JP6525037B2 - Ink jet recording method, ink jet recording apparatus - Google Patents

Description

  The present invention relates to an inkjet recording method and an inkjet recording apparatus.

  Conventionally, various methods are used as a recording method for forming an image on a recording medium such as paper based on an image data signal. Among these, the inkjet method is an inexpensive apparatus, which discharges the ink only to the necessary image area to directly form an image on the recording medium, so that the ink can be efficiently used and the running cost is low. Furthermore, the inkjet method is excellent as a recording method because the noise is small.

  In recent years, an inkjet recording method using a photocurable ink in which a monomer is photopolymerized (cured) by light irradiation forms an image excellent in water resistance and abrasion resistance on the recording surface of a recording medium. It can be used for the production of color filters, printing (recording) on printed circuit boards, plastic cards, plastic sheets, large billboards, and plastic parts, and printing of barcodes and dates.

  For example, Patent Document 1 describes that, as an energy ray-curable ink composition containing a colorant, a polymerizable compound, a photopolymerization initiator, and a surface control agent, the polymerizable compound has an acrylic equivalent of 300 or less and Only a monofunctional monomer having one ethylenic double bond in one molecule and a polyfunctional monomer having an acrylic equivalent of 150 or less and two or more ethylenic double bonds in one molecule, The photopolymerization initiator contains an α-aminoalkylphenone compound and a thioxanthone compound, and the surface control agent discloses an ink composition containing a silicone compound having a polydimethylsiloxane structure. A low viscosity, highly reactive ink composition suitable for an ink jet recording system is obtained by containing a polymerizable compound consisting only of a monofunctional monomer having an acrylic equivalent of 300 or less and a polyfunctional monomer having an acrylic equivalent of 150 or less. It also discloses that a product can be obtained (paragraphs 0006 and 0007 of Patent Document 1).

Patent 4335955 specification

  However, when ink jet recording is performed using the energy ray-curable ink composition disclosed in Patent Document 1, the curability and the ejection stability are inferior, or the temperature in the recording apparatus is significantly after continuous printing (continuous ejection). As a result, the problem of poor image quality stability arises.

  Therefore, it is an object of the present invention to provide an ink jet recording method which is excellent in any of the curability, the ejection stability, and the suppression of the temperature rise in the recording apparatus after continuous printing.

  The present inventors earnestly studied to solve the above problems, and obtained the following findings. When the photocurable ink containing the polymerizable compound is irradiated with light, the polymerizable compound undergoes a photopolymerization reaction, and the photocurable ink solidifies (cures). At this time, reaction heat is generated due to the photopolymerization reaction. However, although the energy ray-curable ink composition disclosed in Patent Document 1 specifies the acrylic equivalent of the polymerizable compound which is one component in order to obtain a low viscosity and high reactivity ink, Since the acrylic equivalent is not defined, the heat of reaction generated upon curing of the ink is not taken into consideration. Therefore, when ink jet recording is performed using the ink composition disclosed in Patent Document 1, the amount of heat of reaction increases with time, the temperature in the ink jet recording apparatus rises significantly, and the viscosity of the ink at the time of discharge increases. As a result of the change, it has been found that the image quality of the obtained image is not stable in terms of graininess and hue due to deviation of the landing position and change of the discharge amount. As described above, when the ink composition disclosed in Patent Document 1 is used for recording for a relatively long time such as continuous printing, good curability and ejection stability can not be compatible, and the recording is difficult. I found out.

  The present inventors have further studied in view of the heat of reaction. First, in order to suppress the amount of reaction heat, it is necessary to increase the viscosity of the ink. Therefore, the temperature of the ink discharged from the head by heating the ink discharged from the head (hereinafter also referred to as “discharge temperature”) It was found that it is necessary to increase.). However, in this case, there arises a problem that the temperature in the ink jet recording apparatus is greatly increased. On the other hand, it has been found that when the viscosity of the ink is lowered to suppress the heating temperature of the ink ejected from the head relatively low, the amount of reaction heat generated at the time of curing increases. Also in this case, there arises a problem that the temperature in the ink jet recording apparatus is significantly increased.

  From the above findings, as a result of earnestly examining the problems caused by the above-mentioned reaction heat, the present inventors stably maintain the temperature in the ink jet recording apparatus, in particular, the discharge temperature relatively low. It has been found that the image quality of the obtained image is stable and excellent. Specifically, it has been found that by maintaining the discharge temperature in the range of 30 to 40 ° C., the reaction heat generated at the time of curing can be sufficiently suppressed. In addition, in order to achieve both the excellent curability and the ejection stability in the ink jet recording method, the present inventors have further studied while considering the lowering of the viscosity of the ink. As a result, a UV curable ink having a viscosity of 25 mPa · s or less at 20 ° C. and an average polymerizable unsaturated double bond equivalent of 100 to 150 is obtained from the head at a discharge temperature of 30 to 40 ° C. The above problem can be solved by an inkjet recording method including: a discharge step of discharging toward a recording medium; and a curing step of curing the ultraviolet curing ink attached to the recording medium by irradiating ultraviolet rays from a light source and curing the ink. The present invention has been completed.

That is, the present invention is as follows.
[1]
A UV curable ink having a viscosity of 25 mPa · s or less at 20 ° C. and an average polymerizable unsaturated double bond equivalent of 100 to 150 is recorded from the head at a discharge temperature of 30 to 40 ° C. A discharge step of discharging toward the medium;
A curing step of curing the ultraviolet curing ink attached to the recording medium by irradiating the ultraviolet radiation from a light source and curing the ultraviolet curing ink.
[2]
The ultraviolet curable ink is discharged from the line head having a length equal to or greater than the width of the recording medium as the head toward the recording medium scanned relative to the line head. The inkjet recording method according to [1], wherein the recording is performed using a line type inkjet recording apparatus.
[3]
It takes 5 seconds or more for the support of the recording medium to pass the position facing the head while supporting the recording medium and moving with the conveyance of the recording medium to return to the same position by the movement. The inkjet recording method according to [1] or [2].
[4]
The inkjet recording method according to [3], wherein the material of the support of the recording medium is metal.
[5]
The inkjet recording method according to any one of [1] to [4], wherein the viscosity of the ultraviolet curable ink at 20 ° C. is 15 to 25 mPa · s.
[6]
The inkjet recording method according to any one of [1] to [5], wherein the light source is a light emitting diode.
[7]
The UV curable ink contains 30 to 70% by mass of monofunctional (meth) acrylate and 20 to 60% by mass of bifunctional or higher functional (meth) acrylate according to [1] to [6] The inkjet recording method as described in any one.
[8]
The inkjet recording method according to any one of [1] to [7], wherein the ultraviolet curable ink is an ink curable by irradiation with irradiation energy of 200 mJ / cm ² or less.
[9]
An inkjet recording device which performs recording by the inkjet recording method according to any one of [1] to [8].

It is a block diagram showing an example of composition of an ink jet recording device of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the vicinity of a head unit, a transport unit, and an irradiation unit in a line printer which is an example of the inkjet recording apparatus of the present invention.

Hereinafter, modes for carrying out the present invention will be described in detail.
In the present specification, the term "recorded matter" refers to an ink on the recording medium in which a cured product is formed. In addition, the hardened | cured material in this specification means the hardened | cured material containing a cured film and a coating film.

  Further, in the present specification, “curing” means that when the ink containing the polymerizable compound is irradiated with light, the polymerizable compound is polymerized to solidify the ink. "Curable" refers to the property of being sensitive to light and curing, also referred to as photopolymerizable. "Cured wrinkles" is an uncured ink present inside the coating to be cured flows irregularly before curing, etc., resulting in a high polymerization volume shrinkage, resulting in a cured coating. It means the wrinkles which occur on the membrane surface.

  Further, in the present specification, the “ejection stability” refers to the property of causing the nozzles to eject ink droplets that are always stable without dropping out of the nozzles.

  Further, in the present specification, “storage stability” refers to the property that the viscosity before and after storage is unlikely to change when the ink is stored. The term "abrasion resistance" refers to the property that when the cured product is rubbed, the cured product is difficult to peel off and to be scratched.

  Further, in the present specification, “(meth) acrylate” means at least one of acrylate and the corresponding methacrylate, and “(meth) acrylic” means at least one of acrylic and the corresponding methacryl. And "(meth) acryloyl" means at least one of acryloyl and the corresponding methacryloyl.

[Ink jet recording method]
One embodiment of the present invention relates to an inkjet recording method (hereinafter, also simply referred to as “recording method”). In the recording method, a UV curable ink having a viscosity in a predetermined range at 20 ° C. and an average polymerizable unsaturated double bond equivalent in a predetermined range is directed from the head to a recording medium at a discharge temperature in the predetermined range. At least a discharging step of discharging and a curing step of curing the ultraviolet curable ink attached to the recording medium. Thus, a cured product of the ultraviolet curable ink is formed by the ultraviolet curable ink cured on the recording medium.

  In the following, first, an ultraviolet curable ink (hereinafter, also referred to as “ink” or “ink composition”) will be described in detail, and then each step included in the recording method will be described.

  The ultraviolet curable ink according to the present embodiment can be used in the above-described ink jet recording method and an ink jet recording apparatus described later. As described above, the ultraviolet curable ink is characterized in that the viscosity at 20 ° C. and the average polymerizable unsaturated double bond equivalent are within the predetermined ranges.

[1. Viscosity of UV-curable ink at 20 ° C.]
The ultraviolet curable ink has a viscosity at 20 ° C. of 25 mPa · s or less, preferably 15 to 25 mPa · s, and more preferably 17 to 23 mPa · s. When the viscosity at 20 ° C. is equal to or less than the above upper limit, the discharge stability of the ink becomes excellent. Moreover, generation | occurrence | production of hardening wrinkles can be effectively suppressed as the viscosity in the said 20 degreeC is more than said lower limit.
In the present embodiment, the viscosity of the ink can be measured using an E-type viscometer as in the examples described later. When using an E-type viscometer, it is a general common sense that measurement is to be performed according to the instruction manual of the viscometer. Therefore, the type and rotational speed of the rotor are to be measured according to the instruction manual. It is needless to say that the viscosity of the ink is set to one that can be measured normally and measured, and the viscosity of the ink to be measured according to the instruction manual according to the instruction manual in this embodiment as well. It is self-evident to set and measure to what can be measured normally.

  Although the principle which hardening wrinkles generate | occur | produces is guessed as follows, the scope of the present invention is not limited at all by the following speculation. In the case of the cured coating, the surface of the coating first cures in the coating of the ink, and then, when the inside of the coating cures later than the surface of the coating, the surface of the coating cured earlier is deformed or the coating is cured later. It is presumed that the ink is generated due to the irregular flow of ink inside the coating film until curing. In addition, a UV curable ink having a low viscosity has a polymerization shrinkage ratio associated with curing (difference between the volume of the ink and the volume of the ink (cured product) after curing with respect to the volume of the ink before curing having a predetermined mass) It is assumed that the occurrence of hardening wrinkles is remarkable. In addition, UV curable inks containing a monofunctional (meth) acrylate to be described later, in particular a vinyl ether group-containing (meth) acrylate represented by the general formula (I) described later, tend to cause curing wrinkles. In particular, it is presumed that the UV curable ink containing a vinyl ether group-containing (meth) acrylate represented by the general formula (I) and having a low viscosity has remarkable occurrence of curing wrinkles. Even when the ultraviolet curable ink used in the ink jet recording method of the present embodiment contains these, by setting the viscosity in the above range, the generation of the cure wrinkle can be effectively suppressed. In addition, the value measured by the method performed in the below-mentioned Example can be employ | adopted for the viscosity in this specification.

  Here, an example of an ink design method for setting the viscosity of the ink in a desired range will be described.

  The mixed viscosity of the entire polymerizable compound contained in the ink can be estimated from the viscosity of each polymerizable compound to be used and the mass ratio of each polymerizable compound to the ink composition.

  It is assumed that the ink contains N kinds of polymerizable compounds of polymerizable compounds A, B (partially omitted). The viscosity of the polymerizable compound A is VA, and the mass ratio of the polymerizable compound A to the total amount of polymerizable compounds in the ink is MA. Let the viscosity of the polymerizable compound B be VB, and let the mass ratio of the polymerizable compound B to the total amount of polymerizable compounds in the ink be MB. Similarly, let the viscosity of the Nth polymerizable compound N be VN, and the mass ratio of the polymerizable compound N to the total amount of polymerizable compounds in the ink be MN. If it shows convincingly, a mathematical expression "MA + MB + ... (partially omitted) ... + MN = 1" holds. Further, the mixed viscosity of the entire polymerizable compound contained in the ink is taken as VX. Then, it is assumed that the following equation (1) is satisfied.

    MA × LogVA + MB × LogVB + (Omitted in the middle) ... + MN × Log VN = LogVX (1)

  For example, when two types of polymerizable compounds are contained in the ink, the mass ratio of the polymerizable compounds after MB is set to zero. The number of types of polymerizable compounds can be any number of one or more.

  Next, an example of procedures (steps 1 to 7) for setting the ink viscosity to a desired range will be described.

First, information on the viscosity at a predetermined temperature of each polymerizable compound to be used is obtained (step 1). As a method of obtaining, it is possible to obtain from a manufacturer catalog or the like, or to measure the viscosity at a predetermined temperature of each polymerizable compound. Since the viscosity of the polymerizable compound itself may differ depending on the manufacturer even if it is the same polymerizable compound, it is preferable to adopt viscosity information from the manufacturer of the polymerizable compound to be used.
Subsequently, a target viscosity is set to VX, and the composition ratio (mass ratio) of each polymerizable compound is determined based on the above equation (1) so that VX becomes the target viscosity (step 2). The target viscosity is the viscosity of the ink composition that is ultimately desired to be obtained, and is, for example, a viscosity within the range of 15 to 25 mPa · s. The predetermined temperature is 20.degree.

Subsequently, the polymerizable compound is actually mixed to prepare a composition of the polymerizable compound (hereinafter, referred to as "polymerizable composition"), and the viscosity at a predetermined temperature is measured (step 3).
Subsequently, when the viscosity of the polymerizable composition is approximately close to the above-mentioned target viscosity (in the present step 4, “target viscosity ± 5 mPa · s” may be obtained), the polymerizable composition and the photopolymerization An ink composition including components other than the polymerizable compound such as an initiator and a pigment (hereinafter, referred to as "components other than the polymerizable compound") is prepared, and the viscosity of the ink composition is measured (step 4). In the step 4, when there is a component other than the polymerizable compound, for example, a component to be mixed in the ink composition in the form of a pigment dispersion, such as a pigment, the polymerizable compound previously contained in the pigment dispersion is also Since the ink composition is carried into the ink composition, the ink composition is obtained by subtracting the mass ratio of the polymerizable compound brought into the ink composition as a pigment dispersion from the composition ratio of each of the polymerizable compounds determined in step 2 It is necessary to adjust the composition.

  Subsequently, the difference between the measured viscosity of the ink composition and the measured viscosity of the polymerizable composition is calculated, and this is taken as VY (step 5). Here, it usually becomes "VY> 0." VY depends on the containing conditions such as the type and content of components other than the polymerizable compound, but in the examples described later, VY was 3-5 mPa · s.

  Subsequently, "target viscosity-VY of step 2" is determined for VX, and from the above equation (1), the composition ratio of the respective polymerizable compounds such that Vx becomes "target viscosity-VY for step 2" defined above Are determined again (step 6).

  Subsequently, each polymerizable compound having the composition ratio determined in step 6 and a component other than the polymerizable compound are mixed to prepare an ink composition, and the viscosity at a predetermined temperature is measured (step 7). If the measured viscosity is the target viscosity, the ink composition adjusted in step 7 is obtained as the ink composition having the target viscosity.

  On the other hand, when the measured viscosity of the composition of the prepared polymerizable compound does not fall within the range of “target viscosity ± 5 mPa · s” in Step 3, the following fine adjustment is performed, and then the process is repeated from Step 3. First, when the measured viscosity is too high, the content of the polymerizable compound whose viscosity as a single substance is higher than the target viscosity is reduced, and the content of the polymerizable compound whose viscosity as a single body is lower than the target viscosity is increased. Make fine adjustments. On the other hand, when the measured viscosity is too low, the content of the polymerizable compound whose viscosity as a single substance is lower than the target viscosity is reduced, and the content of the polymerizable compound whose viscosity as a single substance is higher than the target viscosity is increased. Make fine adjustments. When the measured viscosity of the prepared ink composition does not reach the target viscosity in Step 7, the same adjustment as the above-described fine adjustment is performed, and the process is repeated from Step 7.

[2. Average Polymerizable Unsaturated Double Bond Equivalent of UV-Curable Ink]
The ultraviolet curable ink is characterized in that the average polymerizable unsaturated double bond equivalent is in the range of 100 to 150, preferably 110 to 150, and more preferably 120 to 150. When the average polymerizable unsaturated double bond equivalent is at least the above lower limit, the amount of reaction heat generated due to curing can be suppressed to a low level, so that temperature rise after continuous printing can be suppressed, and storage stability is It will be excellent. In addition, when the average polymerizable unsaturated double bond equivalent is less than or equal to the above upper limit, the curability is excellent.

  Here, the "average polymerizable unsaturated double bond equivalent" in the present specification can be replaced with the average equivalent weight of the polymerizable unsaturated double bond. The compound having a polymerizable unsaturated double bond can also be referred to as a compound having a polymerizable functional group having a polymerizable unsaturated double bond, and is not limited to the following, for example, a (meth) acrylate compound, vinyl A compound, a vinyl ether compound, and an allyl compound are mentioned. The above-mentioned compound having a polymerizable unsaturated double bond may be a compound having one or more polymerizable functional groups, and in the case of having two or more polymerizable functional groups, the same kind of polymerizable functional groups may be used. It may be or may be a different kind of polymerizable functional group. In addition, each of the compounds described above is a polymerizable compound having an aromatic ring skeleton, a polymerizable compound having a cyclic or linear aliphatic skeleton, and a polymerizable compound having a heterocyclic ring structure from the structure other than the above-mentioned polymerizable functional group It can also be classified as a compound.

  In the present specification, the average polymerizable unsaturated double bond equivalent of the ultraviolet curable ink can be determined as follows. First, for each of the polymerizable compounds contained in the ink, the polymerizable unsaturated double bond equivalent of the polymerizable compound is calculated by the following formula (2).

Polymerizable unsaturated double bond equivalent of the polymerizable compound = molecular weight of the polymerizable compound / number of polymerizable unsaturated double bonds contained in the molecule of the polymerizable compound (2)
In the above formula (2), as the molecular weight of the polymerizable compound and the number of polymerizable unsaturated double bonds, values calculated from values of manufacturer catalogs and chemical structural formulas can be adopted.

  Next, the average polymerizable unsaturated double bond equivalent of the ink is calculated by the following formula (3).

Average polymerizable unsaturated double bond equivalent of ink = (polymerizable unsaturated double bond equivalent of polymerizable compound A × content of polymerizable compound A in ink + polymerizable unsaturated double bond of polymerizable compound B Equivalent weight × content of polymerizable compound B in the ink + ·· + polymerizable unsaturated double bond equivalent weight of the polymerizable compound n × content of the polymerizable compound n in the ink) / (in the ink of the polymerizable compound A) Content of the polymer + content of the polymerizable compound B in the ink + · · · + content of the polymerizable compound n in the ink) · · · (3)
The equation (3) is an equation when it is assumed that the ink contains n kinds of polymerizable compounds, and the “n” is an arbitrary integer of 1 or more. In the above formula (3), “content” represents mass% relative to the total mass of the ink.

  The smaller the average polymerizable unsaturated double bond equivalent of the ink, the more the ink has a polymerizable unsaturated double bond, and the larger the reaction heat generated with the polymerization of the ink. On the other hand, the larger the average polymerizable unsaturated double bond equivalent of the ink, the smaller the number of polymerizable unsaturated double bonds in the ink, and the smaller the heat of reaction generated with the polymerization of the ink.

  Hereinafter, additives (components) that may be included in the ultraviolet curable ink in the present embodiment will be described.

[3. Polymerizable compound]
The polymerizable compound contained in the ink can be polymerized at the time of light irradiation alone or by the action of a photopolymerization initiator described later, and the printed ink can be cured. As the polymerizable compound, various monomers and oligomers known in the prior art such as monofunctional, bifunctional and trifunctional or higher polyfunctional can be used. Examples of the above monomers include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, and salts or esters thereof, urethanes, amides and their anhydrides, acrylonitrile, styrene, and the like. And unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Moreover, as the above-mentioned oligomer, for example, an oligomer formed from the above-mentioned monomer such as linear acrylic oligomer, epoxy (meth) acrylate, oxetane (meth) acrylate, cyclic or linear aliphatic urethane (meth) acrylate, Aromatic urethane (meth) acrylates and polyester (meth) acrylates can be mentioned.

  Among the above, esters of (meth) acrylic acid, that is, (meth) acrylates are preferred. Among the (meth) acrylates, combined use of monofunctional (meth) acrylate and difunctional or higher (meth) acrylate is preferable, and combined use of monofunctional (meth) acrylate and difunctional (meth) acrylate is more preferable.

  Hereinafter, the polymerizable compound will be described in detail focusing on these (meth) acrylates. Further, among the above monofunctional (meth) acrylates, vinyl ether group-containing (meth) acrylic esters represented by the general formula (I) are preferably exemplified, so first, the above vinyl ether group-containing (meth) acrylics Let us explain the acid esters.

(3-1. Vinyl ether group-containing (meth) acrylic acid esters)
The ink preferably contains vinyl ether group-containing (meth) acrylic acid esters represented by the following general formula (I).
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(Wherein, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms A group)

  When the ink contains the vinyl ether group-containing (meth) acrylic acid esters, the viscosity of the ink can be lowered, the curability of the ink can be made excellent, and the generation of curing wrinkles It can be effectively suppressed. Furthermore, it is better to use a compound having both a vinyl ether group and a (meth) acrylic group in one molecule rather than separately using a compound having a vinyl ether group and a compound having a (meth) acrylic group. It is preferable to improve the curability.

In the above general formula (I), as the divalent organic residue having 2 to 20 carbon atoms represented by R ² , linear, branched or cyclic substitution of 2 to 20 carbon atoms is preferable. An alkylene group, an optionally substituted alkylene group having 2 to 20 carbon atoms, and an oxygen atom having an ether bond and / or an ester bond in the structure, or an optionally substituted divalent carbon number of 6 to 11 Aromatic groups are preferred. Among these, alkylene groups having 2 to 6 carbon atoms, such as ethylene group, n-propylene group, isopropylene group, and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group, oxybutylene group, etc. The C2-C9 alkylene group which has an oxygen atom by an ether bond in the structure of these is used suitably.

In the above general formula (I), as the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ , linear, branched or cyclic substitution of 1 to 10 carbon atoms is preferable. An alkyl group and an optionally substituted aromatic group having 6 to 11 carbon atoms are preferable. Among these, an alkyl group having 1 to 2 carbon atoms which is a methyl group or an ethyl group, and an aromatic group having 6 to 8 carbon atoms such as a phenyl group and a benzyl group are preferably used.

  When each of the above organic residues is a group which may be substituted, the substituent is divided into a group containing a carbon atom and a group containing no carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

  Examples of the vinyl ether group-containing (meth) acrylic acid esters include, but are not limited to, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl (meth) acrylic acid, for example. -2-vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethyl (meth) acrylate Propyl, 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl (meth) acrylate 2-vinyloxypropyl, 2-vinyloxybutyl (meth) acrylate, (meth) acid 4-vinyloxycyclohexyl methacrylate, 6-vinylhexylhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) acrylic acid 2-vinyloxymethylcyclohexylmethyl, (meth) acrylic acid p-vinyloxymethylphenylmethyl, (meth) acrylic acid m-vinyloxymethylphenylmethyl, (meth) acrylic acid o-vinyloxymethylphenyl methyl, (meth) acrylic acid 2- (vinyloxyethoxy) ethyl acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxy) acrylate Ethoxy) isopropyl, (meth) acrylic acid 2- Vinyloxyisopropoxy) propyl, (meth) acrylate 2- (vinyloxyisopropoxy) isopropyl, (meth) acrylate 2- (vinyloxyethoxyethoxy) ethyl, (meth) acrylate 2- (vinyloxyethoxyisopropoxy) ) Ethyl, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate (Meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) propyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) propyl, (meth) acrylic acid 2- (vinyloxyisopropoxyisopropoxy) propyl, (Meth) acrylic acid 2- (vinylo Xyethoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxy) Isopropoxy) isopropyl, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxy) (meth) acrylate ) Ethyl, 2- (isopropenoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxy) (meth) acrylate The ) Ethyl, and (meth) Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among these, the viscosity of the ink can be further lowered, the flash point is high, and the curability of the ink is excellent. Therefore, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxy acrylate) At least one of ethoxy) ethyl and 2- (vinyloxyethoxy) ethyl methacrylate is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. In particular, 2- (vinyloxyethoxy) ethyl acrylate and 2- (vinyloxyethoxy) ethyl methacrylate each have a simple structure and a small molecular weight, so that the viscosity of the ink can be significantly reduced. Examples of (meth) acrylic acid 2- (vinyloxyethoxy) ethyl include (meth) acrylic acid 2- (2-vinyloxyethoxy) ethyl and (meth) acrylic acid 2- (1-vinyloxyethoxy) ethyl Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate and 2- (1-vinyloxyethoxy) ethyl acrylate. Incidentally, 2- (vinyloxyethoxy) ethyl acrylate is superior to 2- (vinyloxyethoxy) ethyl methacrylate in the curability.

  The vinyl ether group-containing (meth) acrylic acid esters may be used alone or in combination of two or more.

  The method for producing the vinyl ether group-containing (meth) acrylic acid esters is not limited to the following, but a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (Process B), (meth) acrylic acid halide Of esterifying a hydroxyl group-containing vinyl ether (process C), a method of esterifying a (meth) acrylic anhydride and a hydroxyl group-containing vinyl ether (process D), an ester of (meth) acrylic acid ester and a hydroxyl group-containing vinyl ether Method of exchange (process E), method of esterifying (meth) acrylic acid and halogen-containing vinyl ether (process F), method of esterifying alkali (earth) metal salt of (meth) acrylate with halogen-containing vinyl ether (Preparation method G), hydroxyl group-containing (meth) acrylic acid ester and carboxylic acid How to vinyl exchange and Le (Procedure H), hydroxyl group-containing (meth) How to ether exchange and acrylic acid ester and an alkyl vinyl ether (Process I).

  Among these, since the desired effect can be exhibited further in the present embodiment, the production method E is preferable.

(3-2. Monofunctional (meth) acrylate)
The ink preferably contains a monofunctional (meth) acrylate. Here, when the ink contains the above-mentioned vinyl ether group-containing (meth) acrylic acid esters (provided that they are monofunctional (meth) acrylates), the vinyl ether group-containing (meth) acrylic acid esters are also Although it shall be contained in the said monofunctional (meth) acrylate, the description about the said vinyl ether group containing (meth) acrylic acid esters is abbreviate | omitted. Below, monofunctional (meth) acrylates other than the above-mentioned vinyl ether group containing (meth) acrylic acid esters are demonstrated. When the ink contains the monofunctional (meth) acrylate, the viscosity of the ink can be lowered, the curability of the ink is further improved, and the solubility of the photopolymerization initiator and other additives is also excellent. It becomes a thing. Furthermore, the ink discharge stability is further improved due to the excellent solubility of the photopolymerization initiator and other additives, and the toughness, heat resistance, and resistance of the coating film are also improved. Chemical property increases.

  Examples of the monofunctional (meth) acrylate include phenoxyethyl (meth) acrylate, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, Isomyristyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) Acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxy diethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) a Lilate, methoxypropylene glycol (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (Meth) acrylate, lactone modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, benzyl (meth) acrylate, ethoxy Nonylphenyl (meth) acrylates, alkoxylated nonylphenyl (meth) acrylates, p-cumylphenol EO modified (meth) acrylates may be mentioned.

  Among the above, monofunctional (meth) acrylates having an aromatic ring skeleton in the molecule are preferable because the curability, storage stability, and solubility of the photopolymerization initiator are further excellent. Examples of monofunctional (meth) acrylates having an aromatic ring skeleton include, but are not limited to, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyphenoxypropyl (meth) acrylate, and phenoxydiethylene glycol (for example) Meta) acrylates are preferably mentioned. Among these, it is possible to lower the viscosity of the ink and to be excellent in curability, abrasion resistance, adhesion of the ink to the recording medium, and solubility of the photopolymerization initiator. And at least one of phenoxyethyl (meth) acrylate and benzyl (meth) acrylate is preferable, and phenoxyethyl (meth) acrylate is more preferable.

  The monofunctional (meth) acrylates other than the above vinyl ether group-containing (meth) acrylic esters may be used alone or in combination of two or more.

30-70 mass% is preferable with respect to the total mass (100 mass%) of ink, and, as for content of monofunctional (meth) acrylate, 40-60 mass% is more preferable. When the content is in the above range, both the ink viscosity, specifically, the ink viscosity at 20 ° C. and the ink viscosity at the ejection temperature can be easily made into a desired range. In addition, when the content is the above lower limit value or more, the curability is further improved, and the solubility of the photopolymerization initiator is also excellent. On the other hand, when the content is equal to or less than the above upper limit, the curability is further improved, and the adhesion is also excellent.
The content of the monofunctional (meth) acrylate is a content including the vinyl ether group-containing (meth) acrylic acid esters in which the ink is a monofunctional (meth) acrylate.

  In particular, when the ink contains the vinyl ether group-containing (meth) acrylic acid ester, the content of the vinyl ether group-containing (meth) acrylic acid ester is 10 to 10% of the total mass (100% by mass) of the ink. 50 mass% is preferable, and 15-40 mass% is more preferable. When the content is at least the above lower limit, the viscosity of the ink can be reduced, and the curability of the ink can be further improved. On the other hand, when the content is equal to or less than the above upper limit, the storage stability of the ink can be maintained in a good state, and the generation of curing wrinkles can be further effectively suppressed.

  Moreover, when ink contains monofunctional (meth) acrylates other than the said vinyl ether group containing (meth) acrylic acid esters, 10-40 mass% is preferable, and, as for content of the said (meth) acrylate, 10-30 % By mass is more preferred. When the content is equal to or more than the above lower limit value, the solubility of the photopolymerization initiator is further improved in addition to the curability. On the other hand, when the content is equal to or less than the above upper limit value, in addition to the curability, the adhesion is further improved. As the monofunctional (meth) acrylates other than the above vinyl ether group-containing (meth) acrylic esters, the curability and the solubility of the photopolymerization initiator are further improved, so a monofunctional (having an aromatic ring skeleton ( Meta) acrylate is preferred.

((Meth) acrylate of 3-3.2 functional or higher)
The ink preferably contains a bifunctional or higher functional (meth) acrylate. As described above, it is more preferable to use a monofunctional (meth) acrylate and a bifunctional or higher (meth) acrylate in combination.

  Examples of difunctional (meth) acrylates include diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, dipropylene glycol di Meta) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonane Diol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, EO (ethylene oxide) adduct of bisphenol A Data) acrylate, PO-bisphenol A (propylene oxide) adduct di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, and polytetramethylene glycol di (meth) acrylate.

  Examples of trifunctional or higher polyfunctional (meth) acrylates include trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate and pentaerythritol tetra (meth) acrylate. Acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxy tri (meth) acrylate, cowprolactone modified trimethylolpropane tri (meth) acrylate, pentaerythritol ethoxy tetra (meth) acrylate, And caprolactam modified dipentaerythritol hexa (meth) acrylate.

  The bifunctional or higher (meth) acrylate may be used alone or in combination of two or more.

  The content of the bifunctional or higher (meth) acrylate is preferably determined in relation to the above-mentioned preferred content of monofunctional (meth) acrylate. 20-60 mass% is preferable with respect to the total mass (100 mass%) of ink, and, as for content of the bifunctional or more (meth) acrylate, 20-50 mass% is more preferable. When the content is in the above range, the curability of the ink and the abrasion resistance of the cured product become excellent, and the viscosity of the ink can be easily designed to a desired viscosity. In addition, monofunctional (meth) acrylates having a relatively low viscosity of a single polymerizable compound, particularly the vinyl ether group-containing (meth) acrylic esters having a particularly low viscosity, and other polymerizable compounds having a relatively high viscosity. Are preferably combined. This makes it easy to design the viscosity of the above-described ink in a desired range.

  The total content of the polymerizable compound is preferably about 50 to 95% by mass with respect to the total mass (100% by mass) of the ink, in relation to the content of other components.

  In addition, it is possible to omit the addition of the photopolymerization initiator by using a photopolymerizable compound as the polymerizable compound, but when the photopolymerization initiator is used, the initiation of polymerization is easily adjusted. Can be preferred.

[4. Photopolymerization initiator]
The ink in the present embodiment may contain a photopolymerization initiator. The said photoinitiator is used in order to harden the ink which exists on the surface of a recording medium by photopolymerization by irradiation of an ultraviolet-ray, and to form printing. By using ultraviolet light (UV) among lights, it is possible to achieve excellent safety and reduce the cost of the light source lamp. There is no limitation as long as active species such as radicals and cations are generated by the energy of ultraviolet light to initiate the polymerization of the above-mentioned polymerizable compound, but use of a photo radical polymerization initiator or a photo cationic polymerization initiator It is preferable to use an optical radical polymerization initiator among them.

  Examples of the above-mentioned photo radical polymerization initiators include aromatic ketones, acyl phosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), and hexaarylbiphenyls. Examples include imidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, an acyl phosphine oxide compound is preferable because the curability of the ink can be particularly improved.

  Specific examples of the photo radical polymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenyl acetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole , 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1- (4-isopropylphenyl)- 2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Oxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxides, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide It can be mentioned.

  As a commercial item of a radical photopolymerization initiator, IRGACURE 651 (2, 2- dimethoxy- 1, 2- diphenyl ethane 1-one), IRGACURE 184 (1- hydroxy- cyclohexyl- phenyl- ketone), DAROCUR 1173 is mentioned, for example. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl] -2-methyl-propan-1-one}, IRGACURE 907 (2-methyl-1- (4-methylthiophenyl) -2-morpholine Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4-) Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethyl benzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2, 4,6-trimethyl benzoyl) -phenyl phosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1) (I)-Phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGA CURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (A mixture of (2-hydroxyethoxy) ethyl ester) (above, product name made by BASF Corp.), KAYACURE DETX-S (2,4-diethylthioxanthone) (trade name of Nippon Kayaku Co., Ltd.) ), Speedcure TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Spe dcure DETX (2,4-diethylthioxanthen-9-one) (above, trade name of Lambson), Lucirin TPO, LR8893, LR8970 (above, BASF trade name), and Ubekryl P36 (trade name of UCB) And the like.

A photoinitiator may be used individually by 1 type, and may be used in combination of 2 or more type.
The content of the photopolymerization initiator can improve the ultraviolet curing rate to make the curability excellent, and in order to avoid the unmelted residue of the photopolymerization initiator and the coloring derived from the photopolymerization initiator, It is preferable that it is 20 mass% or less with respect to the total mass (100 mass%) of ink.

  In particular, when the photopolymerization initiator contains an acylphosphine oxide compound, the content thereof is more preferably 5 to 15% by mass, based on the total mass (100% by mass) of the ink, and 7 to 13% More preferably, it is%. When the content is at least the above lower limit value, the curability is further excellent. More specifically, in particular, a sufficient curing rate can be obtained at the time of curing with an LED (preferred emission peak wavelength: 360 nm to 420 nm), and the curability is further excellent. On the other hand, when the content is at most the above upper limit value, the solubility of the photopolymerization initiator is further excellent.

[5. Color material]
The ink in the present embodiment may contain a colorant. As the colorant, at least one of a pigment and a dye can be used.

(5-1. Pigment)
By using a pigment as a coloring material, the light resistance of the ink can be improved. As the pigment, any of inorganic and organic pigments can be used.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black, channel black and the like, iron oxide and titanium oxide can be used.

  As organic pigments, azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Polycyclic pigments, dye chelates (eg basic dye type chelates, acid dye type chelates etc.), dyed lakes (basic dye type lakes, acid dye type lakes), nitro pigments, nitroso pigments, aniline black, daylight Fluorescent pigments are mentioned.

  As a pigment used for white ink, C.I. I. Pigment white 6, 18, 21 may be mentioned.

  As a pigment used for yellow ink, C.I. I. Pigment yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 154, 154, 154, 167, 172, 180 can be mentioned.

  Examples of pigments used for magenta ink include C.I. I. Pigment red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 , 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

  As a pigment used for cyan ink, C.I. I. Pigment blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60 can be mentioned.

  Further, as pigments other than magenta, cyan and yellow, for example, C.I. I. Pigment green 7, 10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 1,2,5,7,13,14,15,16,24,34,36,38,40,43,63.

  The said pigment may be used individually by 1 type, and may use 2 or more types together.

  When using said pigment, 300 nm or less is preferable and, as for the average particle diameter, 50-200 nm is more preferable. When the average particle diameter is in the above range, the reliability of the ink such as ejection stability and dispersion stability can be further enhanced, and an image of excellent image quality can be formed. Here, the average particle size in the present specification is measured by a dynamic light scattering method.

(5-2. Dye)
Dyes can be used as coloring materials. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1, 12, 24, 23, 35, 55, 58, 86, 132, 142, 144, 173, C.I. I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive red 14, 32, 25, 57, 249, C.I. I. Reactive black 3, 4, 35 can be mentioned.

  The above dyes may be used alone or in combination of two or more.

  The content of the coloring material is preferably 1 to 20% by mass with respect to the total mass (100% by mass) of the ink, since excellent hiding power and color reproducibility can be obtained.

[6. Dispersant]
When the ink in the present embodiment contains a pigment, a dispersant may be contained in order to make the pigment dispersibility better. The dispersant is not particularly limited, and examples thereof include dispersants commonly used for preparing pigment dispersions such as polymer dispersants. Specific examples thereof include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins. Among resins, resins containing one or more as a main component are mentioned. As a commercial product of a polymer dispersant, Addisper Series (trade name) manufactured by Ajinomoto Fine Techno Co., Ltd., Solspers series (Solsperse 32000, 36000, etc. available from Avecia Co., etc. [trade names]) And DISKAVIC series (trade name) manufactured by BYK Chemie, and DISPARON series (trade name) manufactured by Enomoto Kasei.

  The dispersant may be used alone or in combination of two or more. The content of the dispersant is not particularly limited, and a preferable amount may be added as appropriate.

[7. Other additives]
The ink in the present embodiment may contain additives (components) other than the above-described additives. Such components are not particularly limited, but, for example, conventionally known fluorescent brighteners (sensitizers), surfactants such as silicones, polymerization inhibitors, polymerization accelerators, penetration accelerators, and wetting agents There may be (humectants) as well as other additives. Examples of the above-mentioned other additives include, for example, conventionally known fixing agents, mildewproofing agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusters, and thickeners.

  Subsequently, each process included in the recording medium and the recording method used for the recording method will be described in detail.

[8. Recording medium]
Examples of the above-described recording medium include non-ink-absorbing or low-absorbing recording media. Among the recording media, as a non-ink-absorbing recording medium, for example, on a substrate such as a plastic film which is not surface-treated for inkjet recording (that is, no ink absorbing layer is formed), paper, etc. Those coated with plastic, those bonded with a plastic film, and the like. Examples of the plastic referred to here include polyvinyl chloride (vinyl chloride), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyurethane (PU), polyethylene (PE), polypropylene (PP) and the like. Examples of the low-ink-absorbing recording medium include printing paper such as art paper, coated paper, matte paper, and the like.

[9. Discharging process]
The discharge process in the present embodiment discharges the ultraviolet curable ink from the head toward the recording medium at a discharge temperature in a predetermined range. And the said discharge temperature is 30-40 degreeC.

  The above-mentioned temperature of 30 to 40 ° C. is a relatively low temperature as the temperature raised by heating. As described above, when the temperature (ejection temperature) of the ejected ink is relatively low, there is almost no variation in temperature, and the advantageous effect that the ejection stability of the ink becomes good can be obtained.

  Here, the discharge temperature in this specification shall adopt the value measured by the following method. The temperature of the thermocouple provided on the nozzle surface of the nozzle plate provided on the head is measured before the start of printing, and this is taken as the discharge temperature. However, the said method does not limit the measuring method of discharge temperature which the present invention can adopt at all. The ink heating device is disposed in a path for supplying the ink from the ink cartridge containing the ink to the head, and the ink is heated to a predetermined discharge temperature by supplying the heated ink to the head. be able to.

  The above discharge temperature will be described more specifically below. When the temperature is 30 ° C. or more, the discharge stability is excellent. In addition to this, the UV curable ink that can be discharged at less than 30 ° C. has a very low viscosity, but this low viscosity causes a problem that curing wrinkles easily occur. On the other hand, the ink in the present embodiment can avoid the problem. The above problem is particularly remarkable when the printer system is a line printer and when the light source is a light emitting diode (LED). Therefore, when the line printer or the LED is used in the present embodiment, a particularly great effect is brought about.

  On the other hand, when the discharge temperature is 40 ° C. or less, the temperature rise in the recording apparatus can be suppressed.

  Moreover, in order to make the above-mentioned effect larger, and to avoid the above-mentioned problem more certainly, as for the above-mentioned discharge temperature, 34-40 ° C is preferred.

  Moreover, 8-15 mPa * s is preferable and, as for the viscosity of the ink in said discharge temperature, 8-13 mPa * s is more preferable. When the viscosity is in the above range, the occurrence of curing wrinkles caused by the composition of the ink can be effectively suppressed, and the instability of the ejection caused by the high viscosity is prevented, and the ejection stability is further enhanced.

  Further, as described above, since the ultraviolet curable ink has a viscosity higher than that of an aqueous ink used in a general inkjet ink, the viscosity fluctuation due to the temperature fluctuation at the time of ejection is large. Such viscosity fluctuations of the ink have a great influence on the change in droplet size and the change in droplet discharge speed, which can in turn cause the image quality deterioration. Therefore, it is preferable to keep the temperature of the ejected ink (ejection temperature) as constant as possible. The ink according to the present embodiment has a relatively low discharge temperature, and the discharge temperature can be kept substantially constant by temperature control by heating. Therefore, the ink in the present embodiment is also excellent in image quality stability.

[10. Curing process]
The curing step included in the recording method of the present embodiment is to cure the ultraviolet curable ink attached to the recording medium by irradiation of ultraviolet light (light) from a light source. In this step, the photopolymerization initiator contained in the ink is decomposed by the irradiation of ultraviolet rays to generate initiation species such as radicals, acids and bases, and the polymerization reaction of the polymerizable compound is promoted by the function of the initiation species. Be done. Alternatively, in this step, the polymerization reaction of the polymerizable compound is initiated by the irradiation of ultraviolet light. At this time, when the sensitizing dye is present together with the photopolymerization initiator in the ink, the sensitizing dye in the system absorbs ultraviolet rays to be in an excited state, and contacts the photopolymerization initiator to accelerate the decomposition of the photopolymerization initiator And a higher sensitivity curing reaction can be achieved.

  As a light source (ultraviolet light source), a mercury lamp, a gas / solid laser, etc. are mainly used, and a mercury lamp and a metal halide lamp are widely known as a light source used for curing the ultraviolet curable ink. On the other hand, at present there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN based semiconductor ultraviolet light emitting device is very useful industrially and environmentally. Furthermore, LEDs (light emitting diodes) such as ultraviolet light emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small in size, long in life, high in efficiency, and low in cost, and are expected as light sources for ultraviolet curing inks. ing.

  As described above, the UV curable ink in this embodiment can be suitably used regardless of whether the light source is an LED or a metal halide lamp, and among these, the LED is preferable.

  The emission peak wavelength of the above light source (ultraviolet light source) is preferably in the range of 360 to 420 nm, and more preferably in the range of 380 to 410 nm. When the emission peak wavelength is in the above-mentioned range, it is preferable because the UV-LED can be easily obtained and inexpensive.

Further, the peak intensity of ultraviolet light emitted from a light source (preferably LED) having an emission peak wavelength in the range (irradiation peak intensity) is preferably not 500 mW / cm ² or more, more preferably 800 mW / cm ² or more And more preferably 1,000 mW / cm ² or more. When the irradiation peak intensity is in the above range, the curability is further improved, and the generation of curing wrinkles can be more effectively suppressed. In particular, by setting the irradiation peak intensity of the ultraviolet light which is irradiated first to the ink ejected to the recording medium in the above-mentioned range, the generation of the curing wrinkle can be suppressed more effectively. The principle of generation of curing wrinkles is presumed as described above, but if the irradiation peak intensity is within the above range, curing can be performed simultaneously with curing of the coating surface, and generation of curing wrinkles effectively It is speculated that it can be suppressed. Furthermore, when the viscosity at 20 ° C. of the ink according to the present embodiment is 15 mPa · s or more, the generation of curing wrinkles can be more effectively suppressed. In particular, when the ultraviolet curable ink contains a vinyl ether group-containing (meth) acrylic acid ester represented by the above general formula (1) and the irradiation peak intensity is in the above range, the curability is further improved, and The generation of curing wrinkles can be suppressed more effectively.

  In addition, the irradiation peak intensity in this specification employ | adopts the value measured using ultraviolet intensity meter UM-10 and light-receiving part UM-400 (all are the products made by Konica Minolta Sensing (KONICA MINOLTA SENSING, INC.)). . However, this does not mean that the method of measuring the irradiation peak intensity is limited, and conventionally known measurement methods can be used.

Moreover, it is preferable that the ultraviolet curing ink in this embodiment is curable by irradiating irradiation energy of 200 mJ / cm ² or less. By using the ultraviolet curable ink in the recording method of the present embodiment, curing becomes possible even with the use of an LED having a relatively small amount of irradiation energy, and the heat generation of the LED can be reduced, and low cost printing can be achieved. A large printing speed can be realized. The lower limit of the irradiation energy capable of curing the ink is not particularly limited, but may be 100 mJ / cm ² or more.
Further, radiation energy in performing recording, to suppress the heat generation due to irradiation, preferably in the 600mJ / cm ² or less, and more preferably set to 500 mJ / cm ² or less. Although the lower limit of the irradiation energy at the time of recording is not particularly limited, it is preferably 200 mJ / cm ² or more for sufficient curing. Here, the irradiation energy at the time of performing the above-mentioned recording is the total irradiation energy which totaled each irradiation energy, when irradiation is performed several times.

  The irradiation energy in the present specification is calculated by multiplying the time from the start of irradiation to the end of irradiation by the irradiation peak intensity. Moreover, when irradiation is performed multiple times, said irradiation energy is represented by the irradiation energy amount which totaled several times of irradiation. The emission peak wavelength may be one or more within the above-mentioned preferred wavelength range. The total irradiation energy amount of the ultraviolet light having the emission peak wavelength in the above-mentioned range even if there are a plurality of irradiation energy is the above-mentioned irradiation energy.

  Such an ink can be obtained by containing at least one of a photopolymerization initiator that decomposes by ultraviolet irradiation in the above wavelength range and a polymerizable compound that starts polymerization by ultraviolet irradiation in the above wavelength range.

In addition, the amount of ink ejected (per unit area) at the time of ejection onto the recording medium is preferably 5 to 16 mg / in ^{2 in} order to prevent wasteful use of the ink.

Although the discharge amount of ink per unit area varies depending on the recording resolution and the amount of ink ejected per recording unit area (pixel) defined by the recording resolution, the recording resolution (printing resolution) When expressed by “resolution × resolution in a direction (main scanning direction) crossing the sub scanning direction”, 300 dpi × 300 dpi to 1500 dpi × 1500 dpi is preferable. Then, it is preferable to adjust the nozzle density and the discharge amount of the head according to the recording resolution.
The amount of ink ejected per pixel is preferably 2 to 50 ng / pixel, more preferably 3 to 20 ng / pixel. The nozzle density (the distance between nozzles in the nozzle row) is preferably 180 to 720 dpi, and more preferably 300 to 720 dpi.

  As described above, according to the present embodiment, the ink jet recording is excellent in any of the curability, the ejection stability, and the suppression of the temperature rise in the recording apparatus after the continuous printing, and the generation of the curing wrinkles can also be suppressed. We can provide a way. Furthermore, the recording method of the present embodiment raises the temperature in the recording apparatus after continuous printing while securing excellent curability and ejection stability even when using a low viscosity ultraviolet curing ink. It is excellent in the suppression of

[Ink jet recording apparatus]
One embodiment of the present invention relates to an inkjet recording apparatus, that is, an inkjet printer. The said recording device utilizes the inkjet recording method of the said embodiment. Hereinafter, the recording apparatus (printer) of the present embodiment for implementing the recording method will be described in more detail with reference to the drawings. The scope of the present invention is not limited to the following drawings.

  FIG. 1 is a block diagram showing an example of the configuration of the ink jet recording apparatus of the present embodiment. A printer driver is installed in the computer 130, and print data corresponding to the image is output to the printer 1 in order to cause the printer 1 to record the image. The printer 1 includes a conveyance unit 20, a head unit 30, an irradiation unit 40, a detector group 110, a memory 123, an interface (I / F) 121, and a controller 120. The printer 1 receiving the print data from the computer 130, which is an external device, controls each unit by the controller 120 to record an image on the recording medium according to the print data. The situation in the printer 1 is monitored by the detector group 110, and the detector group 110 outputs the detection result to the controller 120. The controller 120 controls each unit based on the detection result output from the detector group 110. The controller 120 stores print data input via the interface 121 in the memory 123, and includes a CPU 122 and a unit control circuit 124. The memory 123 also stores control information for controlling each unit.

  The printer according to this embodiment can record various colors of ink on a recording medium (form an image). For example, an image is formed using four colors of ink of CMYK (cyan, magenta, yellow, black). And forming a base image that imparts excellent concealability to a recording medium using a white ink.

  Examples of the type of printer according to this embodiment include a line printer and a serial printer, any of which can be used. These differ in the printer method.

  A line printer, which is a line-type inkjet recording apparatus, includes a line head having a length equal to or greater than the width of a recording medium as a head. The line head and the recording medium move toward the recording medium while moving the position relatively in the scanning direction intersecting the width direction, that is, toward the recording medium to be scanned relative to the line head, Ink is ejected from the line head. Then, in the line printer, the head is fixed without (almost) moving, and printing is performed in one pass (single pass). The line printer is advantageous over the serial printer in that the recording speed is high.

  Here, the above-mentioned "line head having a length corresponding to the width of the recording medium" is not limited to the case where the width of the recording medium and the length (width) of the line head completely coincide with each other. It may be different. For example, the length (width) of the line head corresponds to the width (recording width) of the recording medium on which the ink is to be ejected (the image is to be recorded). The case is

  On the other hand, serial printers, which are serial type inkjet recording apparatuses, perform main scanning (pass) that discharges ink while moving in the main scanning direction in which the head intersects the sub-scanning direction of the recording medium. Recording is performed by (multi-pass).

[Ink jet head]
The head unit 30 of the ink jet recording apparatus (printer 1) includes a head (ink jet head) that discharges ultraviolet curable ink toward a recording medium to perform recording. The head is provided with a cavity for discharging the accommodated ink from the nozzle, a discharge driving unit provided for each of the cavities for applying a driving force to the ink, and a head for each of the cavities. And a nozzle for discharging the ink to the outside. The cavity, and the ejection drive unit and the nozzle provided for each cavity may be provided in plural on one head independently of each other. The ejection drive unit is formed using an electromechanical conversion element such as a piezoelectric element that changes the volume of the cavity by mechanical deformation, or an electrothermal conversion element that generates bubbles in the ink by emitting heat and discharges the ink. be able to. In the inkjet recording apparatus, one head or plural heads may be provided for ink of one color, and in the case where plural heads are provided, line heads are arranged by arranging plural heads in the width direction of the recording medium. In this case, the above-mentioned recording width can be increased. When recording is performed using inks of a plurality of colors, the ink jet recording apparatus includes a head for each ink. The head can be configured, for example, as shown in FIG. 3 of JP 2009-279830 A.

  Hereinafter, with reference to FIG. 2, a line printer which is an example of the printer of the embodiment will be described in detail. In FIG. 2 used in the following description, the scale of each member is appropriately changed in order to make each member have a recognizable size.

[Line printer]
FIG. 2 is a schematic cross-sectional view showing an example of the vicinity of the head unit, the transport unit, and the irradiation unit in the line printer described above which is an example of the printer according to the embodiment.

  The conveyance roller (the upstream roller 25A and the downstream roller 25B) is rotated by the conveyance motor (not shown), and the conveyance drum 26 is driven. The recording medium S is transported along the transport rollers 25A and 25B and the circumferential surface of the transport drum 26 which is a support, as the transport roller rotates. Each line head including the head K, the head C, the head M, and the head Y is disposed around the transport drum 26 so as to face the transport drum 26.

The support has a surface on which the recording medium S is conveyed, supports the recording medium S, moves relative to the head, and moves relative to the head. . Referring to FIG. 2, the transport drum 26 corresponding to the support has a surface on which the recording medium S is transported, supports the recording medium S, and moves relative to the head. It passes through the position facing the line head. When the support moves relative to the head while supporting the recording medium S, the time (period) for returning from an arbitrary position to the same position is preferably 5 seconds or more, preferably 6 seconds. It is more preferable that The temperature rise can be suppressed by the thermal radiation of a support body as the said time is in the said range. The upper limit of the cycle is not particularly limited, but may be, for example, 15 seconds or less in order to realize high-speed printing.
The movement of the support by the predetermined cycle may be performed at least while ink jet recording is performed, and may be continuously or intermittently performed while ink jet recording is performed.

The shape of the support is not limited to the drum-like support as shown in FIG. 2 and is not limited to the following. For example, the drum-like, roller-like and belt-like supports, and the recording medium S A plate-like support (platen or the like) for supporting is also preferably mentioned. The movement of the support relative to the head may be movement (rotation) in one direction to return to the same position, and movement in one direction and movement in another direction may be the same position. It is also possible to move back. In the latter case, the movement in the certain direction is the movement accompanying the recording on the single recording medium, and the movement in the other direction is the recording on the one recording medium. There is a mode of moving for recording on the next recording medium.
In the case of a serial printer, the movement in the above direction corresponds to sub-scanning. Also, the movement of the support relative to the head may be any relative movement of the support relative to the head, including movement such that the head moves relative to the support.

  Examples of the material of the support include, but are not limited to, metals, resins, and rubbers. Among them, metals are preferable. Unlike the case where the material is a metal, when the material is a polymer material such as rubber, even if the support is used for a long time, cracking which is considered to be deterioration due to heat does not occur, and the long time use becomes possible. Such metals include, but are not limited to, for example, aluminum, stainless steel, copper, and iron, and alloys thereof. Furthermore, the surface of the metal support, that is, the transport surface of the recording medium S may be coated with a coating agent or the like. Thereby, the hardness of the surface of the support can be improved more than that of the non-painted support, and it is possible to make the surface less slippery with the recording medium. Although the said coating agent is not limited to the following, For example, Organic type coating agents, such as resin, Inorganic type coating agents, such as an inorganic compound, These composite coating agents are mentioned. The above matters relating to the support are applicable not only to the line printer but also to the serial printer.

As described above, the recording operation is performed by the discharge operation of discharging and adhering the ink to the recording medium S opposed to each line head. The temporary curing irradiation units 42 a, 42 b, 42 c, and 42 d are disposed downstream of the line heads in the conveyance direction, and irradiate the ultraviolet light toward the recording medium S. At the further downstream side in the transport direction, the main curing irradiation unit 44 is disposed. Such a recording apparatus can be configured, for example, as shown in FIG. 11 of JP-A-2010-269471.
In the present specification, "temporary curing" means temporary fixing (pinning) of the ink, and more specifically, curing before main curing for preventing bleeding between dots and controlling the dot diameter. means. In general, the degree of polymerization of the polymerizable compound in temporary curing is lower than the degree of polymerization of the polymerizable compound in main curing performed after temporary curing. Further, “main curing” refers to curing the dots formed on the recording medium to a cured state necessary for using the recorded matter. Here, the term "curing" in the present specification means the above-mentioned full curing unless otherwise stated.

  In addition, since it is sufficient that the ultraviolet ray is irradiated from the main curing irradiation unit 44 and the main curing be performed, the temporary curing irradiation sections 42a, 42b, 42c, and 42d are not irradiated with the ultraviolet ray from a part or all The curing operation may be terminated by irradiating ultraviolet rays from the main curing irradiation unit 44. As described above, the curing operation may perform only main curing without performing temporary curing.

  As described above, according to the present embodiment, the ink jet recording is excellent in any of the curability, the ejection stability, and the suppression of the temperature rise in the recording apparatus after the continuous printing, and the generation of the curing wrinkles can also be suppressed. An apparatus can be provided. Furthermore, even if the low viscosity UV curable ink is used, the temperature rise in the printing apparatus after continuous printing is ensured while securing excellent curability and ejection stability. It is excellent in the suppression of

  Hereinafter, the present embodiment will be more specifically described by Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Material used]
The materials used in the examples and comparative examples are as follows.
[Polymerizable compound]
-VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., monofunctional (meth) acrylate)
New Frontier PHE (phenoxyethyl acrylate, trade name of Dai-ichi Kogyo Seiyaku Co., Ltd., monofunctional (meth) acrylate, hereinafter referred to as "PEA")
APG-100 (Dipropylene glycol diacrylate, trade name of a product of Shin-Nakamura Chemical Co., Ltd., bifunctional (meth) acrylate, hereinafter referred to as "DPGDA")
A-DPH (tripropylene glycol diacrylate, bifunctional (meth) acrylate, trade name of Shin-NAKAMURA CHEMICAL CO., LTD.)
[Photopolymerization initiator]
DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, trade name by BASF, hereinafter referred to as "TPO")
IRGACURE 819 (bis (2,4,6-trimethyl benzoyl) -phenyl phosphine oxide, trade name of BASF, hereinafter referred to as "819")
[Color material]
-Cyanine Blue KRO (CI pigment blue 15: 3 (phthalocyanine pigment), trade name from SANYO COLOR WORKS, Ltd., pigment particle diameter 80 nm, hereinafter described as "PB 15: 3")
Dispersant
Solsperse 32000 (trade name of Avecia, hereinafter referred to as "32000")

[Preparation of UV Curing Inks 1 to 11]
Each material described in the following Table 1 is added so as to have the content (unit: mass%) described in Table 1 and stirred with a high-speed water-cooled stirrer to obtain ultraviolet curable inks 1 to 11 I got In addition, the viscosity of each ink was made into the desired value according to the above-mentioned viscosity design method.

[Measurement and evaluation items]
[1. Average polymerizable unsaturated double bond equivalent of ink]
The average polymerizable unsaturated double bond equivalent of the ink was calculated by the above formulas (2) and (3).
Evaluation criteria are as follows. The evaluation results are shown in Table 1 below divided into actual values and the following ranks (standards).
It was 1: 100 or more and 150 or less.
2: less than 100.
It exceeded 3: 150.

[Viscosity measurement of ink at 2.20 ° C. (rank)]
The viscosity of each ink prepared above was measured under the conditions of 20 ° C. and a rotation number of 10 rpm using a DVM-E rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.).
The rotor used was a DVM-E type cone having a cone angle of 1 ° 34 'and a cone radius of 2.4 cm.
Evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
It was less than 1:15 mPa · s.
2: 15 mPa · s or more and 25 mPa · s or less.
3: It exceeded 25 mPa · s.

[3. Evaluation of ink curability]
Each ink prepared above is coated on a PET film (PET 50 (K 2411) PA-T18 LK [trade name], manufactured by Lintec Corporation) using a bar coater, and a coating film of 10 μm thickness is formed. Obtained. Then, ultraviolet light having an irradiation intensity of 1,000 mW / cm ² and a peak wavelength of 395 nm was irradiated from an ultraviolet irradiation device (UV-LED) for a predetermined time to cure each of the above coatings. In addition, it was judged that it hardened | cured when the tackiness of the image (coating film surface) was lose | eliminated by the finger touch test.

The evaluation was performed by calculating the irradiation energy of ultraviolet light required for curing. The irradiation energy [mJ / cm ² ] was obtained from the product of the irradiation intensity [mW / cm ² ] on the irradiated surface irradiated from the light source and the irradiation duration [s]. The measurement of the irradiation intensity was performed using a UV intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by KONICA MINOLTA SENSING, INC.).
Evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
A: Curing was carried out with an irradiation energy of 200 mJ / cm ² or less of accumulated light quantity.
B: Cured with irradiation energy exceeding 200 mJ / cm ^{2 of} integrated light quantity.

[4. Evaluation of storage stability of ink]
Each ink whose viscosity was measured in the above "2." was put in a 50 mL glass bottle, sealed, and then put into a 60 ° C. thermostat to store for 1 week. Thereafter, the viscosity of each of the inks whose temperature was lowered to room temperature was measured in the same manner as the above "2.". Then, the storage stability was evaluated by the viscosity ratio before and after storage (the ratio of the viscosity of the ink after storage to the viscosity of the ink before storage).
Evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
A: The thickening rate was less than 5%.
B: The thickening rate was 5% or more.

  The ultraviolet curable inks 1 to 4 and 9 correspond to the ink that can be used as an example, and the ultraviolet curable inks 5 to 8 and 10 and 11 correspond to the ink used in the comparative example.

  Hereinafter, the recording method in each example and each comparative example will be described.

Example 1
As shown in FIG. 2, a line printer having a line head having a length substantially corresponding to the width (recording width) on which the image of the recording medium is to be recorded is formed by arranging four heads in the width direction did. Among the head and light source shown in FIG. 2, the head C, the light source 42 b and the light source 44 were used, and the other ones were not used.

  The transport drum 26 is made of aluminum, and the diameter of the transport drum 26 is 500 mm, the printing speed is 285 mm / s, and the drum rotation cycle is 5.5 s.

The ink 1 shown in Table 2 is directed from the head C having a nozzle density of 600 dpi to the PET film (PET 50 (K 2411) PA-T 18 LK) at a recording resolution of 600 dpi x 600 dpi and one pass (single pass). Ejection was continued for 10 minutes (continuous printing for 10 minutes was performed). The amount of ink droplets per pixel was adjusted so that the film thickness after curing was 11 μm. The amount of ink droplets of this example 1 was 7 ng. Thus, a solid pattern image was formed. The solid pattern image means an image in which dots have been recorded for all the pixels of the minimum recording unit area defined by the recording resolution.
The temperature at the time of the discharge was 35 ° C. shown in the “discharge temperature” column in Table 2. Here, the discharge temperature was measured by the following method. An ink heater was disposed in a path for supplying the ink to the head C, and the ink heated to a predetermined temperature was supplied to the head. The temperature of the thermocouple provided on the nozzle surface of the head C was measured before the start of printing, and this was used as the discharge temperature. The nozzle surface (nozzle plate) was made of stainless steel.

Subsequently, the ink attached to the PET film was irradiated with ultraviolet light from a light source to cure the ink. Specifically, first, an LED having a peak wavelength of 395 nm and an irradiation peak intensity of 500 mW / cm ² was used as the light source 42 b. Pre-curing was performed by irradiating ultraviolet light with an irradiation energy of 20 mJ / cm ² from the LED. Further, as the light source 44, an LED having a peak wavelength of 395 nm and an irradiation peak intensity of 1,500 mW / cm ² was used. The solid pattern image was cured by irradiating an ultraviolet ray having an irradiation energy of 400 mJ / cm ² from the LED for a predetermined time. Thus, a recorded matter in which the solid pattern image was cured was obtained. In addition, it was confirmed by the finger touch test that the tackiness of the image (coated film surface) was lost.

[Examples 2 to 7, Comparative Examples 1 to 12]
A recorded matter was obtained in the same manner as in Example 1 except that the used ink and the ejection temperature were as described in Tables 2 and 3 below, respectively.

[Example 8]
A recorded matter was obtained in the same manner as in Example 1 except that the diameter of the transport drum 26 was 318 mm and the drum rotation period was 3.5 s (the printing speed is the same value as in Example 1).

[Example 9]
A recorded matter was obtained in the same manner as in Example 1 except that a metal halide lamp (abbreviated as "metahara" in Table 2) was arranged instead of the LED as the light source 42b.

[Example 10]
Recording was performed in the same manner as in Example 1 except that a serial printer was used in place of the line printer, and an LED with a peak intensity of 500 mW / cm ² was mounted on the side of the carriage as a light source. The serial printer used is the ink jet printer described in FIG. 2 of JP-A-2010-167677. Ink 1 was filled in the nozzle row of the head (serial head). Assuming that the nozzle density of the head is 300 dpi, the droplet weight is 7 ng, and the recording resolution is 600 dpi × 600 dpi (however, the recording resolution per pass is 300 dpi × 300 dpi), and the above PET film is identical under the conditions of ejection temperature 35 ° C. Four passes (two passes in the main scanning direction × two passes in the sub scanning direction) were performed to form dots on the recording area. Thus, a solid pattern image having a thickness of 11 μm was printed.

On the carriage of the printer, the same LED as the light source 42b mounted on the line printer is provided for the same length as the length in the sub scanning direction of the head. The preliminary curing was performed for each pass, with the irradiation energy per pass set to 40 mJ / cm ² . The same LED as the light source 44 mounted on the line printer is provided downstream of the carriage of the printer in the conveyance direction of the recording medium by the same length as the width of the recording medium, and the irradiation energy is 400 mJ / cm ² A certain ultraviolet light was irradiated for a predetermined time to cure the solid pattern image of the recording medium conveyed to the downstream side of the conveyance direction of the recording medium with respect to the carriage. Thus, a recorded matter in which the solid pattern image was cured was obtained. As in Example 1, it was confirmed by the finger touch test that the tackiness of the image (coated film surface) was lost.

[Measurement and evaluation items]
[5. Discharge stability evaluation]
Continuous printing was performed for 10 minutes from the 300 nozzles using the ink numbers shown in Table 2 and Table 3 below (the ink was continuously discharged for 10 minutes). Before the start of printing, 500 drops of ink are discharged from the nozzle onto the plate to measure the discharge amount (mass) per drop, and immediately after the end of printing, the discharge amount per drop (mass) in the same manner as before the start of printing Was measured.
Evaluation criteria are as follows. The evaluation results are shown in Tables 2 and 3 below.
A: There was no non-ejection nozzle during continuous printing. The change in mass of the discharge amount after the end of printing relative to the discharge amount per ink droplet before the start of printing was 5% or less.
B: There was no non-ejection nozzle during continuous printing. The change in mass of the discharge amount after the end of printing relative to the discharge amount per ink droplet before the start of printing exceeded 5%.
C: There was an ejection failure nozzle during continuous printing.

  The following items “6.” and “7.” are all evaluations regarding temperature rise in the recording apparatus after continuous printing, but the evaluation results can be obtained by performing the evaluation at a plurality of locations in the recording apparatus. It will increase the reliability. Therefore, the nozzle surface of the nozzle plate on the head side and the drum on the recording medium side were selected as a plurality of locations in the recording apparatus.

[6. Evaluation of temperature rise on nozzle face of head after continuous printing]
Before the start of printing, the temperature of the thermocouple provided on the nozzle surface of the nozzle plate was measured. Then, continuous printing was performed for 10 minutes, and the temperature of the thermocouple was measured after continuous printing. Then, the difference between the temperature before the start of printing and the temperature after continuous printing was evaluated as the temperature rise at the nozzle surface of the head after continuous printing.
Evaluation criteria are as follows. The evaluation results are shown in Tables 2 and 3 below. In the table, it is abbreviated as "the nozzle surface temperature rise after continuous printing".
A: It was less than 10 ° C.
B: 10 ° C. or more and less than 15 ° C.
C: 15 ° C. or higher.

[7. Evaluation of temperature rise in drum after continuous printing]
Each Example and each comparative example except Example 10 evaluated as follows. The surface temperature of the surface of the transfer drum which could face the head was measured before the start of printing. Then, continuous printing was performed for 10 minutes, and the surface temperature of the transfer drum that could face the head was measured after continuous printing, as before the start of printing. Then, the difference between the surface temperature before the start of printing and the surface temperature after continuous printing was evaluated as the temperature rise in the transport drum after continuous printing.
On the other hand, Example 10 is the same as the above Examples and Comparative Examples except that the surface temperature of the platen, not the transfer drum, which can be opposed to the head is measured before the start of printing and after continuous printing. It evaluated.
Evaluation criteria are as follows. The evaluation results are shown in Tables 2 and 3 below. In the table, it is abbreviated as "the drum temperature rise after continuous printing". In addition, “the drum temperature rise after continuous printing” in the tenth embodiment is exactly the platen temperature rise after continuous printing.
A: It was less than 10 ° C.
B: 10 ° C. or more and less than 15 ° C.
C: 15 ° C. or higher.

[8. Hardened wrinkle evaluation]
The surface of the cured film (cured coating film) was visually observed for the recorded matter obtained in each of the above Examples and Comparative Examples. Evaluation criteria are as follows. The evaluation results are shown in Tables 2 and 3 below.
A: There were no wrinkles at all.
B: Wrinkles were generated in a part of the cured film.
C: Wrinkles were generated on the entire surface of the cured film.

  From the above results, the UV curable ink having a viscosity of 20 mPa · s or less at 20 ° C. and an average polymerizable unsaturated double bond equivalent of 100 to 150 at an ejection temperature of 30 to 40 ° C. The ink jet recording method (each example) includes a discharge step of discharging from the head toward the recording medium, and a curing step of curing the ink attached to the recording medium by irradiating ultraviolet light from the light source and curing the ink. It was found that the curing property, the ejection stability, and the suppression of the temperature rise after continuous printing were all superior as compared with the recording methods (comparative examples) which are not used, and that the generation of the curing wrinkles can be suppressed. Hereinafter, although examination is given for every Example and a comparative example, the following examination does not limit the scope of the present invention at all.

  First, when the viscosity at 20 ° C. of the ultraviolet curable ink was 25 mPa · s or less, the curability was excellent. In addition, when the average polymerizable unsaturated double bond equivalent of the ultraviolet ray curable ink is 100 or more, the storage stability of the ink is excellent. Furthermore, when the said equivalent is 150 or less, it was excellent in curability. When the equivalent weight is 150 or less, the curability of the ink is excellent. Therefore, in the case of actual printing performed using a plurality of colors of ink, it is necessary for the minimum curing to prevent color mixing between the inks. Therefore, the irradiation energy from the light source 42b can be made smaller, and the temperature rise of the transport drum 26 can be reduced due to the irradiation from the light source 42b and the heat generation of the light source 42b. Ru.

Also, when the average polymerizable unsaturated double bond equivalent of the ultraviolet curable ink is less than 100 or the discharge temperature exceeds 40 ° C., the temperature rise on the nozzle face of the head after continuous printing and the conveying drum after continuous printing The temperature rise in was remarkable. More specifically, when the average polymerizable unsaturated double bond equivalent is less than 100, it is presumed that the temperature is significantly increased in the recording apparatus after continuous printing because the reaction heat amount at the time of curing is large.
If the temperature of the conveyance drum after continuous printing is significantly increased, the recording medium may be deformed by heat, which causes a problem that the quality of the obtained recording material is inferior. On the other hand, if the temperature is significantly increased at the nozzle surface of the head after continuous printing, the change in the discharge amount becomes large, which causes a problem of deteriorating the image stability. On the other hand, according to each embodiment, since the temperature rise in both the conveyance drum and the nozzle surface after continuous printing can be effectively suppressed, the above problem does not occur.

  Further, according to Example 8, when the drum rotation period (s) was further shortened, the temperature was further raised in the transfer drum after continuous printing, as compared with the other examples.

  Moreover, from Example 9, when it changed to LED and used the metal halide lamp as a light source for hardening, compared with the case where LED was used, the temperature rise of the conveyance drum after continuous printing was large. It is presumed that this is because the temperature rise of the drum was large due to the heat generation of the metal halide lamp. When a metal halide lamp is used as the light source, the recording medium may be deformed by heat due to the rise in drum temperature due to heat generation, and since it is a large light source as compared to the LED, an installation space may be required. That is, it is preferable to use the LED because the temperature rise in the transport drum after continuous printing can be effectively suppressed, and it is also preferable from the viewpoint of being able to be a low heat generation and space saving recording apparatus.

  Also, from Example 10, when a serial printer was used instead of a line printer, the temperature rise was smaller compared to the line printer, but the recording speed was smaller. That is, according to the recording method of the present invention, it is presumed that even when high-speed printing is performed by a line printer, recording capable of effectively suppressing the occurrence of curing wrinkles can be performed.

In addition, although not shown as an Example, as the irradiation peak intensity of LED of the light source 42b was made high, the cure wrinkle was able to be suppressed effectively. Especially, a radiation peak intensity of a light source to first irradiate the ink adhered is discharged toward a recording medium, preferably 500 mW / cm ² or more, more preferably by a 800 mW / cm ² or more, more curing wrinkles It was possible to suppress effectively.

  Also, although not shown as an example, it is carried out in the same manner as in Example 1 except that the material of half of the drum radius other than the shaft side of the drum, ie, the surface side of the drum is not aluminum but rubber. As a result, cracking occurred with long-term use (6 months). This is presumed to be due to the fact that the surface of the rubber drum has been deteriorated by heat. Therefore, the material of the transport drum is presumed to be metal.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 20 ... conveyance unit, 25A ... upstream side roller, 25B ... downstream side roller, 26 ... conveyance drum, 30 ... head unit, 40 ... irradiation unit, 42a, 42b, 42c, 42d ... irradiation part for temporary hardening, 44: irradiation unit for main curing, 110: detector group, 120: controller, 121: interface, 122: CPU, 123, memory, 124: unit control circuit, 130: computer, K, C, M, Y: head, S: Recording medium.

Claims (11)

A monofunctional (meth) acrylate having a viscosity at 25 ° C. of 25 mPa · s or less and an average polymerizable unsaturated double bond equivalent of 100 to 150 and an aromatic ring skeleton is used as the total mass of the ink Bis containing 20 to 40% by mass and containing 20 to 48% by mass of a bifunctional or higher functional (meth) acrylate based on the total mass of the ink, which is an acyl phosphine oxide compound as a photopolymerization initiator Discharging the ultraviolet curable ink containing (2,4,6-trimethylbenzoyl) -phenylphosphine oxide from the head toward the recording medium at a discharge temperature of 30 to 40 ° C .;
Curing the UV curable ink attached to the recording medium by irradiating the UV from a light source and curing the UV curable ink;
The curing step includes a step of irradiating ultraviolet rays from the irradiation portion for temporary curing, and a step of irradiating ultraviolet rays from the irradiation portion for main curing,
Ink jet recording method.   The ultraviolet curable ink is discharged from the line head having a length equal to or greater than the width of the recording medium as the head toward the recording medium scanned relative to the line head. The inkjet recording method according to claim 1, wherein the recording is performed using a line type inkjet recording apparatus.   It takes 5 seconds for the support which has a surface on which the recording medium is transported, supports the recording medium, and moves relative to the head, to return to the same position by the movement. The ink jet recording method according to claim 1 or 2, which is the above.   The ink jet recording method according to claim 3, wherein a material of the support of the recording medium is metal.   The ink jet recording method according to any one of claims 1 to 4, wherein the viscosity of the ultraviolet curable ink at 20 ° C is 15 to 25 mPa · s.   The ink jet recording method according to any one of claims 1 to 5, wherein the light source is a light emitting diode.   The ink jet recording method according to any one of claims 1 to 6, wherein the ultraviolet curable ink contains 30 to 70% by mass of a monofunctional (meth) acrylate. The ultraviolet curable ink is a curable ink by irradiating the irradiation energy of 200 mJ / cm ² or less, the ink jet recording method according to any one of claims 1 to 7. The inkjet recording method according to any one of claims 1 to 8, wherein in the step of irradiating the ultraviolet light from the main curing irradiation portion, the peak intensity of the ultraviolet light irradiated is 500 mW / cm ² or more. The inkjet recording method according to any one of claims 1 to 9 , wherein the bifunctional or higher (meth) acrylate is dipropylene glycol di (meth) acrylate. An ink jet recording apparatus which performs recording by the ink jet recording method according to any one of claims 1 to 10 .

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