JP2007326907A - Uv-curing type ink for stencil printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a UV-curing type ink for stencil printing having a high yield value without spoiling viscosity stability to temperature change and separation stability in a long term preservation. <P>SOLUTION: The UV-curing type ink for stencil printing contains hydrophilic silica. A type of the ink containing additional hydrophobic silica and a type of the ink containing at least one of a monomer or an oligomer having 0.02-1.5 Pa s viscosity at 25°C, more preferably 0.02-0.3 Pa s, in addition to the hydrophobic silica are preferable. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultraviolet curable ink for stencil printing that has a high yield value and can prevent ink dripping when left in a printing machine for a long time.

Conventionally, emulsion ink has been used as ink for stencil printing. However, when the emulsion ink is slow to dry and there are many solid parts on the printed matter, it is set off, that is, the printed matter that has just been printed is overlaid. There was a problem that the ink of the adjacent printed matter sometimes adhered and soiled the printed matter.
Therefore, ultraviolet curable inks have been used instead of conventional emulsion inks. Since this ultraviolet curable ink is cured immediately upon irradiation with ultraviolet rays, when printing is performed using the ultraviolet curable ink, the ink is more than the commonly used W / O (water-in-oil) emulsion ink. It has the advantages of good dryness and no set-off.

Conventionally, various proposals have been made as technologies relating to the ultraviolet curable ink for stencil printing. For example, an ultraviolet curable ink using an ultraviolet curable resin as a main component and using organic bentonite as an extender has been proposed (see Patent Document 1). However, an ink using an ultraviolet curable resin, such as the proposed ink, has a large temperature dependence of the resin, so that the viscosity change with respect to the temperature of the ink is large, and image fading at a low temperature becomes a problem. Further, an ink using organic bentonite as an extender pigment like this proposed ink has a problem in that each component is separated when stored for a long period of time.
For the viscosity change with respect to the temperature, an emulsion-type ultraviolet curable ink has been proposed (see Patent Document 2). However, in this proposal, by emulsifying the ink, the change in viscosity with respect to temperature can be made comparable to that of conventional emulsion inks for stencil printing. However, when stored for a long period of time, the water content of the ink evaporates on the printing press. As a result, the ink was separated as a result of the change in viscosity.
Further, when the ultraviolet curable ink is left in a printing machine for a long time, there is a problem in that ink dripping occurs on the printing machine and a good printed matter cannot be obtained when it is used again.

  Therefore, the development of UV curable ink for stencil printing that can prevent ink dripping when left in a printing machine for a long time without impairing stability against temperature change and stability during long-term storage is desired. The current situation is rare.

Japanese Patent No. 2660000 JP-A-9-20876

This invention is made | formed in view of this present condition, and makes it a subject to solve the said problem in the past and to achieve the following objectives. That is, an object of the present invention is to provide an ultraviolet curable ink for stencil printing having a high yield value without impairing viscosity stability against temperature changes and separation stability during long-term storage.
The “yield value” here means “the value of the minimum shearing force necessary to cause flow”. If the yield value of the ink is high, the shape becomes stable when the ink is left in a state where no external force is applied, and ink dripping can be prevented.

Means for solving the problems are as follows. That is,
<1> An ultraviolet curable ink for stencil printing, comprising hydrophilic silica.
The ultraviolet curable ink for stencil printing according to <1> can increase the yield value by containing the hydrophilic silica. Accordingly, it is possible to prevent the ink from dripping when left in the printing machine for a long time.
<2> The ultraviolet curable ink for stencil printing according to <1>, which contains hydrophobic silica.
The curable ink for stencil printing according to <2> further comprises the hydrophobic silica in addition to the hydrophilic silica, thereby giving the ink a plastic viscosity without impairing the viscosity stability against temperature change. The separation stability can be improved.
<3> Containing at least one of a monomer and an oligomer, wherein the viscosity of the monomer and the oligomer is 0.02 to 1.5 Pa · s at 25 ° C. It is the ultraviolet curable ink for stencil printing described.
<4> The ultraviolet curable ink for stencil printing according to <3>, wherein the viscosity of the monomer and the oligomer is 0.02 to 0.3 Pa · s at 25 ° C.
The curable ink for stencil printing according to <3> and <4> comprises at least one of the monomer and the oligomer as a polymerization component, and the viscosity of the monomer and the oligomer is 0 at 25 ° C. By changing the pressure to 0.02 to 1.5 Pa · s, preferably 0.02 to 0.3 Pa · s, the change in viscosity with respect to temperature can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the conventional problem can be solved, and the ultraviolet curable ink for stencil printing with a high yield value can be provided, without impairing the viscosity stability with respect to a temperature change, and the separation stability at the time of long-term storage. .

The ultraviolet curable ink for stencil printing of the present invention (hereinafter sometimes simply referred to as “ink”) contains hydrophilic silica, preferably contains hydrophobic silica, more preferably a polymerization component. It contains at least one of a monomer and an oligomer, and further contains other components as necessary.
The ink of the present invention may be composed of a material that is solidified by radical polymerization, or may be composed of a material that is solidified by cationic polymerization.

<Hydrophilic silica>
The hydrophilic silica is silica having an OH group on the surface of the molecule.
The hydrophilic silica is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, and Aerosil 380 (all manufactured by Nippon Aerosil Co., Ltd.). It is done.
As the specific surface area of the hydrophilic silica is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably ^{250~400m 2 / g, 350~400m 2 /} g is more preferable.

The said hydrophilic silica may be used individually by 1 type, and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said hydrophilic silica, Although it can select suitably according to the objective, 0.5-20 mass% is preferable with respect to the total mass of ink, and 1-10 mass%. Is more preferable. If the content is less than 0.5% by mass, the content of extender pigment decreases, so the yield value of the ink cannot be increased, and ink dripping may not be prevented. If it exceeds%, the yield value is too high, and the fluidity of the ink may be impaired.

<Hydrophobic silica>
The hydrophobic silica is silica obtained by replacing (hydrophobizing) about 80% of OH groups on the surface of the hydrophilic silica with a hydrophobic group such as a methyl group.
There is no restriction | limiting in particular as said hydrophobic silica, According to the objective, it can select suitably, For example, Aerosil R972, R974, R202, R805, R812, R812S, RX200, RY200 (Nippon Aerosil) etc. are mentioned. .
There is no restriction | limiting in particular as a specific surface area of the said hydrophobic silica, Although it can select suitably according to the objective, 70-300 m < ² > / g is preferable, 70-200 m < ² > / g is more preferable, 70-150 m < ² >. / G is particularly preferred.

The said hydrophobic silica may be used individually by 1 type, and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said hydrophobic silica, Although it can select suitably according to the objective, 0.5-20 mass% is preferable with respect to the total mass of ink, and 1-10 mass% Is more preferable. If the content is less than 0.5% by mass, the plastic viscosity may be too low, and if it exceeds 20% by mass, the plastic viscosity may be too high and the fluidity of the ink may be impaired.

  The change in the viscosity of the ink due to the change in the content of the hydrophilic silica and the hydrophobic silica can be adjusted to some extent by the viscosity of the monomers and oligomers described below, but the silica content is too high. If it is too small, the film strength and temperature characteristics of the ink may be impaired.

<Monomer and oligomer>
The monomer or oligomer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include urethane-based, epoxy-based, polyester-based, and polyol-based (meth) acrylic acid-modified monomers or oligomers. Can be mentioned.
In addition, the said oligomer in this specification is a low polymer whose degree of polymerization is about 2-20 among the polymers formed by polymerizing monomers, and has one or more acryloyl groups or methacryloyl groups. means.
Moreover, the said (meth) acrylic acid means the term which generically refers to acrylic acid, methacrylic acid, and mixtures thereof, and the same applies to other similar expressions.

  Specific examples of the monomer include monofunctional or polyfunctional (meth) acrylate monomers. More specifically, dicyclopenterethyl acrylate, isobornyl acrylate, phenol ethylene oxide modified acrylate, tripropylene glycol diacrylate, caprolactone modified hydroxypivalate ester neopentyl glycol, 1,6-hexanediol diacrylate, bisphenol A diacrylate Glycidyl ether diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, propylene oxide modified glycerol triacrylate, ethylene oxide (EO) modified trimethylolpropane triacrylate (EO: 1) -5), propylene oxide (PO) modified trimethylol Lopantriacrylate (PO: 1 or 2) (A315, A316), pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate (A331), pentaerythritol ethoxytetraacrylate (A336), dipentaerythritol hexaacrylate, 1,4-butanediol di Examples include methacrylate, hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, and the like.

  Specific examples of the oligomer include epoxy acrylate, epoxy oil acrylate, urethane acrylate, unsaturated polyester, polyester acrylate, vinyl acrylate, and the like.

  The viscosity of the monomer and oligomer is not particularly limited and may be appropriately selected according to the purpose. However, in order to reduce the change in viscosity with respect to temperature, 0.02 to 1.5 Pa · s at 25 ° C. Preferably, 0.02 to 0.3 Pa · s is more preferable. If the viscosity is less than 0.02 Pa · s, there may be a problem with image quality due to poor fluidity of the ink, and if it exceeds 1.5 Pa · s, the viscosity change with respect to temperature may increase. .

The said monomer and oligomer may be used individually by 1 type, and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said monomer and oligomer, Although it can select suitably according to the objective, 15-95 mass% is preferable with respect to the total mass of ink, and 50-80 mass% is more. preferable. When the content is less than 15% by mass, the cured film strength may be insufficient, and when it exceeds 95% by mass, a sufficient ink yield value may not be obtained.

<Other ingredients>
The other components in the ink of the present invention are not particularly limited and can be appropriately selected according to the purpose within a range not impairing the effects of the present invention. For example, the hydrophilic silica and the hydrophobic silica Other extender pigments, colorants, colorant dispersants, polymerization initiators, polymerization inhibitors, vegetable oils, and the like.

-Body pigments other than hydrophilic silica and hydrophobic silica-
The extender pigment other than the hydrophilic silica and the hydrophobic silica is not particularly limited and may be appropriately selected depending on the intended purpose. For example, organic bentonite, white clay, talc, clay, calcium carbonate, barium sulfate, titanium oxide Inorganic fine particles such as alumina white, diatomaceous earth, kaolin, mica, aluminum hydroxide; polyacrylate, polyurethane, polyester, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polysiloxane, phenol resin, epoxy Organic fine particles such as resins; or fine particles made of a copolymer thereof;

The extender pigments other than the hydrophilic silica and the hydrophobic silica may be used alone or in combination of two or more.
There is no restriction | limiting in particular as content of extender pigments other than the said hydrophilic silica and hydrophobic silica, Although it can select suitably according to the objective, 0.1-50 mass% with respect to the total mass of ink. Is preferable, 1-15 mass% is more preferable, and 2-5 mass% is especially preferable.

-Colorant-
There is no restriction | limiting in particular as said coloring agent, Insoluble coloring agents, such as a well-known pigment and disperse dye of various colors, can be used.
Specific examples of the colorant include carbon blacks such as acetylene black, channel black, and furnace black; metal powders such as aluminum powder and bronze powder; petals, yellow lead, ultramarine, chromium oxide, and titanium oxide. Inorganic pigments; azo pigments such as insoluble azo pigments, azo lake pigments, and condensed azo pigments; phthalocyanine pigments such as metal-free phthalocyanine pigments and copper phthalocyanine pigments; anthraquinone pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments Condensed polycyclic pigments such as dyes, dioxazine dyes, selenium dyes, perylene dyes, perinone dyes, thioindigo dyes, quinophthalone dyes, metal complexes; organic pigments such as lakes of acidic or basic dyes; Dyes, oil-soluble dyes such as anthraquinone dyes, fluorescent pigments, etc. It is below.

  As the fluorescent pigment, a so-called synthetic resin solid solution obtained by dissolving or dyeing a fluorescent dye that develops various hues after bulk polymerization of a synthetic resin or by pulverizing and refining the obtained colored bulk resin The type is preferable, and examples of the synthetic resin carrying a dye include melamine resin, urea resin, sulfonamide resin, alkyd resin, and polyvinyl chloride resin.

  Moreover, as said coloring agent, a commercial item can be used, for example, as a commercial item of the said carbon black, MA-100, MA-7, MA-70, MA-77, MA-11, # 40, # 44 (all manufactured by Mitsubishi Chemical Corporation), Raven 1100, Raven 1080, Raven 1255, Raven 760, Raven 410 (all manufactured by Colombian Carbon).

  The colorant is present in a dispersed state in the ink. The average particle size of the colorant dispersed in the ink is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.1 to 10 μm, and preferably 0.1 to 1.0 μm. More preferred. If the average particle size is less than 0.1 μm, the pigment may permeate the paper immediately after printing, and a desired effect on the image density may not be obtained. If it exceeds 10 μm, the ink stability is poor. Sometimes.

The said colorant may be used individually by 1 type, and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said coloring agent, Although it can select suitably according to the objective, Usually, 2-15 mass% is preferable with respect to the total mass of ink.

-Colorant dispersant-
The colorant dispersant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include sorbitan fatty acid esters such as sorbitan sesquiolate, polyglycerin fatty acid esters such as hexaglycerin polyricinoleate, polyoxyethylene, and the like. Nonionic surfactants such as glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylamine fatty acid amide; alkylamine polymer compound; aluminum chelate compound; styrene-anhydrous malee Acid copolymer polymer compound; Polycarboxylic acid ester type polymer compound; Aliphatic polyvalent carboxylic acid; Amine salt of polymer polyester; Ester type anionic surfactant; Long chain amino acid of high molecular weight polycarboxylic acid Salts: Long-chain polyaminoamides and polymeric acid polyester salts; Polyamide compounds; Phosphate ester surfactants; Alkyl sulfocarboxylates; Sulfonates; α-Olefin sulfonates; Dioctyl sulfosuccinates; An alkylolamine salt; a resin having an insoluble colorant-dispersing ability such as an alkyd resin;

  Moreover, a commercial item can be used as said coloring agent dispersing agent, for example, Solspers series (S3000, S5000, S9000, S13240, S13940, S16000, S17000, S20000, S24000, S26000, manufactured by Nippon Lubrizol Co., Ltd. S27000, S28000, S31845, S31850, S32000, S32550, S34750, S41090, S53095, etc.); Ajinomoto Fine Techno Co., Ltd. Plain Act AL-M, Ajisper series (PB711, PM821, PB821, PB811, PN411, PA111, etc.); Nikko Chemicals TMGS-15, TMGO-15, Decaglyn series (1-L, 1-M, 1-O, etc.), TL-10, TP-10, TO-10, TI 10, BL-21, BC-15TX, BC-23, BC-30TX, BC-40TX, BS-20, BO-10TX, TAMNS-10, TAMNS-15, TAMNO-5, TAMNO-15, TDMNS-8, OTP-100, OTP-75; etc. are mentioned.

The colorant dispersant may be used alone or in combination of two or more.
There is no restriction | limiting in particular as content of the said colorant dispersing agent, Although it can select suitably according to the objective, 40 mass% or less is preferable with respect to the total mass of a colorant, and 2-35 mass% is preferable. More preferred.

-Polymerization initiator-
The polymerization initiator is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include benzophenone, acetophenone, 4,4′-bisdiethylaminobenzophenone, benzoin, and benzoin ethyl ether.

  As the polymerization initiator, commercially available products can be used. For example, IRGACURE series (651, 184, 907, 369, 379), DAROCUR series (1173) manufactured by Ciba Specialty Chemicals; Nippon Kayaku Kayacure-DETX, Kayacure-ITX;

The said polymerization initiator may be used individually by 1 type according to a light source, and may use 2 or more types together. Moreover, you may use together aliphatic amines, such as n-butylamine, triethylamine, and p-dimethylamine ethyl benzoate, aromatic amines, etc. as a sensitizer.
There is no restriction | limiting in particular as content of the said polymerization initiator, Although it can select suitably according to the objective, 1-25 mass% is preferable with respect to the total mass of ink, and 1-10 mass% is more. preferable.

-Vegetable oil-
If necessary, the ink of the present invention may use vegetable oil as long as it does not impair the curing properties.
The vegetable oil is not particularly limited and may be appropriately selected depending on the intended purpose.For example, soybean oil, rapeseed oil, corn oil, sesame oil, tall oil, cottonseed oil, sunflower oil, safflower oil, walnut oil, Examples include poppy oil and linseed oil.
In addition, as the vegetable oil, esterified vegetable oil can also be used. Examples of the ester include methyl ester, butyl ester, isopropyl ester, and propyl ester.

The said vegetable oil may be used individually by 1 type, and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said vegetable oil, Although it can select suitably according to the objective, 5-70 mass% is preferable with respect to the total mass of ink, and 30-50 mass% is more preferable.

ただし、前記式において、τは、せん断応力を表す。τ_０は、降伏値を表す。Ｅｔａは、塑性粘度を表す。Ｄは、せん断速度を表す。 <Method for producing UV curable ink for stencil printing>
The method for producing the ultraviolet curable ink for stencil printing of the present invention is not particularly limited, and can be appropriately selected from known methods according to the purpose. For example, each component is mixed by a conventional method. It can manufacture by performing dispersion processing using dispersers, such as a three roll mill.
The viscosity of the ink for the stencil printing system can be adjusted by the stirring conditions, and is not particularly limited as long as it is suitable for the system, but the viscosity at a shear rate of 20 s ⁻¹ is 2 to 40 Pa · s. It is preferably 10 to 30 Pa · s. In addition, from the viewpoint of rolling up the paper after printing, the plastic viscosity of the ink approximated by the Casson approximation expressed by the following formula is preferably 2.0 Pa · s or less, and 1.0 Pa · s or less is preferable. More preferred.

In the above equation, τ represents shear stress. τ ₀ represents a yield value. Eta represents the plastic viscosity. D represents the shear rate.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Examples 1-7 and Comparative Examples 1-2)
-Preparation of UV curable ink for stencil printing-
In accordance with the formulation shown in Table 1, a colorant, a colorant dispersant, an extender pigment, a polymerization component and a polymerization initiator are mixed, and dispersion treatment is performed using a three-roll mill (manufactured by Inoue Seisakusho Co., Ltd.). UV curable inks for stencil printing of ~ 7 and Comparative Examples 1-2 were prepared.

＊１：表２に示す。
＊２：表３に示す。

* 1: Shown in Table 2.
* 2: Shown in Table 3.

[Evaluation]
Using the ultraviolet curable inks for stencil printing of Examples 1 to 7 and Comparative Examples 1 and 2, ink sag, separation stability, film strength, and temperature characteristics were evaluated according to the following contents. Each evaluation result is shown in Table 4.

ただし、前記式において、τは、せん断応力を表す。τ_０は、降伏値を表す。Ｅｔａは、塑性粘度を表す。Ｄは、せん断速度を表す。 <Evaluation of ink sag>
(1) Measurement of Yield Value Using the ultraviolet curable inks for stencil printing of Examples 1 to 7 and Comparative Examples 1 and 2, the yield value of each ink was determined as a stress rheometer (“CSR-10”; manufactured by Borin). It was measured by. Specifically, using a cone having a diameter of 2 cm and an angle of 2 degrees, a flow curve up to a stress of 12.5 Pa to 150 Pa is measured at a measurement temperature of 23 ° C., and according to Casson's approximate expression represented by the following formula: The Casson yield value was calculated.

In the above equation, τ represents shear stress. τ ₀ represents a yield value. Eta represents the plastic viscosity. D represents the shear rate.

(2) Evaluation of sagging property Based on the yield value calculated in the above (1), the sagging property of ink was evaluated based on the following two-stage evaluation criteria.
-Evaluation criteria-
○: Yield value is 60 Pa or more ×: Yield value is less than 60 Pa

<Evaluation of ink separation stability>
Using the ultraviolet curable inks for stencil printing of Examples 1 to 7 and Comparative Examples 1 and 2, each ink was put in a glass bottle and allowed to stand at 50 ° C. for 3 months. It observed visually and evaluated based on the following three evaluation criteria.
-Evaluation criteria-
○: Separation is hardly observed.
(Triangle | delta): Separation is seen a little (a level which is satisfactory practically).
X: Significant separation is observed.

<Evaluation of film strength>
Using the UV curable inks for stencil printing of Examples 1 to 7 and Comparative Examples 1 and 2, images were printed using a stencil printing machine ("Preport N800"; manufactured by Ricoh Co., Ltd.), and then on the printed image The fabric was rubbed with a cloth, and the degree of soiling of the cloth was visually evaluated based on the following three-stage evaluation criteria.
-Evaluation criteria-
○: Dirt is hardly seen.
Δ: Dirt is slightly observed (a level that causes no problem in practical use).
X: Significant dirt is observed.

<Evaluation of temperature characteristics>
Images obtained by printing images at 10 ° C. and 23 ° C. using Ricoh Co., Ltd. stencil printing machine Preport N800 using the ultraviolet curable inks for stencil printing of Examples 1 to 7 and Comparative Examples 1 and 2 the ratio of the consumed amount of the ink per 1 m ^2, was evaluated based on the evaluation criteria for the following three levels.
The ink consumption per 1 m ² of the image was determined by printing 100 images of 100 cm ² at 10 ° C. or 23 ° C. and measuring the weight of the engine part before and after printing.
-Evaluation criteria-
○: Consumption at 23 ° C./10 consumption at 10 ° C. is less than 1.5 Δ: Consumption at 23 ° C./10 consumption at 10 ° C. is 1.5 or more and less than 1.8 (a level causing no problem in practical use).
X: Consumption at 23 ° C./10 consumption at 10 ° C. is 1.8 or more

  From the results shown in Table 4, the UV curable inks for stencil printing of Examples 1 to 7 containing hydrophilic silica are more viscous to temperature changes than the UV curable inks for stencil printing of Comparative Examples 1 and 2. It was found that dripping of ink can be prevented because the yield value is high without inferior stability and separation stability during long-term storage. In particular, Example 4 containing hydrophobic silica in addition to hydrophilic silica was found to be more excellent in ink separation stability.

The UV curable ink for stencil printing of the present invention has a high yield value without impairing the viscosity stability against temperature changes and the separation stability during long-term storage, so it is used in offices where there is no dedicated operator, for example. It is very useful as an ink for use in a printing press.

Claims (4)

  An ultraviolet curable ink for stencil printing, comprising hydrophilic silica.   The ultraviolet curable ink for stencil printing according to claim 1, comprising hydrophobic silica.   The ultraviolet ray for stencil printing according to any one of claims 1 to 2, comprising at least one of a monomer and an oligomer, wherein the viscosity of the monomer and the oligomer is 0.02 to 1.5 Pa · s at 25 ° C. Curing ink. The ultraviolet curable ink for stencil printing according to claim 3, wherein the viscosity of the monomer and oligomer is 0.02 to 0.3 Pa · s at 25 ° C.