JPH0399880A - Pressure-sensitive copy paper for back carbon - Google Patents

Abstract

PURPOSE:To suppress the uneven application of a back carbon ink to a recording sheet, to improve setting properties of the ink and to prevent a strike through to a developing layer by setting the Bekk smoothness of a coat layer to a specific value and by specifying the oil absorbency through dripping of linseed oil. CONSTITUTION:A coat layer to be provided on the rear face of a pressure- sensitive recording color paper is 80-400 seconds in Bekk smoothness and more preferably 90-300 seconds, and is 20-100 seconds in linseed oil absorbency and more preferably 30-70 seconds. A preferred composition example for obtaining the coat layer is obtained when, e.g. a coating liquid composed of kaolin with 1mum and less mean particle size, calcium carbonate with 3mum and less means particle size and binder is applied as pigment to the rear face of a pressure- sensitive recording color paper.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to pressure-sensitive copying paper for back carbon, which has a carbonless color developing layer on the front surface and a colored carbon ink layer on the back surface, and particularly relates to a The present invention relates to a pressure-sensitive copying paper for back carbon that suppresses uneven coating on a recording sheet, has good ink setting properties, prevents strike-through to a developing layer, and has excellent copying ability.

"Prior Art" Pressure-sensitive copying paper (so-called carbonless paper) is made of electron-donating color formers (hereinafter referred to as color formers) such as crystal violet lactone and benzoyl leucomethylene blue, as well as activated clay, bentonite, phenolic resin, and aromatic carbon. It utilizes the color-forming reactivity of an electron-accepting color developer (hereinafter referred to as a color developer) such as a polyvalent metal salt of an acid, and is produced by methods such as phase separation method, interfacial polymerization method, and 1n-situ method. A top paper with color developer-containing microcapsules coated on the back side of the base paper, and a bottom paper with a color developer coated on the front side of the base paper, each coated side facing each other, and the surface of the top paper was used for writing and typewriting. - etc., it is possible to obtain a colored image on the lower paper by pressure printing. If you wish to make even more copies, insert the required number of inner sheets coated with the color developer on the front side of the base paper and microcapsules on the back side between the upper and lower sheets. You can obtain one copy.

Also, so-called self-coloring paper in which the above-mentioned microcapsules and color developer are formed as a laminated or mixed layer on the same surface of a base paper is also well known as a form of pressure-sensitive copying paper.

On the other hand, back carbon paper uses colored pigments such as black, blue, and red on the back side of copy paper, waxes such as wood wax and paraffin wax, non-drying oils such as castor oil and cylinder oil, and titanium oxide, kaolin, calcium carbonate, etc. Colored carbon ink mixed with white pigment is heated and melted, printed using a flexo printing machine or a letterpress printing machine, and then cooled and fixed. Usually, the back carbon copy is printed on plain paper such as high-quality paper. When sheets of paper are stacked and pressure is applied using a pen or a typewriter, the carbon ink in that area is transferred to the plain paper and printed.

These types of copy paper have shown remarkable growth in recent years, and their application fields are wide-ranging, including general slips, delivery slips, contract documents, computer paper, and the like. Furthermore, there are a wide variety of usage formats, including a combination of pressure-sensitive copying paper and back carbon paper. Against this background, there is an increasing demand for pressure-sensitive copying paper for carbon backing, which has both the functions of pressure-sensitive copying paper and the functions of backing carbon paper.

Pressure-sensitive copying paper for carbon-less paper has a developing layer for carbon-free paper on the surface of the support, a coating layer on the back surface, and a carbon ink layer on the coat layer. It is made by applying a coating layer to the back side, heating and melting colored carbon ink on top of it, and printing with a flexo printing machine or a letterpress printing machine.

The following qualities are particularly important for pressure-sensitive copying paper for back carbon.

■Printing must be uniform and clear.

■The carbon ink must be applied evenly and evenly to the printing surface.

■The carbon ink sets well and does not stain the white paper surface due to contact or friction.

■There is little strike-through of carbon ink.

If carbon ink is printed on the back side (base paper side) of normal carbonless base paper for pressure-sensitive copying paper for back carbon, the ink will penetrate and be absorbed into the base paper layer, resulting in poor copying ability and strike-through. It becomes worse and becomes a practical problem.

Therefore, in order to solve the above-mentioned difficulties, a coating layer is provided in advance on the back side of the pressure-sensitive copying paper for back carbon in order to fix the carbon ink.

However, the quality required for pressure-sensitive copying paper for back carbon as shown in items 1 to 2 above depends on the behavior of the non-drying oil in the carbon ink. For this reason, the back coat layer has a smooth surface that receives carbon ink uniformly, and after receiving it, works to quickly and reliably fix it, and also prevents oil from penetrating into the coat layer or the base paper layer. There is a need. That is, the back coat II is required to satisfy ink receptivity, setting properties, and barrier properties for carbon ink at the same time.

Conventionally, in order to meet these above-mentioned qualities, proposals have been made such as (method of internally adding oil-absorbing pigments to the base paper and (II) method of providing a back coating layer using a specific pigment (Japanese Patent Laid-Open No. 59-31187). However, although method (A) improves setting properties, problems remain with ink receptivity and barrier properties, and method (0) improves barrier properties and setting properties, but leaves problems with ink receptivity. The current situation is that not all qualities are necessarily satisfied, such as the quality is still unsatisfactory.

"Problems to be Solved by the Invention" The present invention suppresses uneven coating of back carbon ink on a recording sheet, improves ink setting properties (and prevents strike-through to the developing layer). , to provide a pressure-sensitive recording paper for carbon backing with excellent copying ability.

"Means for Solving the Problems" The present invention has a coating layer on the back side of color paper for pressure-sensitive recording,
Further, in the pressure-sensitive copying paper for back carbon, which has a colored carbon ink layer provided on the coat layer, the Beck smoothness of the coat i is 80 to 400 seconds, and the oil absorption by dropping linseed oil is 20 to 100 seconds. It is characterized by:

"Function" As described above, the present invention is a pressure-sensitive copying paper for back carbon having a coating layer on the back side of a coloring paper for pressure-sensitive recording, in which the coat i is defined by a specific oil absorption and a specific smoothness. be.

As already mentioned, the barrier property or receptivity to oil of the backside coating layer is an important factor in the quality of the pressure-sensitive copying paper for carbon backing.

That is, as a result of various studies by the present inventors on the oil absorption obtained by dripping linseed oil as an indicator of the oil barrier property of the back coating layer, we have found that it is possible to grasp the quality of pressure-sensitive copying paper for back carbon with good reproducibility. I found it. Here, the oil absorption by dropping linseed oil as referred to in the present invention is 0.03 m
1 of linseed oil was dropped onto the coating layer on the back side of pressure-sensitive copying paper for back carbon, and the time (in seconds) it took for this linseed oil to completely penetrate from the back side to the coloring layer on the front side was measured. .

Among the qualities required for pressure-sensitive copying paper for back carbon, copying ability and strike-through are due to the barrier properties of the back coat layer. The higher the oil absorption, the more preferable.

However, in order to improve the setting properties of carbon ink,
It is better if the carbon ink is fixed after permeating into the back coating layer, and it is better if the oil absorption of linseed oil is not too high. Also, for carbon ink receptivity, a similar level of carbon ink penetration is required.

Regarding carbon ink receptivity, the smoothness of the back coating layer also influences; when the smoothness is high, the carbon ink receptivity is good, and when the smoothness is low, the receptivity decreases and a uniform ink layer is not formed. On the other hand, if the smoothness is too high, the ink receptivity will be too good, resulting in poor setting properties and staining.

As described above, the quality of pressure-sensitive copying paper for back carbon is controlled by conflicting factors, and it has been difficult to set an appropriate quality that satisfies all of them.

Due to the above-mentioned circumstances, the present inventors conducted intensive research on the behavior of carbon ink and the characteristics of the back coating layer, and as a result, the present inventors developed a pressure-sensitive recording method for coating layers with a specific smoothness and oil absorption. They have discovered a pressure-sensitive copying paper for back carbon that has extremely excellent quality by providing it on the back side of colored paper.

That is, the coating layer provided on the back side of the pressure-sensitive recording coloring paper has a Bekk smoothness of 80 to 400 seconds, more preferably 90 to 30 seconds.
0 seconds, and the oil absorption of linseed oil is 20 to 100 seconds,
It is important that the time is more preferably 30 to 70 seconds.

As a preferred example of a formulation for obtaining the above-mentioned coating layer, for example, a coating liquid consisting of kaolin with an average particle diameter of 1 μm or less as a pigment, calcium carbonate with an average particle diameter of 3 μm or less, and a binder is applied to the back side of color paper for pressure-sensitive recording. Obtained by coating. Kaolin has the effect of suppressing excessive penetration of carbon ink, and calcium carbonate has the effect of fixing carbon ink appropriately. As the blending ratio of kaolin increases, copying performance and strike-through improve, but setting properties worsen. do. On the other hand, when the blending ratio of calcium carbonate increases, the setting property improves, but the copying ability decreases.

Therefore, in order to achieve the object of the present invention in a well-balanced manner, a blending ratio of 25 to 80 parts of kaolin and 20 to 75 parts of calcium carbonate, more preferably 40 to 80 parts of kaolin and 20 to 60 parts of calcium carbonate is desirable.

Examples of the binder used in the present invention include starch, cellulose, proteins, gum arabic, polyvinyl alcohol, styrene-maleic anhydride copolymer salt, carboxy-modified styrene-butadiene copolymer emulsion, vinyl acetate-maleic anhydride. Acid copolymer salts, polyacrylates, etc. are appropriately selected and used. Particularly for the purpose of suppressing penetration of carbon ink, a carboxy-modified styrene-butadiene copolymer emulsion with high film-forming ability is preferred.

When the binder compounding ratio is high, the oil absorption of linseed oil becomes high, and the setting property of the carbon ink to the back coating layer becomes poor. If the blending ratio is low, sufficient barrier properties will not be imparted to the back coating layer, resulting in poor strike-through.
Furthermore, the copying ability is also inferior.

Therefore, the blending ratio of the binder to achieve the object of the present invention in a well-balanced manner is 15 to 40 parts, more preferably 20 to 35 parts, based on 100 parts of the pigment.

In addition, various auxiliary agents such as a waterproofing agent, an immobilizing agent, a water retaining agent, and an antifoaming agent are also appropriately selected and blended into the coating liquid for the backside coating layer, if necessary.

There are no particular limitations on the method of applying the coating liquid that requires backside coating, and examples include air knife coater, roll coater,
A dry weight of 2 to 10
A coating liquid of g/rrf, more preferably 4 to 7 g/n-r, is applied and dried.

The method of smoothing the back coat layer is not particularly limited either, and the smoothing process is performed using a super calender, soft calender, metal calender, etc. to obtain a desired degree of smoothness.

The colored paper for pressure-sensitive copying paper used in the present invention includes, for example, U.S. Pat.
7389, Special Publication No. 40-9309, Special Publication No. 42-2
0144, Special Publication No. 49-10856, Special Publication No. 52-13
Various forms described in 27 etc. can be applied.

"Example" The present invention will be described in more detail with reference to Examples below, but it is of course not limited to these.

Further, "parts" and "%" in the examples indicate "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 [Preparation of bottom paper] 65 parts of aluminum hydroxide, 20 parts of zinc oxide, 3,5-
Mixture of zinc di(α-methylbenzyl)salicylate and α-methylstyrene-styrene copolymer (melt ratio 80/
20) 42 parts of carboxy-modified styrene-butadiene copolymer latex (48% solids) is added to a dispersion obtained by milling 15 parts of polyvinyl alcohol aqueous solution (3% solids) and 300 parts of water in a ball mill for 24 hours. A developer coating solution prepared by adding
It was coated and dried using an air knife coater so as to have the following properties: f, and then subjected to calender treatment to prepare a base sheet for pressure-sensitive copying paper.

[Creation of back coat layer]

0.2 parts of sodium polyphosphate as a dispersant was dissolved in 25 parts of water, and 60 parts of kaolin having an average particle size of 0.4 μm was added to this solution to obtain a kaolin dispersion. Next, 0.1 part of sodium polyacrylate was dissolved in 35 parts of water, and the average particle size was 2.4μ.
40 parts of calcium carbonate was added to obtain a calcium carbonate dispersion.

85 parts of the kaolin dispersion thus obtained and 75 parts of the calcium carbonate dispersion were mixed, and 30 parts of carboxy-modified styrene-butadiene copolymer latex (solid content 48%) and 40 parts of dissolved oxidized starch (solid content) were mixed. 25%) and adjusted the solid content concentration to 25%, apply the coating liquid required for back coating to the back side of the pressure-sensitive copying paper base paper with a dry weight of 5 g.
/rrT after coating with an air knife coater and drying, smoothing was performed using a super calender with a nip linear pressure of 80 kg/cm to prepare a pressure-sensitive copying paper for back carbon. The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 165 seconds, and the oil absorption of linseed oil was 47.
It was seconds.

Example 2 The nip linear pressure of the super calender is 120 kg/c
A pressure-sensitive copying paper for back carbon was obtained in the same manner as in Example 1 except that the paper was changed to m. The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 240 seconds, and the oil absorption of linseed oil was 49 seconds.

Example 3 60 parts of carboxy-modified styrene-butadiene copolymer latex (solid content 48%) and 20 parts of dissolved oxidized starch were added to the mixed dispersion of kaolin and calcium carbonate prepared in Example 1.
(solid content 25%) and adjusted the solid content concentration to 45%, the coating liquid required for back coating was applied to the back side of the bottom paper for pressure-sensitive copying paper using a blade coater so that the dry weight was 7 g/rrr. After coating and drying, nip linear pressure 80kg/cn+
A pressure-sensitive copying paper for back carbon was prepared by smoothing with a super calender.

The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 285 seconds, and the oil absorption of linseed oil was 66 seconds.

Example 4 [Preparation of self-coloring paper] Water was added to 37.5 parts of a 20% aqueous solution of a copolymer consisting of 15 mol% vinyl sulfonic acid, 5 mol% styrene, 70 mol% acrylic acid, and 10 mol% ethyl acrylate. 112゜5
20% aqueous sodium hydroxide solution to adjust the pH to 4.6, which was used as an aqueous medium for capsule production.

To this was added 105 parts of diisopropyl naphthalene (trade name Nini-113, manufactured by Kureha Chemical Co., Ltd.) in which 5 parts of crystal violet lactone was dissolved, and after emulsifying and dispersing so that the average particle size was 5 μm, the temperature of the emulsion was The temperature was raised to 70°C.

Next, the methylated methylolmelamine initial condensate (
Add 20 parts of Beckamine AI'M (trade name: 80% concentration, manufactured by Dainippon Ink Chemical Co., Ltd.), maintain the temperature of the system at 70°C for 1 hour while continuing to stir, and then cool to disperse milky white capsules. I got the liquid.

Next, 50 parts of wheat starch powder and 3 parts of pulp powder were added to this dispersion.
0 parts and 40 parts of carboxy-modified styrene-butadiene copolymer latex (solid content concentration 50%) were added, and water was added so that the solid content concentration was 23% to obtain a capsule coating liquid.

100 parts of the above capsule coating liquid (solid content) and 5 parts of the developer coating liquid
A self-coloring paper coating liquid was prepared by mixing 0 parts (solid content).

The back coat shoe coating liquid prepared in Example 1 was applied for 40 minutes in advance.
g/rrf base paper with an air knife coater so that the dry weight is 7 g/n sheets, and after smoothing with a super calender with a nip linear pressure of 120 kg/cm, the above-mentioned self-coloring paper was applied. The coating liquid was applied to the opposite side using an air knife coater so that the dry weight was 9 g/rrf to obtain a self-coloring recording paper for back carbon. The Beck smoothness of the back coating layer of the obtained self-coloring recording paper for back carbon was 150 seconds, and the oil absorption of linseed oil was 66 seconds.

Comparative Example 1 The pressure-sensitive copying paper for back carbon prepared in Example 1 was not subjected to supercalender treatment. The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 54 seconds, and the oil absorption of linseed oil was 44 seconds.

Comparative example 2 Super calender nip linear pressure 400 kg/l
A pressure-sensitive copying paper for back carbon was obtained in the same manner as in Example 1 except that the following was changed. The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 520 seconds, and the oil absorption of linseed oil was 140 seconds.

Comparative Example 3 To the mixed dispersion of kaolin and calcium carbonate prepared in Example 1, 10 parts of carboxy-modified styrene-butadiene copolymer latex (solid content 48%) and 10 parts of dissolved oxidized starch were added.
(solid content 25%) and adjusted the solid content concentration to 25%, the back coating solution was applied to the back side of the bottom paper for pressure-sensitive copying paper using an air knife coater so that the dry weight was 5 g/bore. After coating and drying, the coating was smoothed using a super calender with a nip line pressure of 80 kg/cm to prepare a pressure-sensitive copying paper for back carbon.

The back surface coating layer of the obtained pressure-sensitive copying paper for back carbon had a Beck smoothness of 125 seconds and an oil absorption of linseed oil of 14 seconds.

Comparative Example 4 80 parts of carboxy-modified styrene-butadiene copolymer latex (solid content 48%) and 30 parts of dissolved oxidized starch were added to the mixed dispersion of kaolin and calcium carbonate prepared in Example 1.
(solid content 25%) and the back coating solution adjusted to a solid content concentration of 25% was coated on the back side of the bottom paper for pressure-sensitive copying paper using an air knife coater so that the dry weight was 5 g/%. After coating and drying, smoothing was performed using a super calender with a nip line pressure of 80 kg/cm to prepare a pressure-sensitive copying paper for back carbon.

The Beck smoothness of the back coating layer of the obtained pressure-sensitive copying paper for back carbon was 210 seconds, and the oil absorption of linseed oil was 160 seconds.

[Back carbon ink printing]

Carbon ink (manufactured by Naigai Ink, for rubber protrusions) was applied to the back side of the pressure-sensitive copying paper for back carbon shown in the above Examples and Comparative Examples.
10-ink) was printed at a rate of 3 to 5 g/n, and the following quality test was conducted.

(1) Copying ability Pressure-sensitive copying paper for back carbon with carbon ink printed on the back side is layered on top of high-quality paper, a load of 600 kg/cta is applied, and the concentration of the carbon ink transferred to the high-quality paper is measured using a Macbeth densitometer (RD). -914 model, filter visual).

[The larger the number, the higher the copying ability. ]

(2) Strike-through The density of the carbon ink printed surface was measured using a Macbeth densitometer from the developing surface (opposite side to the printed surface).

[The smaller the number, the more suppressed the strike-through is.

(3) Friction stains Pressure-sensitive copying paper for back carbon with carbon ink printed on the back side is placed on top of high-quality paper, and rubbed together 5 times under a load of 4 kg/cm2 to determine the degree of stains caused by carbon ink on the high-quality paper. was determined.

〔Evaluation criteria〕

○... is hardly dirty.

Δ...Slightly dirty.

×: Extremely dirty.

(4) Carbon ink receptivity It was visually determined whether the carbon ink was evenly and uniformly printed on the back coating layer.

〔Evaluation criteria〕

○...Extremely good.

Δ...Good.

×...Bad.

The results are shown in Table 1.

Table 1 "Effects of the Invention" As is clear from the results in Table 1, the carbon back pressure-sensitive copying paper obtained in the example of the present invention has excellent copying ability and prevents strike-through and friction stains. Furthermore, it was capable of uniformly accepting carbon ink.

Claims (1)

[Claims] In a pressure-sensitive copying paper for back carbon, which has a coating layer on the back side of a colored paper for pressure-sensitive recording, and further provides a colored carbon ink layer on the coating layer, the Bekk smoothness of the coating layer is 80 to 400 seconds. A pressure-sensitive copying paper for back carbon, characterized in that the oil absorption upon dropping linseed oil is 20 to 100 seconds.