JPH0825334B2 - Method for manufacturing thermosensitive recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a heat-sensitive recording containing a colorless or light-colored color-forming agent and a color-forming agent that reacts with the color-forming agent to produce a color when heated. More particularly, the present invention relates to a method for producing a heat-sensitive recording material having a uniform and stable coating layer structure having excellent smoothness and excellent recording mechanical properties such as a facsimile.

(B) Conventional Technology A thermosensitive recording medium provided with a color-forming layer containing a color-forming agent and a color-forming agent that reacts with the color-forming agent to produce a color is relatively inexpensive, and the recording machine is compact. Since its maintenance is easy, it is used in a wide range of fields as a recording medium such as a facsimile and a printer. Recently, with downsizing and speeding up of facsimiles, there has been a demand for a heat-sensitive recording body capable of high-speed recording with low energy.

As one of the methods for improving the high-speed recording property, that is, the dynamic sensitivity of the thermosensitive recording material, a substance that melts at a lower temperature than the color former or the color former in the color forming layer and dissolves both or one (that is, a sensitivity improver) ) Is known, and various sensitivity improvers are used. However, in order to add these sensitivity improvers to improve the dynamic sensitivity, it is necessary to add a large amount, but there is a problem that the addition of a large amount causes dust adhesion and sticking to the thermal head.

As another method of improving the dynamic sensitivity, there is a method of increasing the density of the color-forming component by reducing the content of a component that does not contribute to color development in the thermosensitive color-forming layer, such as a filler or a binder. However, in this method, since the adhesion of dust to the thermal head is increased, improvements have been made such as providing an undercoat layer containing a filler with a large oil absorption between the support and the color forming layer. However, even with this method, satisfactory results have not been obtained as long as the conventional coloring layer coating method is used. For example, in the air knife coating method, since the coloring layer coating liquid is applied at a low concentration, the binder in the coating liquid is easily absorbed by the undercoat layer at the time of coating, and uneven absorption due to uneven coating of the undercoat layer is caused. A colored layer that is uniform and has excellent smoothness cannot be obtained. On the other hand, the blade coating method has an advantage that a high-concentration coating solution can be used, but has a drawback that scratches, so-called streaks, occur under the high shearing force of the blade blade.

Regarding suitability for recording machines, in order to improve the adhesion between the thermal head and the surface of the thermal recording medium, it has been customary to smooth the surface of the color forming layer with a super calender or gloss calender during production of the thermal recording medium. However, even if the smoothness of the surface of the color developing layer is increased simply by supercalendering, not only is it not possible to obtain a satisfactory dynamic sensitivity, but it also causes background fog and sticking due to pressure, resulting in naturalness. It becomes a thermosensitive recording medium lacking.

(C) Problems to be Solved by the Invention In view of the present situation, the present inventors have solved the above drawbacks,
As a result of diligent research on a thermal recording material having a balanced quality aptitude, when a color-forming layer is provided on a support by a roll blade coating method, the surface roughness Ra and printing smoothness of the color-developing surface based on JIS-B0601 method. By adjusting the Rp value in a specific range, a thermosensitive recording medium having a uniform and stable coating layer structure with excellent smoothness even when the degree of calendering is mild and having excellent recording machine suitability is obtained. It was a successful one.

(D) Means for Solving the Problems The present invention provides a method for producing a thermosensitive recording medium, which comprises a color-forming agent and a color-forming layer containing a color-forming agent that reacts with the color-forming agent to produce a color. When the layer is provided on the support by the roll blade coating method, the surface roughness of the surface of the color-developing layer according to JIS-B0601 method is 1.0 μm or less and the pressing force is 5 kg / c.
This can be achieved by adjusting the printing smoothness Rp at m ² to be 7.8 μm or less.

The surface roughness Ra in the present invention is measured based on the JIS-B0601 method, and Ra means the center line average roughness and is defined by the following general formula.

(L: measurement length, y = f (X): roughness curve) In addition, in order to reduce the measurement error, a stylus type three-dimensional surface roughness analyzer (SPA-11 model made by Kosaka Laboratory) was used for the measurement. The surface roughness Ra was obtained.

Surface roughness Ra of the color-developing layer surface measured under such conditions is
When it is larger than 1.0 to 1.2 μm, even if the pressure of the platen for pressing the thermal recording medium against the thermal head is adjusted, satisfactory dynamic sensitivity can no longer be obtained. Therefore, the surface roughness Ra of the surface of the color forming layer of the heat-sensitive recording material of the present invention is 0.6 to 1.0 μm.

In terms of dynamic sensitivity, it seems that the smaller the surface roughness Ra of the surface of the color forming layer is, the more it can be obtained. However, according to the study by the present inventors, when the surface roughness Ra is too small, the thermal head is It became clear that the suitability for recording machines such as dust adhesion and sticking to the recording machine deteriorates, and the dynamic sensitivity also decreases. Therefore, as a result of further diligent research on a thermal recording material having high quality balanced in dynamic sensitivity, recording machine suitability, etc., the printing smoothness of the surface of the thermal recording material having the specific surface roughness Ra as described above. It has been found that is a very important requirement for balancing such quality. That is, if the printing smoothness Rp at a pressure of 5 kg / cm ^{2 on} the surface of the color forming layer is larger than 7.8 μm, the surface roughness Ra is
It was revealed that even if the thickness is 1.0 μm or less, the quality balance is lost, and it is impossible to obtain a thermal recording material having good dynamic sensitivity and recording machine suitability.

Thus, the thermosensitive recording medium of the present invention is adjusted not only to have the specific surface roughness Ra as described above, but also to have a printing smoothness Rp of 4.0 to 7.8 μm at a pressing force of 5 kg / cm ^2. It

In the present invention, the printing smoothness Rp of the surface of the color developing layer is measured by a printing smoothness tester (manufactured by Toyo Seiki Seisakusho Co., Ltd., an optical contact rate measuring device Micropotograph).
Is to give an amount proportional to the average depth of the depressions on the surface of the sample pressed onto the reference plane (prism). More specifically, the Rp value is measured at the wavelength (λ), as published in the Japan Society of Printing, Vol. 17, No. 3 (1978), the 60th Spring Meeting of the Printing Society of Japan (1978), etc. ) Is obtained, the ratio of the amount of transmitted light to the amount of incident light obtained, that is, each value of the optical contact rate (F (λ)) is obtained, and is substituted into the exponential function formula approximated by the following formula to obtain F _{Find 0} and k.

F (λ) = F ₀ + (1-F ₀ ) (1-e ^−kλ ) ... [1] F ₀ is the ratio of the area where the paper physically contacts the prism, and k is the shape of the paper. It is a constant related to distribution. The Rp value is given by the following equation: Rp = (1-F (λ)) dλ (2) Substituting the equation [1] into the equation [2], Rp is Rp = (1-F ₀ ) / k Therefore, the Rp value can be obtained from the previously obtained F ₀ and k.

The present inventors, the roll blade coating method as a coating method for forming such a color-forming layer, without the occurrence of streaks in coating a high-concentration coating liquid on a support,
In addition, as a result of earnest research, it was also found that this is the most suitable method because uneven absorption of the binder in the coating liquid does not occur. The roll blade coating method, also called bar coating method, measures and smoothes the coating amount with a rod, and engraves a smooth round bar (plain roll), a wire-wound rod, or a groove according to the purpose. It is possible to properly use three types of rods, and a round bar having an excellent smoothing effect is preferable in the present invention.

As the color-forming agent contained in the color-forming layer of the present invention, triphenylmethane-based and fluoran-based lactone compounds, which are usually called leuco dyes, can be used. Examples of the triphenylmethane compound include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,
3-bis (p-dimethylaminophenyl) phthalide, 3
-(P-dimethylaminophenyl) -3- (1,2-dimethylaminoindol-3-yl) phthalide and the like can be mentioned, and as the fluorane compound, 2-anilino-3-methyl-6-dimethylaminofluorane, 2-anilino
3-methyl-6- (methylcyclohexylamino) fluorane, 2-anilino-3-methyl-6- (ethylisobenzylamino) fluorane, 2- (p-chloroanilino) -3-methyl-6-diethylaminofluorane, 2
-(P-Fluoroanilino) -3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-
(P-toluidinoethylamino) fluorane and the like can be mentioned, and these color formers can be used alone or in combination.

Further, as a color developing agent that reacts with a color developing agent when heated,
p-octylphenol, p-tert-butylphenol, 1,1-bis (p-hydroxyphenyl) propane 2,2
-Bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) cyclohexane, 4,4 '
-Thiobisphenol, 4,4'-sulfonyldiphenol, bis (3-allyl-4-hydroxyphenyl) sulfone, novolac type phenol resin, p-hydroxybenzoic acid ester, dimethyl 4-hydroxyphthalate, 5
-Ethyl hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid and its metal salt, 3,5-di-α-methylbenzylsalicylic acid and its metal salt, and the like.

On the other hand, as the binder for binding and supporting the color former and the color former on the support, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxy-modified polyvinyl alcohol, polyacrylamide, polyacrylic acid, starch and the like. Examples thereof include water-soluble polymer compounds such as derivatives, casein, gelatin, alkali salts of styrene-maleic anhydride copolymers, and aqueous emulsions of the above water-insoluble resins.

Examples of the sensitivity improver include higher fatty acid amides such as stearic acid amide, benzyl p-benzyloxybenzoate, dibenzyl terephthalate, diphenyl sulfone and 2-benzyloxynaphthalene.

As the filler, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silica, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, other inorganic fine powder of surface-treated calcium carbonate or silica,
Examples include organic fine powders such as urea-formalin resin and polystyrene resin.

As other additive substances, lubricants such as zinc stearate and calcium stearate, various surfactants, antifoaming agents and the like are added as necessary.

As the support on which the thermosensitive color forming layer is provided, paper, synthetic paper, film and the like are used, but those having excellent smoothness are preferred in the present invention. If necessary, a filler having a large oil absorption such as calcined kaolin or silica is coated with a binder such as styrene-butadiene latex, starch or polyvinyl alcohol on a support to form an undercoat layer. can do.

The coating amount of the coating liquid for forming the color forming layer on the support is not particularly limited, but is usually 2 to 15 g / dry weight.
It is in the range of m ² , preferably 3 to 12 g / m ² . The formed coloring layer is surface-treated with a super calendar or the like as necessary, but of course the surface roughness Ra of the coloring layer surface is Ra.
And the printing smoothness Rp is processed in a range so as to have a specific value of the present invention.

(F) Examples Examples are shown below to more specifically describe the present invention, but the present invention is not limited thereto.
The parts and% in the examples are parts by weight and% by weight, unless otherwise specified.

Example 1 A mixture having the following composition was used, each having an average particle size of 2 μm.
Disperse with a sand mill so as to be less than m
Solution C was prepared.

(A) 2-anilino-3-methyl-6-diethylaminofluorane 10 parts 10% hydroxyethyl cellulose aqueous solution 5 parts water 15 parts (B) bisphenol A 20 parts 10% polyvinyl alcohol aqueous solution 20 parts water 60 parts (C) stearic acid Zinc 10 parts Calcium carbonate 40 parts 5% Methylcellulose aqueous solution 50 parts Water 50 parts Next, solution A 6 parts, solution B 20 parts, solution C 20 parts, 10% polyvinyl alcohol solution 30 parts, 20% stearic acid amide Emulsion (Chukyo Yushi, trade name Hydrin M-
25 parts of 7) were mixed and stirred to prepare a heat-sensitive coating liquid. The concentration of this coating liquid was 22% and that of clay was 200 cps.

An undercoat layer composed of 100 parts of calcined kaolin and 10 parts of styrene-butadiene latex by a roll blade coating method (plain roll 10 mmφ140 rpm) and a coater speed of 300 m / m (coating amount 8 g / m ² ).
^On a high-quality paper of 50 g / m ² having a coating amount of 5 g / m ² after drying.
The coating was dried so that The surface roughness Ra of the color-developing layer of the obtained thermosensitive recording material which has not been subjected to calendar treatment is 0.86 μm, the printing smoothness Rp is 7.69 μm and the Beck's smoothness is 200 seconds when the pressing force is 5 kg / cm ^2. Met.

A commercially available facsimile (Matsushita Electric Co.,
When printed with Panafax UF-7), the obtained print density (D) was 1.24, and no sticking was observed.

Example 2 The thermal recording material obtained in Example 1 was subjected to a mild calendering treatment at a linear pressure of 40 kg / cm to obtain a thermal recording material having a Bekk smoothness of 400 seconds. Surface roughness of the color-developing layer of the resulting thermosensitive recording medium
Ra is 0.64 μm, and printing smoothness Rp is 4.9 when the applied pressure is 5 kg / cm ^2.
It was 1 μm. Almost no pressure fog was observed.

When printing this thermal recording material with a commercially available facsimile,
The print density (D) obtained was 1.29, and no sticking was observed.

Comparative Example 1 Water was added to the coating liquid prepared in the same manner as in Example 1 to obtain a coating liquid having a concentration of 16% and clay of 100 cps.

This coating solution was applied by air knife coating to a fine paper having the same undercoat layer as in Example 1 at a coater speed of 200 m / m so that the coating amount after drying was 5 g / m ² . The surface roughness Ra of the color-developing layer of the obtained heat-sensitive recording material without calendar treatment was 1.38 μm, and the applied pressure was 5 Kg /
The printing smoothness Rp at cm ² was 17.63 μm, and the Beck's smoothness was 100 seconds.

When printing this thermal recording material with a commercially available facsimile,
The obtained print density (D) was 1.01. In addition, there was uneven printing in the printed area, which was probably caused by uneven absorption of the coating liquid, and sticking was also observed.

Comparative Example 2 The thermal recording material obtained in Comparative Example 1 was calendered at a linear pressure of 80 kg / cm to obtain a thermal recording material having a Beck smoothness of 420 seconds. The surface roughness Ra of the coloring layer of the obtained recording material is 0.74μ.
The printing smoothness Rp was 5.23 μm when the pressure was 5 kg / cm ² and the pressure was 5 kg / cm ² , but pressure fog was noticeable.

When printing this thermal recording material with a commercially available facsimile,
The obtained print density (D) was 1.24, but there was print unevenness that was probably caused by uneven absorption of the coating liquid in the print area.
At the same time, sticking was also seen.

(G) Effect of the Invention As is clear from the examples, the thermal recording material obtained by the method for producing a thermal recording material according to the present invention has a uniform and smooth color-forming layer and therefore exhibits excellent motion with a mild calendering treatment. Since it is possible to obtain the desired sensitivity, there is no pressure fog and the suitability for a recording machine is excellent. Therefore, the invention can be said to be a very useful invention for obtaining a heat-sensitive recording material having a well-balanced quality.

Claims (1)

[Claims] 1. A method for producing a thermosensitive recording medium comprising a color-forming layer and a color-forming layer containing a color-forming agent which reacts with the color-forming agent to form a color on a support by a roll blade coating method. , The surface roughness Ra based on JIS-B0601 method of the coloring layer is 0.6 to 1.0 μm, and the pressing force is 5 k.
A method for producing a thermosensitive recording medium, characterized in that the printing smoothness Rp at g / cm ² is adjusted to be 4.0 to 7.8 μm.