JPH06212108A - Ink for watermark printing and method of watermark printing by using same - Google Patents

Abstract

PURPOSE:To provide easily a translucent watermark by using a printing ink which forms a W/O emulsion comprising a specified transparent resin, a surfactant and water. CONSTITUTION:An example of the transparent resin is one that is normally solid and has a refractive index in the range of 1.3-1.6, for example, an alicyclic saturated hydrocarbon resin of a molecular weight of 200-3000. Its amount of addition is 10-50wt.% based on the total weight of the ink. The organic solvent may be any of nonpolar organic solvents, and a paraffinic solvent of a boiling point of 140-400 deg.C is particularly desirable. Its amount of use is 10-40wt.% based on the total weight of the ink. Although not particularly limited, a sorbitan/fatty acid ester is desirable as the surfactant. Its amount of addition is 1-10wt.% based on the total weight of the ink. Highly pure water such as deionized water is desirable as the water, and its content is 20-70wt.%. It is also possible to provide a lightly colored watermark by adding a small amount of an oil-soluble dye to the oil phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for imprinting watermarks on paper by printing, and more specifically, by using a printing ink containing a transparent resin having a light refractive index of 1.3 to 1.6 which is close to that of cellulose. The present invention relates to a technique for making a printed portion semi-transparent and a watermark.

[0002]

2. Description of the Related Art Watermarks are one of the paper processing methods that have been developed for a long time in order to prevent tampering with important documents and banknotes. It is manufactured by giving a difference in the density of the fibers that make up the paper. It is also possible to partially press the paper to create a difference in light transmittance between a pressed portion and a non-pressed portion, so that various patterns and characters can be displayed in a watermark. Recently, there has been a strong demand for watermarked paper in fields other than important documents due to its high-class feel, and for example, paper with company name, slips with company name, personal demand, etc. are mentioned as obvious or potential uses. However, as described above, the production of the watermarked paper is mainly performed in the paper making stage, and the production cost in a small amount is extremely high. The above-described watermarking method by pressurization also requires a large-sized press machine and requires an expensive die for each watermark pattern, and therefore cannot meet a small amount of demand at a low price.

Japanese Patent Publication No. 44-21574, Japanese Patent Publication No. 6-6
4-9957, JP-A-63-58716,
Japanese Laid-Open Patent Publication No. 2-127599 proposes a watermark forming method by a printing method using a substance having a light refractive index similar to that of cellulose as an ink main component. For example, Japanese Patent Publication No. 64-
In 9957, the ink main ingredient is sucrose acetate isobutyrate having a photorefractive index of 1.45, which is close to that of cellulose, and its organic solvent solution is used as it is or the solution has a photorefractive index similar to that of cellulose. A watermark printing method has been proposed in which a normal temperature solid resin is added to form a printing ink and a printing portion is made into a semitransparent watermark state. In these watermark printing methods, it is not possible to make the paper surface semi-transparent unless the ink penetrates well into the paper surface of the printing portion, but when the ink penetrates to areas other than the printing portion, the watermark image becomes unclear, which is not preferable. Therefore, it is required to have a performance that allows easy penetration in the vertical direction and difficult penetration in the horizontal direction. Therefore, Japanese Patent Publication No. Sho 64-9957 proposes a method of treating a printed matter at a high temperature after printing by using an ink having a low permeability at a normal temperature and an improved permeability at a high temperature. Further, in JP-A-2-127599, in addition to a normal-temperature solid resin having a photorefractive index similar to that of cellulose in a printing ink, wax, animal or vegetable oil, or the like is added to the ink for viscosity, penetrability into paper, and spinnability. By adjusting various physical properties related to the ink performance such as peelability, an ink suitable for watermark printing is obtained.

However, all of the above-described watermark printing methods described above use offset printing or gravure printing as a printing means, and are not in a situation in which a user can easily perform watermark printing. That is, in recent years, a plate making integrated type stencil printing machine has been developed so that users can easily print it.However, when stencil printing is performed using the conventional watermark printing ink, an ink suitable for printing at the time of stencil printing is printed. It is difficult for a user to perform stencil printing with a simple stencil printing machine, because the conditions are not compatible with the proper ink conditions for watermark printing. This point will be described in more detail below. In stencil printing, the ink is supplied to the paper through the fine holes on the stencil surface, and thus the stencil printing ink is required to have a lower viscosity than the offset printing ink. In addition, higher viscosity is required than the gravure printing ink. However, even if the viscosity of these inks is adjusted to appropriately reduce the spinnability and tackiness, the printability such as curling up and plate discharge during printing is not improved. Further, in the above-mentioned watermark printing ink developed for offset printing and gravure printing, when the viscosity is adjusted to a suitable viscosity for stencil printing and used, the ink adhesion amount becomes 2 to 4 during offset printing or gravure printing. Therefore, troublesome phenomena such as ink bleeding and peeling of excess ink deposited on the printing surface may occur. Furthermore,
If the printing machine is left with the ink having the viscosity adjusted, the plate cylinder may be clogged.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems found in the prior art, and makes it possible to easily and inexpensively obtain a desired watermark-containing paper in a small amount at a low cost. It is an object of the present invention to provide an ink and a watermark printing method using the ink.

[0006]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a W / O type emulsion is formed by including an organic solvent solution of a transparent resin having an optical refractive index of 1.3 to 1.6 which is a solid at room temperature, a surfactant and water. A featured watermark printing ink and a watermark printing method using the ink are provided.

The transparent resin used in the watermark printing ink of the present invention is solid at room temperature and has a light refractive index in the range of 1.3 to 1.6. Examples of such a resin include an alicyclic saturated hydrocarbon resin, a chain saturated hydrocarbon resin, and an alkyd resin. As the alicyclic saturated hydrocarbon resin, one or a mixture of two or more of styrene, α-methylstyrene, indene, methylindene, propenylbenzene, vinylxylene and the like is polymerized, and then the benzene ring in the carbon chain is hydrogenated. A resin converted to a cyclohexane ring is generally used, but a petroleum resin containing a cyclopentane ring in the carbon chain or a solid resin obtained by hydrorefining a terpene-based oligomer can also be used. The chain saturated hydrocarbon resin includes solid oligomers obtained by polymerizing one kind or a mixture of two or more kinds such as ethylene, propylene and butene. The resin preferably used in the present invention is an alicyclic saturated hydrocarbon resin having a molecular weight of 200 to 3000. These transparent resins are used alone or as a mixture of two or more kinds. When a mixture is used, the mixed resin has a light refractive index of 1.3 to 1.6 which is close to that of cellulose. Good. The amount of the transparent resin added is 10 to 50%, preferably 20 to 40% of the total weight of the ink.

Although all nonpolar organic solvents can be used as the solvent for the transparent resin, paraffinic solvents having a boiling point of 140 to 400 ° C. are particularly preferable. The amount of the organic solvent used is preferably as small as possible in the range where additives such as transparent resin are sufficiently dissolved and a stable W / O type emulsion can be formed, and generally 10 to 40% of the total weight of the ink is preferable. Is 15 to 25%, and if the amount used is too large, there are problems such as deterioration of drying property after printing and bleeding of printing watermarks. This bleeding is suppressed by adding 12-hydroxystearic acid corresponding to 3 to 10% by weight of the ink to the solution, which is presumed to be due to hardening of the resin in which the compound is dissolved. In the present invention, a solvent having a boiling point of 250 ° C. or higher is used in an amount of 5% by weight of the entire ink.
By adding the above, it is possible to prevent clogging of the plate cylinder due to the adhered ink without cleaning the printing machine after printing, but in this case, a solvent having a boiling point of 250 ° C. or higher is also preferably a paraffinic solvent, and the boiling point range of the solvent. Is 250 to 600 ° C, preferably 250 to 350 ° C. Boiling point 2 used here
If the amount of the solvent used at 50 ° C. or more is too large, it is difficult to volatilize from the printed matter, so that the watermark pattern becomes blurred and becomes unclear. Therefore, the amount used is 5 to 20% by weight, preferably 7 to 1% of the total ink.
4% by weight is good. In addition, in order to prevent bleeding in this case, it is preferable to add the 12-hydroxystearic acid in the same amount as above.

In the present invention, the surfactant used for forming the W / O type emulsion is a nonionic, anionic or amphoteric surfactant. Examples of the nonionic surfactant include sorbitan fatty acid ester and aliphatic monoglyceride, as well as higher alcohol, alkylphenol, and ethylene oxide adduct of fatty acid. Of these, sorbitan fatty acid esters are particularly preferred,
Specifically, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquioleate and the like are preferable. Further, as the aliphatic monoglyceride, oleic acid monoglyceride and the like are preferable. As the anionic surfactant, alkyl phosphate, polyoxyethylene alkyl ether phosphate, alkyl sulfocarboxylate and the like are preferably used. As the amphoteric surfactant, betaine type, glycine type, alanine type and the like may be used alone or in combination of two or more. These surfactants may be used alone or in admixture of two or more, and the addition amount thereof is 1 to 10% by weight, preferably 3 to 6% by weight of the total ink.

When electrophotographic copying or laser printing is performed on a paper on which a watermark pattern is formed by the method of the present invention, if an ionic compound is present on the paper to be copied, the ionic compound forms a latent image. There is a possibility of contaminating a drum such as an electrophotography formed. This contamination of the drum reduces the latent image forming ability of the drum, so it is desirable that the paper being copied be free of ionic compounds. Therefore, a nonionic surfactant is desirable for the surfactant used in the watermark printing ink of the present invention,
Since nonionic surfactants are not inferior to anionic surfactants and amphoteric surfactants in terms of ability, not only when using watermarked paper for the above-mentioned copy etc.,
Nonionic surfactants should be used except in special cases.

The water used for the internal phase in the emulsion type watermark printing ink of the present invention is preferably high-purity water such as ion-exchanged water, and this water is frozen such as ethylene glycol. Inhibitors and preservatives such as phenols, methyl P-oxybenzoate and salicylic acid can be added. If necessary, polyacrylic acid and triethanolamine may be added as a thickener for the aqueous phase. In the emulsion type watermark printing ink of the present invention, it is preferable that the water content is 20 to 70% by weight, preferably 30 to 50% by weight. I can't get right. Further, if the content is too high, the stability of the ink is impaired, and wrinkles such as curls and irregularities occur on the paper surface after printing.

The watermark printing ink of the present invention includes various additives added to conventional watermark printing inks, for example, paraffin wax such as polyethylene wax and higher fatty acid ester such as palmitate. May be added as necessary, and the addition of these can further improve the printing suitability of the printing ink.
The above-mentioned additives are also effective for preventing blocking after printing. Further, these additives may be added to a solution in which the transparent resin is dissolved in an organic solvent, and the additives are present in the oil phase which is the outer phase in the emulsion type ink of the present invention. In addition to the above, by adding a fine oil-soluble dye to the oil phase, it is possible to lightly color the watermark pattern, and thereby to give a special texture. In addition, the addition of a transparent pigment improves the writing property. The transparent pigment is an additive for preventing the portion on which the pear pattern is formed by the method of the present invention from being resinized by the permeation of the transparent resin, which makes it difficult to write on the surface. In addition to titanium, transparent resin and fine powder of barium sulfate, montmorillonite, etc. are preferably used.

According to the present invention, by using a W / O type emulsion as the ink, it is possible to obtain an ink having a low viscosity while maintaining a high viscosity. Therefore, it can be used for stencil printing with a high viscosity, and watermark printing by stencil can be performed without bleeding due to excess amount of ink and peeling phenomenon on the printing surface. Further, the phenomenon such as deterioration of plate discharge property, which is often observed when the ink is left on the printing machine, is also improved by using the W / O type emulsion ink of the present invention. It is presumed that this is because the W / O type emulsion ink of the present invention is also different from the conventional oil-based ink in terms of thixotropy.
Furthermore, a part of the organic solvent used in the present invention has a boiling point of 25.
When the organic solvent is used at 0 ° C. or higher, the ink does not cure even when the ink is left on the printing machine, so that the plate cylinder is not clogged. Further, the watermark printing method of the present invention using the W / O type emulsion ink can be carried out by a stencil printing machine, either a plate-making integrated type or a simple type. Further, in the watermark printing method of the present invention, watermark printing is possible from the front surface side or the back surface side of the paper, and it is necessary to add a transparent pigment such as hydrophobic silica to the watermark printing ink of the present invention. Can also improve the printability of the printed surface.

[0014]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, all the numbers indicating the ink compositions in the present example and the comparative example are described in parts by weight.

Examples 1 to 9 and Comparative Example 1 Tables 1 and 2 show the composition of the watermark printing ink used in the experiment.

[Table 1]

[0016]

[Table 2]

In Tables 1 and 2, the alcon used for the transparent resin is an alicyclic saturated hydrocarbon resin manufactured by Arakawa Chemical Co., Ltd.
-90 is a weight average molecular weight 570, P-125 is a weight average molecular weight 750, M-100 is a weight average molecular weight 620, M
-135 has a weight average molecular weight of 860. The optical refractive index of these transparent resins at 20 ° C. is 1.52, respectively.
8, 1.535, 1.546 and 1.522. Each of these resins is produced by polymerizing an aromatic hydrocarbon having an olefin bond in its side chain and then hydrogenating it. The waxes added in Table 1 are all microwaxes manufactured by Mobil Corp. Microwax 160 has a melting point of 68 ° C and microwax 180 has a melting point of 83 ° C. Further, Isopar used as a solvent is an isoparaffin-based solvent manufactured by Exxon Corporation, Isopar L has a boiling point of 188 to 210 ° C, and Isopar V has a boiling point of 273 to 310 ° C.

The surfactants listed in Tables 1 and 2 are all Nikko chemical products, SO-30 and SO-10.
Both are sorbitan trioleates, but HLB
Are different. That is, SO-30 is 1.7 and SO-10 is 4.3. HLB is hyd
rophile-lipophile balance
Is an abbreviation of "," and is one of the indexes showing the effect of the surfactant. DOP-8N is a mixture of 8 parts of POE and 1 part of sodium oleyl ether phosphate, where POE is an abbreviation for polyoxyethylene. The oil-soluble dye added to the watermark printing ink of Example 2 is a red dye,
Orient Chemical Co., Ltd. oil Pink 312.
Further, the hydrophobic silica added to the watermark printing ink of Example 5 is Syroid 266 manufactured by Fuji Devison,
It is fine powdery silica having a particle size of 1 to 7 μm (average particle size 3.0 μm).

The watermark printing inks having the compositions shown in Tables 1 and 2 are prepared by dissolving a transparent resin in a predetermined amount in an organic solvent having a predetermined composition, and then adding 12-hydroxystearic acid as an additive, a wax or an oil-soluble dye. It is easily formed by dissolving the above, adding a predetermined amount of ion-exchanged water and a surfactant, and stirring well. Further, the hydrophobic silica of Example 5 was added when the organic solvent solution and the ion-exchanged water were mixed, but this may be added after the emulsion formation and stirred until uniform. The watermark printing ink produced as described above was used to print on ordinary copy paper [Ricoh type 6000] with a Ricoh stencil printer Preport VT-2500. When using the inks of Examples 1 to 9, No roll-up or plate discharge property was observed, and there was no problem such that the watermark printed product became blurred due to bleeding or the like. However, when the ink of Comparative Example 1 was used, it rolled up and could not be printed.

Table 2 shows that 12-
The compositions of the inks to which hydroxystearic acid was added are shown. The inks of Examples 6 to 9 listed in Table 2 have a greater bleeding preventing effect than the inks of the compositions listed in Table 1, and therefore, the organic compounds at the time of ink formulation It was confirmed that the range of solvent usage expanded. Watermark prints using the inks of Examples 3 and 8 did not cause troubles such as deterioration of the latent image forming photoconductor even when used for electrophotographic copying. Further, regarding the inks of Examples 4 and 9,
An attempt was made to leave it in the printing machine for 4 weeks, but no trouble such as clogging of the plate cylinder occurred. The printed matter using the ink of Example 5 could be easily written on the printed surface with a fountain pen.

[0020]

Since the w / o type emulsion ink of claim 1 has high viscosity and low tackiness, it can be used for watermark printing without causing problems such as winding even when used in stencil printing. The w / o type emulsion ink according to claim 2 or 5,
Similar to the ink according to the first aspect, stencil printing can be performed without problem watermark printing, and since the printed watermark pattern is lightly colored, a unique texture can be provided. The w / o type emulsion ink of claim 3 can be watermark-printed without problems by stencil printing like the ink of claim 1, and the watermark printing surface can be improved by adding a transparent pigment. A printed matter is obtained. The w / o type emulsion ink of claim 4 is capable of watermark printing without problems by stencil printing similarly to the ink of claim 1, and when the amount of the organic solvent used during the ink preparation is slightly large or in the solvent. Since it is possible to prevent ink bleeding even when the high boiling point content ratio of is large,
The degree of freedom in ink formulation increases.

The w / o type emulsion ink of claim 6 can be used for stencil printing without any problem in the same manner as the ink of claim 1, and the obtained watermark printed matter can be used for electrophotographic copying paper. When used for laser printing paper, it does not contaminate the latent image forming photoconductor of a copying machine or a laser printing machine and deteriorate the photosensitivity. Claim 7
Similar to the ink of claim 1, the w / o type emulsion ink of (1) can be used for stencil printing without any problem, and the clogging of the plate cylinder can be prevented even if the printing machine is left uncleaned after printing. Since it does not occur, it is suitable for an amateur to easily perform watermark printing. Further, this ink does not cause clogging of the plate cylinder as described above, but does not cause troubles such as discoloration and bleeding during long-term storage. W of claims 1-7
The / o type emulsion ink can be used for both a plate-making integrated stencil printing machine and a simple stencil printing machine, and an amateur can easily perform watermark printing at home. According to the printing method of claim 8, it is possible to easily and inexpensively obtain a desired watermark-containing paper even in a small amount.

Claims (8)

[Claims] 1. An organic solvent solution of a transparent resin, which is a solid at room temperature and has a photorefractive index of 1.3 to 1.6, a surfactant and water, and W /
A watermark printing ink characterized by forming an O-type emulsion. 2. A W / O type emulsion is formed by including an organic solvent solution of a transparent resin having a solid-state normal temperature and a photorefractive index of 1.3 to 1.6, a colorant, a surfactant and water. Characteristic watermark printing ink. 3. A W / O type emulsion is formed by containing an organic solvent solution of a transparent resin having a light refractive index of 1.3 to 1.6 which is a solid at room temperature, a transparent pigment, a surfactant and water. Characteristic watermark printing ink. 4. A W / O type emulsion is formed by containing an organic solvent solution of a transparent resin having a photorefractive index of 1.3 to 1.6 which is solid at room temperature, a surfactant, 12-hydroxystearic acid and water. Ink for watermark printing characterized by being present. 5. The watermark printing ink according to claim 2, wherein the colorant is an oil-soluble dye. 6. The watermark printing ink according to claim 1, wherein the surfactant is a nonionic surfactant. 7. The organic solvent for dissolving the transparent resin is a mixed solvent, and the amount of the solvent having a boiling point of 250 ° C. or higher in the mixed solvent is 5% by weight or more of the total weight of the ink. The watermark printing ink according to any one of to 6. 8. A watermark printing method, wherein the watermark printing ink according to claim 1 is used, and a stencil printing method is used to bring a printed portion into a semi-transparent watermark.