JPH01146786A - Coating composition for ink jet recording sheet - Google Patents

Abstract

PURPOSE:To enhance water resistance without deteriorating the light resistance of a recorded image and to contrive a sharp and high-density image, by mainly containing a pigment slurry using a polyethylene-imine as a dispersant and cationic aqueous copolymer dispersions. CONSTITUTION:As a polyethylene-imine serving as a dispersant to obtain a pigment slurry, a polyethylene-imine having a molecular weight of 200-10,000 is preferably used in the addition amount of 0.05-2pts.wt. per 100pts.wt. of the pigment. As the pigment, calcium bicarbonate having a high isoelectric point is preferably used. Cationic aqueous copolymer dispersions obtained by using a material containing cationic monomer as the component of the copolymer in combination with a material polymerized by a cationic emulsifier are preferably used. The cationic aqueous copolymer dispersions (solid content) are preferably used in the range of 5-25pts.wt. per 100pts.wt. of the pigment.

Description

Detailed Description of the Invention 41 Object of the Invention [Industrial Field of Application] The present invention provides an inkjet recording paper that is highly water resistant without impairing its water-based ink absorbability. An object of the present invention is to provide an improved coating composition for inkjet recording paper that has the ability to

[Conventional technology]

In inkjet recording, characters and images are generally expressed on paper by spraying low-viscosity ink directly onto the paper from a thin nozzle with a diameter of 50 to 100 μm. Because it is necessary to eject ink stably from a nozzle with such pores, it is difficult to incorporate pigments, resins, etc. into the ink used for inkjet recording, unlike ordinary printing ink. For this purpose, low-viscosity water-based inks containing water-soluble dyes such as direct dyes and acid dyes are generally used. Therefore, inkjet recording has the drawback of being inferior in printing suitability such as density, gloss, light resistance, and water resistance compared to general printing methods.

However, with the spread of office automation equipment such as color printers, the field of use of the inkjet recording method has expanded, and the performance during recording includes ink absorption, ink drying, resolution, density, sharpness of color tone, and after recording. Mr. Le requires performance such as water resistance and light resistance of images.

became.

Various proposals have been made in the past as methods for improving these performances. For example, JP-A-52-53012
In this issue, an inkjet recording paper made by moistening a low-size base paper with a coating for surface treatment was also published in Japanese Patent Application Laid-Open No. 58-49.
No. 113 discloses an inkjet recording paper in which a sheet containing urea/formalin resin powder is impregnated with a water-soluble polymer. However, although these general paper type inkjet recording papers absorb ink quickly, they have the disadvantage that the periphery of dots tends to be blurred and the dot density is low.

In addition, in order to form images with excellent water resistance and high resolution,
No. 78885, No. 59-96988 and No. 59-1
No. 06989 proposes an inkjet recording sheet whose surface contains a water-soluble compound of a divalent or higher valent metal, including a halide of magnesium or calcium. However, none of these proposed methods has the problem that sufficient water resistance cannot be obtained.

On the other hand, JP-A-55-5830 discloses an ink-jet recording paper having an ink-absorbing coating layer on the surface of the support, and JP-A-55-51583 discloses non-colloidal silica powder as a pigment in the coating layer. An example using JP-A-55
No. 11829 discloses an example of a smear paper having a two-layer structure with different ink absorption speeds. These coated paper type inkjet recording papers are improved over the above-mentioned general paper type inkjet recording paper from the viewpoint of reproducibility of dot diameter, shape, density, and color tone, but if the recorded image is exposed to water, etc. There was a problem that the dye would dissolve again and ooze out.

In order to improve the problems caused by this lack of water resistance,
JP-A-55-53591 discloses an example in which a water-soluble metal salt is applied to the recording surface, and JP-A-56-84992 describes an example of a recording medium containing a polycationic polymer electrolyte on the surface. JP-A-55-150896 discloses an example of applying a water-resistant agent that forms a chelate with the dye in the ink after inkjet recording, and JP-A-56-58869
In JP-A No. 61-63477, there is an example in which a recording sheet coated with a water-soluble polymer is made water resistant by insolubilizing the water-soluble polymer after inkjet recording. Examples have been disclosed in which water resistance is achieved by incorporating. However, these waterproofing methods have the problem that their effectiveness is low, and that the waterproofing agent conversely reduces the storage stability of the dye, so inkjet recording paper with sufficient quality and performance has not yet been obtained. The reality is that there is no such thing, and this solution was desired.

[Problems to be solved by the present invention]

Therefore, the present inventors have attempted to improve water resistance without impairing the light resistance of recorded images in inkjet recording paper on which images are recorded with water-based ink using water-soluble dyes, and to ensure that the images are clear and free of bacteria. We have repeatedly studied inkjet recording paper that has a high density.

[Means for solving problems]

As a result, a coating composition coated on inkjet recording paper mainly contains a pigment slurry prepared using polyethyleneimine as a dispersant and a cationic aqueous copolymer dispersion as a binder. The inventors have discovered that the above-mentioned problems can be solved, and have completed the present invention.

[Object of the present invention]

The purpose of the present invention is to solve the above-mentioned problems with inkjet recording paper, that is, to improve water resistance without impairing the light resistance of recorded images, and to enable the images to be recorded with clarity and high density. An object of the present invention is to provide a coating composition for circular inkjet recording paper.

2. Structure of the Invention [Structure of the Present Invention] That is, the present invention provides an inkjet recording coating composition characterized by polyethyleneimine.

The present invention will be explained in more detail below.

Polyethyleneimine, which is used as a dispersant to obtain the pigment slurry used in the present invention, is an essential component in the present invention. When conventional anionic dispersants and nonionic dispersants are used in cationic paint compositions, the former has a fundamental problem of lack of stability of the paint itself, and the latter causes foaming during paint preparation. There are problems in terms of business performance. By using polyethyleneimine as a dispersant in the present invention, a paint for inkjet recording paper can be obtained that has excellent dispersibility and viscosity stability over time, and also has excellent printability when applied to inkjet recording paper. Polyethyleneimine generally has low molecular weight, medium molecular weight, and high molecular weight, but polyethyleneimine with a molecular ff of 1200 to 10,000 is preferable (this is used). The amount is preferably 0.05 to 2 parts by weight, more preferably 0.1 to 1 part by weight.

Pigments used in the present invention include pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, talc, titanium oxide, zinc oxide, diatomaceous earth, and synthetic silica, among which pigments are said to generally have a high isoelectric point. Heavy calcium carbonate is preferably used.

The cationic aqueous copolymer dispersion of the present invention means an emulsion or latex in which the copolymer particle surface has a positive charge and is present in a dispersed state in an aqueous phase. Specifically, these include: (1) copolymers using a cationic monomer as a component, (2) polymerization using a cationic emulsifier, (2) polymerization with a cationic surfactant added after polymerization, (2) Examples include those polymerized using a cationic polymerization initiator, but in the present invention, a cationic aqueous copolymer dispersion obtained by any of these methods or a combination of these methods may be used. Can be done.

Among these, those obtained by combining (1) and (2) are preferably used. The amount used is 5 parts of the cationic aqueous copolymer dispersion (solid content) per 1.00 parts by weight of the pigment.
A range of 25 parts by weight is preferred.

Other ingredients such as cationized starch, antifoaming agent, mL type agent, etc. may be used as appropriate in the coating composition obtained in the present invention. In addition, when coating inkjet recording paper, coating can be performed using a coater such as a size press coater, gate roll coater, air knife coater, or blade coater, and the coating amount at that time is 2. ~157/rrL2 (solid content) is preferred.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited in any way by the examples.

In addition, all parts and parts in the examples mean parts by weight unless otherwise specified.

0 Example-1 (Production of cationic aqueous copolymer dispersion) Into an autoclave that had been purged with nitrogen in advance, 100 parts of ion-exchanged water, 30 parts of butadiene, 65 parts of styrene, and 3-methacryloxy-2-hydroxypropyltrimethylammonium were added. 2 parts of chloride, further 2 parts of lauryltrimethylammonium chloride, 0.3 part of tert-dodecylmercaptan and 0.1 part of 2,2-azobis-(2-aminodipropane) hydrochloride were charged, and the temperature was raised to 50°C with stirring. Heat to initiate polymerization.

When the polymerization conversion rate of the monomer reached 80%, the temperature was increased to 60°C.
The temperature was raised to 99%, and the polymerization was carried out to a polymerization conversion rate of 99%.

Thereafter, it was cooled, and unreacted monomers were removed by stripping to obtain cationic latex A.

(Preparation of coating composition) Polyethyleneimine with molecules xi, s・00 was purified with hydrochloric acid.
Adjust to H3.5 and create a dispersant.

Based on the following recipe, each component was added while stirring to prepare a coating composition (2) with a final solid content of 60%. The resulting coating composition had a viscosity of 750 cps1 and a pH of 7.5.

Prescription water: Desired amount *1 Heavy calcium carbonate: 100 parts Polyethyleneimine dispersant 20.2 parts (solid content) *2 Cationized starch: 4 parts (〃) Cationic latex A: 12 parts (〃) * l: Softon+22
00 (manufactured by Bihoku Funka Kogyo ■) *2: Egg 485 (manufactured by Tamago Paper Manufacturing ■) was crushed and dissolved at 90'C.

(Coating and performance evaluation of inkjet recording paper) Using the obtained coating composition
rL2) was subjected to coating fJj,, 109/rn2te coating treatment.

Solid printing was performed on the obtained coated paper using an inkjet printer (Sharp model 700) with blue, red, yellow, and black inks, and the suitability of the image area was measured in the following manner. The results are shown in Table-1.

Light resistance: The image area is irradiated for 40 hours at 40° C. and 60% relative humidity using a xenon fedometer (manufactured by Suga Test Instruments), and the color density before and after irradiation is measured using a Macbeth densitometer RD514. Light resistance was determined using the following formula.

The larger the value, the better the light resistance.

Water resistance: The coated paper is immersed in running water at 28°C for 5 minutes, and the color density of the image area before and after immersion is measured using a Macbeth densitometer RD514. Water resistance was determined using the following formula.

The larger the number, the better the water resistance.

0 Comparative Example 1 In place of the coated paper type inkjet paper of the present invention, a general paper type inkjet paper (commercially available paper used in Sharp's inkjet printer model 700) was used, and the same procedure as in Example 1 was carried out. It was printed and its suitability for inkjet printing was measured. The results are shown in Table-2.

Table-1 Inkjet suitability (coated paper of the present invention) Table-2 Inkjet suitability (general paper type/commercial product) Effects of the invention [Effects of the present invention] The coating composition for inkjet recording paper obtained by the present invention is When used for coating inkjet recording paper that records images with water-based ink using water-soluble dyes, the water resistance improves without impairing the light resistance of the image, and the image is clear and high quality. It has the excellent effect of being a degree. Furthermore, the coating composition has excellent dispersibility and viscosity stability over time.

Claims (1)

[Claims] 1. A coating composition for inkjet recording paper, which mainly contains a pigment slurry using polyethyleneimine as a dispersant and a cationic aqueous copolymer dispersion.