JP7792291B2 - Pretreatment liquid and printing method - Google Patents

Description

The present invention relates to a pretreatment liquid applied to the surface of a substrate, and a printing method using the pretreatment liquid.

It has been known for some time that a primer layer can be formed on the surface of a substrate to improve adhesion between the substrate and the ink (see, for example, Patent Document 1). In this method, after a primer layer is formed on the surface of the substrate, ultraviolet-curable ink (hereinafter referred to as UV ink) is ejected onto the surface using an inkjet method, and the ink is irradiated with ultraviolet light to cure it. This improves adhesion between the substrate and the ink.

Japanese Patent Application Laid-Open No. 2015-9392

The surface of the substrate may be coated with oil or other contaminants. In this case, with the printing method disclosed in Patent Document 1, it is necessary to wipe the surface of the substrate with alcohol or the like to remove the contaminants before forming a primer layer on the surface of the substrate, which is time-consuming to then apply the primer or other contaminants. Furthermore, when the substrate is acrylic, adhesion is often poor after printing directly with an inkjet printer and the ink is cured.

The present invention was made in consideration of the above circumstances, and aims to provide a pretreatment liquid and printing method that can improve adhesion between the surface of a substrate and ultraviolet-curable ink (UV ink), and can also remove any deposits on the surface of the substrate.

A pretreatment liquid according to one aspect of the present invention is applied to the surface of a printing substrate before ink is applied, and contains a volatile solvent and benzyl alcohol, with the benzyl alcohol content being 1 vol% or more and 50 vol% or less.

In one embodiment of the present invention, the benzyl alcohol content is 1 [vol%] or more and less than 10 [vol%].

In one embodiment of the present invention, the benzyl alcohol content is 1 [vol%] or more and less than 5 [vol%].

In one embodiment of the present invention, in addition to the volatile solvent and benzyl alcohol, water is contained.

In another embodiment of the present invention, the substrate is acrylic. The target acrylic can be any acrylic, regardless of manufacturing method.

In yet another embodiment of the present invention, the volatile solvent is a lower alcohol represented by C _X H _Y —OH, where X is 2 or 3 carbon atoms.

In yet another embodiment of the present invention, the ink is an ultraviolet-curable ink.

A printing method according to one aspect of the present invention includes the steps of applying the pretreatment liquid to the surface of the substrate to modify and clean the surface of the substrate, ejecting the ultraviolet-curable ink onto the modified and cleaned surface of the substrate, and irradiating the ultraviolet-curable ink with ultraviolet light.

This invention not only removes any deposits from the surface of the substrate, but also improves the adhesion between the surface of the substrate and the ink. In particular, when the substrate is acrylic, improving ink adhesion by modifying the surface and improving adhesion by cleaning the surface can be achieved simultaneously, which also has the effect of reducing the number of work steps required before printing.

FIG. 10 is an explanatory diagram for explaining a pre-processing step in the printing method according to the embodiment of the present invention. 3A to 3C are explanatory diagrams for explaining printing steps in a printing method according to an embodiment of the present invention. FIG. 10 is a diagram showing experimental results regarding a pretreatment liquid according to an embodiment of the present invention.

The pretreatment liquid and printing method according to the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the following embodiments do not limit the inventions according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions. Note that in the following embodiments, identical or corresponding components are given the same reference numerals, and redundant explanations will be omitted. Furthermore, in the embodiments, the arrangement, scale, dimensions, etc. of each component may be exaggerated or minimized and may not correspond to the actual ones, and descriptions of some components may be omitted.

[Printing method steps]
Fig. 1 is an explanatory diagram for explaining a pre-treatment process in a printing method according to an embodiment of the present invention. Fig. 2 is an explanatory diagram for explaining a printing process in a printing method according to an embodiment of the present invention. The acrylic plate in Figs. 1 and 2 shows its cross section.

The pretreatment liquid and printing method according to this embodiment are applicable to, for example, inkjet printers (printing devices) that use ultraviolet-curable ink. However, this is not limited to ultraviolet light, and the method can also be applied to printing devices that use ink that cures when exposed to light.

The printing substrate shown in Figures 1 and 2 is, for example, an acrylic plate 10. There are two main methods for manufacturing acrylic plate 10: extrusion and casting. The differences in manufacturing methods result in acrylic plates 10 with different properties. One of the differences in properties is manifested in molecular weight. Acrylic plates 10 made by extrusion tend to have higher adhesion to ultraviolet-curable ink (hereinafter referred to as UV ink 50) compared to acrylic plates 10 made by casting, while acrylic plates 10 made by casting tend to have lower adhesion to UV ink 50 due to their larger molecular weight and stronger chemical resistance. In general, extrusion is easier to apply than casting for direct printing with an inkjet printer using UV ink 50.

In addition, even in the case of acrylic sheets 10 manufactured using the extrusion method, adhesion of UV ink 50 may be poor, and although UV ink 50 can be printed directly onto acrylic sheets 10, it is difficult to ensure adhesion. However, because acrylic sheets 10 are transparent and have a wide range of uses, there is a demand for printing with UV ink using an inkjet printer.

The acrylic plate 10 is a highly transparent material and is provided with a protective film attached to prevent scratches on the surface. Therefore, after the protective film is peeled off, oil used to attach the protective film may remain on the surface of the acrylic plate 10. If oil remains on the surface, the adhesion of the UV ink 50 to the acrylic plate 10 will be poor, even if the UV ink 50 is cured by irradiating it with ultraviolet light after printing. Therefore, before printing on the acrylic plate 10, an alcohol-based solvent is used to thoroughly remove any oil from the surface of the acrylic plate 10, and then printing is carried out.

The pretreatment process shown in Figure 1 is a process in which a pretreatment liquid 30 is applied to the surface 10A of the printing substrate (acrylic plate 10) to modify and clean the surface 10A of the printing substrate (acrylic plate 10).

As shown in FIG. 1(A), oil or other deposits 20 are attached to the surface 10A of the acrylic plate 10. As shown in FIG. 1(B), a pretreatment liquid 30 is applied to the surface 10A of the acrylic plate 10. The pretreatment liquid 30 contains a volatile solvent and benzyl alcohol. The contents of the volatile solvent and benzyl alcohol will be described later (see FIG. 3).

Possible methods for applying the pretreatment liquid 30 to the surface 10A of the acrylic plate 10 include, for example, a method in which an operator wipes the surface 10A of the acrylic plate 10 with a cloth moistened with the pretreatment liquid 30, or a method in which an operator applies the pretreatment liquid 30 to the surface 10A of the acrylic plate 10 and then wipes off any excess pretreatment liquid 30 with a cloth. By applying the pretreatment liquid 30 to the surface 10A of the acrylic plate 10 and wiping it off, any deposits 20 adhering to the surface 10A of the acrylic plate 10 are removed. Note that, in order to avoid applying too much pretreatment liquid 30 to the acrylic plate, it is recommended to moisten a cloth with the pretreatment liquid 30 and then wipe it off.

As shown in Figure 1(C), the surface 10A of the acrylic plate 10 is modified by the pretreatment liquid 30 to have high adhesive properties due to changes in density caused by changes in molecular arrangement, improving the adhesion of the UV ink 50. Furthermore, because the pretreatment liquid 30 is primarily composed of a volatile solvent, it evaporates within a specified time.

The printing process shown in Figure 2 involves ejecting UV ink 50 onto the surface 10A of the modified and cleaned printing substrate (acrylic plate 10), and irradiating the UV ink 50 with ultraviolet light UV.

The print head 40 is configured to be movable in the printing direction indicated by the arrow in the figure by a drive mechanism. The print head 40 includes an inkjet recording head unit 41 and an ultraviolet irradiation device 42.

As shown in FIG. 2(A), the inkjet recording head unit 41 ejects UV ink 50 while moving in the printing direction. The UV ink 50 may be a single color or multiple different colors. Various inks, such as clear ink and white ink, may also be used. Because the surface 10A of the acrylic plate 10 has been modified with the pretreatment liquid 30, the UV ink 50 adheres closely to the surface 10A of the acrylic plate 10 after printing and curing.

The ultraviolet irradiation device 42 is mounted on the rear side of the inkjet recording head unit 41 in the printing direction. As shown in Figure 2 (B), the ultraviolet irradiation device 42 irradiates ultraviolet light UV onto the UV ink 50 ejected onto the surface 10A of the acrylic plate 10. This hardens the UV ink 50.

[Experimental Results Regarding Pretreatment Liquid 30]
Next, experimental results regarding the pretreatment liquid 30 will be described. FIG. 3 is a diagram showing experimental results regarding the pretreatment liquid 30 according to an embodiment of the present invention. In FIG. 3, "CAS No." refers to a CAS Registry Number (registered trademark), which is a number used to identify a chemical substance. Furthermore, "bp" refers to the boiling point of each chemical substance.

Experiments were conducted using a solvent containing at least one of ethanol, 2-propanol, 1-propanol, water, and benzyl alcohol as the pretreatment liquid 30.

Ethanol is, for example, a compound represented by the following formula (1):

2-Propanol is, for example, a compound represented by the following formula (2):

1-Propanol is, for example, a compound represented by the following formula (3):

Benzyl alcohol is, for example, a compound represented by the following formula (4):

In this embodiment, ethanol, 2-propanol, 1-propanol, and combinations thereof may be referred to as volatile solvents or alcohol-based solvents. In Figure 3, the unit of compound content is [vol%].

In Figure 3, "Adhesion" represents the degree of adhesion between the surface 10A of the acrylic plate 10 after modification with the pretreatment liquid 30 and the UV ink 50 after curing. This adhesion is measured, for example, based on the "JIS K5600 4-6 cross-cut method." High adhesion is marked with "◯," low adhesion with "×," and intermediate adhesion with "△."

"Transparency" indicates the transparency of the surface 10A of the acrylic plate 10 after modification with the pretreatment liquid 30. High transparency (i.e., the acrylic plate 10 does not become cloudy) is marked with "Good," and low transparency (i.e., the acrylic plate 10 becomes cloudy) is marked with "Poor."

"Drying property" indicates whether all of the pretreatment liquid 30 dries and the time it takes for the pretreatment liquid 30 to dry. High drying property, i.e., when all of the pretreatment liquid 30 dries within 10 seconds (sec), is marked "Good." Medium drying property, i.e., when the pretreatment liquid 30 dries within 10 seconds but some of the pretreatment liquid 30 remains, is marked "Good." Low drying property, i.e., when the pretreatment liquid 30 dries in more than 10 seconds but some of the pretreatment liquid 30 remains, is marked "Poor."

The "overall rating" is a comprehensive assessment of all the items: "adhesion," "transparency," and "drying speed." If all items are rated "good," the overall rating is rated "good." If only adhesion is rated "good" and the other items are rated "good," the overall rating is rated "good." If even one item is rated "bad," the overall rating is rated "bad."

Experiments in Examples 1 to 12 were conducted using pretreatment solutions 30 with different volatile solvent and benzyl alcohol contents. Examples 1 to 14 are described below.

[Example 1]
This is an example for a pretreatment liquid 30 containing 100% ethanol. In this case, the adhesion was rated "x", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "x".

[Example 2]
This is an example for a pretreatment liquid 30 containing 99% ethanol and 1% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "good".

[Example 3]
This is an example for a pretreatment liquid 30 containing 98% ethanol and 2% benzyl alcohol. In this case as well, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "good".

[Example 4]
This is an example for a pretreatment liquid 30 containing 95% ethanol and 5% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", the drying property was rated "fair", and the overall evaluation was rated "fair".

[Example 5]
This is an example for a pretreatment liquid 30 containing 91% ethanol and 9% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", the drying property was rated "fair", and the overall evaluation was rated "fair".

[Example 6]
This is an example for a pretreatment liquid 30 containing 90% ethanol and 10% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", the drying property was rated "poor", and the overall evaluation was rated "poor".

[Example 7]
This is an example for a pretreatment liquid 30 containing 75% ethanol and 25% benzyl alcohol. In this case as well, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "poor", resulting in an overall rating of "poor".

[Example 8]
This is an example for a pretreatment liquid 30 containing 50% ethanol and 50% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "fair", and the drying property was rated "poor", resulting in an overall rating of "poor".

[Example 9]
This is an example for a pretreatment liquid 30 containing 25% ethanol and 75% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "poor", and the drying property was rated "poor", resulting in an overall rating of "poor".

[Example 10]
This is an example for a pretreatment liquid 30 containing 0% ethanol and 100% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "poor", and the drying property was rated "poor", resulting in an overall rating of "poor".

[Example 11]
This is an example for a pretreatment liquid 30 containing 98% 2-propanol and 2% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "good".

[Example 12]
This is an example for pretreatment liquid 30 containing 49% ethanol, 49% 2-propanol, and 2% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "good".

[Example 13]
This is an example for a pretreatment liquid 30 containing 86.3% ethanol, 3.9% 2-propanol, 7.8% 1-propanol, and 2% benzyl alcohol. In this case, the adhesion is rated "good", the transparency is rated "good", the drying property is rated "good", and the overall evaluation is rated "good". The solvent in Example 13 is sometimes called denatured alcohol. As the denatured alcohol, neoethanol PIP, for example, is used.

[Example 14]
This is an example for a pretreatment liquid 30 containing 88% ethanol, 10% water, and 2% benzyl alcohol. In this case, the adhesion was rated "good", the transparency was rated "good", and the drying property was rated "good", resulting in an overall rating of "good".

As shown in Figure 3, when the benzyl alcohol content in the pre-treatment liquid 30 is 1% or more, adhesion is improved. Furthermore, when the benzyl alcohol content in the pre-treatment liquid 30 is 5% or more, drying properties are slightly worsened, and when the benzyl alcohol content is 10% or more, drying properties are worsened. Furthermore, when the benzyl alcohol content in the pre-treatment liquid 30 is more than 50%, transparency is worsened. For these reasons, it is preferable that the benzyl alcohol content in the pre-treatment liquid 30 be 1 vol% or more and 50 vol% or less. It is more preferable that the benzyl alcohol content in the pre-treatment liquid 30 be 1 vol% or more and less than 10 vol%. It is even more preferable that the benzyl alcohol content in the pre-treatment liquid 30 be 1 vol% or more and less than 5 vol%.

The volatile solvent (alcohol-based solvent) is not limited to the solvents shown in Figure 3, as long as it has a fast evaporation rate at room temperature.

Furthermore, the main solvent of the volatile solvent (alcohol-based solvent) may be a lower alcohol (alcohols are represented by the general formula R—OH (R is a saturated or unsaturated hydrocarbon chain), but this hydrocarbon chain has a small number of carbon atoms). For example, the main solvent of the volatile solvent may be a lower alcohol represented by C _X H _Y —OH, where X is 2 or 3 carbon atoms.

As described above, according to this embodiment, before printing, the pretreatment liquid 30 is applied to the surface 10A of the acrylic plate 10 using a cloth or the like, and dirt is simultaneously wiped away, thereby modifying and cleaning the surface of the acrylic plate 10. This improves the adhesion of the UV ink 50 to the acrylic plate 10 after printing and curing, making it possible to perform direct printing. In addition, the surface 10A of the acrylic plate 10 can also be cleaned at the same time, further improving the adhesion of the UV ink 50.

The total content of the volatile solvent and benzyl alcohol does not have to be 100%. That is, the pretreatment liquid 30 may contain water or a solvent (compound) other than the volatile solvent and benzyl alcohol. For example, the pretreatment liquid 30 of Example 14 contains water in addition to the volatile solvent and benzyl alcohol.

In addition, while the printing substrate is an acrylic plate 10 in the above example, it does not have to be plate-shaped. Furthermore, the printing substrate may be an object other than an acrylic product, as long as the effects of the pretreatment liquid 30 (adhesion, transparency, and drying properties) are not impaired. Furthermore, it may be an acrylic plate manufactured by a method other than extrusion or casting, and the printing method is not limited to inkjet printing. Furthermore, the ink does not have to be UV-curable, as long as it can be printed on the printing substrate.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

10 Acrylic plate (printing material, acrylic)
10A Surface 30 Pretreatment liquid 40 Print head 41 Inkjet recording head unit 42 Ultraviolet irradiation device 50 Ultraviolet curable ink (UV ink, ink)

Claims (6)

a step of applying a pretreatment liquid to the surface of a substrate to be printed before the ultraviolet curable ink is applied, the pretreatment liquid containing a volatile solvent and benzyl alcohol, the benzyl alcohol content of which is 1 [vol %] or more and 50 [vol %] or less , to the surface of the substrate to modify and clean the surface of the substrate;
A step of ejecting the ultraviolet curable ink onto the surface of the printing substrate that has been modified and cleaned;
irradiating the ultraviolet curable ink with ultraviolet light;
A printing method comprising : The printing method according to claim 1 , wherein the content of the benzyl alcohol is 1 vol % or more and less than 10 vol %. The printing method according to claim 1 , wherein the content of the benzyl alcohol is 1 vol % or more and less than 5 vol %. The printing method according to claim 1 , further comprising water in addition to the volatile solvent and the benzyl alcohol. The printing method according to claim 1 , wherein the printing substrate is made of acrylic. 2. The printing method according to claim 1, wherein the volatile solvent is a lower alcohol represented by C _X H _Y -OH, where X is 2 or 3 carbon atoms.