of the removable printing layer is 1.2 g / m². 2 Above and less than 2.6 g / m 2 When the curing agent is prepared, the amount of NCO / OH molar ratio is less than 1.05; When other printed layers are formed on the removable printed layer, the coating amount of the other printed layers is 2.2 g / m². 2 Above and 11.9g / m 2 The coating amount of the removable printing layer is 2.6 g / m². 2 Above and 5.1g / m 2 In the following cases, the curing agent is formulated in an amount where the NCO / OH molar ratio is less than 4.

2. Wherein, the curable resin is a urethane-based resin, When no other printed layers are formed on the release printed layer and the coating amount of the release printed layer is 1.2 g / m² 2 Above and less than 2.6 g / m 2 When the curing agent is prepared, the amount of NCO / OH molar ratio is less than 0.53; When no other printed layers are formed on the release printed layer and the coating amount of the release printed layer is 2.6 g / m² 2 Above and 5.1g / m 2 In the following cases, the curing agent is formulated in an amount where the NCO / OH molar ratio is less than 1.07; When other printed layers are formed on the removable printed layer, the coating amount of the other printed layers is 2.2 g / m². 2 Above and 11.9g / m 2 The coating amount of the removable printing layer is 1.2 g / m². 2 Above and less than 2.6 g / m 2 When the curing agent is prepared, the amount of NCO / OH molar ratio is less than 1.07; When other printed layers are formed on the removable printed layer, the coating amount of the other printed layers is 2.2 g / m². 2 Above and 11.9g / m 2 The coating amount of the removable printing layer is 2.6 g / m². 2 Above and 5.1g / m 2 In the following cases, the curing agent is formulated in an amount where the NCO / OH molar ratio is less than 3.

2.

2. The printing film according to claim 1, wherein, The coefficient of dynamic friction on the surface of the clear varnish layer is less than 0.

8.

3. The printed film according to claim 1 or 2, wherein, A sealant layer is formed on the side of the substrate film opposite to the removable printed layer.

4. The printing film according to claim 3, wherein, The substrate film is a stretched film formed of olefin resin or polyester resin, and the sealant layer is an unstretched film or amorphous film of the same type as the laminated substrate film.

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