JPH0428553B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to recording paper, and particularly to inkjet recording paper that has high image density, clear image tone, and high resolution. In recent years, inkjet recording systems have been used in information equipment and other applications, with features such as high-speed printing, low noise, flexibility in recording patterns, and easy multicolor printing.
It has an excellent position in various uses. Furthermore, the images formed by the multicolor inkjet method are comparable to those produced by normal multicolor printing, do not require plate making, and are cheaper than multicolor printing by the normal plate making method when the number of copies to be produced is small. Since then, attempts have been made to apply the inkjet method not only to mere recording purposes but also to the field of multicolor printing. Art paper and coated paper used for general printing have significantly poor ink absorbency, so ink remains on the surface for a long time even after inkjet recording, and can be touched by the operator or parts of the device. If the recording surface is rubbed, residual ink will stain the image. In addition, in high-density image areas, there is a problem that a large amount of attached ink may mix without being absorbed or flow out, making it impractical. In other words, the recording paper has a high density,
Clear images can be obtained, the ink is absorbed quickly and no ink runs out, and in addition, the horizontal diffusion of ink dots on the sheet surface is suppressed and the resolution is increased at the same time. required. However, the characteristics of ink absorption and resolution, that is, lateral diffusion of ink, are such that the higher the absorption, the more lateral diffusion, and if this is controlled, the absorption itself will decrease. It is obvious that these are contradictory characteristics. In order to solve these problems, we adjusted the size of the paper, added fillers with a large specific surface area, such as clay, talc, calcium carbonate, urea-formalin resin, etc.
There are products that have a certain degree of inkjet suitability, such as by coating fine silica or providing a coating layer with ink absorbing ability on the surface, but most of these do not have the above-mentioned inkjet suitability. Although some of these aspects are satisfied, it is not possible to obtain the sharpness of image tones or the good appearance seen in multicolor printing such as ordinary offset printing. Here, the present inventors have determined that the ink absorbency, the lateral diffusion of ink dots, the sharpness of images in multicolor recording, the finished visual effect, etc., depend on the type of pigment applied to the surface of the recording paper, the adhesive, etc. Based on the knowledge that it is greatly influenced by That is, the present invention provides a recording paper in which a coating layer containing an inorganic pigment and an aqueous adhesive is provided on the surface of a support, in which 1 to 50% by weight of the inorganic pigment in the coating layer is
of solid dispersion wax to the inorganic pigment.
By providing a coating layer dispersed in 50% by weight water-based adhesive, it is possible to improve the ink absorbency, sharpness of tone, and resolution, that is, the lateral diffusion of ink dots, which are important for inkjet recording paper, in a well-balanced manner. This is due to the discovery of Even when the recording paper of the present invention is used as a recording paper for optically readable barcode printing, a printing surface with sharp edges and a high density can be obtained, which is preferable. Resolution is improved by including the solid dispersed wax in the coating layer. The theoretical cause and effect of this is not clear, but inorganic pigments generally have an affinity for inkjet ink vehicles, and when an ink droplet comes into contact with a surface coated with inorganic pigment, the ink droplet Alternatively, it is the voids between the inorganic pigments or the entire surface of the inorganic pigment itself, including its internal surface, that absorbs the vehicle.
Therefore, in that case, the absorption force is considered to work almost equally in both the depth and direction as well as the surface direction. It is thought that the presence of a solid with a suitable volume that has a hydrophobic surface and does not absorb an aqueous vehicle prevents the ink from spreading in the lateral direction, contributing to improved resolution. Here, an appropriate volume is preferably smaller than the ink droplets that make up the dots, and is also below the resolving power limit of the human eye.However, if it is too small, the ink will be absorbed into the inorganic pigment, and the pigment's inherent absorbency will increase. Taking into account that it will not be effective unless it is present to the extent that it inhibits the
50 μm, preferably 5 μm to 30 μm. The more hydrophobic solids having such size are present inside the coating layer, preferably distributed near the surface of the coating layer, the better the resolution will be, and the more the absorption will not be inhibited. In order to distribute a large amount near the surface of the coating layer, by selecting a hydrophobic solid with a low specific gravity, the difference in specific gravity with the pigment can be used to allow the hydrophobic solid to gather on the surface when drying the coating. This goal can be achieved by applying a two-layer coating and incorporating a hydrophobic solid on the surface. Hydrophobic solid dispersions suitable for this purpose are waxes that are solid at room temperature. Solid wax can be molded into the desired size using a pulverizer or the like, and can also be obtained in a form dispersed with an emulsifier or the like. The solid dispersed waxes used in the present invention include animal waxes such as beeswax and serratus wax, vegetable waxes such as carnauba wax,
Petroleum waxes such as paraffin waxes and microcrystalline waxes, polyethylene waxes, and other synthetic waxes, such as polyhydric alcohol esters of higher fatty acids and polyvalent metal salts, are used as fine powders or emulsions. be done. Good results are obtained when these solid dispersion waxes are used in an amount of 1 to 50% by weight, particularly 5 to 20% by weight, based on the inorganic pigment. If the amount of the solid dispersion wax added is too small, the effect of improving resolution cannot be obtained, and if it is too large, the resolution will be good, but the absorbency will be lowered and the color will also be lowered, which is not preferable. Examples of inorganic pigments used in the present invention include clay, talc, calcium carbonate, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, aluminum hydroxide, and diatomaceous earth. , silicic acid, calcium silicate, magnesium silicate, alumina, lithopone, etc. are used alone or as a mixture of two or more. Among them, silicic acid and silicic acid compounds having a large surface area are most suitable as absorbent inorganic pigments for carrying out the present invention. Examples of water-based adhesives include starches such as oxidized starch, etherified starch, esterified starch, and dextrin, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, casein, gelatin, soybean protein, polyvinyl alcohol and its derivatives, and maleic anhydride. Acid resins, conjugated diene polymer latexes such as ordinary styrene-butadiene copolymers and methyl methacrylate-butadiene copolymers, acrylic polymer latexes such as polymers or copolymers of acrylic acid esters and methacrylic acid esters, Vinyl polymer latices such as ethylene-vinyl acetate copolymer, functional group-modified polymer latexes using monomers containing functional groups such as carboxyl groups of various polymers thereof, thermosetting synthetic resin adhesives such as melamine resins, etc. Agents etc. are used. These adhesives contain 2 parts per 100 parts of inorganic pigment.
It is sufficient to use 5 parts to 50 parts, preferably 5 parts to 30 parts, but the ratio is not particularly limited as long as the amount is sufficient to bind the inorganic pigment. However, if 100 parts or more of the adhesive is used, the ink absorbency of the coating layer may be inhibited, which is not very preferable. Furthermore, if necessary, pigment dispersants, thickeners, flow modifiers, antifoaming agents, foam inhibitors, mold release agents, coloring agents, etc. may be appropriately added without any problem as long as the properties are not impaired. Examples of the coating machine of the present invention include blade coaters, air knife coaters, roll coaters, brush coaters, curtain coaters, chamber coaters, bar coaters, gravure coaters, etc. that are generally used in the production of pigment-coated paper. can also be applied. Furthermore, the size press on the paper machine,
It is also possible to apply a gate roll device or the like. The coating amount is usually 0.5 g/m ² to 40 g/m ² , preferably 2 g/m ² to 30 g/m ² . As the support, appropriately sized paper, non-sized paper, thermoplastic synthetic resin film, etc. can be used, and there are no particular restrictions on the material, but thermoplastic synthetic resin films usually include polyester, Polystyrene, polyvinyl chloride, polymethyl methacrylate, cellulose acetate, etc. are used. Since the sheet is simply a coating layer provided on a support, its smoothness and gloss are poor, and the image after multicolor recording using an ink jet does not look very good. Therefore, as mentioned above, after coating and drying, it is possible to improve the finish of the inkjet image by passing it between roll nips under heat and pressure using, for example, a super calender or gloss calender to give the inkjet image smoothness. In this case, supercalendering compresses and densifies the coated layer, thereby slightly reducing the ink absorption ability, which is one of the factors for inkjet suitability. Gloss calendering, on the other hand, creates a temporary plastic state in the surface that provides a higher finish without over-compacting the substrate, resulting in a bulkier coating layer. , this bulk is more desirable for purposes of the present invention because it provides ink absorption. The present invention will be described below with reference to examples, but it is not limited to these examples. Note that parts and percentages shown in the examples mean parts by weight and percentages by weight. Methods for measuring various physical property values in Examples are shown below. (1) Ink absorption speed Ink droplet of water-based ink for inkjet 0.0006
The time from the moment ml was applied to the surface until it was completely absorbed was measured under a microscope. (Seconds) (2) Resolution A droplet of water-based inkjet with a diameter of 100μ was attached to the surface, and after being absorbed, the area marked by the ink droplet was measured to calculate the diameter.
(μm), the smaller the diameter, the better the resolution. (3) Color properties Four colors, cyan, magenta, yellow, and black, were recorded using an inkjet device, and the color densities were measured using a Sakura densitometer PDA45. (OD) Example 1 100 parts of LBKP was beaten to a water content of 400 ml of CSF, 8 parts of talc, 0.6 parts of saponified rosin, and 2 parts of sulfuric acid were added to make a base paper with a basis weight of 64 g/m ² using a Fourdrinier paper machine. During paper making, oxidized starch was deposited at a solid content of 2 g/m ² using a size press. 100 parts of light calcium carbonate, 0.3 parts of sodium hexametaphosphate, 15 parts of oxidized starch, and 10 parts of oxidized paraffin dispersed in a ball mill to an average particle size of 40 μm.
A coating solution with a solids content of 40% was prepared. The coating solution was applied to the above-mentioned base paper using an air knife coater to give a coating solution of 15 g/m ² on one side, and then dried. The paper was then passed through a super calender to smooth the surface and used as recording paper. Table 1 shows the test results for this recording paper. Example 2 A recording sheet was obtained in exactly the same manner as in Example 1, except that microcrystalline wax emulsion (average particle size: 6 μm) was used instead of oxidized paraffin. Table 1 shows the test results for this recording paper. Example 3 A recording sheet was obtained in exactly the same manner as in Example 1, except that polyethylene wax emulsion (average particle size 1 μm) was used instead of oxidized paraffin. Table 1 shows the test results for this recording paper. Example 4 A recording sheet was obtained in exactly the same manner as in Example 1, except that aluminum stearate was ground in a ball mill and a dispersion liquid having an average particle size of 30 μm was used instead of oxidized paraffin. Table 1 shows the test results for this recording paper. Comparative Example 1 40% solids consisting of 100 parts of light calcium carbonate, 0.3 parts of sodium hexametaphosphate, and 15 parts of oxidized starch
A recording paper was obtained in exactly the same manner as in Example 1, except that the coating liquid was used. The test results of the obtained paper are shown in Table 1. Comparative Example 2 A recording sheet was obtained in exactly the same manner as in Example 1, except that a heavy oil emulsion that was liquid at room temperature was used instead of oxidized paraffin. Table 1 shows the paper test results for this paper.

[Table] From Table 1, it is clear that compared to Comparative Example 1, which did not contain solid dispersed wax, and Comparative Example 2, which used liquid oil, Examples 1 to 4, which contained various solid dispersed waxes, had lower resolution. improved, and other properties were almost the same. Examples 5 to 9 A mixed inorganic pigment consisting of 80 parts of synthetic silica (white carbon) and 20 parts of heavy calcium carbonate, 18 parts of polyvinyl alcohol, and paraffin with a melting point of 96°C were ground and dispersed in a ball mill to an average particle size of 20 μm. Add the amount (parts) shown in Table 2, solid content 20%
A coating solution was prepared. This was applied to the same base paper as used in Example 1 using an air knife coater to give a coating weight of 13 g/m ² on one side, and then dried. Next, the paper was passed through a super calender to smooth the surface and used as recording paper. For comparison, recording sheets without the addition of pulverized paraffin (Comparative Example 3), those with 0.6% added (Comparative Example 6), and those with a large amount added (Comparative Examples 4 and 5) were prepared in exactly the same manner. The test results for these recording papers are shown in Table 2.

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Claims (1)

[Claims] 1. In a recording paper in which a coating layer containing an inorganic pigment and a water-based adhesive is provided on the surface of a support, the coating layer contains 1 to 50% by weight of the inorganic pigment with an average particle diameter of 1 to 50 μm. a solid dispersion wax, which is
An inkjet recording paper comprising 2 to 50% by weight of an aqueous adhesive.