JPH0720735B2 - Thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-sensitive recording material utilizing a color-forming reaction between a leuco dye and a developer.

[Problems to be Solved by Conventional Techniques and Inventions] A so-called two-component thermal recording material utilizing a color reaction between a colorless or light-colored electron-donating dye precursor and an electron-accepting compound is an electron-donating dye precursor. It is produced by dispersing a body and an electron-accepting compound in the form of fine particles, mixing an adhesive, a pigment, a wax, etc., and applying the mixture to a support such as paper, synthetic paper, a synthetic resin film, etc., and drying. A color image record is obtained by utilizing the color reaction that occurs when one or both of them are melted or vaporized by heating with a means such as a hot pen or a thermal head.

These two-component thermal recording materials have a primary color and do not require development, can be printed out using a relatively simple and compact device, are easy to handle, and have a high color density. It has a great utility value because it can be easily used for heat-sensitive recording materials of various coloring colors.

Therefore, it is most widely used as a recording material. In recent years, in particular, the use in facsimiles, computer output, recorders for medical measurement, CAD printer paper, and label fields such as POS has become remarkable.

However, when such a thermal recording material is continuously subjected to thermal printing one by one by a recording device having an automatic paper feeding mechanism, static electricity is generated due to friction between the thermal recording materials and becomes charged. Therefore, in the case of sheet type thermal paper, 2 to 4
Sheets are fed in multiple layers, which may cause a failure of the thermal head unit or paper feeding unit. Further, the generated static electricity may damage the thermal head.

In order to solve these problems, it has been proposed to form a coating film-a so-called backcoat layer-containing a conductive agent that reduces the electric resistance value on the surface opposite to the heat-sensitive layer-coated surface.

As the back coat layer, JP-B-62-33673 discloses the use of a styrene-based polymer having an aliphatic quaternary ammonium group as a conductive agent. However, the water resistance is insufficient with the conductive polymer alone, and further, the swelling of the back coat layer occurs under high humidity, and blocking between the front surface and the back surface occurs, thereby impairing the commercial value. In addition to this, it has been announced that an alkali salt of an isobutylene-maleic anhydride copolymer is used (JP-A-55-9091), but this case is also insufficient in water resistance.

Another problem is that after printing for a certain period of time, when the temperature of the thermal head rises and printing is stopped and reprinted, the back coat layer adheres to the platen roll due to heat,
Printing failure may occur, and improvement in this respect has been desired.

The present invention aims to improve such problems.

[Means for Solving the Problem] The present invention provides a backing containing a silica-containing acrylic emulsion and polystyrene sulfonate as main components on the back side of a heat-sensitive layer forming surface containing a leuco dye and a color developer of a support. The present invention relates to a heat-sensitive recording material having a coat layer.

In the present invention, the polystyrene sulfonate contained as one of the main components of the back coat layer formed on the back surface of the support acts as a conductive agent, and sodium polystyrene sulfonate, ammonium polystyrene sulfonate, etc. can be used. Polystyrene sulfonate is an anionic conductive agent, and therefore is superior in compatibility with an adhesive, particularly an emulsion adhesive, as compared with a cationic conductive agent containing a quaternary ammonium group or the like.

As the adhesive, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid ester, polymethacrylic acid ester, ethylene / vinyl acetate copolymer can be used. It is conceivable that heat resistance is particularly required in this application, and therefore, in the present invention, a silica-containing acrylic emulsion, which is the other main component of the back coat layer, is contained as an adhesive, and both water resistance and heat resistance are included. It is necessary to have the characteristics of

The hydrophilic polymer substances conventionally proposed and used for this purpose are not suitable because they have insufficient water resistance. On the other hand, synthetic resin emulsions are preferable in terms of water resistance, but have a problem of poor heat resistance. .

In the present invention, by using the silica-containing acrylic emulsion, this problem can be solved. The silica-containing acrylic emulsion can be obtained by dropping a polymerization initiator and an acrylic monomer into an aqueous solution in which colloidal silica is dispersed and performing emulsion polymerization. In this silica-containing acrylic emulsion, silica was contained in the emulsion particles, whereby the heat resistance of the dry film was greatly improved. In addition, the result that the heat resistance of the colloidal silica after addition after the emulsion polymerization was inferior to that of the emulsion polymerization in the presence of the above silica was obtained.

Figure 1 shows the experimental results (penetration mode) based on the penetration method by TMA (Thermo Mechanical Analyzer). The evaluation by this method is considered to be the most appropriate for evaluation of heat resistance. In Fig. 1, the measurement conditions by the TMA method are as follows: TMA range: 500 μm-fs, heating rate: 5
C / min, load: 640 g / cm ² , atmosphere He 40 ml / min.

As is clear from FIG. 1, the emulsion polymerized in the presence of silica had very good heat resistance.

The reason for this is not clear, but when emulsion polymerization is carried out in the presence of silica, it is considered that a complex of pigment and emulsion is formed, and therefore, the reinforcing effect of the pigment is superior to that of the blend. It is estimated that

The hardness of the acrylic emulsion can be freely controlled depending on the composition of the monomers used.
A glass transition temperature of -10 ° C to + 30 ° C is appropriate. The glass transition temperature is a measure of hardness, but at a glass transition temperature of -10 ° C or lower, there is a sticky feeling, and it is + 30 ° C
In the above cases, the film forming property was insufficient, and sufficient coating film strength could not be obtained.

The silica content in the emulsion should be 20-50.
Parts are suitable, preferably 30-40 parts.

Further, the back coat layer of the thermal recording paper according to the present invention preferably contains a pigment. The amount is preferably in the range of 20 to 60 parts, and more preferably 30 to 50 parts. The pigment is preferably an inorganic pigment such as zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, wax, kaolin, calcined clay, and aluminum hydroxide.

The composition ratio of the back coat layer is preferably 5 to 30 parts of polystyrene sulfonic acid (solid content ratio) and 30 to 60 parts of silica-containing acrylic emulsion. Particularly preferred is polystyrene sulfonic acid 10 to 20 parts, silica-containing acrylic emulsion 40 to 50 parts.

The coating amount (dry weight) of the back coat layer affects the electric resistance value of the back layer, and the surface electric resistance value is 5.
It is preferably set to 0 × 10 ⁹ or less. For this reason 0.
The amount is ^{2 to 5} g / m ² , preferably 0.2 to 3 g / m ² .

A surfactant and a defoaming agent may be added to the coating liquid for the stability and defoaming of the coating liquid.

The thermosensitive coloring layer of the present invention is formed by a conventional method. A coating solution containing a dye and a color developer which are usually used in this field, and optionally an inorganic or organic pigment, a binder and the like is applied to paper, synthetic paper or synthetic resin film.

The dye and the developer are separately dispersed in the water-soluble polymer substance (binder) using a dispersing machine such as a ball mill and a sand grinder. If necessary, a sensitizer is used and dispersed in the same manner as the dye and the developer. Dispersion is performed until it becomes 2 μ or less, more preferably 1 to 0.5.
Let μ. After the dispersion is completed, the dye dispersion, the developer dispersion, the sensitizer dispersion, the pigment and the adhesive are mixed to prepare a heat-sensitive coating liquid.

It is also possible to form an overcoat layer composed of an aqueous resin composition, a filler, and a crosslinking agent on the thermosensitive coloring layer in order to improve the plasticizer resistance and the storage stability.

[Examples] Examples of the present invention are shown below. In the examples, parts and% represent parts by weight and% by weight, respectively.

Example 11 1) Thermosensitive coloring layer [A liquid] 3-N-methyl-N-cyclohexyl amino 6-methyl-7-anilinofluorane ...... 300 parts 10% polyvinyl alcohol aqueous solution ...... 300 parts water ...... 400 parts [B Liquid] 4,4'-isopropylidene bis (2,6-dibromophenol) ...... 300 parts 10% polyvinyl alcohol aqueous solution ...... 200 parts water ...... 400 parts [C liquid] adipic acid di-o-chlorobenzene ...... 100 parts Calcium carbonate ...... 300 parts 10% Polyvinyl alcohol ...... 200 parts Water ...... 300 parts Disperse each of the above compositions using a sand grinder until the particle size reaches 0.8 ± 0.1 μm. B
Solution and C solution are obtained, and then 20 parts of solution A, 70 parts of solution B and 10 parts of solution C are mixed to prepare a working solution for use in a thermosensitive color developing layer.
μm film method polyolefin resin synthetic paper (Yupo FP
The weight after drying on G80 Oji Oka Synthetic Paper Co., Ltd. is 5g / m ²
And dried with a Mayer bar to form a thermosensitive coloring layer.

Further, a coating solution having the following composition was applied on the heat sensitive layer to form a protective layer.

The coating amount of the protective layer was set to 3.0 g / m ² (dry weight).

Kaolinite clay 5 parts 10% aqueous polyvinyl alcohol solution 50 parts zinc stearate 2 parts water 39 parts 2) Backcoat layer A backcoat layer having the following composition is used as the thermosensitive coloring layer,
A thermosensitive recording paper was obtained by coating the back surface of the support having a protective layer so that the dry coating amount was 1 g / m ² .

Kaolinite clay 40 parts (dry weight part) Silica-containing acrylic emulsion (L-8920A Hoechst Synthetic Chemical Co., Ltd.) 50 parts (dry weight part) Sodium polystyrene sulfonate (Chemist 6120 Sanyo Chemical Industry Co., Ltd.) 10 Parts (dry weight part) Example 2 A back coat layer having the following composition was coated and formed on the back surface of a support having the same thermosensitive coloring layer and protective layer as in Example 1 so that the dry coating amount was 1 g / m ^2. A thermosensitive recording paper was obtained.

Kaolinite clay 40 parts (dry weight part) Silica-containing acrylic emulsion (L-8910A manufactured by Hoechst Synthetic Chemical Co., Ltd.) 50 parts (dry weight part) Sodium polystyrene sulfonate (Chemist 6120 Sanyo Chemical Industry Co., Ltd.) 10 parts (Dry parts by weight) Comparative Example 1 A back coat layer having the following composition was coated and formed on the back surface of a support having the same thermosensitive coloring layer and protective layer as in Example 1 so that the dry coating amount was 1 g / m ^2. A thermosensitive recording paper was obtained.

Kaolinite clay 40 parts (dry weight part) SBR latex (SBR latex PT-1022 manufactured by Zeon Corporation) 50 parts (dry weight part) Sodium polystyrene sulfonate (Chemist 6120 manufactured by Sanyo Kasei Co., Ltd.) 10 parts ( Dry part by weight) Comparative Example 2 The same thermosensitive coloring layer and protective layer as in Example 1 were formed on the back surface of the support to form a backcoat layer having the following composition so that the dry coating amount would be 1 g / m ² and heat sensitivity. I got the recording paper.

Diisobutylene-maleic acid copolymer ammonium salt (Isoban 04 Kuraray Co., Ltd.) 50 parts (dry weight part) Calcium carbonate (Brilliant 15 Shiraishi Industry Co., Ltd.) 40 parts (dry weight part) Sodium polystyrene sulfonate 10 Parts (dry parts by weight) Comparative Example 3 A thermosensitive material was formed by coating a backcoat layer having the following composition on the back surface of the support having the thermosensitive coloring layer and protective layer of Example 1 so that the dry coating amount was 1 g / m ^2. I got the recording paper.

Diisobutylene-maleic acid copolymer (Isoban 04 Kuraray Co., Ltd.) 50 parts Calcium carbonate (Brilliant 15 Shiraishi Kogyo Co., Ltd.) 50 parts Comparative experiments of the thermal recording papers obtained in Examples and Comparative Examples are as follows. I went like.

(1) Blocking 40 ℃, 90% RH under the protective layer surface and the back surface overlap 10g / cm
After applying a load of ² and leaving it for 24 hours, it was peeled off and the strength of adhesion was sensory evaluated. The evaluation was performed as follows.

◯ = No adhesion Δ = Slight adhesion, but no problem in practical use × = Complete adhesion

(2) Heat resistance test 30 solid black prints were continuously printed using an image printer of Toshiba Medical Co., Ltd., left for 30 minutes and restarted to evaluate the adhesiveness to the platen roll.

○: There is no adhesion to the platen roll and the vehicle runs without problems.

△: Blocking on the platen roll slightly, and when restarting, there is a blocking noise, but the car runs.

×: Completely adhered to the platen roll, and the thermal paper entered the recording machine.

(3) Surface electrical resistance value Yokogawa Hewlett-Packard surface electrical resistance meter 4329
Using A, the surface electric resistance value of the back layer was measured at 20 ° C. and 65% RH.

[Advantages of the Invention] According to the present invention, it is possible to provide a heat-sensitive recording material having a low surface electric resistance value, water-resistant blocking property, and good heat resistance.

[Brief description of drawings]

FIG. 1 relates to the experimental results showing the superiority of the silica-containing acrylic emulsion for the back coat layer in the present invention.

Claims (1)

[Claims] 1. A silica-containing acryl obtained by emulsion-polymerizing an acrylic monomer in the presence of silica on the back surface of a support, wherein a thermosensitive recording layer containing a leuco dye and a color developer is provided on one surface of the support. A heat-sensitive recording material comprising a back coat layer comprising an emulsion and a polystyrene sulfonate as main components.