JP5102566B2 - Curing method of UV curable ink - Google Patents

Description

  In particular, the present invention relates to a method for curing an ultraviolet curable ink in which an ultraviolet curable ink is irradiated with ultraviolet rays to be cured.

  Generally, the main inks used for printing include ultraviolet curable (UV) inks and oil-based inks. Among these, UV curable ink is composed of ink (pigments), monomers, prepolymers, polymerization initiators, sensitizers, etc., and irradiates with ultraviolet rays having a wavelength range of 200 nm to 400 nm to excite the polymerization initiators. It is cured. Ultraviolet curable inks are more frequently used in the printing field because they are faster to dry than oil-based inks and do not contain organic solvents.

  In addition, UV curable inks can be printed on films and plastics because they cure quickly and cure quickly, and since drying time is not required, the next process can be performed quickly and printing time can be shortened. .

  By the way, it is known that UV curable inks cause reaction inhibition when they come into contact with oxygen during curing. Thus, there are various curing methods for ultraviolet curable inks that prevent reaction inhibition by oxygen.

  When ultraviolet rays are irradiated in the air, polymerization of the coated surface is inhibited due to the influence of oxygen in the air. For this reason, there is a limit to the coating surface characteristics. In order to solve this problem, by performing ultraviolet irradiation in a nitrogen gas atmosphere, the polymerization inhibition can eliminate the curing failure of the coating surface layer and the degradation of coating performance, and promote an efficient curing polymerization reaction. According to the method of Patent Document 1, ultraviolet irradiation is performed on an ultraviolet curable ink in a nitrogen atmosphere, thereby eliminating oxygen on the ink surface and deoxygenating.

A sensitizer, which is a composition of ultraviolet curable ink, starts a polymerization reaction when used together with a photopolymerization initiator, and many amines are generally used. Addition of amines accelerates the curing rate because oxygen in the air delays surface curing, whereas amine has the action of reducing oxygen dissolved in the composition, so the hydrogen abstraction action Hydrogen is supplied to the photopolymerization initiator to accelerate the reaction rate.
JP 2003-285424 A

  In the conventional ultraviolet curable ink, as a means for deoxygenation of oxygen that hinders the reaction, a part of the ultraviolet curable ink printing machine is irradiated with ultraviolet rays in a nitrogen atmosphere. At this time, in order to obtain a nitrogen atmosphere, the cost of equipment such as equipment and a nitrogen gas tank becomes high. Moreover, in order to accelerate | stimulate hardening of ink, it was necessary to increase the addition amount of the sensitizer containing an amine, and there existed a problem that raw material cost started.

  In general, the curing speed of the ultraviolet curable ink differs depending on the color. For example, the curing speed decreases in the order of red, yellow, blue, and black. Black ultraviolet curable ink has the characteristic that carbon used for black ink absorbs light. The ultraviolet rays irradiated from the discharge tube are almost absorbed by the carbon, and the initiator as a catalyst is not sufficiently irradiated with light. For this reason, even if it irradiates with an ultraviolet-ray, an initiator does not function and hardening becomes inadequate. Therefore, the curing speed is slow compared to other colors and it is difficult to cure.

In order to solve the above-mentioned problems of the prior art, an object of the present invention is to prevent reaction inhibition due to oxygen of ultraviolet curable ink.
Another object of the present invention is to accelerate the curing speed of ultraviolet curable ink.

  The curing method of the ultraviolet curable ink of the present invention is a method of curing an ultraviolet curable ink in which an application surface of the ultraviolet curable ink is cured by irradiating the ultraviolet curable ink. It is characterized by generating ozone from oxygen on the coated surface.

In this case, the ultraviolet rays may be ultraviolet rays in a UVA wavelength region generated from a low pressure discharge tube.
The low-pressure discharge tube may be coated with europium and strontium boron oxide in the tube.

  According to the present invention, as a pretreatment for ultraviolet irradiation for curing the ultraviolet curable ink, the application surface of the ultraviolet curable ink is irradiated with vacuum ultraviolet rays. Ozone is generated by irradiating oxygen in the air on the application surface of the ultraviolet curable ink with vacuum ultraviolet rays. The generated ozone removes oxygen on the application surface of the ultraviolet curable ink and avoids contact between the ultraviolet curable ink and oxygen on the application surface. Thereby, reaction inhibition of the ultraviolet curable ink by oxygen can be prevented.

  After the generation of ozone, the UV curable ink is cured by immediately irradiating the UV curable ink application surface with UV rays in the UVA wavelength region. Therefore, since oxygen in the air on the ink application surface is ozone, the ultraviolet curable ink can be effectively cured without causing reaction inhibition by oxygen.

  The generated ozone finally returns to oxygen after irradiation with ultraviolet rays in the UVA wavelength region at the subsequent stage, so that no post-treatment is necessary. Moreover, it has no influence on the curing of the ultraviolet curable ink. Ozone is generated only on the ink application surface, and ozone can be easily generated on the application surface by a vacuum ultraviolet lamp.

  The ultraviolet rays of the ultraviolet curable ink are irradiated with ultraviolet rays having a wavelength of 365 nm, for example, a UVA wavelength range (315 nm to 400 nm) by a low pressure discharge tube. Conventionally, ultraviolet rays were irradiated using a high-pressure discharge tube. Since the high-pressure discharge tube consumes a large amount of power and generates heat, the high-pressure discharge tube has been arranged away from the application surface on which the ultraviolet curable ink has been applied. The wavelength range of the high-pressure discharge tube is 200 nm to 1500 nm, and various wavelengths are generated over a wide range up to the infrared wavelength range. However, ultraviolet irradiation by the low-pressure discharge tube of the present invention has high irradiation efficiency at 365 nm wavelength and generates little heat, so that the discharge tube can be placed close to the coating surface without deformation of the printed material due to heat generation. The reaction can be promoted, and since the low-pressure discharge tube is used, the power consumption is as low as several tens of watts, and the power consumption can be reduced.

The method for curing the ultraviolet curable ink of the present invention will be described in detail below with reference to the accompanying drawings.
FIG. 1 is an explanatory view of a method for curing an ultraviolet curable ink of the present invention.
The ultraviolet curable ink 10 is a mixed solution in which a pigment, a polymerization initiator, a sensitizer, and the like are mixed. The sensitizer and the polymerization initiator initiate a polymerization reaction by irradiation with ultraviolet rays to cure the liquid pigment. In general, polymerization initiators used for ultraviolet curable inks include a photocleavage type, a hydrogen abstraction type, and an ion reaction type (radical).

  In the curing method of the present invention, two types of ultraviolet rays are irradiated. First, the vacuum ultraviolet lamp 14 irradiates ultraviolet rays having a shortest wavelength range of 10 nm to 200 nm among ultraviolet rays. In this embodiment, ultraviolet rays having a wavelength range of 185 nm are irradiated. By irradiating with a wavelength of 185 nm from a vacuum ultraviolet lamp, ozone is generated from oxygen in the air. Note that general ultraviolet curable inks are not cured only by irradiation with vacuum ultraviolet rays.

  Next, a low-pressure discharge tube 20 is used as a discharge tube for irradiating ultraviolet rays for curing the ultraviolet curable ink. The low-pressure discharge tube 20 is a long cylindrical lamp (fluorescent lamp), and contains a fluorescent substance in the tube. In the present invention, europism and strontium boron oxide are used as the fluorescent material. An example of the manufacturing method of the low-pressure discharge tube 20 is shown below. The powdered europism and strontium boron oxide are mixed with a binder such as butyl acetate or nitro estate. Next, this mixed solution is applied to the inner wall of the lamp by spraying. After the applied europism and strontium boron oxide coating is dried, an electrode is inserted into the lamp to seal the lamp. The low-pressure discharge tube 20 is disposed close to the vacuum ultraviolet lamp 14 as shown in FIG. This is because ozone generated by irradiation with vacuum ultraviolet rays irradiates ultraviolet rays in the UVA wavelength region after a predetermined time has passed and before returning to oxygen. In this embodiment, the vacuum ultraviolet lamp 14 is attached to the upstream side in the conveyance direction of the substrate 12 and the low-pressure discharge tube 20 is disposed so as to contact the downstream side thereof.

  FIG. 2 is a diagram showing the wavelength region of the low-pressure discharge tube. The low-pressure discharge tube shows a wavelength region of 365 nm to 436 nm as shown in the figure, and particularly has a strong peak at a wavelength of 365 nm and good irradiation efficiency. The low-pressure discharge tube has a low power of several tens of watts, for example, 60 W, and the heat generation amount is significantly smaller than that of the high-pressure discharge tube. For this reason, there is little power consumption for ultraviolet irradiation, and there is no deformation | transformation of the to-be-printed material, for example, a film, etc. by a heat | fever.

A method for curing the ultraviolet curable ink of the present invention having the above-described configuration will be described below.
The ultraviolet curable ink 10 is applied to the substrate 12. As the printing material 12, printing paper, metal, film, or the like can be used.

Next, ultraviolet rays having a wavelength range of 185 nm are irradiated on the coated surface of the ultraviolet curable ink 10 by the vacuum ultraviolet lamp 14 (FIG. 1 (1)). Ozone is generated from oxygen on the coated surface by irradiating the coated surface of the ultraviolet curable ink with ultraviolet light having a wavelength range of 185 nm. Here, the amount of ozone generated by irradiating oxygen on the coating surface with vacuum ultraviolet rays in the wavelength range of 185 nm is 1.2 g · sec ⁻¹ . With the generation of ozone, oxygen on the coated surface is removed.

  Next, the ultraviolet curable ink 10 is irradiated with ultraviolet rays by the low-pressure discharge tube 20 that irradiates the UVA wavelength region (FIG. 1 (2)). In the present invention, ultraviolet rays are irradiated by the low-pressure discharge tube 20 having a wavelength region of 365 nm.

  During the irradiation of ultraviolet rays, the ultraviolet curable ink 10 does not come into contact with oxygen due to the generated ozone on the coated surface of the ultraviolet curable ink 10. Therefore, the ultraviolet curable ink 10 is cured without being affected by the oxygen inhibition reaction. After the ultraviolet curable ink 10 is cured, ozone returns to oxygen and no post-treatment is required (FIG. 1 (3)).

  Here, the curing speed of the ultraviolet curable ink varies depending on the color. For example, the curing speed decreases in the order of red, yellow, blue, and black. Black ultraviolet curable ink has the characteristic that carbon used for black ink absorbs light. The ultraviolet light irradiated from the UV lamp is almost absorbed by the carbon, and the initiator as a catalyst is not sufficiently irradiated with light. For this reason, even if it irradiates with an ultraviolet-ray, an initiator does not function and hardening will become inadequate. Therefore, it is difficult to cure as compared with other colors. However, the generation rate of ozone on the coated surface according to the present invention and the irradiation with ultraviolet light increase the curing rate. This is thought to be due to the high curing efficiency due to the high removal efficiency of ozone by the generation of ozone on the coated surface and the irradiation efficiency of ultraviolet light with a wavelength of 365 nm by a low-pressure discharge tube.

  In general, when printing on a metal plate such as a tin plate or a film such as a plastic resin, unlike the paper, the UV effect ink is difficult to penetrate and the ink is difficult to cure. However, generation of ozone on the coated surface of the present invention and irradiation with high-intensity ultraviolet rays can be performed by the low-pressure discharge tube, and even black ultraviolet-curable ink can be cured.

  Although the low-pressure discharge tube of the present invention has been described using a discharge tube in which europium and strontium boron oxide are applied in the tube, cerium can be applied in the tube and irradiated with ultraviolet rays through a low-pressure discharge tube having a wavelength region of 320 nm. Similar effects can be obtained.

  The present invention is particularly useful in the field of curing an ultraviolet curable ink, paint, or adhesive by irradiating with ultraviolet rays.

It is explanatory drawing of the hardening method of the ultraviolet curable ink of this invention. It is a figure which shows the ultraviolet wavelength range of a low pressure discharge tube.

Explanation of symbols

10 ......... UV curable ink, 12 ......... Substrate, 14 ......... Vacuum UV lamp, 20 ......... Low pressure discharge tube.

Claims (3)

In the curing method of the UV curable ink, which is cured by irradiating the UV curable ink with ultraviolet rays,
A method for curing an ultraviolet curable ink, characterized in that ozone is generated from oxygen on an application surface of the ultraviolet curable ink by irradiating with vacuum ultraviolet rays as a pretreatment for ultraviolet curing.   The method of curing ultraviolet curable ink according to claim 1, wherein the ultraviolet rays are ultraviolet rays in a UVA wavelength region generated from a low-pressure discharge tube.   The method of curing an ultraviolet curable ink according to claim 2, wherein the low-pressure discharge tube is coated with europium and boron strontium oxide in the tube.

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