JPH0362554B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to paper necessary for pressure-sensitive copying that can transfer onto plain paper. More specifically, the present invention relates to a plain paper transfer type pressure-sensitive copying paper with improved transfer density. Plain paper transfer type pressure-sensitive copying paper is a pressure-sensitive copying paper that has a color former and a color developer on one side of the base paper, and can form a copied image on the plain paper.
No. 16728, Japanese Patent Application Laid-Open No. 159008/1982, and Japanese Patent Application No. 26390/1982 filed on March 3, 1980, filed by one of the present inventors. The present invention involves stacking a large number of sheets of plain paper transfer type pressure-sensitive copying paper having a coating layer containing color former-containing microcapsules and a color developer on the back side of a base paper with a plain paper surface.
Alternatively, multiple sheets of plain paper transfer-type pressure-sensitive copying paper and one sheet of paper with plain paper surfaces on both sides at the bottom, or one sheet of plain paper transfer-type pressure-sensitive copying paper and a sheet of paper with plain paper surfaces on both sides at the bottom Pressure-sensitive copying in which the image is transferred to the surface of the plain paper by overlapping it with a sheet of paper, then writing on the surface of the topmost plain paper transfer type pressure-sensitive copying paper, applying pressure with a typewriter, etc. to destroy the microcapsules. In the plain paper transfer type pressure-sensitive copying paper paper used in the method, which has a plain paper surface on at least one side, it contains a filler with an average particle size of 0.2 to 2.0 μm, and the peak of the void volume distribution curve of the paper is 0.5 to 1.5 μm. This is a plain paper transfer type pressure-sensitive copying paper (hereinafter referred to as copying paper) which is characterized by having a thickness of .mu.m. Therefore, the pressure-sensitive copying method using the copying paper of the present invention is essentially different from conventional carbon-backed copying paper or carbonless copying methods in its copying mechanism. Copy paper must meet the following conditions: In other words, (1) the transfer density is high and uniform, (2) a large number of copies can be made, (3) the transfer surface does not yellow over time, and (4) the copied print does not change over time. It is. We investigated the use of commercially available high-quality paper, coated paper, or medium-quality paper as copying paper. However, with high-quality paper, it is not possible to obtain a sufficiently high and uniform transfer density, with coated paper, although a uniform transfer density can be obtained, it is not possible to make many copies, and with medium-quality paper, not only is it not possible to obtain a sufficient transfer density. Both types of paper were unsuitable for use as copying paper because of problems such as yellowing of the transfer surface over time. The present invention improves these problems. SUMMARY OF THE INVENTION An object of the present invention is to provide a copying paper sheet which has a high and uniform transfer density and which does not cause problems in the number of copies and storage stability. In order to solve the above-mentioned problems, the present inventors investigated the mechanism by which the solvent containing the coloring agent, color developer, etc. in the pressure-sensitive coating layer is transferred to the copying surface. Not only the capillary action from inside to
It was also found that the intrusion effect caused by pressure during writing or typewriter printing was also involved.
From the viewpoint of capillary action, it is preferable that the paper has many fine voids, but from the viewpoint of press-fitting action, fine voids are not preferable because they require a large press-fitting pressure. Therefore, it is considered that paper having a peak of the void volume distribution curve within a certain size range is advantageous in terms of transferability. The peak of the void volume distribution curve of paper can be changed to some extent by beating or wet pressure, but it is 2.0μ.
It is practically impossible to make it less than m. It has been found that in order to make the peak of the void volume distribution curve 2.0 .mu.m or less, it is advantageous from a technical and cost point of view to incorporate a filler having an average particle size of 0.2 to 2.0 .mu.m into the paper. In addition, although it varies slightly depending on the water content of the pulp, the density of the paper, etc., the peak of the void volume distribution curve may be less than 0.5 μm in paper containing 20% or more of filler with an average particle size of 0.5 μm or less. I'm making sure. Based on the above knowledge, the average particle size is 0.2~
As a result of examining the suitability of paper with a void content distribution curve peak of 0.5 to 1.5 μm as a copy paper, we investigated the suitability of paper with a void content distribution curve peak of 0.5 to 1.5 μm by adding a filler of 2.0 μm. The inventors discovered that when used as a copying paper, a uniform and high transfer density can be obtained, and there are no problems with the number of copies and changes over time, leading to the completion of the present invention. That is, the present invention contains a filler with an average particle size of 0.2 to 2.0 μm, and the peak of the void volume distribution curve of paper is
By adjusting the thickness to 0.5 to 1.5 μm, a copying paper sheet with improved transfer density is provided. The fillers of the present invention include clay, kaolin, talc,
These include aluminum hydroxide, calcium carbonate, titanium oxide, magnesium carbonate, alumina, activated clay, synthetic silica, zinc oxide, barium sulfate, calcium sulfate, etc., and they can be used alone or in combination. Further, as a method for incorporating it into paper, in addition to internal addition, it is also possible to use a combination of internal addition and light coating such as coating with a size press. The void volume distribution curve of paper is published in the Journal of the Paper and Pulp Technology Association (No.
It was obtained by plotting the injection amount against the pore diameter corresponding to the injection pressure using a mercury porosimeter (Carlo Erba Model 1500) according to the method described in Vol. 33, No. 5, pp. 40-41). The measurement principle of the mercury intrusion method is as follows. That is, when mercury as a non-wetting liquid is injected into a sample in a vacuum, intrusion of mercury occurs in the void where the capillary pressure is equal to the intrusion pressure. By gradually increasing or decreasing the mercury pressure and measuring the mercury level at that time, a capillary pressure-cumulative volume curve on the pressurized side or the depressurized side can be obtained. The mercury is injected through the path that is easiest to pass, regardless of the length, direction, or tortuosity of the void path. By differentiating the cumulative volume curve obtained in this way, a void volume distribution curve is obtained, and the peak of the void volume distribution curve indicates the position where the void volume frequency is highest. The copying paper of the present invention contains additives commonly used in paper making, such as dyes, sizing agents, dry paper strength enhancers, wet paper strength enhancers, fixing agents, and retention aids, as required. If necessary, surface treatment can be carried out by using starch, polyvinyl alcohol, etc., or a combination thereof with a styrene-maleic acid-based, acrylic-based, polyurethane-based, or α-olefin-maleic anhydride-based surface sizing agent. As in the present invention, a filler with an average particle size of 0.2 to 2.0 μm is contained, and the peak of the void volume distribution curve is 0.5 to 1.5 μm.
m, it is possible to obtain copy paper with uniform and high transfer density. The present invention will be described in detail below with reference to Examples. Note that the present invention is not limited to the examples. In the Examples, all parts and percentages are by weight. Example 1 A paper weighing 50 g/m ² containing the following components in the following content was hand-sheeted, and after applying a wet pressure of 7.0 Kg/cm ² to the wet paper,
Dry on a cylindrical dryer at 105°C. A 7:3 weight ratio mixture of hardwood bleached kraft pulp and softwood bleached kraft pulp beaten to 350 ml with a beater at Canadian standard water level: 100 parts calcium carbonate (average particle size of 0.2, 0.5, 1.0 and
2.0 μm): 30 parts Cationic starch (Kate 2, manufactured by Oji National Co., Ltd.): 1.0 parts Epoxidized higher fatty acid amide (NS manufactured by Kindai Kagaku Co., Ltd.)
-715): 0.4 parts Oxidized starch (manufactured by Nihon Shokuhin Kako Co., Ltd.) was added to the obtained handmade paper.
MS-3800) was subjected to size press treatment so that the adhesion amount was 1.5 g/m ² , and supercalender treatment was performed so that the density of the paper was 0.80 g/cm ³ to obtain copy paper. This sample was divided into 1-7 and 1-1 particles, respectively, depending on the average particle size of the internally added calcium carbonate.
2, 1-3 and 1-4. Note that the filler content in the paper was 15%. Example 2 Three types of copy paper sheets were produced in exactly the same manner as in Example 1, except that 30 parts of each of the following fillers having an average particle size of 1.0 μm were added instead of calcium carbonate. The internally added fillers were clay, kaolin, and talc, and these samples were designated as 2-1, 2-2, and 2-3, respectively. Example 3 In Example 1, the average particle size of calcium carbonate was
Handmade paper was manufactured using the same method except that the oxidized starch and the average particle size were 1.0 μm, except that the amount added was 13.5 parts.
A liquid containing calcium carbonate in a weight ratio of 2:1 was size-pressed so that the adhesion amount of calcium carbonate was 0.75 g/ ^m2 , and supercalendered in the same manner as in Example 1 to obtain copy paper. Ta. This sample is designated as 3-1. Comparative Example 1 In Example 1, the same method was used except that the average particle size of calcium carbonate was changed to 3 levels: 0.1 μm and 30 parts added, 0.5 μm and 40 parts added, and 5.0 μm and 30 parts added. Manufactured various types of copy paper. These materials are 1-6, 1-1, respectively.
and 1-5. Comparative Example 2 Commercially available wood-free paper (basis weight 52.3 g/m ² ), coated paper (basis weight 64.0 g/m ² ), and medium-quality paper (basis weight 523 g/m 2 )
m ² ) are used as samples, and are respectively designated as 4-1, 4-2, and 4-3. The results are summarized in Table 1.

【table】

[Table] The number of sheets transferred was good, except for the coated paper of sample number 4-2, which had a problem with the transfer density decreasing with the number of sheets as mentioned above. There was no problem except for the medium-quality paper in -3. Further, there was no problem with the aging of the printed characters that were copied. From the above results, it is found that the filler contains filler with an average particle size of 0.2 to 2.0 μm, and the peak of the void volume distribution curve is 0.5 to 2.0 μm.
It can be seen that the paper having a thickness of 1.5 μm has a high transfer density and is a copy paper that does not cause any problems with regard to the number of sheets transferred or yellowing over time. (Note 1) The average particle size of a filler is the particle size at which the weight cumulative particle size distribution is 50%. (Note 2) The transfer density was measured on a plain paper transfer type pressure-sensitive copying paper obtained by applying a coating solution prepared as described below to the back side of the sample at a concentration of 6 g/m ² . The coated side of this plain paper transfer type pressure-sensitive copying paper was placed face down on an uncoated sample, and printing was performed using an IBM 820 typewriter at printing pressure No. 5, and the density of the blue transferred image on the uncoated sample was measured using Sakura Density. It was measured using a tometer PDA45 (manufactured by Konishirokusha). Unless the densitometer reflection density index of the recorded image transferred by the pressure-sensitive copying method using the copying paper of the present invention is 0.41 or more, it is not practical to read or identify the recorded image. (Method for producing coating liquid) A microcapsule dispersion containing a coloring agent was prepared as follows. A color former solution was prepared by dissolving 20 parts of crystal violet lactone in 300 parts of diisopropylnaphthalene. In this oily solution, as a wall-forming substance,
Hexamethylene diisocyanate and trimethylolpropane adduct containing isocyanate groups 60
part was added and dissolved. This oily solution was added to 550 parts of water at 20°C in which 30 parts of carboxymethyl cellulose and 30 parts of polyvinyl alcohol were dissolved, with vigorous stirring, and oil droplets with a diameter of 4 to 8 μm were formed.
It was diluted by adding 500 parts of water. Encapsulation was completed by adding 60 parts of ethylenediamine and raising the temperature of the system to 70°C. A microcapsule dispersion containing a color developer was prepared as follows. 100 parts of a 10% aqueous solution of ethylene-maleic anhydride copolymer, 10 parts of urea, 1 part of resorcinol, and 200 parts of water
A mixed solution was prepared, and the pH was adjusted to 3.5 using a 20% aqueous sodium hydroxide solution. 60 parts of P-phenyl-phenol formalin resin was dissolved in 140 parts of diisopropylnaphthalene to prepare a color developer solution. The color developer solution was emulsified and dispersed in the above mixed aqueous solution until the oil droplets were 3 to 5 μm in size, and then 37% formalin aqueous solution was added.
25 parts were added and the temperature of the system was maintained at 55°C while stirring. After reacting for 2 hours, the system was cooled down to PH9.5.
and finished encapsulation. Microcapsule dispersion containing the above coloring agent 91
23 parts of a microcapsule dispersion containing a color developer;
Fatty acid amide 0 (manufactured by Kao Soap Co., Ltd., oleic acid amide, unsaturated fatty acid amide with 18 carbon atoms) 30
17 parts of % dispersion, 67 parts of 45% paraffin wax emulsion, 100 parts of 25% dispersion of castor wax
1 part were mixed and stirred, and water was added to make the solid content 20% to prepare an aqueous dispersion coating solution.

Claims (1)

[Claims] 1. Multiple sheets of plain paper transfer type pressure-sensitive copying paper having a coating layer containing color former-containing microcapsules and color developer on the back side of base paper with a plain paper surface, or multiple sheets of plain paper transfer type pressure-sensitive copying paper. and one sheet of paper with plain paper sides on both sides at the bottom, or one sheet of plain paper transfer type pressure-sensitive copying paper and one sheet of paper with plain paper sides on both sides at the bottom, and then a sheet of paper with plain paper sides on both sides at the top. Paper transfer type Pressure-sensitive copying A plain paper transfer type having a plain paper surface on at least one side, used in a pressure-sensitive copying method that transfers an image to a plain paper surface by applying pressure to the surface of the paper and destroying the microcapsules. Pressure-sensitive copying paper contains a filler with an average particle size of 0.2 to 2.0 μm, and the peak of the paper void distribution curve is 0.5 to 1.5 μm.
A plain paper transfer type pressure-sensitive copying paper paper characterized by: m.