JPH01216882A - Upper sheet for pressure-sensitive copying paper to be printed on both sides - Google Patents

Abstract

PURPOSE:To improve offset of a printed image from occurring due to strike through, by using a raw paper having an opacity not less than a specified value as an upper sheet for a pressure-sensitive copying paper to be printed on both sides thereof in which microcapsules each containing an oil drop with an electron-donative organic color developer dissolved therein are applied to one side of a raw paper having a paper thickness not more than a specified value. CONSTITUTION:A raw paper having an opacity (JIS P 8136) of at least 68% is used as an upper sheet for a pressure-sensitive copying paper to be printed on both sides thereof in which microcapsules each containing an oil drop with an electron-donative organic color developer dissoled therein are applied to one side of a raw paper having a paper thickness of not more than 70mum. If the paper thickness is more than 70mum, the opacity is less than 68%, and a strike through problem is generated. The raw paper with the thickness of not more than 70mum and the opacity of at least 68% can be obtained by, for exam ple, a method wherein at the time of conditioning a pulp for making the raw paper therefrom, an inorganic or organic pigment is added to the pulp so that the raw paper produced will have an opacity of at least 68%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a top paper for pressure-sensitive copying paper, and more particularly to improvement of show-through due to strike-through of a top paper for printing on both sides.

(Prior Art) Pressure-sensitive copying paper generally uses an electron-donating organic coloring agent such as crystal violet lactone or benzoyl leucomethylene blue, and a color developer such as activated clay, phenolic resin, or polyvalent metal salt of an aromatic carboxylic acid. Copying paper that utilizes the color reaction of carbon dioxide has shown remarkable growth in recent years, and its applications are wide-ranging, with a focus on general slips, contract documents, computer paper, etc.

When used for slips, contract documents, etc., various types of printing may be done on both sides of the top, middle, and bottom sheets of pressure-sensitive copying paper depending on the purpose. However, when using thin base paper for each of the above-mentioned papers that make up pressure-sensitive copying paper, depending on the purpose of use, the inner paper and bottom paper are coated with a color developer, so the color developer However, especially in the case of top paper coated only with microcapsules, there is a problem in that the printed images on both sides show through from the opposite side (strike-through).

This problem becomes more noticeable as the paper becomes thinner.
When the paper thickness is less than 70 μm, the printed image becomes extremely difficult to read.

For example, when pressure-sensitive copying paper is used for terms and conditions such as regulations, one side may be printed with printing ink of low color density, such as eye color, gray color, or sepia color. In such a case, if the opposite side is printed with ink with a high color density, this high-density printed image will be reflected on the opposite side by a strike-through phenomenon, making the printed image with a low color density difficult to read. Also, when printing with high-density ink on both sides, the printed images of the opposite side appear on the opposite side due to a strike-through phenomenon, and -
Difficult to decipher layers.

(Problems to be Solved by the Invention) An object of the present invention is to improve the show-through of printed images due to strike-through when double-sided printing is performed on top paper for pressure-sensitive copying paper using base paper with a paper thickness of 70 μm or less. That is.

(Means for Solving the Problems) The present invention provides a pressure-sensitive copying machine in which microcapsules containing oil droplets in which an electron-donating organic coloring agent is dissolved are coated on one side of a base paper having a paper thickness of 70 μm or less, and printed on both sides. This paper is characterized by using a base paper with an opacity (JIS P 8138) of 68% or more.

(Function) In the above configuration, the paper thickness of the base paper for the top paper is specified as 70μ, because base paper of 70μ or more has an opacity of 68% or more based on the thickness, and this can be used as is for printing. This is because, even if the paper is configured, show-through of the printed image will not be a problem. That is, the bleed-through phenomenon of printed images is a problem that only begins to occur on base paper with a paper thickness of 70 μm or less. When the paper thickness is less than 70 μm, the opacity is also less than 68%, which causes the problem of strike-through.

Therefore, as a means for increasing the opacity of base paper with a paper thickness of 70μ or less to 68% or more, for example, inorganic or organic pigments are added to the base paper during pulp tonality at the papermaking stage so that the opacity of the base paper is 68% or more. It is best to contain it so that Incidentally, although the pigment for this purpose is not specified, if it is necessary to impart an opaque effect without increasing the pigment content, it is desirable to use a pigment with as high a refractive index as possible.

Furthermore, when using pigments with high oil absorption among pigments, they have excellent absorption of printing ink, which has the effect of increasing opacity and preventing printing ink from penetrating in the longitudinal direction of the base paper. , as a result, the impact of strike-through can be eliminated. However,
If a large amount of a highly oil-absorbing pigment is used, the oil that is released when the capsule breaks during copying and should be transferred to the color developer is adsorbed by the oil-absorbing pigment, reducing the transfer rate and resulting in poor color development. There is a risk that it will happen. Therefore, it is desirable to refrain from using large amounts of highly oil-absorbing pigments.

Pigments that increase opacity include metal oxides such as titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, and silicon oxide, metal carbonates such as magnesium carbonate, calcium carbonate, and barium carbonate, and metal sulfates such as barium sulfate. , kaolin, clay, inorganic pigments such as hydrated silicic acid, hydrated aluminum silicate, and calcium silicate, and organic pigments, and these may be used alone or in combination.

The amount of these pigments to be added cannot be specified because the opacity varies depending on the type of pigment and the thickness of the base paper. Therefore, the amount added is based on the opacity (JIS P 8183) for base paper with a thickness of 70μ or less.
) should be added so that it is 68% or more.

Examples of the present invention will be described below, but it goes without saying that the present invention is not limited only to these examples.

Example 1 [Preparation of capsule coating liquid] Ethylene maleic anhydride copolymer [EMA-31J manufactured by Monsanto Chemical Co., Ltd.] was placed in a stirring mixing container equipped with a heating device.
) was added thereto, and the pH was adjusted to 4.0 with a 20% caustic soda aqueous solution to prepare an aqueous medium.

A capsule core material obtained by dissolving 5 parts by weight of crystal violet lactone in 100 parts by weight of diisopropylnaphthalene was added to the above aqueous medium and emulsified and dispersed so that the average particle size was 5 μm.

Separately, 10 parts by weight of melamine and 1 part by weight of glycine were added to 30 parts by weight of formalin and heated to 60°C to prepare a melamine prepolymer liquid. This prepolymer liquid was added to the emulsified dispersion liquid heated to 60°C, and the system was heated to 70°C and reacted for 3 hours while stirring. The synthetic resin wall capsule was conditioned by lowering the temperature to room temperature. To the thus obtained capsule dispersion, 75 parts by weight of wheat starch and 25 parts by weight (solid content) of dissolved oxidized starch were added to each 100 parts by weight of the core substance in the capsule to prepare a capsule dispersion.

[Creating the top paper]

The above capsule coating liquid was applied to paper thickness 54μ, opacity (JIS
P 8138) on one side of 74% base paper by dry weight.
．． The coating was coated and dried to a thickness of 0.087 m to obtain a top paper for pressure-sensitive copying paper.

[Printing on the capsule coating surface]

Partial off-cent edge printing and character printing were performed on the capsule-coated side (back side) of the above paper.

(The ink used was the black ink "Nuuchi Numpiwa F Gloss 85" manufactured by Dainippon Ink ■, and the printing machine was Business Form Printing arl'Nn+J manufactured by Mei Seisakusho II.) [Printing on the non-capsule coated surface] The above printing was performed. Lines and text were printed on the opposite side (front side) of the top paper. (The same ink and printing machine were used as above) [Status of show-through due to strike-through] Comparative example 1 as shown in the attached table [Creation of upper paper] The above capsule coating liquid was applied to paper thickness 54μ, opacity (JIS
A top paper for pressure-sensitive copying paper was obtained in the same manner as in Example 1, except that 65% of P 8138') was coated on the base paper. Printing on the coated surface] Printed in the same manner as in Example 1 [Status of show-through due to strike-through] See attached table Note) *Print density of the solid printed surface Value measured by a Macbeth densitometer *Printing density Show-through Density The print density of the solid printed side measured from the opposite side using a Macbeth densitometer ○ indicates a difficult condition. There is no problem in reading. ×... The show-through is severe and it is extremely difficult to read. However, there is no problem of show-through of the printed image due to the strike-through phenomenon. Therefore, the printed image on both sides is not affected by show-through (can be clearly read) by the printed image on the opposite side.

Claims (1)

[Claims] (1) In top paper for pressure-sensitive copying paper, in which microcapsules containing oil droplets containing an electron-donating organic coloring agent are coated on one side of a base paper with a paper thickness of 70 μm or less and printed on both sides, the opacity ( A top paper for pressure-sensitive copying paper, characterized in that a base paper with JISP8138) of 68% or more is used.