JPH11105416A - Microcapsule sheet for pressure-sensitive recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the contamination resistance at the time of high temperature storage without spoiling the recording property by a method wherein when a color-developing agent microcapsule for a film material consisting of a urea/ formaldehyde resin is applied, the paper surface of a base paper is adjusted to a specified range. SOLUTION: As a base paper, as long as the paper surface pH is in a range of 6-9, any paper can be used. When the paper surface pH is less than 6 or more than 9, in either case, the contamination resistance is not improved. As a paper with the paper surface pH of 6-9, there is a neutral paper for which calcium carbonate is made a paper internal filling material. Also, a paper on the surface of which a pH regulating agent such as a water-soluble salt is applied, can be used. Then, a color-developing microcapsule to be used comprises a film material of a urea/formaldehyde resin, and on the coating layer, a binder, a stay material and an assistant or the like can be used in addition to the capsule. Also, as the coating method, an air knife coater and a bar coater or the like can be appropriately selectively used. By this method, the contamination resistance at the time of high temperature storage can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pressure-sensitive recording paper,
In particular, the present invention relates to a pressure-sensitive recording microcapsule sheet of an upper paper type and a middle paper type, which is excellent in stain resistance during high-temperature storage without impairing recording performance.

[0002]

2. Description of the Related Art Pressure-sensitive copying paper is based on a color former microcapsule composition containing as a main component a microcapsule containing an oily substance in which an electron-donating almost colorless organic compound (hereinafter referred to as a color former) is dissolved. An upper paper coated on one side of the paper,
One side of the base paper is coated with a developer composition mainly composed of an electron-accepting compound (hereinafter referred to as a color developer) that causes the color former to be colored when it comes into contact with the color former, and the other side is coated. And medium paper coated with a color former microcapsule composition, and lower paper coated with a color developer composition on one side of a base paper. In general, upper paper-lower paper or upper paper-middle paper-lower paper are used in this order in combination so that the colorant microcapsule composition coated surface and the developer composition coated surface are in contact with each other. The microcapsules are broken by the pressure, and the oil in which the color former is dissolved is transferred to the color developer layer, and the color is developed by reacting with the color developer. In addition, a self-coloring type pressure-sensitive copying paper in which a coloring agent microcapsule and a color developing agent are coated on the same surface of a base paper to enable pressure-sensitive recording with one sheet is also known as one form thereof.

[0003] Pressure-sensitive copying paper is used for various slips and is used as a copying set of upper and lower sheets or a copying set in which a required number of medium sheets are sandwiched between upper and lower sheets. These copy sets can be easily taken out one at a time from the slip spelling, and the sheets of the copy set are adhered and stored so that they do not fall apart and are separated one by one with the minimum necessary force. ing.

If the microcapsule coating layer and the color developing agent layer are stacked in contact with each other in this manner, for example, when transported by car in summer, the color developing agent layer is exposed to high temperatures and becomes colored and contaminated. In some cases, the value of the product was lost. Further, when the middle paper is taken up, the same phenomenon is observed when the colorant microcapsule coating layer and the color developer layer come into contact with each other and are transported overseas by ship. On the other hand, by increasing the thickness of the capsule wall or reducing the diameter of the capsule to increase the strength of the entire capsule, the stain resistance can be improved, but at the same time, the recording performance is impaired. On the other hand, the same effect can be expected by increasing the amount of the capsule protective material to be blended in the capsule coating layer called the stay material, but a decrease in the recordability was still unavoidable.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an upper paper and a medium paper type microcapsule sheet for pressure-sensitive recording which is excellent in stain resistance during high-temperature storage without impairing the recording performance. I do.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, it has been found that the heat resistance of the color former microcapsule itself of the film material made of urea / formaldehyde resin deteriorates due to acidity. Further, although the cause is unknown, it was found that the heat resistance as a color-developing agent microcapsule-coated paper deteriorated even in alkaline. Furthermore,
The pH dependence of the heat resistance of the capsule itself can be adjusted by the pH of the base paper, and the stain resistance during high-temperature storage is good when the paper surface pH of the base paper coated with the color former microcapsules is in the neutral to slightly alkaline range. The inventors have found that the present invention is improved, and arrived at the present invention. That is, the present invention relates to a pressure-sensitive recording microcapsule sheet having a coating layer containing a microcapsule of a film material composed of a urea / formaldehyde resin encapsulating an electron-donating color former on one surface of a base paper,
The present invention relates to a microcapsule sheet for pressure-sensitive recording, wherein the base paper has a paper surface pH of 6 to 9.

In the present invention, the problem that the stain resistance of the pressure-sensitive copying paper at the time of high-temperature storage is reduced when the color forming agent microcapsules of the film material composed of urea / formaldehyde resin is applied is reduced. By adjusting the pH to a range from neutral to slightly alkaline, the stain resistance of the color developer layer during high-temperature storage is improved without impairing the recording properties.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The base paper in the present invention is not particularly limited as long as the paper surface pH is 6 to 9, and those manufactured by a method known in the papermaking field can be used. Generally, paper is produced by using a pulp made of vegetable fiber as a main raw material, adding various additives such as fillers and sizing agents as needed to prepare a pulp slurry, and making the paper with a fourdrinier paper machine or the like. The filler is usually contained in the pulp slurry at about 3 to 30% by weight.

In the present invention, neither when the paper surface pH is less than 6 nor when it is greater than 9, the stain resistance is not improved. As paper having a paper surface pH of 6 to 9, neutral paper using so-called calcium carbonate as a filler in paper is known. Further, without using an alkaline filler such as calcium carbonate as a filler in the paper, disclosed in JP-A-5-287694, JP-A-5-31598, and JP-A-6-73692, Paper of a type coated with a pH adjusting agent such as a water-soluble salt can also be used. In the case of this type of neutral paper, the filler contained in the paper preferably has a pH of 4 to 8 when 10% by weight of the filler is dispersed in water. For example, kaolin, illite, dioxide Titanium, plastic pigment and the like can be mentioned, and kaolin and illite are particularly preferable. Examples of the water-soluble pH adjuster include sodium hydrogen carbonate,
Examples thereof include alkali metal salts of weak acids such as sodium carbonate, potassium carbonate, disodium hydrogen phosphate, and sodium phosphate. Particularly preferred are sodium hydrogen carbonate, sodium carbonate, and disodium hydrogen phosphate.

The color former microcapsules used in the present invention comprise a urea / formaldehyde resin film material. The method for producing the microcapsules may be a usual method known in the field of pressure-sensitive recording, as described in detail in JP-A-53-84882. The particle size of the microcapsules is 1 to 10 μm, preferably 2 to 8 μm.
It is. In the microcapsule coating layer, in addition to capsules,
Binders, stays, auxiliaries and the like can be used. As the binder, natural and synthetic polymers such as polyvinyl alcohol, methyl cellulose, starch, and styrene / butadiene latex can be used alone or in combination of two or more. The stay material is added as a protective material for the capsule as described above, and for example, starch particles, cellulose particles, and the like can be used. The size of the stay material is usually about 2 to 5 times the capsule diameter. Auxiliaries include fluidity modifiers, pH adjusters, defoamers, preservatives,
A coloring agent, a waterproofing agent, and the like can be appropriately added.

The coating method can be appropriately selected from coating methods using known coating machines such as an air knife coater, a bar coater, a curtain coater and a roll coater.

The coating amount of the microcapsule coating layer is not particularly limited as long as the recording property is within a predetermined range.
Although it varies depending on the prescription and the like, it is about ² to 6 g / m ² .

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Unless otherwise specified, parts and% described below indicate parts by weight and% by weight, respectively. In addition, the test, the measuring method, and the evaluation standard performed in the Example and the comparative example are as follows.

(1) Color-forming property The upper paper and the lower paper are processed at a combined pressure of 30 kg / cm ² , partially colored, and the color density 24 hours later is measured at 9 points using a Macbeth densitometer RD-914. The average value was shown. (2) Stain resistance at high temperature storage Combination of upper paper and lower paper under a load of 30 g / cm ² and evaluation of the stain resistance of the lower paper at high temperature (100 ° C., 24 hours) by color development after processing. did. ：: Little color development Δ: Slight color development ×: Remarkable color development

[Preparation of Capsule Slurry] To 160 parts of a 5% aqueous solution of an acrylic copolymer emulsifier, 10 parts of urea and 1 part of resorcinol were added and dissolved by stirring. On the other hand, 80 parts of diisopropylnaphthalene in which 3.5% crystal violet lactone was dissolved was added to the above aqueous solution, vigorously stirred and emulsified to obtain an O / W type emulsion having an average oil droplet diameter of 5 μm. After adding 22 parts of a 37% aqueous formaldehyde solution to this emulsion under stirring, the temperature of the system was heated to 55 ° C., and the temperature was maintained under stirring for 2 hours. Thereafter, the temperature was returned to room temperature to obtain a capsule slurry, which was adjusted to a solid concentration of 25%.

[Preparation of Coloring Agent Layer Coating] 35 parts of starch granules, 400 parts of capsule slurry and 180 parts of 10% polyvinyl alcohol were mixed with 200 parts of water while stirring sequentially, and water was added to make a final concentration of 18%. .

[Preparation of Developed Color Sheet] Zinc 3,5-di (α-methylbenzyl) salicylate was uniformly dispersed by a sand grinder to obtain a 20% dispersion having an average particle size of 2 μm.
Further, 50 parts of light calcium carbonate was added to 50 parts of the dispersion.
% Dispersion solution and 100 parts of water were added and dispersed, and then 60 parts of a 10% aqueous solution of polyvinyl alcohol and 35 parts of a 40% styrene-butadiene latex were added to give a final concentration of 25%. One side of 50 g / m ² acidic high-quality paper was coated with the above coating material at a solid content of 6 g / m ² using an air knife coater, and used as a lower sheet of pressure-sensitive recording paper.

Examples 1 to 3 and Comparative Examples 1 to 3 Each of the base papers shown in Table 1 was coated with a color former layer coating material at a solid content of 4 g / m ² by an air knife coater to obtain a pressure-sensitive recording paper. The paper was evaluated as an upper sheet. In Table 1, the filler dispersion pH is 10% by weight of the filler.
Represents the pH of the dispersion when water is dispersed in water.

[0019]

[Table 1] Table 1

[0020]

The microcapsule sheet for pressure-sensitive recording of the upper paper and the middle paper type of the present invention is excellent in stain resistance during high-temperature storage without impairing the recording properties, and is of extremely high practical value.

Claims (2)

[Claims] 1. A pressure-sensitive recording microcapsule sheet comprising a base paper provided with a coating layer containing a microcapsule of a film material made of a urea / formaldehyde resin encapsulating an electron-donating color former on one surface of the base paper. Base paper pH is 6 ~
9. A microcapsule sheet for pressure-sensitive recording, which is 9. 2. The method according to claim 1, wherein the base paper contains a filler, and 10% by weight of the filler is dispersed in water.
The pressure-sensitive recording microcapsule sheet according to claim 1, wherein H is 4 to 8.