JPH0452231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording sheet, and more particularly to a recording sheet comprising a support and a coating layer suitable for a color inkjet system or the like provided on one side of the support. In recent years, attempts have been made to create color images using inkjet recording systems, and the development of hard copies thereof is rapidly progressing. However, although many proposals have been made so far regarding the recording sheet used for this purpose, no satisfactory one has yet been obtained. When a general inkjet recording sheet with a coating layer is used for color printing using the color inkjet method, ink dots of several colors overlap at the same location on the surface of the recording sheet, so the amount of ink received is lower than in the case of a single color. This causes dot disturbances and ink flow, making it difficult to reproduce a desirable image. In general, as a method to improve ink absorption,
One possible method is to use pigments with good liquid absorption, that is, generally large oil absorption, in the coating layer of the recording sheet, but although this method solves the problem of ink absorption itself, it does not improve color reproducibility. In many cases, there are disadvantages such as deterioration due to heat. In other words, the technical issues that currently need to be solved for recording sheets for color inkjet are that ink absorption is good (fast) and that ink droplets do not spread more than necessary on the surface of the recording sheet. The color density of each dot is high and clear, and it is desired that these characteristics be highly balanced. In an attempt to overcome the disadvantages of using pigments with high oil absorption, JP-A-55-11829 discloses a method of reducing the ink absorption of the surface layer and increasing the ink absorption of the lower layer. JP-A-58-110287 has fine particles (0.2 μm) on the surface layer.
A coating layer using a granulated pigment consisting of is provided, and a preferable peak of coating layer pore diameter is defined for the uppermost layer and the entire ink-receiving layer. All of these proposals are attempts to satisfy the above requirements. However, in order to realize these proposals, it is necessary to prepare two types of coating liquids containing two types of pigments with different average particle sizes, and a two-step coating process is required. The current situation is that not only is there a problem in that the production of the recording sheet is complicated, which leads to an increase in the cost of the recording sheet, but also that the effectiveness of the proposal is by no means sufficient. In view of the current situation, the inventors of the present invention have conducted intensive research on how to achieve both the above contradictory required characteristics required for color inkjet recording sheets, and as a result, the average particle diameter of the pigment used in the coating layer has been determined. The inventors have discovered that oil absorption and the appropriate aggregation state of this pigment, in other words, the formation of a porous condensed state, form extremely effective factors in solving the above technical problems, and have completed the present invention. Ivy. Regarding pigments to be used in the coating layer, pigments with large oil absorption have been proposed mainly from the viewpoint of ink absorption. However, in the present invention,
Completely different from conventional thinking, we used a pigment with a large average particle size and low oil absorption, and we made it possible for this pigment to form an appropriate aggregation state, that is, a porous condensation state, in the coating layer. It has the most significant feature. Only the present invention, which has such characteristics, has made it possible to reproduce extremely clear, high-resolution color images that were unachievable with the prior art. From the perspective of color density, it can be said that the larger the average particle diameter of the pigment, the better. However, if it exceeds 13 μm, the surface smoothness of the recording sheet will deteriorate, although this will vary depending on the surface characteristics of the support and the thickness of the coating layer. The quality of the image deteriorates and it becomes impossible to obtain a good quality image. Further, pigments with a diameter of less than 2 μm are not preferred from the viewpoint of color density. Regarding oil absorption, excessive absorption leads to a decrease in the surface strength of the coating layer, which is also unfavorable from the viewpoint of color density. Furthermore, the use of highly oil-absorbing pigments not only ultimately increases the amount of adhesive used, resulting in higher costs, but also halves the original meaning of using highly oil-absorbing pigments. The present invention is characterized by the use of a pigment with an oil absorption of 150 ml/100 g or less and an average particle size of 2 to 13 μm, but when such a pigment is used, the coating liquid after preparation is generally Stability becomes very poor and application is often impossible due to rapid settling of the pigment. Therefore, it has hitherto been difficult to use these pigments as coating pigments. The present inventors have solved these drawbacks of pigments by using a setting aid, and have also developed a coating composition that combines a setting aid and an adhesive with a pigment having an average particle size within the range specified in the present invention. It has been found that the surface of the layer can provide a highly satisfactory balance between ink absorption and color reproducibility.
That is, the coagulation aid in the present invention has extremely favorable effects in both improving the stability of coating solutions containing pigments that tend to settle and improving image reproducibility.
It is generally known that when the pigments in a coating liquid form an aggregated (condensed) state, the volume of pigment settling increases, and the coating layer obtained using such a coating liquid has a more porous structure. It is also known that In the present invention, from the viewpoint of color image reproducibility, a pigment with a small oil absorption amount and a large average particle size is used, and in order to counter the relative decrease in ink absorption caused by this, the coating layer is made to have a more porous structure. By blending a coagulation aid for this purpose, a coating layer suitable for a color inkjet recording sheet was completed. To produce the recording sheet of the present invention, first, for example, the pigment and dispersant are mixed with water to form an aqueous slurry with a high solids concentration, and then the pigment is dispersed using a dispersing machine such as a sand grinder to reduce the average particle diameter of the pigment. Adjust, add setting aid, adhesive and water,
A coating solution having a desired solid content concentration is obtained. Next, this coating solution is applied to one side of an appropriate support using an appropriate coating method so that the desired solid content is applied, and after drying the coated support, it is calendered. and use it as a record sheet. The support used in the recording sheet of the present invention may be sized paper, non-sized paper, synthetic resin film, etc., but there are no particular limitations on the material. The type of raw material used for the coating layer of the recording sheet must have an oil absorption of 150 ml/100 g or less, preferably 100 ml/100 g or less, and an average particle size of 2 to 2.
There is no particular problem if the pigment is mainly in the range of 13 μm, preferably 2 to 10 μm, but the aspect ratio (/d) of the pigment is relatively small,
The sharper the particle size distribution of the pigment, the more favorable results can be obtained. Examples of pigments used include aluminum silicate, silicic acid, aluminum hydroxide, calcium carbonate, and the like. A pigment having a desired average particle size can be easily prepared by using a dispersing machine such as a sand grinder or a homomixer. As a coagulation aid, the specific sedimentation volume of a coating solution using the above pigment is 10% compared to the specific sedimentation volume when no coagulation aid is added.
% or more and which has good redispersibility of the pigment in the coating liquid. Specific examples include alkali aluminates such as sodium aluminate and potassium aluminate, magnesium compounds such as magnesium hydroxide, magnesium oxide, and magnesium carbonate, and water-soluble polymer cationic resins, with magnesium compounds being particularly preferred. The amount of these coagulation aids added varies depending on the type, but
Generally, the amount is 0.1 to 10 parts per 100 parts of pigment. Adhesives used to hold pigments include modified starches, cellulose derivatives, protein adhesives, polyvinyl alcohol, synthetic latex, and the like. These adhesives contain 3 parts per 100 parts of pigment.
~25 copies are usually used. To form a coating layer on the support, a coating solution containing the above-mentioned components is applied using a commonly used coating machine such as a bar coater, blade coater, air knife coater, roll coater, or sprayer. It is applied onto a support and dried to obtain a recording sheet. The recording sheet of the present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these examples. Note that parts and percentages shown in the examples are by weight unless otherwise specified. First, methods for evaluating various physical properties regarding the raw materials and recording sheets shown in the following examples will be explained. (1) Average particle size Measure the particle size distribution of a slurry of pigment particles dispersed with a sand grinder or homomixer using a Coulter Counter TA model (manufactured by Coulter Electronics, Inc., USA) to determine the particle size of 50% of the cumulative volume. It was taken as the average particle diameter. (2) Oil absorption The oil absorption of pigment particles was measured according to the method of JIS K5101 (using linseed oil). (3) Specific sedimentation volume Pour 10ml of the finished coating solution into a graduated test tube, centrifuge at 2700 rpm for 10 minutes in a centrifuge to determine the sedimentation volume, and divide by the solid weight to find the specific sedimentation volume. And so. The rate of increase in this value relative to the specific sedimentation volume of the coating solution containing no coagulation aid is expressed as a percentage. (4) Redispersibility of the coating solution Pour 100ml of the finished coating solution into a sedimentation tube, leave it for 2 days, and then shake it gently by hand.The settled pigment will be easily redispersed and the state will be the same as before leaving it was judged to have good redispersibility. (5) Thickness of coating layer Coating is performed using a Mayer bar on a PET (polyethylene terephthalate) film with a thickness of 50 μm to a solid content of 20 g/ ^m2 , and the thickness of the coated sheet after drying is compared with that of the PET film. The difference was determined and used as the thickness of the coating layer. (6) Surface strength of coating layer Cellophane tape was adhered to the surface of the coating layer and slowly peeled off in a 180° direction, and the strength was determined if the coating layer was not removed on the adhesive side of the cellophane tape. (7) Color development A solid print was made in 7 colors using a Sharp IO-700 type inkjet printer, and the hue error and saturation were measured. (8) Absorption speed When a 7-color solid print is made using the Sharp IO-700 type inkjet printer, the ink absorption speed is fast if the boundary line between the adjacent two-color overlapping print area is a clean straight line without blurring. , If the ink is smeared, the ink absorption speed is slow. Also, one second after performing the above solid printing, rub the printed area with your finger,
Paper that does not get stained with ink has a fast absorption rate. (9) Circularity of dots One dot was printed using an inkjet device that discharges ink droplets with a diameter of 8 μm, and its circularity was measured. (10) Dot density Print with an inkjet recording device using black water-based ink for inkjet (using the ink attached to the A-1210 inkjet recording device manufactured by Canon Inc.) so that the diameter of the ink droplet is 80 μm, and after leaving it overnight, print the dot. The concentration of was measured using a Sakura microdensimeter (manufactured by Konishiroku Photo Industry Co., Ltd.). (11) Macbeth density Black, magenta, cyan,
The four-color yellow water-based ink (same as above) was set so that the diameter of the ink droplets was 80 μm, and the dot density was 2.5 dots/mm vertically and 3.3 dots/mm horizontally. After leaving it overnight. The concentration was measured using a Macbeth reflection densitometer RD-514 (manufactured by Macbeth, USA). Example 1 An aqueous coating solution with a solid content concentration of 40% was prepared using 100 parts of aluminum silicate (Kyowa Kagaku Kogyo Co., Ltd., Kyoword 700 Osif) as a pigment and 5 parts of polyvinyl alcohol (Gosenal T350, made by Nippon Gosei Kagaku Kogyo Co., Ltd.) as a dispersant. After making a slurry, it was dispersed using a sand grinder, and the average particle diameter of the pigment was adjusted to 9 μm. Then, adjust the pH of the coating solution to 4.0 with 1/10N hydrochloric acid.
To this was added 0.5 part of sodium aluminate as a coagulation aid (alumina content (Al ₂ O ₃ )).
Polyvinyl alcohol (same as above) was added to this so that the volume ratio of adhesive to pigment was 8:2.
Water was added to prepare a coating solution with a solid content concentration of 25%.
This liquid was applied to one side of high-quality paper with a smoothness of 80 seconds to give a solid content of 10 g/ ^m2 , and after drying, the linear pressure was 50
A recording sheet was obtained by supercalendering at Kg/cm ² . Examples 2 to 5 The average particle diameter of aluminum silicate as a pigment was set to 13, 9, 5, and 2.5 μm, respectively, 5 parts of heavy magnesium carbonate (manufactured by Kyowa Chemical Industry Co., Ltd.) was used as a coagulation aid, and the pH was not adjusted. A coating liquid was prepared in the same manner as in Example 1 except for this. This was coated on one side of the same high-quality paper used in Example 1 in the same manner as in Example 1 to obtain samples of Examples 2 to 5. Example 6 To 100 parts of heavy calcium carbonate (manufactured by Shiroishi Calcium Co., Ltd., Whiten B, average particle size 4 μm) as a pigment, 4 parts of heavy magnesium carbonate (same as above) as a coagulation aid was added, and polyvinyl alcohol (same as above) was added.
5 parts of were added to form a slurry with a solid content concentration of 30%. This was dispersed using a homomixer, a coating liquid was prepared in the same manner as in Example 2, and this was applied to obtain a sample of Example 6. Example 7 Aluminum hydroxide (Hygilite H32, manufactured by Showa Light Metal Co., Ltd.) with an average particle size of 6 μm was used as a pigment, and magnesium hydroxide (Kiyowa Suimag, manufactured by Kyowa Chemical Industry Co., Ltd., was pre-milled with a sand grinder to an average particle size of 5 μm as a coagulation aid). dispersed)
A sample of Example 7 was obtained in the same manner as in Example 2 except that 2 parts of the sample were used and the solid content concentration was 30%. Example 8 Clay with an average particle size of 4 μm (manufactured by Sieglite Co., Ltd., PF Filler) was used as a pigment, and polyamine sulfone (manufactured by Nittobo Co., Ltd., PAS) was used as a coagulation aid.
A sample of Example 8 was obtained in the same manner as in Example 2 except that 0.1 part of -H-10-L) was added. Comparative Example 1 Example 1 except that sodium aluminate in Example 1 was removed and pH adjustment was not performed.
The test of Comparative Example 1 was obtained by operating in the same manner as above. Comparative Examples 2 and 3 Average particle diameter of aluminum silicate 15 and 1.5 μm
The procedure was carried out in the same manner as in Example 2 except that the pigment was used.
Samples of Comparative Examples 2 and 3 were obtained. Comparative Examples 4, 6, 7 Comparative Examples 4,
Six and seven samples were obtained. Comparative Example 5 In Example 6, heavy calcium carbonate (manufactured by Bihoku Funka Kogyo Co., Ltd., BF-300, average particle size 15μ) was used as the pigment.
A sample of Comparative Example 5 was obtained in the same manner as in Example 6 except that m) was used. Comparative Example 8 Average particle diameter of secondary aggregate particles as pigment: 7μ
5 parts of polyvinyl alcohol was added to 100 parts of colloidal silica (manufactured by Fuji Davison Chemical Co., Ltd., Thyroid 74) of m, to give a solid content of 25%, and after dispersing with a homomixer, the same procedure as in Examples 2 to 5 was carried out, A sample of Comparative Example 8 was obtained. Comparative Example 9 The same procedure as Comparative Example 8 was carried out, except that a urea resin pigment (manufactured by Ciba Geigy, Pergo Pack M-2) with a large oil absorption and average particle diameter of 6 μm was used as the pigment, and the solid content was 15%. Nine samples were obtained. Comparative Example 10 Average particle diameter of secondary aggregate particles as pigment: 7 μm
A sample of Comparative Example 10 was obtained in the same manner as in Comparative Example 8 except that synthetic aluminum silicate (Zeolex 17S, manufactured by Coughlan Chemical Co., Ltd.) was used and the solid content was 25%. Comparative Example 11 A sample of Comparative Example 11 was obtained by adding 5 parts of magnesium carbonate as a coagulation aid to the sample of Comparative Example 8. These samples were recorded using an inkjet recording device (IO-700 manufactured by Sharp Corporation and A-700 manufactured by Canon Corporation).
1210) and the results of inkjet recording using the ink attached to these devices.
Shown in the table. As can be seen from this table, the examples equipped with the constituent elements of the present invention had no problems at all in the coating process, and were good in all aspects of color development, absorption rate, dot circularity, dot density, and Macbeth density. showed good results. On the other hand, Comparative Examples 1, 4, 6, 7
Not only did the coating process have problems, but the color density was also low, and Comparative Examples 4, 6, and 7 had slow absorption rates. It was also found that Comparative Examples 3, 8, 9, 10, and 11 had very poor color development, and Comparative Examples 2 and 5 had poor dot circularity. Furthermore, the surface strength of the coating layer of Comparative Example 11 was very weak. 【table】

Claims (1)

[Scope of Claims] 1. A pigment with an oil absorption of 150 ml/100 g or less and an average particle size of 2 to 13 μm on one side of a support, which increases the specific sedimentation volume by 10% or more when added to a dispersion of this pigment. A recording sheet for an inkjet comprising a coating layer containing a setting aid and an adhesive. 2. The recording sheet for an inkjet according to claim 1, which contains a magnesium compound as a coagulation aid. 3. The recording sheet for inkjet according to claim 1, which contains a pigment having an oil absorption of 100 ml/100 g or less. 4. The recording sheet for an inkjet according to claim 1, which contains a pigment having an average particle diameter of 2 to 10 μm.