JP2007045128A - Printing method for ultraviolet-hardening type ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing method for an ultraviolet-hardening type ink to a plastic film, which can independently control an ultraviolet irradiation dosage and a heating amount, can perform high speed printing because a process for cooling the film is not required, and in addition, can prevent the insufficient hardening of the ink from occurring even in the high speed printing. <P>SOLUTION: This printing method for the ultraviolet-hardening type ink includes a printing process, a heating process, and an ultraviolet ray irradiation process. In this case, in the printing process, printing is performed with the ultraviolet-hardening type ink at least on one surface of the plastic film. In the heating process, heating is performed. In the ultraviolet ray irradiation process, the irradiation with an ultraviolet ray is performed with a light-emitting diode as a light source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for printing ultraviolet curable ink using a light emitting diode light source.

  Currently, plastic containers such as PET bottles, metal bottles such as bottle cans, glass bottles, etc. are widely used as containers for beverages such as tea and soft drinks, seasonings, foods, cosmetics, and chemicals. ing. These containers and various articles are often equipped with plastic labels for display, decoration, and functionality. These plastic labels have a wide range of decoration, workability (followability to containers), and wideness. Shrink labels and stretch labels are widely used because of merits such as display area. Usually, ink is applied and printed on the surface of these labels for the purpose of imparting decorative properties such as letters and designs, and imparting functionality such as scratch prevention and slipperiness.

  Among the above printing inks, UV curable inks are superior in terms of environment and safety because they use almost no organic solvent such as toluene, and are mainly surface-printed because of their excellent wear resistance. Widely used for tack labels.

  Conventionally, however, electroded and electrodeless UV lamps have been used for UV curing (see, for example, Patent Document 1), but these UV lamps generate a certain amount of heat rays as they are used. Therefore, in the case of a shrink film that is weak against heat load, there has been a problem of causing deformation. In contrast, for example, in the case of letterpress printing, a method of preventing deformation is performed by bringing the film into close contact with the drum and cooling, but cooling efficiency decreases when the process speed is increased. This hinders the increase in production efficiency due to the increased speed. Further, in the gravure printing method and the like where it is difficult to introduce a cooling process, the UV curing method cannot be adopted at present.

On the other hand, as an ultraviolet ray generating device that replaces an ultraviolet lamp, in recent years, a device using a light emitting diode (LED) as a light source has been developed. For example, an ultraviolet irradiation device for curing an adhesive is known (see, for example, Patent Document 2). ). However, the current situation is that no example of applying the LED to the printing ink curing process is known yet.
JP 62-299379 A JP 2004-358770 A

  An object of the present invention is to provide a printing method of an ultraviolet curable ink that suppresses the thermal effect on the plastic film in the curing process of the ultraviolet curable ink and does not cause insufficient curing even when the speed is increased. is there.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have used a certain heat treatment and ultraviolet irradiation using an LED light source in combination in the printing ink curing process, thereby making the basis of the degree of ink curing and heat load. The inventors have found that the deformation of the material can be both suppressed and completed the present invention.

  That is, the present invention includes a printing step of printing an ultraviolet curable ink on at least one surface of a plastic film, a heating step of heating, and an ultraviolet irradiation step of irradiating ultraviolet rays using a light emitting diode as a light source. Provided is a method for printing an ultraviolet curable ink.

  Furthermore, the present invention provides the above-described ultraviolet curable ink printing method, wherein the plastic label is a transparent plastic film, and the ultraviolet irradiation is performed on the plastic film from the side opposite to the side on which the ultraviolet curable ink is printed. To do.

  Furthermore, this invention provides the printing method of the said ultraviolet curable ink whose plastic film is a shrink film.

  Furthermore, this invention provides the printing method of the said ultraviolet curable ink whose printing is gravure printing or flexographic printing.

  Furthermore, the present invention provides the method for printing an ultraviolet curable ink as described above, wherein the ultraviolet curable ink is a cationic polymerization type ultraviolet curable ink.

  Furthermore, this invention provides the printing method of the said ultraviolet curable ink which performs the ultraviolet irradiation process which irradiates an ultraviolet-ray after the heating process which heats.

  Furthermore, this invention provides the printing method of the said ultraviolet curable ink using the light emitting diode light source whose light emission wavelength is 330-450 nm.

  The printing method of the ultraviolet curable ink of the present invention makes it easy to control the thermal load applied to the base film, and also does not cause insufficient curing due to insufficient ultraviolet irradiation, thereby enabling a high-speed process and improving productivity. To do. Among them, it is particularly useful as a printing application for inks such as shrink labels that are easily deformed by heat.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating an example of a printing process, a heating process, and an ultraviolet irradiation process in the printing method of the ultraviolet curable ink of the present invention when a gravure printing method is used. After the ink 1 is attached to the rotating plate cylinder 3 (gravure plate) and the non-printed portion (portion other than the cell portion of the gravure plate) is removed by the doctor blade 2, it is pressed against the plastic film 5 by the impression cylinder 4. Thus, the printing layer 6 is formed by transferring the ink to the film. Thereafter, the printed layer 6 on the plastic film 5 is heated by the heating device 7 and cured by being irradiated with ultraviolet rays on the transport roll 9 by the LED ultraviolet irradiation device 8.

  In the printing method of the ultraviolet curable ink of the present invention, the ink is applied to at least one surface of a plastic film to form a printing layer (referred to as a printing step), and the ultraviolet curable ink or the printing layer is heat-treated. A process (referred to as a heating process) and a process for performing ultraviolet irradiation on the printed layer (referred to as an ultraviolet irradiation process). The heating process and the ultraviolet irradiation process are collectively referred to as a curing process.

  In the present invention, a plastic film is used as a substrate. The type of plastic film used in the present invention can be appropriately selected according to the required physical properties, application, cost, etc., and is not particularly limited. For example, polyester, polyolefin, polystyrene, polyvinyl chloride, polyamide, Resins such as aramid, polyimide, polyphenylene sulfide, and acrylic can be used. Among these, a polyester film, a polyolefin film, a polystyrene film, and a polyvinyl chloride film are preferable, and a polyester film and a polyolefin film are more preferable. As the polyester, polyethylene terephthalate (PET) or poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) can be used, and as the polyolefin, polypropylene, polyethylene, cyclic olefin, or the like can be used. is there.

  The plastic film may be a single-layer film or a laminated film in which a plurality of film layers are laminated according to required physical properties, applications, and the like. In the case of a laminated film, film layers made of different resins may be laminated. For example, it may be a three-layer laminated film composed of a central layer and a surface layer portion (inner layer, outer layer), a film in which the central layer is composed of a polyolefin resin or a polystyrene resin, and a surface layer is composed of a polyester resin.

  As the plastic film, any of an unstretched film, a uniaxially oriented film, and a biaxially oriented film may be used depending on the required physical properties and applications. In particular, when the plastic film is a shrink film, a uniaxial or biaxially oriented film is often used, and in particular, a film (substantially oriented in the film width direction (direction that becomes the label circumferential direction)). A film uniaxially stretched in the width direction is generally used. Since the curing process of the present invention has a feature of low heat load, it is preferably used in the case of a shrink film that is easily deformed by heat.

  The heat shrinkage rate (90 ° C., 10 seconds) of the plastic film is not particularly limited. For example, in the case of shrink label use, the longitudinal direction is −3 to 15% and the width direction from the viewpoint of shrink workability. Is preferably 20 to 80%.

  Moreover, when the said plastic film is transparent, it is possible to irradiate with an ultraviolet-ray from the opposite side to the surface in which the printing layer is provided.

  Although the thickness of the said plastic film changes with uses and is not specifically limited, 10-200 micrometers is preferable, for example, in the case of a shrink label use, 20-80 micrometers is preferable, More preferably, it is 30-60 micrometers.

  In the ultraviolet curable ink printing method of the present invention, printing is usually performed by feeding a long plastic film wound in a roll shape to a line while feeding it out. The printing may be single color printing or multicolor printing. In the case of monochromatic printing, the printing process, the heating process, and the ultraviolet irradiation process may be performed at least once, and in the case of multicolor printing, the monochromatic printing process may be performed a plurality of times. In addition, although an ultraviolet irradiation process must be performed after a printing process, the order of a printing process and a heating process and a heating process and an ultraviolet irradiation process is not specifically limited. Moreover, the heating process and the ultraviolet irradiation process may be included twice or more. Preferably, at least one heating step should be included prior to or simultaneously with the ultraviolet irradiation step. For example, printing process-heating process-UV irradiation process, heating process-printing process-heating process-UV irradiation process, printing process-heating process-UV irradiation process-heating process, printing process-(heating process, UV irradiation process simultaneously It is preferable that the printing / curing treatment is performed in the order of the curing step). However, in the case of multicolor printing, the above-mentioned process order is applied to the printing / curing process for each color.

  In the printing process of the ultraviolet curable ink printing method of the present invention, ink is applied to at least one surface of a plastic film to form a printed layer. The printing layer is usually a layer for displaying characters such as product names, illustrations, handling precautions, images, and the like. The printing layer of the present invention can be formed by conventional printing methods such as screen printing, letterpress printing, flexographic printing, and gravure printing. The printing process of the present invention is preferably coated by gravure printing or flexographic printing from the viewpoints of cost, productivity, printing decoration, etc. Among them, the printing method of the present invention is particularly effective during high-speed printing. Therefore, it can be particularly preferably used in the case of gravure printing capable of high-speed printing. Note that the printing layer is not necessarily provided on the entire surface of the plastic film, and may be formed partially.

  When the gravure printing is used in the printing process of the present invention, the gravure printing may be a system in which ink is supplied directly from the ink vat to the plate cylinder as shown in FIG. A method of supplying

  The printing ink used in the present invention is an ultraviolet curable printing ink, and more preferably a cationic polymerization type ultraviolet curable ink. The composition of the ink varies depending on the printing method and required characteristics and is not particularly limited. For example, a resin component such as a photopolymerizable oligomer (prepolymer) or a photopolymerizable monomer (reaction diluent), a photopolymerization initiator, etc. Consists of In addition, additives such as pigments, sensitizers, lubricants and the like may be contained depending on the required performance.

  The resin component (photopolymerizable oligomer or monomer) is not particularly limited, but is a general light such as a radical polymerizable compound having an acryloyl group or a vinyl group, or a cationic polymerizable compound having an epoxy group or a vinyl ether group. A polymerizable compound can be used. Examples of the radical polymerizable compound include urethane acrylate, epoxy acrylate, ester acrylate, and acrylate resins. Examples of the cationic polymerizable compound include epoxy-based, vinyl ether-based, and oxetane-based resins. Among these, cationically polymerizable resins are preferable, and epoxy-based and oxetane-based resins are particularly preferable. These may use only 1 type and may mix and use 2 or more types.

  Among these, when an oxetane compound and an epoxy compound are used as a resin component, heat resistance after curing, scratch resistance, and the like are improved, which is particularly preferable. Examples of the oxetane compound include 3-ethyl-3-[(phenoxy) methyl] oxetane, 3-ethyl-3- (hexyloxymethyl) oxetane, and 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane. , 3-ethyl-3- (hydroxymethyl) oxetane, 3-ethyl-3- (chloromethyl) oxetane, 1,4-bis [(3-ethyl-3oxetanylmethoxy) methyl] benzene, bis {[1-ethyl (3-oxetanyl) methyl]} ether and the like. Examples of the epoxy compound include propylene glycol glycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis- (3,4-epoxycyclohexyl) adipate, bisphenol A glycidyl ether, and bisphenol A. Glycidyl ether condensates, and epichlorohydrin modified products of novolak resins and cresol resins. These resins may further contain silicone having an epoxy group. The silicone having an epoxy group is a silicone having at least one epoxy group in the molecule (epoxy-modified silicone). Note that the base silicone may be a polysiloxane whose main chain is composed of a siloxane bond.

  Although it does not specifically limit as said photoinitiator, A photocationic polymerization initiator is preferable. Although it does not specifically limit as a photocationic polymerization initiator, For example, a diazonium salt, a diaryl iodonium salt, a triaryl sulfonium salt, a silanol / aluminum complex, a sulfonic acid ester, an imide sulfonate etc. are mentioned. Moreover, the content of the photopolymerization initiator with respect to the entire printing ink of the present invention is not particularly limited, but is preferably 0.5 to 7% by weight, more preferably 1 to 5% by weight.

  Examples of the pigment include white pigments such as titanium oxide (titanium dioxide), indigo pigments such as copper phthalocyanine blue, and organic and inorganic pigments such as red and yellow, carbon black, aluminum flakes, mica (mica), and the like. Can be selected and used according to the application. In addition, extender pigments such as alumina, calcium carbonate, barium sulfate, silica, and acrylic beads can be used for the purpose of adjusting gloss. Among them, as the titanium oxide, any of rutile type (tetragonal high temperature type), anatase type (tetragonal low temperature type), and brookite type (orthogonal crystal) may be used. For example, oxidation by Ishihara Sangyo Co., Ltd. Titanium particles such as “Taipeke” are available. Moreover, the average particle diameter of the titanium oxide particles (in the case where an aggregate is formed, the particle diameter of the aggregate, so-called secondary particle diameter) is, for example, 0.01 to 1 μm, preferably 0.1 to 0.00. It is about 5 μm. If the average particle size is less than 0.01 μm, the dispersibility is poor, and if it exceeds 1 μm, the film surface becomes rough and the appearance tends to deteriorate. Further, the content of the pigment of the present invention varies depending on the type of pigment and the required color density, but for example, when titanium oxide is used as the pigment, from the viewpoint of concealability and suppression of coarse protrusion formation, the coating agent as a whole is used. On the other hand, 20 to 60 weight% is preferable, More preferably, it is 30 to 55 weight%.

  Moreover, it is preferable to add a sensitizer to the printing ink of this invention as needed from a viewpoint of improving production efficiency. This is particularly effective when the titanium oxide pigment is used. In this case, the sensitizer can be selected from existing sensitizers in consideration of the type of active energy ray used. For example, (1) amine sensitizers such as amines containing nitrogen in the ring, such as aliphatic, aromatic amines, piperidine, (2) urea sensitizers such as allyl, o-tolylthiourea, (3) sodium Sulfur compound sensitizers such as diethyldithiophosphate, (4) anthracene sensitizers, (5) nitrile sensitizers such as N, N-disubstituted-p-aminobenzonitrile compounds, (6) tri -Phosphorus compound sensitizers such as n-butylphosphine, (7) Nitrogen compound sensitizers such as N-nitrosohydroxylamine derivatives and oxazolidine compounds, (8) Chlorine compound sensitizers such as carbon tetrachloride, etc. Sensitizers. Also in the above, in particular, anthracene sensitizers are preferred because of their strong sensitizing action. Of these, thioxanthone and 9,10-dibutoxyanthracene are preferably used. The content of the sensitizer is not particularly limited, but is preferably 0.1 to 5% by weight, particularly preferably 0.3 to 3% by weight, based on the entire coating agent.

  Furthermore, in the printing ink of the present invention, if necessary, various waxes such as polyolefin wax such as polyethylene wax, fatty acid amide, fatty acid ester, paraffin wax, polytetrafluoroethylene (PTFE) wax, carnauba wax, etc. A lubricant may be added. Furthermore, in addition to the above, a dispersant, an antioxidant, a fragrance, a deodorant, a stabilizer and the like may be added to the printing ink of the present invention to such an extent that the effects of the present invention are not impaired.

  The ink temperature immediately before being supplied to the plate cylinder of the printing ink of the present invention is preferably 10 to 50 ° C, more preferably 15 to 50 ° C. When the ink temperature is less than 10 ° C., the ultraviolet curing reaction may be delayed or the viscosity may be increased, resulting in fading in printing. On the other hand, when the temperature exceeds 50 ° C., the viscosity of the ink is too low, and printing failure may occur.

  Although it does not restrict | limit especially as thickness of the printing layer of this invention, 0.1-20 micrometers is preferable, More preferably, it is 0.5-10 micrometers. When the thickness of the printing layer is smaller than 0.1 μm, it may be difficult to provide the printing layer uniformly, and troubles such as fading may occur. On the other hand, if the thickness is larger than 20 μm, a large amount of ink is required, which is not preferable in terms of cost, and it may be difficult to sufficiently cure when the process speed is increased.

  The curing process of the ultraviolet curable ink of the present invention needs to include a heating process. The ultraviolet irradiation apparatus using the LED of the present invention as a light source hardly generates heat, and thus has an advantage that it is easy to control the curing by irradiation time and irradiation intensity, but the LED alone requires a long curing time. Decreases. For this reason, it is effective from the viewpoint of productivity improvement to promote the ultraviolet curing reaction by heating. As described above, it is preferable that at least one heating step is provided before or simultaneously with the ultraviolet irradiation step. By performing the heating step before or simultaneously with ultraviolet irradiation and performing the ultraviolet curing reaction in a state where the ink is heated to some extent, the curing reaction is further promoted and the productivity is improved.

  The heating step of the present invention is a step of heating the printing ink and / or the printing layer. That is, the printing ink may be heated before being printed on the base film, or may be heated after being formed as a printing layer on the base film. Here, both the case where the printing ink itself is heated and the case where the printing layer is heated before the ultraviolet irradiation have an effect of promoting the ultraviolet curing reaction immediately after the ultraviolet irradiation. On the other hand, when the printing layer is heated after ultraviolet irradiation, since the printing layer is not heated immediately after ultraviolet irradiation, the curing reaction is slow, and then the heating reaction is accelerated by heating the printing layer. For this reason, from the viewpoint of the thermal load on the film and the degree of curing, it is preferable to heat the former printing ink itself and to heat the printing layer before ultraviolet irradiation. In particular, it is most preferable to use heating of the printing ink itself and heating of the printing layer before the ultraviolet irradiation from the viewpoint that it can be heated gently without rapidly increasing the film temperature and the process conditions can be stably controlled.

  When the heating process of the present invention heats the printing ink itself, the ink before being supplied to the plate cylinder may be heated, or the ink may be heated by heating the plate cylinder or the impression cylinder. When heating the ink before being supplied to the plate cylinder, it is possible to use a normal heating method, and although not particularly limited, a line for supplying ink to the ink pan, a line for circulating the ink, and an ink pan are electrically heated. What is necessary is just to heat with heaters, such as. Even when the environmental temperature changes, such as in winter or summer, it is preferable to include a step of heating the ink pan from the viewpoint of stably controlling the ink temperature. When heating the printing ink itself, the ink temperature is preferably 30 to 50 ° C, more preferably 40 to 50 ° C, from the viewpoints of the viscosity of the ink and coating processability. Moreover, when heating a plate cylinder or an impression cylinder, the heating temperature is preferably 30 to 80 ° C, more preferably 40 to 70 ° C.

  When the heating step of the present invention heats the printed layer after printing the ink on the base film, a general heating device capable of heating in-line can be used for the heating step. Preferably, a method using a heating roll, a hot air heater, an oven such as an infrared oven, an infrared heater, or the like can be used. Among these, a hot air heater is particularly preferable from the viewpoint of safety. When heating the printing layer, the heating temperature is preferably 35 to 100 ° C, particularly 35 to 65 ° C, more preferably 40 to 60 ° C in the case of a shrink film. When the heating temperature is less than 35 ° C., the effect of promoting ultraviolet curing is small and may not contribute to the improvement of productivity. When the temperature exceeds 65 ° C., when the plastic film of the base material is a shrink film or the like, deformation such as heat shrinkage may occur and productivity may decrease.

  An ultraviolet irradiation step is required for curing the ultraviolet curable ink of the present invention. The ultraviolet irradiation of the present invention is performed using an LED. As described above, a normal electroded or electrodeless ultraviolet lamp (UV lamp) generates ultraviolet rays and also generates heat. That is, it is difficult to control the amount of ultraviolet irradiation and the amount of heat independently, and in order to secure the amount of ultraviolet irradiation necessary for curing, the amount of heat is excessive and the plastic film as the substrate may be deformed. . Further, since the light source cannot be brought close to the printing layer, there is a drawback that the ultraviolet irradiation amount effective for curing with respect to the ultraviolet irradiation amount becomes small. On the other hand, since the LED light source hardly generates heat, the amount of UV irradiation and the amount of heat can be controlled independently, so that the optimum amount of UV is irradiated at the temperature most effective for UV irradiation. be able to. Furthermore, since the light source can be installed in the immediate vicinity of the ink layer, there is almost no waste or dissipation of the irradiated ultraviolet rays, which is preferable from the viewpoint of energy saving and low cost.

  The wavelength of the LED used in the ultraviolet irradiation process of the present invention varies depending on the material of the plastic film of the substrate and the composition of the printing ink, and is not particularly limited, but the absorption wavelength of the initiator and the absorption wavelength of the sensitizer From the viewpoint of combination, 330 to 450 nm is preferable, and 350 to 420 nm is more preferable. The irradiation intensity and irradiation time also vary depending on the wavelength, printing ink, etc., and are not particularly limited. For example, the irradiation intensity is preferably higher because there is no heat generation, and the power consumption per LED is at least 50 mW or more. Is preferably used, and more preferably 60 mW or more. The irradiation time is preferably from 0.1 to 10 seconds, more preferably from 0.1 to 3 seconds. An LED light source that satisfies the above conditions can be obtained from Nisshin Electronics Industry Co., Ltd., for example.

  In the ultraviolet irradiation step of the present invention, the ultraviolet irradiation distance (distance between the light source and the ink layer) is preferably 5 cm or less, more preferably 2 cm or less. When the irradiation distance exceeds 5 cm, the irradiation time required for curing becomes long, productivity is lowered, and the amount of ultraviolet rays to be dissipated increases, which is not preferable from the viewpoint of energy saving. Furthermore, as shown in FIG. 1, it is preferable to irradiate ultraviolet rays on a transport roll or drum because the light source can be brought close to the film because it is not affected by wrinkles, sagging or fluttering of the film.

  It goes without saying that the ultraviolet irradiation of the present invention can be irradiated from the side of the printed layer, but when the plastic film of the substrate is transparent, the side opposite to the side on which the printed layer is provided passes through the plastic film. Irradiation is also possible. Further, by combining these and irradiating from both sides of the printing layer, curing can be accelerated and production speed can be increased.

  In particular, when irradiating ultraviolet rays from the side opposite to the side on which the printing layer is provided, if UV irradiation is performed on a transparent drum or transparent roll made of glass having LEDs inside, the sagging of a plastic film, etc. It is preferable because it is not affected. A schematic sectional view of the irradiation method is shown in FIG. The plastic film 11 conveyed on the transparent drum 10 (printing layer 13 is opposite to the drum) is irradiated with ultraviolet rays from the LED light source 12 mounted inside the drum through the drum.

  The process speed of the printing method of the present invention varies depending on the printing method and is not particularly limited. For example, in the case of gravure printing and flexographic printing, 30 to 400 m / min is preferable, and more preferably 100 to 300 m / min. is there. The process speed referred to here is the film conveyance speed in the ultraviolet irradiation process. Furthermore, when the printing method of the present invention is used, it is industrially preferable because less power is required for curing.

  The printing method of the present invention comprises a printing ink layer for imparting decorativeness to a plastic label, a transparent coating (sliding medium) layer for improving the slipperiness of the label surface, and a matte coating (matt varnish) for matting the label. Can be used as a layer or the like.

  The printing method of the present invention is used for plastic label applications. Specifically, stretch labels, shrink labels, stretch shrink labels, in-mold labels, tack labels, roll labels (wrap-type glued labels), heat-sensitive adhesive labels Etc. can be used. Especially, since the thermal load with respect to the plastic film of a base material is few, the printing method of this invention is used especially preferably as a shrink label use which tends to raise | generate troubles, such as a deformation | transformation by a heat | fever.

  The plastic label produced using the printing method of the present invention is attached to a container and used as a labeled container. Such containers include, for example, soft drink bottles such as PET bottles, milk containers for home delivery, food containers such as seasonings, alcohol beverage bottles, pharmaceutical containers, containers for chemical products such as detergents and sprays, cups, etc. This includes noodle containers. Also, the material of the container includes plastic such as PET, glass, metal and the like.

[Methods for measuring physical properties and methods for evaluating effects]

(1) Curability (Surface tackiness)
Immediately after performing the curing treatment in Examples and Comparative Examples, touch the printed layer with a finger and visually observe whether the finger is inked. If the ink does not adhere to the finger, the curability is good (O), When ink was applied to the finger, it was determined that the curability was poor (x).

(2) Deformation of the film The size of the printing layer was measured by measuring the size of the printing layer immediately after being applied in the printing process (the width of the printing layer was measured) and the size of the printing layer immediately after being subjected to the curing treatment. A film having a change of less than 3% was judged as having no film deformation (O), and a film having a size change of 3% or more was judged as having a film deformation (x).

(3) Film layer thickness, printing layer thickness The film thickness was measured using a stylus type thickness gauge. The thickness of the printed layer was measured using a three-dimensional microscope (Keyence Co., Ltd. VK8510) for the level difference between the portion provided with the print layer (application surface) and the portion not provided with the print layer (non-application surface).

(4) Plastic film heat shrinkage (90 ° C)
A rectangular sample piece having a length of 200 mm (mark interval 150 mm) and a width of 10 mm is prepared from the plastic film in the measurement direction (longitudinal direction or width direction).
The sample piece is heat-treated in warm water at 90 ° C. for 10 seconds (under no load), the difference between the marked lines before and after the heat treatment is read, and the thermal contraction rate is calculated by the following formula.
Thermal shrinkage (%) = (L ₀ −L ₁ ) / L ₀ × 100
L ₀ : Mark interval before heat treatment L ₁ : Mark interval after heat treatment

  EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1
As a resin component, 3-ethyl-3-hydroxymethyloxetane (manufactured by Toagosei Co., Ltd., trade name “Aronoxetane OXT-101”) 34 parts by weight, 3,4-epoxycyclohexenylmethyl-3 ′, 4′- 15 parts by weight of epoxycyclohexene carboxylate (Daicel Chemical Industries, Ltd., trade name “Celoxide 2021”), both-end epoxy-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “X-22-169B” as Component C) : 3 parts by weight of an alicyclic epoxy group, epoxy equivalent 1700), 3 parts by weight of a photopolymerization initiator (Asahi Denka Co., Ltd., trade name “Adekaoptomer SP-150”), photosensitizer (Nippon Kayaku) Co., Ltd., trade name “KAYACURE-DETX-S” 1 part by weight, white pigment as titanium oxide (Ishihara Sangyo Co., Ltd., trade name “Taipeke PF-7” 6 ") 40 parts by weight, 1 part by weight of silica as a lubricant (manufactured by Tosoh Silica Co., Ltd., trade name" NIPGEL AY-401 "), oxidized polyethylene wax (manufactured by Mitsui Chemicals, Inc., trade name" Mitsui High Wax 220MP ") 3 Weight parts were dispersed and mixed in a disperser for 30 minutes to prepare a printing ink (white ink), but no solvent was used.
Gravure printing mainly on heat-shrinkable PET film (Toyobo Co., Ltd., “Space Clean”, thickness 60 μm, heat shrinkage ratio: 2% (longitudinal direction) / 50% (width direction)) stretched mainly in the width direction (Apparatus: Nissho Gravure Co., Ltd., table-top gravure printing machine “GRAVO PROOF MINI”, gravure plate: 60 lines, plate depth 40 μm), coating the printing ink (room temperature: 23 ° C.) without heating, A printing layer having a thickness of 6 μm was provided in order to obtain Sample 1 (printing layer size: 100 mm × 280 mm).
The sample 1 was heated for 60 seconds at a heating temperature of 50 ° C. using a heating oven (“DRX420DA” manufactured by Advantech Co., Ltd.), and then directed to the printing layer (about 50 ° C.) with an LED irradiator. Irradiation using 1 × 30 (= 360) LEDs (manufactured by Nisshin Denshi Kogyo Co., Ltd.) (hereinafter referred to as “LEDs”), and one LED having a power consumption of 80 mW per wavelength 405 nm and 1 cm ² from the printed layer side. Intensity, ultraviolet irradiation was performed at an irradiation distance of 2 cm. The irradiation time was changed to 5 seconds, 10 seconds, 30 seconds, and 1 minute to obtain a sheet with a printed layer, and the curability was evaluated.
As a result, as shown in Table 1, it had sufficient curability even with an irradiation time of 5 seconds.

Example 2
The experiment was performed using the same sample 1 as in Example 1. The printing layer was heated and irradiated with ultraviolet rays under the same conditions. After the ultraviolet ray irradiation was performed on the printing layer (about 23 ° C.) of Sample 1, the printing layer was heated.
As a result, as shown in Table 1, although the curing was insufficient at the irradiation time of 5 seconds, it had sufficient curability at the irradiation time of 10 seconds.

Example 3
Sample 2 was prepared in the same manner as in Example 1 except that the printing ink was heated to 40 ° C. and applied. With respect to the print layer of sample 2 (about 40 ° C.), the print layer was not heated, but was irradiated with ultraviolet rays under the same conditions as in Example 1 to obtain a sheet with a print layer, and the curability was evaluated.
As a result, as shown in Table 1, although the curing was insufficient at the irradiation time of 5 seconds, it had sufficient curability at the irradiation time of 10 seconds.

Comparative Example 1
The experiment was performed using the same sample 1 as in Example 1. The conditions of ultraviolet irradiation were exactly the same, but the ink and / or printed layer was not heated.
As a result, as shown in Table 1, curing was insufficient even at an irradiation time of 30 seconds.

Comparative Example 2
The experiment was performed using the same sample 1 as in Example 1. The heating conditions were exactly the same, but no ultraviolet irradiation step was performed.
As a result, curing was insufficient. Although ultraviolet rays are not irradiated, in Table 1, all are described as x for convenience.

Example 4
A printing ink was prepared in exactly the same manner as in Example 1. As the base film, a heat-shrinkable PET film (manufactured by Toyobo Co., Ltd., “Space Clean”, width 300 mm, thickness 60 μm) mainly used in the width direction was used.
The printing ink (room temperature: 23 ° C.) was printed at a process speed of 50 m / min using a gravure printing machine while the film wound in a roll shape was rewound so that the width of the printing layer was 250 mm. Thereafter, hot air at 50 ° C. was blown for 3 seconds using a hot air heater, and then ultraviolet rays were irradiated from above 2 mm of the printing surface using an ultraviolet irradiation device shown below to obtain a sheet with a printing layer. . In addition, said printing process, a heating process, and an ultraviolet irradiation process were performed in-line (continuous and series).
As shown in Table 2, the obtained sheet was not deformed and had good curability.
[Ultraviolet irradiation equipment]
An ultraviolet irradiation device having 30 LEDs in the width direction and 300 LEDs in the longitudinal direction was used. The distance between the LEDs in the longitudinal direction and the width direction is 1 cm, and the installation area of the LEDs is 30 cm (width direction) × 3 m (longitudinal direction). One LED is used per 1 cm ² .
The performance of each LED (manufactured by Nisshin Electronics Industry Co., Ltd.) is as follows.
[LED (per unit)]
Size: 5mm x 5mm
Center wavelength: 405 nm
Power consumption: 80mW

Examples 5 and 6
As shown in Table 2, in Example 5, ultraviolet irradiation devices were installed on both sides of the film (printing side, opposite to the printing side). In Example 6, with the same power consumption, the LED was changed to an LED (manufactured by Nisshin Electronics Co., Ltd.) having an ultraviolet wavelength of 375 nm. Conditions other than the above were exactly the same as in Example 3 to obtain a sheet with a printed layer.
As shown in Table 2, the obtained sheets were not deformed and had good curability.

Comparative Example 3
The experiment was performed using the same sample 1 as in Example 1. Without heating, using an electroded UV lamp type UV irradiation device with conveyor (produced by Eye Graphics Co., Ltd., output: 160 mW / cm ² ), a conveyance speed of 30 m / min, irradiation distance (from UV lamp to printing layer) Evaluation was performed using the obtained sheet with a printed layer by irradiating with ultraviolet rays under a condition of 8 cm.
As a result, the printed layer was cured, but deformation of the film was observed.

Comparative Example 4
A sheet with a printed layer was prepared and evaluated in the same manner as in Comparative Example 3 except that the irradiation distance was 15 cm.
As a result, no deformation of the film was observed, but the printed layer was insufficiently cured.

Thus, when a UV lamp is used, the film is deformed (Comparative Example 3) and, on the contrary, the film is not deformed when it is attempted to irradiate the UV intensity necessary for curing due to the heat generated from the UV lamp. When irradiated with UV light, the printed layer was insufficiently cured (Comparative Example 4). Therefore, when UV lamps are used, it is difficult to adjust the UV lamp output, irradiation time (conveying speed), and irradiation distance, and it can be applied to printing on plastic films, especially shrink films, which are susceptible to thermal deformation and deterioration. It was difficult.
On the other hand, since the LED can be irradiated with ultraviolet rays without generating heat, the intensity of ultraviolet irradiation can be adjusted independently of the deformation of the film due to heat, which is preferable.

It is the schematic which shows an example of the printing method of the ultraviolet curable ink of this invention. It is a schematic sectional drawing of the method of irradiating an ultraviolet-ray from the opposite side to a printing layer using the transparent drum of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ink 2 Doctor blade 3 Plate cylinder 4 Pressure cylinder 5 Plastic film 6 Printing layer 7 Heating device 8 LED ultraviolet irradiation device 9 Conveyance roll 10 Transparent drum 11 Plastic film 12 LED ultraviolet irradiation device 13 Printing layer

Claims (7)

  UV curable ink printing comprising: a printing process for printing UV curable ink on at least one side of a plastic film; a heating process for heating; and an UV irradiation process for irradiating UV light using a light emitting diode as a light source. Method.   The method of printing an ultraviolet curable ink according to claim 1, wherein the plastic film is a transparent plastic film, and the ultraviolet irradiation is performed on the plastic film from the side opposite to the side on which the ultraviolet curable ink is printed.   The method for printing an ultraviolet curable ink according to claim 1 or 2, wherein the plastic film is a shrink film.   The printing method of ultraviolet curable ink according to any one of claims 1 to 3, wherein the printing is gravure printing or flexographic printing.   The ultraviolet curable ink printing method according to claim 1, wherein the ultraviolet curable ink is a cationic polymerization type ultraviolet curable ink.   The ultraviolet curable ink printing method according to claim 1, wherein an ultraviolet irradiation step of irradiating ultraviolet rays is performed after the heating step of performing heating.   The printing method of the ultraviolet curable ink of any one of Claims 1-6 using the light emitting diode light source whose light emission wavelength is 330-450 nm.

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