JP2786490B2 - Pressure-sensitive microcapsule coated sheet - Google Patents

Description

The present invention relates to a pressure-sensitive microcapsule-coated sheet useful as a pressure-sensitive image recording material.

In particular, the present invention relates to a pressure-sensitive microcapsule-coated sheet that gives improved recorded image density.

(B) Prior Art Carbon paper was used as a pressure-sensitive image recording material in the past. However, since colored coloring materials were exposed, fingers and other articles were easily colored and contaminated.

On the other hand, in recent years, colorless carbonless paper (also known as carbonless paper) having a colorless appearance using a combination of an electron-donating colorless dye and an electron-accepting color developer as image-forming active ingredients has been predominantly used. (Eg, Tokiko 46-
No. 37451).

That is, one of the image-forming active ingredients is usually contained in a microcapsule as a solution, and the donor sheet coated on the support sheet is combined with the receptor sheet coated on the other side, and pressure is applied. The microcapsules are broken, and one solution of the image-forming active ingredient is transferred from the donor sheet to the receptor sheet to cause a color-forming reaction, whereby a visible image is formed on the receptor sheet.

As the image-forming active ingredient, a colored dye or pigment can be used from the beginning (for example, JP-A-62-39844). In this case, a solution or dispersion of a colored dye / pigment is sealed in a microcapsule and applied to a support sheet to form a donor sheet. When pressure is applied in combination with a receptor sheet that does not require a color developer, the image-forming active ingredient is transferred from the donor sheet to the receptor sheet, and coloring and dyeing occur on the receptor sheet.

In such prior art, the image density obtained depends first of all on the amount of active ingredient transferred from the donor sheet side to the receptor sheet.

That is, in the case of the carbonless paper, the image-forming active ingredient on the receptor sheet side is usually arranged in an excessive amount stoichiometrically, and is transferred from the donor sheet side (material transfer). Is designed to wait.

 Therefore, the image density is determined by the transfer amount.

Also, in an example utilizing the transfer of colored dyes / pigments, it is obvious that the image density is determined by the transfer amount.

(C) Problems to be Solved by the Invention Conventionally, the rate at which the active ingredient encapsulated in the microcapsules on the donor sheet side is released by pressure rupture of the microcapsules and transfers to the receptor sheet side, that is, the transfer rate, Considerably lower than the residual rate on the donor side,
It is known that active ingredients are not efficiently used for image formation (eg, Japanese Patent Publication No. 1-14037).

Therefore, in the case of a pressure-sensitive image recording material such as carbonless paper, in order to obtain a practically sufficient image density, the amount of the image-forming effective component on the donor sheet side is considered in consideration of a low transfer rate. Has been set a great deal. In other words, resources are not being used effectively.

If the transfer rate of the active ingredient on the donor sheet side by the applied pressure is further improved, the image density is improved accordingly, and the amount of the active ingredient required to obtain the same image density can be reduced. As a result, the industrial technology has great significance.

Here, in order to explain the pressure-sensitive image recording material, a carbon-free paper which is a typical example will be described. The carbon-free paper is usually one of the image forming active ingredients (crystal violet lactone, benzoyl leucomethylene blue, malachite green). It is often an electron-donating colorless dye such as lactone, rhodamine anilinolactam, or 3-diethylamino-6-methyl-7-anilinofluoran, but is electron-accepting such as phenolic resin or a zinc salt of a salicylic acid derivative. Alternatively, one component of a redox coloring system or one component of a chelate coloring system composed of a combination of a metal compound and a ligand may be dissolved in a solvent and encapsulated in microcapsules. , Coated top sheet (donor sheet)
And a lower sheet (receptor sheet) coated with an electron-accepting developer such as acid clay, activated clay, various phenolic resins, and a salicylic acid derivative polyvalent metal salt. When applying pressure with a writing or impact printer, etc. in such a way that the application surfaces are combined so as to face each other, the microcapsules on the upper sheet of the pressurized part are broken, and the solution of the contained active ingredient is released, and % Of the color is transferred to the lower sheet, and a color is formed on the lower sheet to form a visible image (including characters, symbols, figures, and the like). At this time, by using a microcassel containing one of the active ingredients on the back surface and an intermediate sheet (receptor sheet / donor sheet) coated with the other component on the front surface, a larger number of image records can be obtained.

Other examples of the pressure-sensitive image recording material include a light-sensitive pressure-sensitive image recording material, which is a colorless dye (for example, JP-A-58-88739) or a light-curable liquid prepolymer. A sheet in which colored dyes / pigments (eg, JP-A-62-39844) are dissolved or dispersed and microcapsules containing the liquid are coated is referred to as a donor sheet.

This is subjected to image exposure to cure the microcapsules in the exposed portions. Thereafter, when the entire surface is pressed in combination with the receptor sheet, only the unexposed portions of the microcapsules are destroyed and the contents are released, and a part of the content is transferred to the receptor sheet to form an image.

Also at this time, the transfer rate is not large, and a large proportion of the active ingredient is wasted because it does not affect image formation. Although there are few documents describing a method for improving the transfer rate of the active ingredient from the donor sheet, for example, the description can be found in JP-A-57-43895 and JP-A-61-182981. In the former, wax is simply blended into the coating layer of the donor sheet. In this case, the coating layer becomes hydrophobic and water-repellent, so that the aqueous glue (adhesive) does not work, and there is a serious practical disadvantage that the glue with the divided glue, that is, bookbinding, cannot be performed. .

In the latter, a microcapsule containing only an aliphatic hydrocarbon solvent is precoated on a support sheet, and a microcapsule containing a colorless dye (coloring agent) is applied thereon, and the coating is performed twice in a convenient manner. I have. In this case, since the total capsule coating amount becomes abnormally large, the coating sheet is easily curled, and the cost of twice coating is increased.

As described above, the object of the present invention is to significantly improve the transfer rate of an image-forming active ingredient to a receptor sheet from a pressure-sensitive microcapsule-coated sheet, which is a donor sheet in a pressure-sensitive image recording material, The purpose is to find a means for maintaining the hydrophilicity of the coating layer and preventing an increase in production cost.

(D) Means for Solving the Problems The above-mentioned problem is solved by mixing microcapsules containing an image-forming active ingredient and microcapsules containing a wax on a surface of a support sheet and coating the mixture in a single layer state. The use of such a pressure-sensitive microcapsule-coated sheet as a donor sheet provided a remarkable improvement. That is,
Only one single coating solution containing two types of microcapsules
Only by applying once, the transfer rate of the image-forming active ingredient is improved, and further, since the wax is encapsulated in the microcapsules, the coating layer maintains hydrophilicity. This is an advantageous feature.

In the case of the present invention, the internal phase of the wax-encapsulated microcapsules does not contain an image-forming active ingredient and consists essentially of a wax and preferably a solvent. If no solvent is added, the capsule is less likely to be broken by pressure, and the effect of improving the transfer rate is reduced.

Examples of the microencapsulation method include, for example, a coacervation method described in U.S. Patent No. 3,041,289, U.S. Patent Nos. 4,001,140 and 4,100,103
No. 4,233,178 or Japanese Patent Publication No. Sho 42-233.
In the present invention, an interfacial polymerization method as described in JP-A-446, for example, is used, but is not limited thereto.

Examples of the wax useful in the present invention include vegetable waxes such as carnauba wax, candelilla wax, rice wax, and wood wax; animal waxes such as beeswax, spermaceti, and lanolin; petroleum waxes such as paraffin wax and microcrystalline wax. Wax, low molecular weight polyethylene or a derivative thereof, synthetic wax such as accra wax, distearyl ketone, or higher fatty acid amide such as stearic acid amide, and is a wax-like substance which is solid at room temperature.

To encapsulate one or more of these waxes in the microcapsules, the wax is preferably dissolved in a suitable solvent, desirably heated and emulsified in water with a suitable emulsifier, followed by microemulsion. Good to encapsulate.

The image-forming active ingredient is encapsulated in a microcapsule in the form of a solution according to a conventional method.

The microcapsules containing the image-forming active ingredient and the microcapsules containing the wax thus obtained are coated on a support sheet in a single-layer state. It is preferable to add a stilt material, and to prepare an aqueous coating solution containing a water-soluble polymer or latex as a binder, and apply it on a sheet such as paper or film using a coater or a printing machine.
dry.

The inner phase (core substance) of the wax-containing microcapsules is
The wax / solvent (weight ratio) is preferably in the range of 10/90 to 90/10, and more preferably in the range of 25/75 to 75/25. What is necessary is just to determine the ratio. The type of the solvent may be either aromatic or aliphatic as long as it is non-water-miscible, and is also determined experimentally in view of the compatibility between the wax and the solvent.

The preferable addition amount of the wax-containing microcapsules varies depending on the wax concentration of the internal phase of the capsules. Parts, most preferably in the range of 5 to 20 parts. When the internal phase wax concentration is lower, the amount of the capsule needs to be increased, and when it is higher, the capsule can be reduced.

(E) action (A) microcapsules containing an image-forming active ingredient,
(B) If the wax-containing microcapsules are mixed and pressure is applied to a sheet coated in a single layer, both (A) and (B) are destroyed, and both internal phases are released. At this time,
It is considered that since the wax is a low-polarity or non-polarity substance, the image-forming active ingredient, which is a polar substance, repels and is repelled to the lower paper side, thereby increasing the transfer rate. However, the effect of the present invention is not so different regardless of whether the solvent of the internal phase of the wax-containing microcapsules is aromatic or aliphatic. Was that.

Since the wax is covered with a capsule coating,
At the time of non-destruction, surface hydrophilicity is maintained. For this reason, there is no doubt that the coating layer has high wettability of the aqueous paste.

(F) Examples Hereinafter, typical examples of the present invention will be described, but the present invention is not limited thereto.

Further, "parts" in Examples are parts by weight unless otherwise specified.
Represents

Example 1. (Preparation of microcapsule) (A) Microcapsule containing image-forming active ingredient 3 parts of crystal violet lactone (electron-donating colorless dye) as an image-forming active ingredient was used as an aromatic solvent SAS N- 296 (trade name, Nippon Petrochemical Co., Ltd., high boiling point oil) was dissolved in 97 parts, and a styrene-maleic anhydride copolymer was dissolved together with a small amount of sodium hydroxide.
The mixture was emulsified in 100 parts of a 5% aqueous solution of pH 4.0 using a homogenizer.

10 parts of melamine, 25 parts of 37% formalin and 65 parts of water were adjusted to pH 9.0 with sodium hydroxide and heated to 60 ° C. to obtain a transparent melamine-formaldehyde precondensate aqueous solution. This was added to the above-mentioned emulsion, the liquid temperature was adjusted to 60 ° C., stirring was continued for 1 hour, and then cooled to room temperature.

In this way, microcapsules containing a 3% crystal violet lactone solution having an average particle size of 7.0 microns were prepared.

(B) Wax-containing microcapsules Carnauba wax, rice wax, paraffin wax L (mp44 to 46 ° C) and paraffin wax Hm.p. 68 to 70 ° C as examples of wax, and SAS N- as an example of solvent. 296 (above-mentioned aromatic solvent), n-tridecane (linear aliphatic solvent) and IP-2028 (trade name, branched aliphatic solvent manufactured by Idemitsu Petrochemical Co., Ltd.) In total, wax / solvent = 50 parts / 50
Some wax solutions were prepared by warming.

Microcapsulation was performed for 100 parts of each wax solution in the same manner as in the above (A). The particle size was around 3 microns.

Example 2 (Preparation of pressure-sensitive microcapsule coated sheet) 66 parts (solid content) of crystal violet lactone-containing microcapsules prepared in Example 1, wheat starch granules
A coating liquid consisting of 22 parts, 12 parts (solid content) of styrene-butadiene latex, and 100 parts of water was prepared as a basic coating liquid.

A required amount of the wax-containing microcapsules prepared in Example 1 was added to this basic coating solution to form a single solution.
It was applied to a high quality paper of g / m ² using a wire rod so that the amount of dye applied was about 60 mg / m ^2, and dried.

 Detailed numerical values and the like are shown in the table including the comparative examples.

Example 3. (Evaluation of transfer rate improving effect, etc.) The pressure-sensitive microcapsule-coated sheet prepared in Example 2 was evaluated as follows, including a comparative sample.

Coating surface of microcapsule coated sheet and Super CF
N40 (trade name, paper without carbon paper by Mitsubishi Paper Mills, basis weight of about 40 g / m ² )
Pressure was applied through a calender having a nip pressure of 250 kg / cm ² to color the lower sheet, and the blue reflection density of the colored sheet was measured.

For the dye transfer rate, the total amount of dye applied (mg / m ² ) was determined for a fresh sample of each microcapsule-coated sheet, and then the amount of dye (mg / m ² ) of the above-described undercolored paper sheet was determined. It was expressed as a ratio (%) of the latter to the former. The amount of the dye was determined by solvent extraction-acid coloring-absorptiometry.

For the contact angle, for a fresh sample of each microcapsule coated sheet, distilled water or practical glue (aqueous glue for carbonless paper made by Mitsubishi Paper Mills Co., Ltd.) was dropped on the coated surface, and the contact angle immediately after it was measured. It was determined by measuring using a contact angle meter. The smaller the value of the contact angle, the better the wettability of water or glue.

 The test and evaluation results are summarized in the following table.

From this table, it can be seen that the wax-containing microcapsules were added to the colorless dye (image-forming active ingredient) -containing microcapsule coating liquid and applied in a single layer. It can be seen that the density of the color image is improved, and the contact angle of the aqueous paste on the capsule-coated surface can be maintained at a good level (sample Nos. 2 to 21).

In contrast, in the comparative example (sample No. 22) in which the wax was added without being encapsulated in the capsule, the transfer rate was certainly improved, but the contact angle was abnormally large (grouping Even in the bookbinding practical test by brushing with glue, only the No. 22 paper piece did not work with glue and had poor adhesion.)

When a capsule containing only a solvent containing no wax was added (Sample Nos. 23 to 24), the transfer rate was reduced.

(G) Effects of the Invention As described above, coexistence of wax-containing microcapsules in the same layer is an extremely effective method for improving the transferability of the microcapsules containing an image-forming active ingredient under pressure. Moreover, since the hydrophilicity of the layer is not deteriorated, the gluing aptitude can be kept at a good level.

In addition, since a coated sheet can be manufactured in a single coating step, productivity is high.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41M 5/124-5/165

Claims (2)

(57) [Claims] (1) At least one side of a support sheet, (A)
A pressure-sensitive microcapsule coated sheet obtained by coating a microcapsule containing an image-forming active ingredient and (B) a wax-containing microcapsule (but not containing an image-forming active ingredient) in a single layer state. 2. The pressure-sensitive microcapsule-coated sheet according to claim 1, wherein the image-forming active ingredient is at least one of an electron-donating colorless dye, an electron-accepting developer, a colored dye and a pigment.