JP6341390B2 - UV curable ink, recording method, ink jet recording apparatus - Google Patents

Description

  The present invention relates to an ultraviolet curable ink. More specifically, the present invention relates to an ultraviolet curable ink that can provide a printed matter with high safety in skin sensitization and excellent solvent resistance and abrasion resistance. The present invention also relates to a recording method and an ink jet recording apparatus using the ultraviolet curable ink.

In recent years, as an image forming method, the process is simpler than other recording methods, and full colorization is easy, and there is an advantage that a high-resolution image can be obtained even with an apparatus having a simple configuration. Recording methods have become widespread.
As an ink used for the ink jet recording method, an ultraviolet curable ink jet ink using an ultraviolet curable resin together with an aqueous ink and a solvent ink has been studied.

Ink that can be ejected from an ink head as an ultraviolet curable inkjet ink is difficult to eject unless it has a low viscosity. For this reason, low-viscosity materials are often used as monomers.
What becomes a low-viscosity material is often a monofunctional monomer having a small molecular weight, and a polymer of the monofunctional monomer is chain-like, so that it is difficult to form a three-dimensional crosslinked structure. The difficulty in forming a three-dimensional crosslinked structure means that the strength of the coating film is weak and the solvent resistance is poor. The durability of the printed matter is important, and for use, it is preferable for the printed matter to have solvent resistance and abrasion resistance in printing on a non-permeable medium.

  Therefore, it is necessary to obtain a cured product having a highly crosslinked structure by blending a certain amount of a bifunctional or higher polyfunctional monomer. In addition, it is difficult for the monomer component to be completely polymerized in the cured coating film, and usually, very little unreacted monomer component remains. For this reason, the monomer used must be highly safe in terms of skin sensitization so that the residual monomer does not cause skin sensitization when touching the printed matter. It has been difficult to obtain a suitable low-viscosity ink composition and a hard cured product.

  As the ultraviolet curable ink-jet ink, for example, Patent Document 1 discloses a solventless ultraviolet curable marking ink. The UV curable marking ink is a mark that can be easily wiped away with a solvent to remove the mark after use as a mark for lot management or product type classification as an intermediate product at the time of shipment. The ink is intended to be used for marking, can be marked, and can be removed by wiping with a solvent, and the ink coating film strength is not sufficient. There is no description of skin sensitization.

  An object of the present invention is to provide an ultraviolet curable ink that is highly safe in skin sensitization, has little elution of an ink cured product into a solvent, and can produce a hard coating film.

As a result of intensive studies, the inventors of the present invention are ultraviolet curable ink having an SI value lower than 3, and the weight change between the weight of the cured ink after ultraviolet curing and the weight after the ink cured product is immersed in acetone. The above-mentioned problem is solved by the ultraviolet curable ink in which the remaining amount of the cured product is 80% by weight or more and the ink cured product after the ultraviolet curing is F or more in the pencil scratch test in JIS K5600-5-4. As a result, the present invention was reached.
That is, the present invention is as follows.

(1) An ultraviolet curable ink having an SI value lower than 3,
Comprising γ-butyrolactone methacrylate and trimethylolpropane trimethacrylate as monomers,
Containing 30% by mass to 50% by mass of the γ-butyrolactone methacrylate ,
The mass ratio of the γ-butyrolactone methacrylate and the trimethylolpropane trimethacrylate is 40:60 to 50:50,
An ultraviolet curable ink, wherein the mass ratio of the polymerization initiator and γ-butyrolactone methacrylate is 5:50 to 35:50.
( 2 ) The ultraviolet curable ink according to (1) above, containing 30.8% to 45.5% by mass of γ-butyrolactone methacrylate .
( 3 ) The ultraviolet curable ink as described in (1) or (2) above, which can be cured with an integrated light quantity of 0.3 J / cm ² or less.
( 4 ) In the state where the ultraviolet curable ink according to any one of (1) to ( 3 ) is used, the temperature of the ink head is adjusted to 60 ° C., and the ultraviolet curable ink is heated inside the ink head. A recording method, wherein a voltage of 16 volts is applied at a frequency of 5 to 10 kHz with a pulse width of 4.5 microseconds to discharge the ultraviolet curable ink.
( 5 ) A recording method, wherein the ultraviolet curable ink according to any one of (1) to ( 3 ) is used and cured at an integrated light amount of 0.3 J / cm ² or less.
( 6 ) An ink jet recording apparatus comprising at least an ink head for ejecting ink and ultraviolet irradiation means for irradiating the ejected ink with ultraviolet rays, wherein the ink is any one of (1) to ( 3 ). An ink jet recording apparatus, which is an ultraviolet curable ink .

The present invention is an ultraviolet curable ink having an SI value of less than 3, and the remaining amount of the cured product in the weight change between the weight of the ink cured product after ultraviolet curing and the weight of the ink cured product immersed in acetone is 80. By using an ultraviolet curable ink that is not less than wt% and the cured ink after ultraviolet curing is F or more in a pencil scratch test in JIS K5600-5-4, the hardness of the coating film becomes good, There is little elution into the solvent, and a printed matter excellent in solvent resistance can be obtained, and a printed matter excellent in abrasion resistance can be obtained.
The ultraviolet curable ink-jet ink has a viscosity of 15 mPa · s or less at 60 ° C., so that the ink can be ejected from a commercially available ink head. It is possible to obtain an ink jet ink that is good and has a relatively low viscosity.
Furthermore, the ultraviolet curable inkjet ink of the present invention can be cured with an integrated light amount of 0.3 J / cm ² or less, and an ultraviolet curable inkjet ink that can be cured with low energy can be obtained.

It is an example of the schematic block diagram of the inkjet recording device which concerns on embodiment of this invention.

  In the case of inkjet ink, the ink viscosity must be low in order to eject the ink. One effective method is to use a monofunctional monomer as a material that can lower the ink viscosity and has good curability. However, the bond of the cured product in the monofunctional monomer is chain-like, weak compared to the polyfunctional monomer that forms a three-dimensional cross-linked structure, easy to elute into the solvent, and strong mechanical properties as a cured product I can't get it. However, even if it is a monofunctional monomer, relatively strong mechanical properties can be obtained if the polymerization reactivity is good and the molecular weight is increased by photopolymerization. Examples of such monomers that are relatively frequently used in ink jet applications include isobornyl acrylate and formalized trimethylolpropane monoacrylate. The former has a high SI value of 8.3 and the latter 3.6. Therefore, it is not preferable to use it because it is highly toxic from the viewpoint of skin sensitization. 100% complete progression of the photocuring reaction is usually unlikely and slightly unreacted monomer usually remains, so touching the print causes slightly unreacted monomer to cause skin sensitization. This is because there is a possibility.

  In the present invention, a monofunctional (meth) acrylic acid ester having an SI value lower than 3 and a bifunctional or higher (meth) acrylic acid ester having an SI value lower than 3 are simultaneously contained to obtain a cured product. A cross-linked structure is formed in the ink, and the strength of the ink coating film can be improved. In addition, since a compound having an SI value lower than 3 is used, it is safe in skin sensitization, and further, by containing a monofunctional (meth) acrylic acid ester, it has a low viscosity that can be ejected as an inkjet ink. be able to.

  The SI value (Stimulation Index) is an index indicating the degree of skin sensitization, and is obtained by the LLNA method defined by the OECD test guideline 429 and the like. When the SI value is less than 3, it is determined that there is no sensitization, and this is shown, for example, in the following document (Reference: “Functional Materials”, September 2005, Vol. 25, No. .9, P55). The smaller the SI value is, the lower the degree of skin sensitization is. More preferably, it is less toxic if it is less than 2, more preferably less than 1.6.

A specific method for measuring the SI value in the present embodiment will be described in detail below.
(SI value measurement method)
[Test material]
《Positive control substance》
Α-hexylcinnamaldehyde (HCA; manufactured by Wako Pure Chemical Industries, Ltd.) was used as a positive control substance.
《Medium》
As the medium, a mixed liquid in which acetone and olive oil described below were mixed at a volume ratio of 4: 1 was used.
Acetone (made by Wako Pure Chemical Industries),
Olive oil (product of Fujimi Pharmaceutical) was used.

《Animals used》
For each test substance, positive control and vehicle control, 4 female mice were acclimated for 8 days including 6 days of quarantine. During quarantine and habituation, no abnormalities were observed in all animals. Using the body weight measured 2 days before the start of sensitization, it was divided into 2 groups (4 animals / group) so that the body weight of individuals was within 20% of the total average body weight by the random extraction method according to body weight layer. The age of the animals at the start of sensitization was 8-9 weeks. Animals that were excluded by grouping were excluded from the study.
The animals used were identified by applying oil-based ink to the tail throughout the test period, and the cages were identified by labeling.

《Creation environment》
Animals are used throughout the entire breeding period including quarantine and acclimatization period, temperature 21 to 25 ° C., relative humidity 40 to 70%, ventilation rate 10 to 15 times / hour, light / dark cycle 12 hours sense (lights from 7 o'clock to 19 o'clock) Breeding in the breeding room of the barrier system set to “off”.
The cage made of polycarbonate was used as the breeding cage. The animals used were kept at 4 / cage.
The feed used was a solid feed MF for experimental animals (manufactured by Oriental Yeast Co., Ltd.), and was used freely by the animals used. The drinking water was allowed to be freely consumed by the animals using a water supply bottle with tap water added with sodium hypochlorite (Purelux, Oyalax) so that the chlorine concentration was about 5 ppm. Sun flakes (fir, electric planer shavings, manufactured by Charles River Japan) were used for the flooring. The feed and breeding equipment were each autoclaved (121 ° C., 30 minutes).
Cages and bedding were exchanged at the time of grouping and the auricular lymph node intake day (at the time of removal from the breeding room), and the water bottles and racks were exchanged at the time of grouping.

[Test method]
<< Group composition >>
Table 1 shows the group structure used in the SI value measurement test of the present invention.

[Preparation]
<Test substance>
Table 2 shows the weighing conditions of the test substance. The test substance was weighed into a volumetric flask, and the volume was adjusted to 1 mL while adding the medium. The preparation liquid was put in a light-tight airtight container (made of glass).

《Positive control substance》
Approximately 0.25 g of HCA was accurately weighed, and a 25.0 w / v% solution was prepared as 1 mL while adding the medium. The preparation was placed in a light-tight airtight container (made of glass).
<< BrdU >>
200 mg of 5-Bromo-2′-deoxyuridine (BrdU, manufactured by Nacalai Tesque) was accurately weighed into a volumetric flask, physiological saline (manufactured by Otsuka Pharmaceutical Co., Ltd.) was added, and ultrasonic irradiation was performed for dissolution. Thereafter, the volume was adjusted to 20 mL to prepare a 10 mg / mL solution (BrdU preparation solution). The preparation solution was sterilized by filtration using a sterilized filtration filter and placed in a sterilized container.

《Preparation time and storage period》
The positive control substance preparation solution was prepared the day before the start of sensitization and stored in a cold place except when it was used. Media and test substance preparations were prepared on each sensitization day. BrdU solution was prepared 2 days before administration and stored in a cold place until the day of administration.

[Sensitization and BrdU administration]
《Sensitization》
25 μL of each test substance and positive control substance preparation and medium were applied to both ears of the animal. A micro pipettor was used for coating. This operation was performed once a day for 3 consecutive days.
Administration of BrdU
About 48 hours after the final sensitization, the BrdU preparation solution was intraperitoneally administered 0.5 mL per animal.

[Observation and inspection]
《General condition》
All animals used in the test were observed at least once a day from the date of sensitization to the date of collecting auricular lymph nodes (the date of removal from the breeding room). In addition, in the calculation method of the observation date, the sensitization start date was set to Day1.
<< Weighing >>
Body weights were measured on the date of sensitization and the date of collection of auricular lymph nodes (the date of removal from the breeding room). Moreover, the average value and standard error of the body weight for every group were calculated.
《Auricular lymph node collection and weight measurement》
Approximately 24 hours after BrdU administration, the animals were euthanized and auricular lymph nodes were collected. The surrounding tissues were removed and the bilateral auricular lymph nodes were weighed together. Moreover, the average value and standard error of the auricular lymph node weight for each group were calculated. After weighing, each individual was stored frozen in a biomedical freezer set at -20 ° C.

<Measurement of BrdU incorporation>
After returning the auricular lymph node to room temperature, it was ground and suspended while adding physiological saline. After filtering this suspension, 3 wells of each individual were dispensed into 96-well microplates, and the BrdU incorporation was measured by ELISA. Each reagent was obtained from a multi-plate reader (FLUOstar OPTIMA, BMG LABTECH) using a commercially available kit (Cell Proliferation ELISA, BrdU colorimetric, Cat. No. 1647229, manufactured by Roche Diagnostics). For the individual absorbance (OD370nm-OD492nm, BrdU incorporation amount), the average value of 3 wells was taken as the BrdU measurement value of each individual.

[Evaluation of results]
<< Calculation of Stimulation Index (SI) >>
As shown in the following formula 1, the BrdU measurement value of each individual was gradually decreased by the average value of the BrdU measurement values of the vehicle control group, and the SI value of each individual was calculated. The SI value of each test group was the average value of SI of each individual. The standard error of SI for each test group was also calculated. The SI value was rounded off to the first decimal place by rounding off the second decimal place.

Examples of working conditions and usable materials are shown below. However, it is not limited to these.
As monofunctional (meth) acrylic acid ester having an SI value lower than 3, γ-butyrolactone methacrylate (2.1), and as bifunctional or higher (meth) acrylic acid ester, tricyclodecane dimethanol dimethacrylate (1. 3) Polyethylene glycol (400) dimethacrylate [(1.3) This is a methacrylate compound represented by the following general formula (I), and n≈9. ],

Polyethylene glycol (600) dimethacrylate [(1.6) This is a compound represented by the above formula (I), where n≈14], and trimethylolpropane trimethacrylate (1.9) can be used. The numerical values shown in parentheses are SI values.
In the inkjet ink, monofunctional (meth) acrylic acid ester having an SI value lower than 3 is contained in 30 to 50% by weight, and bifunctional or higher functional (meth) acrylic acid ester having an SI value lower than 3 is contained in 25 to 60% by weight. It is desirable to do. Further, the weight ratio of the monofunctional (meth) acrylic acid ester having an SI value lower than 3 and the bifunctional or higher functional (meth) acrylic acid ester having an SI value lower than 3 is 40:60 to 50:50. It is preferable to use it. By setting it as such a composition, it is possible to make the residual amount of the cured product 80 weight% or more in a weight change between the weight of the cured ink after ultraviolet curing and the weight after the ink cured product is immersed in acetone. Become.

  Among radical polymerizable monomers, methacrylic acid ester compounds are useful materials because they have high safety such as low skin irritation coefficient (PI). In addition, regardless of whether it is a methacrylic acid ester compound or an acrylic acid ester compound, the ink cured product weight after UV curing and the ink cured product were immersed in acetone without impairing that the SI value of the ink is lower than 3. The following can also be included as long as the remaining amount of the cured product in a weight change with respect to the subsequent weight can be 80% by weight or more.

(Monofunctional (meth) acrylate)
Phenoxydiethylene glycol (meth) acrylate, isobornyl methacrylate, ethylene oxide modified phenol (meth) acrylate, 2,2,2-trifluoroethyl meta (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate One or two or more of ethylene oxide-modified nonylphenol (meth) acrylate and the like can be used.

(Bifunctional or higher (meth) acrylate)
Ethylene glycol di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, trimethylolpropane (meth) acrylic acid benzoate, diethylene glycol di (meth) acrylate, tri Ethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol polyethylene glycol diacrylate represented by the following chemical formulas (1) to (4),
_{(1) CH 2 = CH-} CO- (OC 2 H 4) n-OCOCH = CH 2 n ≒ 4
_{(2) CH 2 = CH-} CO- (OC 2 H 4) n-OCOCH = CH 2 n ≒ 9
_{(3) CH 2 = CH-} CO- (OC 2 H 4) n-OCOCH = CH 2 n ≒ 14
_{(4) CH 2 = CH-} CO- (OC 2 H 4) n-OCOCH = CH 2 n ≒ 23
Dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol diacrylate represented by the following chemical formulas (5) to (8),
_{(5) CH 2 = CH-} CO- (OC 3 H 6) n-OCOCH = CH 2 n ≒ 12
_{(6) CH 2 = C (} CH 3) -CO- (OC 3 H 6) n-OCOC (CH 3) = CH 2
n ≒ 7
_{(7) CH 2 = CH-} CO- (OC 3 H 6) n-OCOCH = CH 2 n ≒ 12
_{(8) CH 2 = C (} CH 3) -CO- (OC 3 H 6) n-OCOC (CH3) = CH 2
n ≒ 12
Neopentyl glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonane Diol di (meth) acrylate, dimethylol-tricyclodecane dimethacrylate, ethylene oxide modified bisphenol A di (meth) acrylate, propylene oxide modified bisphenol A di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, Ethylene oxide modified 1,6-hexanediol diacrylate, dipentaerythritol hexa (meth) acrylate, (meth) acryloylmorpholine, 2-hydroxyethyl (meth) acrylamide, ethylene oxide modified Tramethylol methane tetramethacrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, dipentaerythritol hydroxypenta (meth) acrylate, caprolactone-modified dipentaerythritol hydroxypenta (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, penta Erythritol tetra (meth) acrylate, trimethylolpropane triacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, caprolactone modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris (2-hydroxyethyl) ) Isocyanurate tri (meth) acrylate, ethylene oxide modification Neopentyl glycol di (meth) acrylate, propylene oxide modified neopentyl glycol di (meth) acrylate, propylene oxide modified glyceryl tri (meth) acrylate, polyester di (meth) acrylate, polyester tri (meth) acrylate, polyester tetra (meth) Acrylate, polyester penta (meth) acrylate, polyester hexa (meth) acrylate, polyurethane di (meth) acrylate, polyurethane tri (meth) acrylate, polyurethane tetra (meth) acrylate, polyurethane penta (meth) acrylate, polyurethane hexa (meth) acrylate One type or two or more types can be used.

  Polymerization initiators for photocuring include benzophenone, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-methyl-1 [4- (methylthio) Phenyl] -2-morpholinopropan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)- Butanone-1,2,2-dimethoxy-1,2-diphenylethane-1-one, 1,2-octanedione- [4- (phenylthio) -2- (o-benzoyloxime)], bis (2,6 -Dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoyl-phos In'okisaido, 2,4-diethyl thioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, can be used in combination one kind or two or more kinds of such [4- (methyl) phenyl] phenyl methanone.

  The photopolymerization initiator is preferably contained in an amount of 5 to 35 parts by weight, more preferably 5 to 25 parts by weight, and still more preferably 10 to 25 parts by weight with respect to 100 parts by weight of the monomer. By containing in these compounding ratios, it is possible to obtain an inkjet ink having good curability and relatively low viscosity. Of course, when a very high energy light source such as electron beam, α, β, γ ray, X-ray is used, the polymerization reaction can proceed without using a polymerization initiator. This is well-known and will not be described in detail in the present invention.

The inkjet ink of the present invention can contain a pigment.
As the black pigment, carbon black produced by the furnace method or the channel method can be used.

  Examples of yellow pigments include Pig. Yellow pigments such as Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 114, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 129, Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 154, Pigment Yellow 155, Pigment Yellow 180, etc. It can be used.

As magenta pigments, Pig. Red pigments such as Pigment Red 5, Pigment Red 7, Pigment Red 12, Pigment Red 48 (Ca), Pigment Red 48 (Mn), Pigment Red 57 (Ca), Pigment Red 57: 1, Pigment Red 112, Pigment Red 122, Pigment Red 123, Pigment Red 168, Pigment Red 184, Pigment Red 202, Pigment Violet 1
9 etc. can be used.

  Examples of cyan pigments include Pig. Blue pigments such as Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 15, Pigment Blue 15: 3, Pigment Blue 15: 4, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Bat Blue 4, Bat Blue 60 or the like can be used.

  White pigments include alkaline earth metal sulfates such as barium sulfate, alkaline earth metal carbonates such as calcium carbonate, silicas such as finely divided silicic acid and synthetic silicates, calcium silicate, alumina, alumina water Japanese, titanium oxide, zinc oxide, talc, clay and the like can be used.

In addition, various inorganic pigments and organic pigments can be used in consideration of physical characteristics as required.
The addition amount of the pigment is preferably 1 to 20% by weight in the inkjet ink. If it is less than 1% by weight, the image quality is deteriorated, and if it is more than 20 parts by weight, the ink viscosity characteristics are adversely affected.

  In addition, the ultraviolet curable inkjet ink of the present invention includes various conventionally known sensitizers, light stabilizers, surface treatment agents, surfactants, viscosity reducing agents, antioxidants, and antioxidants used in inkjet inks. , Crosslinking accelerators, polymerization inhibitors, plasticizers, preservatives, pH adjusters, antifoaming agents, humectants, dispersants, dyes, and the like.

The ultraviolet curable inkjet ink of the present invention has a residual amount of cured product of 80% by weight or more due to a change in weight between the weight of the ink cured product after ultraviolet curing and the weight of the ink cured product after immersion in acetone. Excellent in properties.
The weight change was determined as follows.
1. The glass slide is heat-washed at 450 ° C. for 3 minutes and weighed.
A solid coating film is formed by ink-jet printing ink on the slide glass of 2.1, and photocured with an integrated light amount of 300 mJ / cm ² (a minimum light amount when a large amount of light is required for curing). The details of the ink jet printing conditions will be described later.
3. Measure the weight of the cured product.
{(Slide glass + ink coating film) Weight-Slide glass weight}
4). The entire slide glass coated with ink is immersed in acetone and left at 5 ° C. for 18 hours.
1. The slide glass coated with ink is taken out, washed with acetone, dried, and the weight of the remaining cured product is measured.
The ratio (% by weight) of the remaining amount of the cured product was obtained by the following formula.
(Weight of remaining cured product after immersion in acetone / weight of cured product before immersion in acetone) × 100

  Moreover, the ultraviolet curable inkjet ink of this invention can make the hardness of the hardened | cured ink after hardening into F or more by the pencil scratch test in JISK5600-5-4. By being F or more, the hardness of the coating film becomes good, and a printed matter having excellent printing durability can be obtained.

The ultraviolet curable inkjet ink preferably has a viscosity at 60 ° C. of 15 mPa · s or less. When the viscosity is 15 mPa · s or less at 60 ° C., it becomes possible to discharge ink better than an ink head equipped with a heating device such as a commercially available heater.
The viscosity was measured using a viscometer Toki Sangyo TV-22L rotor 1 ° 34 × R24.

Furthermore, the ultraviolet curable inkjet ink of the present invention can be cured with an integrated light amount of 0.3 J / cm ² or less, and can be obtained with a low energy curable ultraviolet curable inkjet ink. The remaining amount can be 80% by weight or more.
It is also effective to match the absorption wavelength of the polymerization initiator with the wavelength of the UV light used for curing. The integrated light amount is an integrated light amount in a wavelength range effective for curing.

The ink cartridge of the present invention contains the ultraviolet curable ink-jet ink of the present invention in a container, and further includes other members appropriately selected as necessary.
The ink cartridge of the present invention can be used by being detachably mounted on various ink jet recording apparatuses, and is particularly preferably used by being detachably mounted on the ink jet recording apparatus of the present invention described later.

  The ink jet recording apparatus of the present invention preferably includes at least an ink head that ejects ink, and an ultraviolet irradiation unit that irradiates the discharged ink with ultraviolet rays, and the ink head has a heating unit. The ink used is the ultraviolet curable inkjet ink of the present invention.

The ink jet recording apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is an example of a schematic configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. In the ink jet recording apparatus 1 of the present embodiment, the recording medium 5 is transported from the recording medium supply unit 2 to the recording medium stacker unit 4 via the recording medium transport unit 3 and is ejected by the ink head 6. The curable inkjet ink lands on the recording medium 5. Note that the operation of the entire recording apparatus, such as transport for the recording medium and driving for ejecting ink from the ink head, and data processing therefor are controlled by a control circuit (not shown). The ultraviolet curable ink jet ink discharged from the ink head 6 is printed on the recording medium 5.
The recording medium 5 on which the ultraviolet curable inkjet ink has landed is conveyed by the recording medium conveying unit 3 and cured by ultraviolet rays in the irradiation unit 8 of the ultraviolet irradiation device.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Examples 1-4, Comparative Examples 1-6)
As shown in Table 3, inks having different blending ratios (weight ratios) were prepared, and viscosity measurement, evaluation of the remaining ratio in the solvent (solvent elution test), and scratch test were performed.

○ Viscosity measurement Viscometer Toki Sangyo TV-22L Using a rotor 1 ° 34 × R24, the viscosity at 60 ° C was measured.

○ Solvent dissolution test ~ Confirmation procedure ~
1. A glass slide (26 × 76 mm, thickness 0.9 to 1.2 mm) is heat-washed at 450 ° C./3 minutes and weighed.
Create a solid coating by ink-jet printing the ink on the slide glass of 2.1, and photocure it with an integrated light quantity of 0.3 J / cm ² (the minimum light quantity if more light is needed for curing) .
3. Measure the weight of the cured product. {(Slide glass + ink coating film) Weight-Slide glass weight}
4). The entire slide glass coated with ink is immersed in about 200 mL of acetone and left at 5 ° C. for 18 hours.
5. The slide glass coated with ink is taken out, thoroughly washed with acetone, dried and weighed.

~conditions~
Printing: The ink is heated to 60 ° C. by an inkjet discharge head GEN4 manufactured by Ricoh Printing Systems, Inc., which is a commercially available inkjet printing head with a heating function, and 15 pL of ink droplets are ejected by inkjet at 300 × 300 dpi. Solid print.
UV light irradiation device: Fusion UV LH6 D bulb 1 light Use Peak illuminance (Measured with UV illuminance meter EIT UV Power Pack)
^{UVA: 3.6W / cm 2, UVB} : 0.98W / cm 2,
UVC: 0.1 W / cm ² , UVV: 2.5 W / cm ²
Thermal cleaning: Electric furnace 450 ° C./3 minutes Drying: 50 ° C./60 minutes Whether or not it was sufficiently cured was confirmed by touching the coating after irradiation with UV light.
Moreover, the integrated light quantity when fully cured was determined using a UV illuminance meter (UV Power Pack manufactured by EIT). Since UVA is an effective wavelength for 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one used as a polymerization initiator, the value of the integrated light quantity in UVA was determined. The results are shown in Table 3.

○ Pencil scratch test As shown in Table 3, a pencil scratch test was performed on a cured product obtained by applying an ink having a changed blending ratio (weight ratio) to paper and curing it with the integrated light amount shown in Table 3. JIS K5600- Followed 5-4.
Tester: Co-Tech Co., Ltd.
Pencil: Mitsubishi Uni (6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H)
Test procedure:
Push the device at a speed of 0.5-1 mm / s and a distance of at least 7 mm. The surface was inspected with the naked eye and the type of trace was examined.
There are two types of traces:
(1) Plastic deformation; a dent that does not return to its original shape is produced, but there is no breakage.
(2) Cohesive failure; scratches with film material removed.
The test was repeated with the hardness scale raised until the test site produced a scar of at least 3 mm or more.
Evaluation method: The hardness of the hardest pencil that did not cause the scar of (2) above is defined as the pencil hardness.

○ Discharge test A discharge test was performed using an inkjet discharge head GEN4 manufactured by Ricoh Printing Systems, which is a commercially available inkjet printing head having a heating function.
In a state where the temperature of the head was adjusted to 60 ° C. and the ink inside was heated, a voltage of 16 volts was applied at a frequency of 5 to 10 kHz with a pulse width of 4.5 microseconds, and the ink ejection state was observed. .
The evaluation criteria were as follows.
<Evaluation criteria>
○: Stable ejection is possible. There are no white spots, streaks, or jet disturbance in the solid part.
×: Discharge difficult

Since the inks of Comparative Examples 2 and 3 had high viscosity and it was difficult to eject the ink from the ink head, a solid print coating film was prepared by hand coating with a wire bar, and the pencil hardness of the cured coating film And acetone insoluble residue were evaluated.
As can be seen from Examples 1 and 2 and Comparative Examples 1, 2, 3, 4 and 5, when the monofunctional monomer is too much, the viscosity of the printed coating film is weak and the solvent resistance is insufficient, although the viscosity is low. On the other hand, when there are too many polyfunctional monomers more than bifunctional, it will become high viscosity and it will become impossible to perform inkjet printing. However, by optimizing these blending ratios, it is possible to obtain ink jetting properties and excellent hardness of the cured coating film with pencil hardness of F or more. This is an effect obtained by forming a crosslinked structure in which the monomer forming the cured coating film is highly grown by the polymerization reaction until the acetone-insoluble residue reaches 80% or more.
As can be seen from the comparison between Comparative Example 6 and Examples 1, 3, and 4, the coating ratio of the polymerization initiator is optimized to maintain a strong coating strength having ink jetting properties and pencil hardness of F or higher. However, it is possible to control curability and viscosity. However, in Example 4, there was no problem in the heated state at 60 ° C, but precipitation of the initiator component was observed at room temperature (25 ° C). Therefore, since it is necessary to keep the entire ink supply path in a heated state, it is not preferable from the viewpoint of solubility to further increase the amount of the polymerization initiator.
Moreover, when the same evaluation test was performed also about the ink which satisfy | fills the structural requirements of this invention other than the ink used as an Example, the evaluation result similar to an Example was obtained.

DESCRIPTION OF SYMBOLS 1 Recording device 2 Recording medium supply part 3 Recording medium conveyance part 4 Recording medium stacker part 5 Recording medium 6 Ink head part 8 Ultraviolet irradiation means

JP 2002-20671 A

Claims (6)

A UV curable ink having an SI value lower than 3,
Comprising γ-butyrolactone methacrylate and trimethylolpropane trimethacrylate as monomers,
Containing 30% by mass to 50% by mass of the γ-butyrolactone methacrylate ,
The mass ratio of the γ-butyrolactone methacrylate and the trimethylolpropane trimethacrylate is 40:60 to 50:50,
An ultraviolet curable ink, wherein the mass ratio of the polymerization initiator and γ-butyrolactone methacrylate is 5:50 to 35:50. The ultraviolet curable ink according to claim 1, comprising 30.8% by mass to 45.5% by mass of γ-butyrolactone methacrylate . UV-curable ink according to claim 1 or 2, characterized in that at 0.3 J / cm ² or less of accumulated light amount is curable. Using the UV-curable ink according to any one of claims 1 to 3 and the ink head was controlled at 60 ° C., the ultraviolet curable ink inside the ink head in the heated state, pulse width 4.5 A recording method, wherein a voltage of 16 volts is applied at a frequency of 5 to 10 kHz in microseconds to discharge the ultraviolet curable ink. A recording method comprising using the ultraviolet curable ink according to any one of claims 1 to 3 and curing at an integrated light amount of 0.3 J / cm ² or less. 4. An ink jet recording apparatus comprising at least an ink head for ejecting ink and ultraviolet irradiation means for irradiating the ejected ink with ultraviolet light, wherein the ink is the ultraviolet curable ink according to any one of claims 1 to 3. An ink jet recording apparatus.

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