JPH10147060A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensible recording body having a high recording sensitivity and superior picture quality. SOLUTION: The recording body include a thermosensible coloring layer having a number of fine pores formed such that on a sheet-like carrier and one surface of the carrier, coating liquid for a thermosensible coloring layer containing a dye precursor, a developer, and self-emulsion type water dispersive resin is coated and then dried by giving mechanical stirring operation therein, wherein an I/O value (inorganic value/organic value) of the self/emulsion type water dispersive resin being in the range of 0.4-1.2, and an average diameter of pores on the surface of the thermosensible coloring layer being in the range of 0.5-50μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium. More specifically, the present invention relates to a thermosensitive recording medium having high recording sensitivity and excellent image quality.

[0002]

2. Description of the Related Art A thermosensitive recording system is highly evaluated for its advantages in that a colored image can be obtained simply by heating, and a recording device can be relatively easily made compact. It is used for

In particular, in recent years, facsimile and printer devices using such a thermal recording system have been improved, and high-speed recording, which has been conventionally difficult, has become possible. With the increase in the speed of such equipment, the thermal recording medium used is required to further improve the recording sensitivity, and many proposals have been made regarding this.

[0004] In order to improve the recording sensitivity of the thermosensitive recording medium, it is important that the heat insulating property of the substrate of the thermosensitive recording medium is important. Therefore, hydrophobic organic polymer compound particles having a lower thermal conductivity than that of the inorganic pigment are contained in the undercoat layer (JP-A-59-17168).
No. 5, JP-A-60-2397) In order to further enhance the heat insulating property of air, fine particles of a hollow organic polymer compound are contained in an undercoat layer (JP-A-59-1716).
No. 85, Japanese Unexamined Patent Publication No. Sho 59-225987) and the like.

[0005] However, the recording sensitivity of the heat-sensitive layer is improved to some extent by including the above-mentioned material for imparting heat insulation in the undercoat layer, but when an inorganic pigment is used, for example, when the paper is cut, Tends to easily generate paper powder and the like, and in the case of hollow organic polymer compound fine particles, not only the cost is increased but also there is a problem that a surface smoothing treatment is required. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a thermosensitive recording medium having high recording sensitivity and excellent image quality.

[0007]

According to the present invention, there is provided a thermosensitive recording medium comprising:
Sheet-shaped support, on one side of this support, at least a dye precursor, a developer and a thermosensitive coloring layer containing a self-emulsifying type water-dispersible resin-containing coating liquid is subjected to mechanical stirring to apply,
A thermosensitive coloring layer having a large number of fine pores formed by drying, wherein the I / O value (inorganic value / organic value) of the self-emulsifying water-dispersed resin is from 0.4 1.2, and the average pore diameter of the surface of the heat-sensitive coloring layer is in the range of 0.5 to 50 μm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above-mentioned problems, the present inventors have proposed that a dye precursor, at least one surface of a support,
The coating liquid for the thermosensitive coloring layer containing the color developer and the water-dispersible resin is mechanically agitated to apply a foaming coating liquid containing a large number of fine bubbles, and dried to form a void structure ( It has been found that excellent recording sensitivity and image quality can be realized by a method of providing a thermosensitive coloring layer having fine pores. However, in the case of the thermosensitive coloring layer coating liquid, if the capacity of the equipment for mechanical stirring is not sufficient, the desired state of containing fine bubbles may not be obtained. Also,
Even if the capacity of the equipment is sufficient, if it is applied immediately after foaming, fine surface pores can be formed, but fine bubbles coalesce over time, and the bubbles may become large, resulting in quality control. Not preferred.

Therefore, in order to improve the stability of the fine bubbles, a surfactant such as a higher fatty acid, a modified higher fatty acid, or an alkali salt of a higher fatty acid, which is called a foam stabilizer or a foaming agent, for example, polyoxyethylene. The foam stability has been improved by appropriately blending alkyl ether, sodium stearate, sodium alkyl sulfate and the like. However, since these foam stabilizers or foaming agents have the ability to solubilize the dye precursor and the developer, a color-forming reaction occurs in the coating solution, and the background in the heat-sensitive coloring layer after coating and drying. Problems such as fog may occur.

The present inventors have conducted intensive studies on a water-dispersible resin having excellent bubble stability without a foam stabilizer or a foaming agent. As a result, I / O, which is a measure of the balance between hydrophilicity and hydrophobicity, has been studied.
By using a coating liquid containing a self-emulsifying water-dispersible resin having a value (inorganic value / organic value) in the range of 0.4 to 1.2, it is stable without a foam stabilizer or a foaming agent. The present inventors have found that fine bubbles can be formed, and formed a thermosensitive coloring layer having a void structure (fine pores) by using such a self-emulsifying water-dispersed resin, thereby completing the present invention.

That is, the heat-sensitive recording material of the present invention comprises at least a dye precursor, a color developer, and an I / O value (inorganic value /
A foaming coating liquid containing a large number of fine bubbles by mechanically stirring a coating liquid for a thermosensitive coloring layer containing a self-emulsifying water-dispersible resin having an organic value of from 0.4 to 1.2. Is coated on one surface of a sheet-like support and dried to form a thermosensitive coloring layer having fine pores having an average pore diameter of 0.5 to 50 μm in the surface of the coloring layer. .

The self-emulsifying water-dispersible resin in the present invention contains a hydrophilic functional group and can be stably dispersed as particles in water without adding an emulsifier.
In order to provide a hydrophilic functional group, a method of introducing a monomer which originally contains an ionic group or generates an ionic group by adding a neutralizing agent into a polymer chain by a copolymerization method is generally used. It is a target.

Examples of the self-emulsifying water-dispersible resin usable in the present invention include styrene-acrylic copolymer, polyacrylic ester, polymethacrylic ester, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, Ethylene-vinyl acetate copolymer, styrene-butadiene-acrylic copolymer, polyvinylidene chloride, polyurethane, etc., contain monomers that originally contain ionic groups or generate ionic groups by adding a neutralizing agent. Examples include, but are not limited to, those introduced by a copolymerization method. These self-emulsifying water-dispersible resins can be used alone or as a mixture of two or more, if necessary.

The monomer which originally contains an ionic group or forms an ionic group by adding a neutralizing agent includes anionic monomers, cationic monomers and amphoteric monomers. More specifically, examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
There are a tertiary amine-containing monomer and an ammonium salt-containing monomer, and the amphoteric monomer includes N- (3-sulfopropyl) -N-methacrylyloxyethyl-N, N-
Betaine compounds such as dimethylammonium betaine and 1- (3-sulfopropyl) -2-vinylpyridium betaine can be used.

Examples of the neutralizing agent include organic amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine and triethanolamine, and inorganic salts such as sodium hydroxide, potassium hydroxide and ammonia. But
It is not limited to these. Generally, the neutralizing agent is used in an amount sufficient to generate ionic groups.

When a self-emulsifying water-dispersible resin is used for forming a thermosensitive coloring layer having a void structure, the
It is important that the / O value be in the range of 0.4 to 1.2. If the I / O value is less than 0.4, a stable bubble-containing liquid cannot be formed without a foam stabilizer or a foaming agent because the hydrophobicity is too high. In other words, the stability of the bubbles formed and dispersed by the mechanical stirring process is deteriorated (foam breakage and coalescence of the bubbles are likely to occur), and it becomes difficult to hold the fine bubbles. As a result, a favorable void structure (pore diameter on the surface) in the thermosensitive coloring layer cannot be obtained, and the recording performance is reduced. On the other hand, if the I / O value exceeds 1.2, the hydrophilicity is too high, and the self-emulsifying water-dispersed resin cannot be localized at the gas-liquid (bubble) interface, so that it is difficult to exhibit the surface active effect. Inability to form stable foam.

Regarding the I / O value in the present invention, "Organic Conceptual Diagram" (Yoshio Koda, Sankyo Publishing Co., pp. 11-17, 1
984). Since the O value (organic value) is defined as the organic property of one carbon atom being 20, it can be calculated by multiplying the number of carbon atoms contained in the molecule by 20. on the other hand,
The I value (inorganic value) can be obtained from the inorganic values shown in Tables 1 and 2. Also, as shown in Table 2, an O value is also obtained for a substituent having an organic property, and the O value obtained above is obtained. Is added to. The I / O value can be obtained by dividing the I value obtained as described above by the O value. The higher the I / O value, the higher the hydrophilicity, and the lower the I / O value, the higher the hydrophobicity.

[0018]

[Table 1]

In Table 1, the carbon in the inorganic groups is added organically. Φ represents an alkyl group or a phenyl group, and * is applied to an acyclic portion.

[0020]

[Table 2]

In Table 2, it is assumed that the carbon of the organic-inorganic group is already added to the organic. R is an alkyl group, φ
Represents an alkyl group or a phenyl group, # is the value of the part in [], and * is applied to the terminal part.

The dye precursor that can be used in the heat-sensitive layer of the present invention is not particularly limited as long as it is generally used for a pressure-sensitive recording material, a heat-sensitive recording material and the like. Specific examples of the electron-donating color-forming dye precursor include (1) triarylmethane-based compounds such as 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide. (2) Examples of the dimethylphenylmethane-based compound include 4,4-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenylleuco auramine and the like. (3) As a xanthene compound, for example, rhodamine B
-Anilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-butylaminofluoran, 3-diethylamino-7- (2-
Chloroanilino) fluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-ani Linofluoran, 3-diethylamino-6-chloro-7-
(Β-ethoxyethyl) aminofluoran, 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluoran, 3-dibutylamino-6-methyl-7
-Anilinofluoran, 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluoran,
3-ethyl-isoamylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-7-chloroanilinofluoran and the like. These dye precursors can be used alone or in combination of two or more, and are appropriately selected and used depending on the use of the thermosensitive recording medium and desired characteristics.

As the color developer used in the present invention, phenol derivatives and aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. When these are specifically exemplified, phenols include p-octylphenol,
p-tert-butylphenol, p-phenylphenol, 2,2-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethylhexane, 2,2-bis (hydroxy-3,5-dichlorophenyl) propane, dihydroxydiphenyl ether, , 4'-dihydroxydiphenyl sulfone,
4-hydroxy-4'-isopropyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone and the like. Examples of the aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and the above carboxylic acids And the like.

These dye precursors and developers are generally prepared by using water as a dispersion medium, and using various wet pulverizers such as a ball mill, a coball mill, an attritor, and a vertical or horizontal sand mill to obtain polyacrylamide, polyvinylpyrrolidone, polyvinyl After being dispersed together with a water-soluble synthetic polymer such as alcohol, methylcellulose, and a styrene-maleic anhydride copolymer salt, and other surfactants to obtain a dispersion, it is used for preparing a thermosensitive coloring solution.

As the adhesive, for example, polyvinyl alcohol having various molecular weights and saponification degrees and derivatives thereof, starch, derivatives thereof and various modified starches such as oxidized starch, methoxycellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, etc. Nonionic resins such as cellulose derivatives, glue, casein, soy protein, and gelatin can be used in combination.

In the present invention, other materials constituting the heat-sensitive recording layer include a sensitizer, an inorganic or organic pigment, a wax, a metal soap, and if necessary, an ultraviolet absorber, a preservative stabilizer, a fluorescent dye, and a coloring agent. Dye pats can be mentioned.

Examples of the sensitizer include fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, methylolbehenic acid amide, palmitic acid amide, p-benzylbiphenyl, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid. Phenyl, dibenzyl oxalate, di-p-chlorobenzyl oxalate, di-p oxalate
-Methylbenzyl, di-o-chlorobenzyl adipate, 1,2-bis (3-methylphenoxy) ethane,
In addition to 1,2-bis (3,4-dimethylphenyl) ethane and the like, various known thermoplastic substances can be added.

Examples of organic or inorganic pigments include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated calcium carbonate and silica. And fine organic powders such as urea-formalin resin, styrene-methacrylic acid copolymer, and polystyrene resin.

Known waxes such as paraffin, amide wax, bisimide wax, and metal salts of higher fatty acids can be used.

In the present invention, the heat-sensitive color-forming layer comprises a mixture of the above-mentioned dye precursor, color developer and self-emulsifying water-dispersed resin resin containing a large number of fine bubbles, which are then formed into a sheet-like support. It can be obtained by coating on top and drying, but there is no particular strict restriction on the method and equipment for forming and containing bubbles, and the coating method. The bubble-containing state of the mixture liquid containing bubbles is not particularly limited, but preferably, the volume ratio of the bubble-containing liquid to the stock solution (hereinafter referred to as the expansion ratio) is more than 1.3 times and 10 times or less. Preferably, it is more than 1.5 times and 5 times or less. That is, the expansion ratio is a scale indicating the bubble content in the bubble-containing mixture liquid.

The density of the coating layer having a void structure is as follows:
There is a correlation with the expansion ratio. That is, the density of the coating layer coated with the high expansion ratio coating liquid decreases, and conversely, the coating layer density coated with the low expansion ratio coating liquid increases. The density of the coating layer is preferably more than 0.1 and 0.8 g / cm ³ or less, more preferably more than 0.15 and 0.5 g / cm ³ or less. If the density is 0.1 or less, the thickness of the coating film (wall) constituting the bubbles becomes thin, and it may be difficult to maintain the strength of the obtained thermosensitive coloring layer at a sufficient level. If the density exceeds 0.8, the heat insulating properties and cushioning properties become insufficient, and the desired sensitivity and image quality cannot be obtained.

Further, it is considered that the mechanism for developing excellent recording sensitivity and image quality in the present invention is related to physical properties such as heat insulating properties and compression properties of the thermosensitive coloring layer having a void structure.

The size of the pores on the surface of the thermosensitive coloring layer formed on the recording sheet is important. That is, in order to form good image quality on the recording sheet of the present invention when performing thermal recording, the average pore diameter on the surface of the thermal coloring layer is preferably in the range of 0.5 to 50 μm, From 30
If it is in the range of μm, more preferable results are obtained. The pore diameter on the surface of the heat-sensitive recording layer can be measured using an optical microscope or a scanning electron microscope photograph and an image analyzer. The size of the pores is determined by the composition of the mixture before the bubble formation / dispersion treatment, that is, the type of the material, the mixing ratio,
Or, it is often affected by various factors such as the above-mentioned expansion ratio, coating method, and the like, so that appropriate conditions need to be set. Further, the size of the pores on the surface of the heat-sensitive recording layer in the present invention is also related to the size of the bubbles in the bubble-containing mixture obtained by mechanical stirring. Since the pores on the surface of the heat-sensitive recording layer after processing and drying are also reduced, the state of bubbles contained in the mixed liquid is not particularly limited, but the same size as the surface of the heat-sensitive layer, that is, the average diameter is 0.5 to 50 μm. Are preferably dispersed and mixed, and more preferably, the average diameter is in the range of 0.5 to 30 μm. The size of the contained bubbles can be measured with an image analyzer by photographing a part of the bubbles with an optical microscope.

In the present invention, a method for forming and dispersing air bubbles in a mixed solution (hereinafter referred to as a foaming method) is, for example, a so-called confectionery foaming machine having a stirring blade rotating while carrying out planetary motion, generally an emulsification dispersion. Mechanically agitates while continuously feeding a mixture of air and mixed liquid into a stirrer such as a homomixer, cowles dissolver, etc., or a closed system used for etc., and disperses air into fine bubbles A device capable of mixing, for example, a continuous foaming machine of Gaston County, USA, Stoke, the Netherlands, etc. can be used, but there is no particular strict limitation.

As the sheet-like support used in the thermal recording medium of the present invention, high quality paper (acidic paper, neutral paper), medium paper,
One-sided paper, medium quality coated paper, lightly coated paper, coated paper, art paper, cast coated paper, clear coated paper, resin laminated paper is common, but plastic film, synthetic paper, metal foil, etc. Alternatively, a composite sheet in which these are combined can be arbitrarily used.

Coating amount of the heat-sensitive recording layer on the sheet-like support,
That coating amount is preferably such from the dry weight of 1 m ² per on one surface of the support obtained is 2 in the range of 40g (2~40g / m ^2). When the coating amount is less than 2 g / m ² , it is often difficult to sufficiently cover the surface roughness of the support, and a recording sheet having an appropriate smoothness on the surface cannot be obtained. In some cases, sufficient heat insulating properties and compressive deformation properties may not be obtained. On the other hand, it is 40g /
If such exceeding m ^2, the thickness of the coloring layer becomes excessive, the bonding strength of the porous heat-sensitive coloring layer is lowered, the heat-sensitive coloring layer when rubbing occurs a trouble such as peeling, good May not be able to obtain a good record. Therefore, it is natural that the coating amount of the heat-sensitive coloring layer should be adjusted in the same manner as the coating liquid composition.

The coating method for forming the thermosensitive coloring layer on the support includes a Meyer bar method, a gravure roll method, a roll method, a reverse roll method, a blade method, and the like.
It can be arbitrarily selected from known methods such as a knife method, an air knife method, an extrusion method, and a cast method.

The sheet having a thermosensitive coloring layer according to the present invention can provide a good thermosensitive recording image even when the mixed solution containing air bubbles is applied to a sheet-like support and dried, but a metal roll is further required. Using a machine calender composed of two or more stages, or a super calender composed of metal rolls and resin rolls or a combination of metal rolls and cotton rolls as appropriate, apply a finishing treatment to this heat-sensitive coloring layer. The surface smoothness can be further improved. Also, after coating, the surface of the thermosensitive coloring layer of the semi-dried or dried sheet is brought into contact with a mirror-finished heated or non-heated cast drum or the like to improve its surface smoothness. Is also good.
However, when the above-mentioned smooth finishing treatment is performed under excessive pressure,
The wall surrounding the air bubbles in the thermosensitive coloring layer is destroyed, and the thermosensitive coloring layer is densified, resulting in reduced heat insulation and cushioning properties, or deformation or destruction of pores on the surface of the thermosensitive coloring layer. In some cases, excellent high-sensitivity thermal recording performance cannot be obtained. Therefore, it is necessary to sufficiently consider the processing conditions in the above-mentioned smooth finishing.

The thermosensitive coloring layer may be provided with an overcoat layer as required to improve sticking with a thermal head during printing. Here, the amount of the pigment used is desirably added in the range of about 1 to 50 parts by weight per 1 part by weight of the adhesive. The coating amount of the overcoat layer is not particularly limited, but is generally 1 to 2 by dry weight.
It is provided in the range of 0 g / m ² . Furthermore, auxiliary agents such as lubricants such as calcium stearate, zinc stearate, polyethylene wax, paraffin wax, and ester wax, dispersants, and antifoaming agents can be added to the overcoat layer. For the purpose of improving water resistance, a curing agent such as glyoxal, epoxy compound, boric acid, dialdehyde starch, or a methylol group-containing compound can be added.

Further, in order to prevent blocking, charging and curling at the time of contact between the front surface and the back surface of the thermosensitive recording medium obtained as described above, a back layer may be provided on the back surface.

[0041]

The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited by these. In the following Synthesis Examples, Examples and Comparative Examples, “parts” all represent “parts by weight”. Synthesis Example of Self-Emulsifying Aqueous Dispersion Resin Synthesis Example 1 30 parts of methyl ethyl ketone, 47 parts of styrene, and 10 parts of acrylic acid were charged into a reactor equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet tube. To replace dissolved oxygen. After heating the reactor to 78 ° C., a solution prepared by dissolving 0.2 parts of azobisisobutyronitrile in 2 parts of methyl ethyl ketone was added to start polymerization, and further, a solution of 21 parts of styrene dissolved in 20 parts of methyl ethyl ketone from a dropping funnel, And a solution of 0.2 parts of azobisisobutyronitrile dissolved in 10 parts of methyl ethyl ketone was added over 4 hours. After aging for 3 hours, a homogeneous copolymer was obtained.
The copolymer was neutralized by adding 15 parts of triethylamine, and after adding 200 parts of distilled water, methyl ethyl ketone was distilled off under reduced pressure to obtain a self-emulsifying water-dispersed resin having a solid content of 30%.

SYNTHESIS EXAMPLES 2 to 5 Using the monomers shown in Table 3 by the method of Synthesis Example 1, each self-emulsifying water-dispersed resin (solid content: 30%) was obtained.

Synthesis Example 6 An emulsifier (sodium laurate) was added to a reactor equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer and a nitrogen inlet tube.
Parts, 200 parts of distilled water, 0.3 part of potassium persulfate, and 9 parts of butyl acrylate, and dissolved oxygen was replaced with nitrogen gas. The reactor was heated to 78 [deg.] C. to initiate polymerization, and 62 parts of n-butyl acrylate was further added from a dropping funnel over 3 hours. After aging for 2 hours, a water-dispersed resin containing an emulsifier having a solid content of 30% was obtained.

[0044]

[Table 3]

Production Example of Thermosensitive Recording Material Example 1 The following components were mixed to prepare a coating solution for a thermosensitive coloring layer. [Preparation of Dye Precursor Dispersion] 3- (N-ethyl-N-isoamylamino-6-methyl-7-20 parts anilinofluoran) 10% aqueous solution of polyvinyl alcohol 10 parts water 70 parts The mixture was charged into a sand mill (sand grinder manufactured by Igarashi Kikai Seisakusho Co., Ltd.), subjected to a dispersion and fine-graining operation using glass beads of 1.2 mm in diameter as a dispersion medium for 30 minutes, and then the composition was transferred to a horizontal sand mill (trade name: Ultravisco). Mill, manufactured by Igarashi Kikai Seisakusho Co., Ltd.), and subjected to a dispersion fine treatment operation for 10 minutes using glass beads having a diameter of 0.6 mm as a dispersion medium. [Preparation of developer dispersion] 2,2-bis (p-hydroxyphenyl) propane 10 parts p-benzylbiphenyl 10 parts 10% aqueous solution of polyvinyl alcohol 10 parts water 70 parts Dispersed by the same method as the preparation method. [Preparation of Coating Solution for Thermosensitive Coloring Layer] Dye Precursor Dispersion 4
0 parts and 160 parts of the developer dispersion, 40 parts of calcium carbonate, 20 parts of a 30% paraffin dispersion, and 280 parts of the resin of Synthesis Example 1 (30% solid content, I / O value: 1.13) The mixture was mixed and stirred to prepare a coating solution for a thermosensitive coloring layer. The coating solution for the heat-sensitive coloring layer was stirred at a rate of 490 rpm using Kenmix Iko PRO (trade name, manufactured by Aikosha Seisakusho).
m for 5 minutes. The expansion ratio was 1.8 times. Immediately use this foam coating solution as a support,
A high-quality paper (acid paper) of 0 g / m ² was coated with an applicator bar so that the coating amount was 5 g / m ^2, and dried to form a thermosensitive coloring layer having a void structure, thereby producing a thermosensitive recording paper. .

Example 2 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 2 (30% solids concentration). , I / O value: 0.88) A thermosensitive recording paper was produced in the same manner as in Example 1, except that 280 parts were used.

Example 3 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 3 (30% solids concentration). , I / O value: 0.47) A thermosensitive recording paper was produced in the same manner as in Example 1, except that 280 parts were used.

Example 4 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the heat-sensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 1 (30% solids concentration). , I / O value: 1.13) Same as Example 1 except that the expansion ratio of the obtained foam coating liquid was 1.6 times instead of 180 parts and 100 parts of a 10% aqueous solution of polyvinyl alcohol. A thermosensitive recording paper was prepared.

Example 5 A thermosensitive recording paper was produced in the same manner as in Example 1 except that the coating amount of the foam coating solution was changed to 10 g / m ² .

Example 6 The following components were mixed to prepare a coating solution for an undercoat layer. [Preparation of Undercoat Layer Coating Solution] Calcined clay 100 parts 5% modified starch aqueous solution 100 parts 48% styrene-butadiene latex 20 parts Water 90 parts This undercoat layer coating solution was weighed at a basis weight of 50 g / m ^{2 on} a high quality paper Mayer bar. Was applied so that the coating amount was 10 g / m ^2, and dried to form an undercoat layer. A heat-sensitive recording paper was produced in the same manner as in Example 1 except that this undercoat layer-coated paper was used as a support.

Example 7 In the foaming treatment of the coating solution for the heat-sensitive coloring layer, the stirring speed was 49
A foaming treatment was performed at 0 rpm for 15 minutes, and a thermosensitive recording paper was produced in the same manner as in Example 1, except that the foaming ratio of the foamed coating solution obtained was 4.8 times.

Example 8 In the foaming treatment of the coating solution for the thermosensitive coloring layer, the stirring speed was 49
A foaming treatment was carried out at 0 rpm for 1.5 minutes, and a thermosensitive recording paper was produced in the same manner as in Example 1 except that the foaming ratio of the foam coating solution obtained was 1.5 times.

Comparative Example 1 The coating amount of the coating solution for the heat-sensitive coloring layer of Example 1 was applied to a high-quality paper (acid paper) having a basis weight of 50 g / m ² as a support using a Meyer bar without performing the foaming treatment. Coating was performed at 5 g / m ² and drying was performed to form a heat-sensitive recording layer. This was subjected to a super calendering treatment, and the surface smoothness was smoothed to 800 seconds by an Oken-type smoothness meter to produce a heat-sensitive recording paper.

Comparative Example 2 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 4 (30% solids concentration). , I / O value: 1.28) A heat-sensitive recording paper was produced in the same manner as in Example 1, except that the foaming ratio of the obtained foamed coating liquid was 1.2 times instead of 280 parts.

Comparative Example 3 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 5 (30% solids concentration). , I / O value: 0.38) A thermosensitive recording paper was produced in the same manner as in Example 1, except that the foaming ratio of the obtained foamed coating liquid was 1.2 times instead of 280 parts.

Comparative Example 4 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 5 (30% solids concentration). , I / O value: 0.38) instead of 250 parts and a 33% foam stabilizer (trade name: SN Foam 200,
A heat-sensitive recording paper was produced in the same manner as in Example 1 except that 30 parts of San Nopco Co., Ltd. was added.

Comparative Example 5 280 parts of the resin of Synthesis Example 1 (30% solids concentration, I / O value: 1.13) in the coating solution for the thermosensitive coloring layer was replaced with 280 parts of the resin of Synthesis Example 6 (30% solids concentration). , I / O value: 0.61, but containing an emulsifier) except that 280 parts were used, to prepare a thermosensitive recording paper in the same manner as in Example 1.

Comparative Example 6 In the foaming treatment of the coating solution for the thermosensitive coloring layer, the stirring speed was 49
Perform foaming treatment at 0 rpm for 30 minutes. Example 1 except that the expansion ratio of the obtained foam coating liquid was 10 times.
A heat-sensitive recording paper was produced in the same manner as in Example 1.

Evaluation 14 obtained in Examples 1 to 8 and Comparative Examples 1 to 6 were obtained.
The following methods were used to evaluate the types of thermal recording paper. (Measurement method of pore diameter) The pore diameter of the surface of the thermosensitive coloring layer,
After taking a photograph of the surface of the thermosensitive coloring layer using a scanning electron microscope or an optical microscope, the outline of the pores on the surface is accurately drawn on a transparent film with a black pen or the like, and further, a drum scanner (trademark: 2605) The contour information of the pores was optically read by a drum scan densitometer (manufactured by Abe Design Inc.), and measured using an image analyzer (trade name: Luzex III, manufactured by Nireco Co., Ltd.). Since the shape of the pores formed on the surface of the thermosensitive coloring layer is not necessarily a perfect circle, the pore diameter is converted into a circle equivalent diameter based on the area within the contour of the pore obtained by image analysis. displayed.

[Recording Characteristics] The obtained thermosensitive recording paper was solid-printed with a thermal energy of 0.2 mJ / dot using a thermosensitive recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.). The reflection density of the printed portion was measured using a Macbeth reflection densitometer, and the image quality of the printed portion was visually evaluated according to the following criteria. ：: Extremely good without uneven density. ：: density unevenness was slightly observed, but there was no problem in practical use. X: Unevenness in density is remarkably observed, which is not preferable.

[Background Fog] The reflection density of the blank portion of the coated surface of the obtained thermal recording paper was measured using a Macbeth reflection densitometer. The smaller the value, the less the background fog.

[Surface Strength] An adhesive tape was adhered to the surface of the heat-sensitive coloring layer, and the peeling of the coloring layer portion when peeled slowly at an angle of 90 ° C. was visually evaluated. A: No peeling of the coloring layer. ：: Some peeling was observed, but there was no practical problem. ×: Peeling of the coloring layer was observed. In the above evaluation criteria, a level of ○ or higher is good and suitable for practical use, while a level of × is insufficient and not suitable for practical use.

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[Table 4]

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According to the present invention, it is possible to practically use a thermosensitive recording medium having high recording sensitivity and excellent image quality, less background fog, and excellent surface strength of the thermosensitive coloring layer.
It greatly contributes to the industry.

Claims (1)

[Claims] 1. A thermosensitive color-forming layer coating liquid containing at least a dye precursor, a color developer and a self-emulsifying water-dispersible resin is mechanically agitated on a sheet-like support and on one surface of the support. And a thermosensitive coloring layer having a large number of fine pores formed by drying and coating, and the I / O value (inorganic value / organic value) of the self-emulsifying aqueous dispersion resin. Is 0.
A thermosensitive recording medium, wherein the thermosensitive recording medium is in the range of 4 to 1.2, and the average pore diameter of the thermosensitive coloring layer surface is in the range of 0.5 to 50 μm.