JPS6321635B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to recording paper, and particularly to a method for manufacturing inkjet recording paper that has high image density, clear image tone, and high resolution. In recent years, the inkjet recording method has enjoyed an excellent position in a variety of applications, including information equipment, due to its features such as high-speed printing, low noise, flexibility in recording patterns, and easy multicolor printing. be. 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, the image will be smeared with residual ink. 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, the 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 self-evident that these characteristics mutually protect each other. In order to solve these problems, we have adjusted the size of the paper, added fillers with a large specific surface area such as clay, talc, calcium carbonate, urea-formalin resin, etc., and applied fine silica to the surface. There are products that have a certain degree of inkjet suitability, such as by providing a coating layer with ink absorbing ability, but most of these products satisfy some of the above inkjet suitability, but the color tone of the image is affected. You will not be able to get the sharpness or nice looking images that you get with multicolor printing such as normal offset printing. The present inventors have determined that the type of pigment applied to the surface of the recording paper, the adhesive and the coating, etc. Based on the knowledge that the finishing method of the layer has a great influence, we conducted intensive studies, especially regarding the adhesive and the finishing method of the coating layer. It is well known that styrene-butadiene copolymer latex or modified styrene-butadiene copolymer latex, which is currently used as a pigment adhesive for paper coating layers, is used as an adhesive for coating layers; The composition is mainly styrene, butadiene, and acrylic ester. However, when such a conventional styrene-butadiene copolymer latex is used as an adhesive in the coating layer of an inkjet recording paper, sufficient coating layer strength can be obtained, but inkjet suitability is significantly impaired. The present inventors have found that a coating layer with excellent inkjet suitability, that is, fast ink absorption, little lateral diffusion of ink dots, and sharpness of images in multicolor recording, as well as strong coating layer strength, has been obtained. In order to obtain a styrene-butadiene copolymer latex or a modified styrene-butadiene copolymer latex, structural investigations were carried out. the result,
Although the reason is not clear, the present inventors applied an aqueous composition containing an inorganic pigment and an aqueous polymer adhesive to the surface of the support, dried it to form a coated layer, and then heated the coated layer in a calender. In the method for manufacturing recording paper that is finished by pressure bonding, the water-based polymer adhesive is a latex of a styrene-butadiene copolymer or a modified styrene-butadiene copolymer in which the styrene block is an octamer to 40-mer, and is further dried. In finishing with a post-heating calender, the surface of the coating layer is finished at a temperature ranging from 20°C lower than the glass transition temperature (hereinafter referred to as Tg) of the polymer latex to 40°C higher than Tg, which improves inkjet suitability. We have discovered that it is possible to produce excellent paper. That is, when the copolymer latex of the present invention is used, it is possible to obtain a recording paper which has stronger coated paper strength and superior ink jet suitability than a coated paper using a conventional latex of the same composition. Incidentally, when the styrene blocks are 8 to 40 units, it means that the number of polymerized styrene monomers is 8 to 40 in the styrene-butadiene copolymer, and the copolymer latex according to the present invention has 8 to 40 units of styrene monomers. Styrene blocks are optionally present in the copolymer. In addition, the styrene block of ordinary styrene-butadiene copolymer latex is 7
Usually, it is less than quant. The number of styrene polymers in the styrene block referred to herein can be determined by the following method. The magnetic resonance spectra of polystyrene and styrene copolymers with styrene blocks of about octamers or more show that the phenyl group protons of styrene are 7.0 ppm (protons at meta and para positions).
It is well known that it shows two broad absorption peaks at 6.5 ppm (ortho protons) and that the separation of these two peaks becomes clearer as the styrene block becomes larger. Therefore, the size of the styrene block to be determined can be determined by comparing it with the state of separation of peaks in the spectrum of polystyrene of known molecular weight. Specifically, we measured the nuclear magnetic resonance spectrum of standard polystyrene, found the integral value ratio of two absorption peaks at 6.5 ppm and 7.0 ppm, created a calibration curve of molecular weight - peak integral value ratio, and used this to calculate the The size of the styrene block can be estimated. The amount of the copolymer latex in which the styrene block is octamer to 40-mer by the above method is not particularly limited, but is usually 2 parts by weight per 100 parts by weight of the pigment.
~50 parts by weight, preferably 5 to 30 parts by weight. In addition, if the styrene block of the latex used is less than octamer, it will not be possible to achieve the objectives of the present invention, such as fast absorption of ink and little diffusion of ink dots in the lateral direction, and if it is more than 40 mer, coating will be difficult. Paper surface strength is poor. The modified styrene-butadiene copolymer of the present invention is one obtained by reacting styrene and butadiene with an acrylic ester, a methacrylic ester, etc., and an acid monomer such as acrylic acid, itaconic acid, or crotonic acid. . The pigments used in the coated paper of the present invention are not particularly limited, and include clay, kaolin, aluminum hydroxide, calcium carbonate, titanium oxide, silica, barium sulfate, zinc white, satin white, etc.
Any general coating pigment may be used, and these pigments may be used in an appropriate combination depending on the desired quality. In addition, casein, soybean protein, starches such as phosphoric acid ester starch and oxidized starch, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, and conjugated dienes such as ordinary styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer. acrylic polymer latex, acrylic ester and methacrylic ester polymer, or copolymer, ethylene vinyl acetate polymer latex, or various polymers thereof containing functional groups such as carboxyl groups. The styrene-butadiene used in the present invention can be used in general coated paper adhesives such as functional group-modified polymer latexes with monomers, thermosetting synthetic resin adhesives such as polyvinyl alcohol, olefins, maleic anhydride resins, and melamine resins. It can be used with latexes of copolymers or modified styrene-butadiene copolymers. Further, if necessary, antifoaming agents, colorants, flow modifiers, etc. may be used in common to the extent that the properties are not impaired. The coating machine of the present invention includes any blade coater, air knife coater, roll coater, brush coater, curtain coater, channel flex coater, bar coater, gravure coater, etc. that are generally used in the production of pigment-coated paper. can also be applied. The coating layer is usually 0.5 g/m ² to 40 g/m ² , preferably 5 g/m ² to 30 g/m ² . Drying after coating can be carried out by various conventional drying methods such as gas heater, electric heater, steam heater, hot air heating, etc. As the support, appropriately sized paper, unsized 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. A sheet with only a coating layer provided on the support is inferior in smoothness and resolution, and the image after multicolor recording by inkjet does not look very good.
It is not possible to obtain sufficient coating layer strength with the minimum amount of adhesive. 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 a super calender, gloss calender, etc. to provide surface smoothness and coating layer strength. It is. Supercalender equipment is used at relatively high nip pressures of around 200 kg/cm and steel finishing roll temperatures of around 70°C. The method of finishing a paper surface using a gloss calender is to press a coating layer onto an abrasive finishing drum under temperature conditions that induce a temporary plastic state on the paper surface, and the conditions for a gloss calender are generally lower than those for a super calender. , around 90Kg/cm, and is used under high temperature conditions of around 150℃. For this reason, supercalendering compresses and densifies the coated layer, which slightly reduces 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 bulkiness is desirable for purposes of the present invention as it provides better ink absorption. Furthermore, during these processes, it is necessary that the temperature applied to the coated layer from a super calender, gloss calender, etc. is between Tg -20°C and Tg +40°C of the polymer latex in the coated layer, and particularly preferably. Tg-5℃～Tg
It is in the range of +20℃. When treated at a temperature 40°C or more higher than the Tg of the polymer latex, better smoothness can be obtained, but
Fusion and film formation of the polymer latex significantly progresses, resulting in a decrease in ink absorbency, which is an important factor in ink jet suitability. Also, 20℃ below the Tg
If the temperature is lower than that, the ink absorption property is good, but the effect of heating calendering is not exhibited, resulting in a finish with poor adhesion and smoothness. 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) Smoothness Measured using a Beck smoothness tester (manufactured by Kumagai Riki Kogyo). (seconds) (2) 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) (3) Color development The sharpness of the colors printed using an inkjet device using water-based inks of four colors: cyan, magenta, yellow, and black was determined by observing with the naked eye. (4) Coating layer strength The surface strength of the coating layer was measured by printing a sample with ink with a certain tack using an RI printing suitability tester (manufactured by Mei Seisakusho), and observing the peeling of the coating layer on the sample surface. I judged the feeling. The coating layer strength becomes weaker as it goes from 〇 to ×. (5) Spreading of ink dots A 100 μm diameter droplet of aqueous inkjet ink was deposited using an inkjet printer, and the diameter of the ink image after absorption was measured. (μm) Example 1 50 parts of Brilliant 15 (precipitated calcium carbonate manufactured by Shiroishi Kogyo) and 50 parts of Whiten SB Red (ground calcium carbonate manufactured by Shiroishi Calcium) were dispersed in water with 0.3 parts of sodium polyacrylate to form a solid. A pigment dispersion with a pigment content of 68% was obtained. Polyvinyl alcohol (PVA105, manufactured by Kuraray) 3
and three types of styrene as shown in Table 1.
15 parts of butadiene copolymer latex was added to obtain three types of coating liquids each having a solid content of 58%. 7 in Table 1
In the above-mentioned method for determining the number of styrene polymers in a styrene block, the term "submerged" refers to the nuclear magnetic resonance spectrum at 7.0 ppm (meta/para position protons) and 6.5 ppm (ortho position protons) shown by the phenyl group protons of styrene. Indicates that the absorption peak of is not separated. The above type of coating liquid was applied to base paper with a basis weight of 63 g/m ² with a dry solid content of 15 g/m ² using a blade coater.
Dry in an air cap dryer at 120°C.
Furthermore, the gloss calender temperature was adjusted so that the coating layer reached a temperature comparable to the Tg temperature of each polymer latex used, and the nip pressure of the pressure roll was adjusted to 50.
Gloss calendering was performed at a speed of 50 m/min at a speed of 50 m/min to obtain inkjet recording paper. Table 1 shows the results of measuring the inkjet suitability of these recording papers.

[Table] Only the example with 14 styrene blocks had a fast ink absorption rate and sufficient surface strength. Example 2 100 parts of Univar 70 (manufactured by Shiraishi Kogyo, precipitated calcium carbonate) was dispersed in water with 0.3 parts of sodium hexametaphosphate, and further 5 parts of polyvinyl alcohol (PVA105, manufactured by Kuraray) and a styrene block were dispersed.
18 parts of methyl methacrylic acid-modified styrene-butadiene copolymer latex, which is a 14-mer and has a Tg of 60°C, was added to obtain a coating liquid with a solid content of 40%.
Next, the coated base paper with a basis weight of 73 g/m ² was coated with an air knife coater so that the dry solid content was 10 g/m ² on one side, and dried with an air cap dryer at 120°C. The paper smeared in this way was subjected to gloss calendering at five different temperatures, and the nip pressure of the pressure roll was 50.
Recording paper was obtained by adjusting the gloss calender temperature at a speed of 40 m/min at a speed of 40 m/min and adjusting the gloss calender temperature so that the surface temperature of the coated layer was as shown in Table 2. Table 2 shows the results of measuring the inkjet suitability of these recording papers.

[Table] From Table 2, when using a modified styrene-butadiene copolymer latex with a Tg of 60°C, the gloss calender temperature will not provide surface strength if the temperature is 30°C lower than the Tg, and if it is higher than 40°C. At high temperatures, the rate of ink absorption increases dramatically, making it impracticable. Example 3 Sample No. 10 was obtained by adjusting the temperature of the gloss calender for the sample of Example 2 so that the surface temperature of the coated layer was 70°C and applying a nip pressure of 70 kg/cm to the pressure roll. Table 3 shows the results of measuring ink jet suitability using sample No. 11, which was treated with a super calender steel roll surface temperature of 40°C and nip pressure of 50 kg/cm so that the ink absorption strength was almost the same as that of No. 10. .

【table】

Claims (1)

[Scope of Claims] 1. A recording paper in which an aqueous composition containing an inorganic pigment and an aqueous polymeric adhesive is coated on the surface of a support, dried to form a coating layer, and then the coating layer is finished by pressing it against a heating calendar. In the manufacturing method, the water-based polymer adhesive is a latex of a styrene-butadiene copolymer in which the styrene block is an 8- to 40-mer or a modified styrene-butadiene copolymer in which the styrene block is an 8- to 40-mer. and the styrene-butadiene copolymer or modified styrene-
A method for producing recording paper, comprising heating and calendering at a temperature ranging from 20°C lower than the glass transition temperature of a butadiene copolymer to 40°C higher than the glass transition temperature. 2. The method for manufacturing recording paper according to claim 1, wherein the heating calendar is a gloss calendar.