JPH01286890A - Production of raw paper for thermal recording paper - Google Patents

Abstract

PURPOSE:To contrive enhancement of recording sensitivity of a thermal recording paper without causing ground contamination by specifying the surface smoothness of a raw paper through a flattening treatment comprising passing the raw paper through a press nip constituted of a metallic roll and an elastic roll having a specified hardness. CONSTITUTION:A raw paper is flattened by passing the paper through a press nip constituted of a metallic roll and an elastic roll having a Shore A hardness of 42-98 so that the surface smoothness of the raw paper, measured by a regular reflection type smoothness tester under a pressing condition of 20kg/cm<2>, will be at least 10%. If the elastic roll is softer than Shore A 42, a nip pressure will be excessively high, leading to a reduction in the useful life of the elastic material itself. If the elastic roll is harder than Shore A 98, it is difficult to obtain a predetermined surface smoothness. The Shore A hardness of the elastic roll is preferably 70-95. The surface smoothness of the raw paper after the flattening treatment, measured by the regular reflection type smoothness tester, is at least 14%. The metallic roll is desirably heated to or above 80 deg.C. The press nip is preferably a press nip of an on-machine soft calender or the like.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing base paper for thermal recording paper, and in particular, it is possible to extremely efficiently manufacture thermal recording paper that is fully applicable to ultra-high-speed machines without causing background stains. This relates to a method of processing base paper.

"Prior Art" Conventionally, heat-sensitive recording utilizes a coloring reaction between a coloring agent and a coloring agent that develops color when it comes into contact with the coloring agent, and a colored image is obtained by bringing both coloring materials into contact with each other using heat. Paper is well known.

Such thermal recording paper is relatively inexpensive, uses a non-impact recording method, is quiet, and has a fast recording speed, so it is widely used in facsimiles, thermal printers, barcode label printers, and the like.

In addition, with the remarkable increase in the amount of information in recent years, for example, in the field of facsimile, the development of high-speed machines (GIII machines) and even higher speed machines (GIV machines) is progressing.

As the speed of such recording devices increases, the thermal recording paper used in these devices also needs to utilize minute amounts of thermal energy from the recording head more effectively to obtain high print density, and various improvements have been proposed for this purpose. ing.

[Problem to be solved by the invention j However, conventional proposals have focused on improving the materials constituting the recording layer, such as color formers, color formers, and thermofusible substances (sensitizers). Moreover, new defects accompany the improvements, so that satisfactory results are not always obtained.

For example, if the recording sensitivity is increased to the extent that it can respond sufficiently to minute thermal energy, background stains will occur on the surface of the recording layer even before recording, which will not only deteriorate the appearance but also cause defects that will cause the recorded image to lack clarity. do.

As a result of intensive research into improving the above-mentioned drawbacks, the inventors of the present invention have found that these drawbacks are largely caused by the characteristics of the base paper that makes up thermal recording paper, and in particular, the problems caused by machine calendering, etc. It has been found that treatments using a smoothing device, a Yankee dryer, etc. do not give satisfactory results even after various adjustment of the processing conditions.

Based on this knowledge, we conducted further research into the processing method for base paper for thermal recording paper, and as a result, we determined that the base paper should be treated as a metal roll so that the smoothness of the base paper surface, as measured by a special smoothness meter, exceeds a certain value. When the base paper is flattened using a special pressure nip consisting of an elastic roll with a Shore D hardness of The present inventors have discovered that it is possible to easily obtain thermal recording paper that is fully applicable to ultra-high-speed machines, and have completed the present invention.

``Means for Solving the Problems'' The present invention provides a metal roll and a 42 to 98 degree shore so that the measured value of the base paper surface with a specular reflection type smoothness meter is 10% or more under a pressure condition of 20 kg/cffl. This is a method for producing base paper for thermosensitive recording paper, which is characterized by flattening the paper by passing it through a pressure nip composed of elastic rolls having D hardness (A37M standard, D-2240).

"Operation" The elastic roll used for flattening the base paper in the method of the present invention is made of an elastic material having a Shore D hardness of 42 to 98 degrees as defined in the A37M standard and D-2240, as described above. Consists of.

An elastic roll that is softer than 42 degrees requires excessive nip pressure in order to obtain sufficient surface smoothness of the base paper, which significantly shortens the life of the elastic body itself during operation. However, with elastic rolls harder than 98 degrees, it is difficult to obtain appropriate surface smoothness, so elastic rolls with Shore D hardness of 42 to 98 degrees, more preferably 70 to 95 degrees, are selectively used. be done.

The elastic body constituting such an elastic roll is not particularly limited as long as its hardness falls within the above specific range, and examples include natural rubber, styrene rubber, nitrile rubber, chloroprene rubber, chlorosulfonated ethylene rubber, butyl rubber, Various plastic resins such as polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, aromatic polyamide resin, polyimide resin, polyether resin, polyester resin, polycarbonate resin, cotton, paper, etc.
Specific examples include wool, Tetoron, nylon, and mixtures thereof.

Among them, urethane rubber, aromatic polyamide resin, a mixture of paper and wool (wool paper), a mixture of wool and Tetron, a mixture of wool and nylon, a mixture of paper, wool and Tetron, a mixture of paper, wool and nylon, etc. are preferable. In particular, elastic rolls made of urethane rubber and aromatic polyamide resin are most preferably used because they are easy to handle, have a long roll life, and efficiently deliver the desired effects of the present invention.

The elastic rolls used in the present invention as described above are softer than ordinary elastic rolls, so they tend to generate heat even under stable operating conditions, and this tendency is particularly noticeable in elastic rolls made of urethane rubber. The physical properties of the elastic body become unstable due to the heat generation phenomenon, and in extreme cases, the elastic body itself may be damaged by melting due to the accumulated heat. This is a preferred embodiment and includes external cooling, changing the roll diameter,
Various measures, such as changing the thickness of the elastic body, are adopted as appropriate.

The elastic rolls and metal rolls that make up the pressure nip are not particularly limited, and may include chilled rolls, alloy chilled rolls, copper-iron rolls used in flattening processing equipment such as normal super calenders and gross calenders, and even roll surfaces. A hard chrome-plated metal roll or the like is appropriately selected and used. In addition, the form of the pressurizing device, the number of pressurizing nips, etc. are appropriately adjusted according to a normal flattening processing device.

The pressure conditions when passing the base paper through the pressure nip depend on various processing conditions such as the hardness of the elastic roll used, the type of recording paper, paper passing speed, number of nips, and temperature conditions of the metal roll. However, if the nip linear pressure is 20) cg
/cm, it is difficult to obtain the desired effect;
If it exceeds 20 to 400 kg/cm, the heat generation phenomenon of the elastic roll itself will increase, making stable operation difficult.
It is desirable to adjust within a range of about cm.

Therefore, in the method of the present invention, the surface of the base paper after the flattening process has a value of 10% or more, more preferably 14% or more, as measured by a specular reflection type smoothness meter (measurement pressure: 20 kg/cm"). However, the specular reflection type smoothness meter referred to here is a device that measures the smoothness of paper by pressing it against the glass surface under constant pressure conditions, and is a device that measures the smoothness of paper by pressing it against the glass surface under constant pressure conditions. According to the results, it is not affected by the air permeability of paper like the Beck smoothness meter and Parker Print Surf, which are air leak type smoothness measuring instruments used on boats, and is highly correlated with actual smoothness. Excellent measurement values can be obtained, and
This specular reflection type smoothness meter (measurement pressure: 20 kg/cm"
) It has become clear that the desired effect of the present invention can be determined very appropriately by the measured values, and the present invention has been completed.

Note that depending on the quality characteristics required for the thermal recording paper, the metal roll may be heated. In that case, the temperature of the metal roll is higher than the temperature of the base paper at 80°C or higher, preferably 110°C. It is heated more than that. For heating the roll, a method using a medium such as electricity, steam, water, oil, etc. is appropriately selected and used. Further, when the base paper is passed through the pressure nip, there is no particular limitation as to whether the wire side or the felt side of the base paper is brought into contact with the elastic roll.

In the method of the present invention, a metal roll and a specific shore D
A pressure nip composed of an elastic roll having hardness is used as a pressure nip in a suitable flattening device such as a super calender or a soft calender, but is especially suitable for an on-machine super calender or an on-machine soft calender. It is preferable to employ it as a pressure nip. The on-machine super calendar and the on-machine soft calendar are introduced, for example, in the August issue of Paper and Pulp Technology Times (No. 31) and the May issue of 1988 (page 10).

A heat-sensitive recording layer is formed on the base paper that has been subjected to the flattening treatment in accordance with a conventional method. Various combinations of color-forming substances can be used to form the recording layer. Specifically, for example, the following is exemplified.

(a) A melting point of 100 to 100, which has a secondary alcoholic hydroxyl group and is described in Japanese Patent Publication No. 41-14510.
A combination consisting of a 180°C compound, sulfur and metal inorganic salts or metal acetates.

Examples of compounds having a secondary alcoholic hydroxyl group include benzoin compounds such as benzoin, 2-methoxybenzoin, 4-chlorobenzoin, 4-dimethylaminobenzoin, and 2-chloro-4'-dimethylaminobenzoin, and diphenylcarbinol. Carbinols such as
Resorcinol, pyrogallol, 3-hydroxytoluene-
Examples include phenolic compounds such as 4-sulfonic acid, 4-nitroresorcin, and 4,6-dibromoresorcin, fatty acid polyhydric alcohols such as erythritol, sorbitol, galactose, maltose, mannitol, and saccharose. Metal inorganic salts and metal acetates include a large number of metals that react with hydrogen sulfide to produce colored sulfides, such as copper, lead, tin, molybdenum, cobalt, chromium, nickel, manganese, These include titanium, antimony, rhodium, osmium, mercury, iron, barium, bismuth, arsenic, magnesium, indium, and iridium.

(b) A combination described in Japanese Patent Publication No. 41-14511 in which various inorganic metal salts in the composition of (a) are replaced with hexamethylenetetramine/metal salt adducts.

(C) A combination of carbohydrate and dehydrating agent described in Japanese Patent Publication No. 42-13237.

Here, carbohydrates include saccharose, fructose,
Examples of the dehydrating agent include galactose and starch, and examples of the dehydrating agent include sulfuric acid, acetic anhydride, anhydrous zinc chloride, and para-toluenesulfonic acid.

(d) Combinations of long chain fatty acid iron salts such as ferric stearate and ferric myristate with phenols such as tannic acid, gallic acid and ammonium salicylate.

(e) Organic acid heavy metal salts such as nickel, cobalt, lead, copper, iron, mercury, and silver salts such as acetic acid, stearic acid, and palmitic acid; and alkaline earth metal sulfides such as calcium sulfide, strontium sulfide, and barium sulfide. combination of,
Or a combination of the organic acid heavy metal salt and an organic chelating agent such as S-diphenylcarbazide or diphenylcarbazone.

(f) heavy metal oxalates such as silver, lead, mercury, thorium oxalates and Na-tetrathionate, sodium thiosulfate;
Combination with sulfur compounds such as thiourea.

((to) fatty acid ferric salts such as ferric stearate and 3
．． Combination with aromatic polyhydroxy compounds such as 4-dihydroxytetraphenylmethane.

(h) A combination of a noble metal salt of an organic acid such as silver oxalate or mercury oxalate and an organic polyhydroxy compound such as polyhydroxy alcohol, glycerin, or glycol.

(i) A combination of a noble metal salt of an organic acid such as silver behenate or silver stearate with an aromatic organic reducing agent such as protocatechuic acid, spiroindane or hydroquinone.

(j) A combination of a fatty acid ferric salt such as ferric pelargonic acid or ferric lauric acid with thiosemicarbazide or isothiosemicarbazide derivative.

(k) Combinations of organic acid lead salts such as lead caproate, lead pelargonate, lead behenate and thiourea derivatives such as ethylenethiourea and N-dodecylthiourea.

(1) A combination of a higher fatty acid heavy metal salt such as ferric stearate or copper stearate and zinc dialkyldithiocarbamate.

(b)) Those that form oxazine dyes, such as combinations of resorcinol and nitroso compounds, or those that form azo dyes.

(n) Those forming azo dyes, such as combinations of diazonium salts and coupler compounds.

(0) A combination of a colorless or light-colored basic dye such as crystal violet lactone and a coloring agent such as bisphenol A.

Among the above-mentioned various combinations, the combination of a basic dye and a coloring agent is most preferably used and will be explained in more detail below.

Various kinds of basic dyes are known, and the following are exemplified.

3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3.3-bis(p-dimethylaminophenyl)phthalide, 3-(P-dimethylaminophenyl)-3-(1,2 -dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-
3-(2-methylindol-3-yl)phthalide, 3
．． 3-bis(1,2-dimethylindol-3-yl)
-5-dimethylaminophthalide, 3,3-bis(1°2
-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-
3-yl)-6-dimethylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-
Triallylmethane dyes such as 3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'
-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2,4
, diphenylmethane dyes such as 5-trichlorophenylleucoauramine, penzoyl coico methylene blue,
Thiazine dyes such as p-nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-
Ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxyhenzo)
Spiro dyes such as spiropyran, 3-propyl-spirodiihenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (O-chloroanilino) lactam, 3-dimethylamino- 7-methoxyfluorane, 3
-diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6
-Methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-(N-ethyl-p
-Toluidino)-7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino-7-dibenzylaminofluoran Orane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N
-chloroethyl-N-methylaminofluorane, 3-diethylamine-7-N-diethylaminofluorane, 3
-(N-ethyl-p-)luidino)-6-methyl-7~
Phenylaminofluorane, 3-(N-ethyl-p-)
luidino)-6-methyl-7-(p-toluidino)fluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3-dibutylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino -7-(2-carbomethoxy-phenylamino)fluorane, 3-(N-cyclohexyl-N-methylamine)
-6-Methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl- 7-xylidinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-dibutylamino-7-(o-chlorophenylamino)fluoran, 3-
Pyrrolidino-6-methyl-7-P-butylphenylaminofluorane, 3-(N-methyl-Nn-amyl)amino-6-methyl-7-phenylaminofluorane, 3-
(N-ethyl-Nn-amyl)amino-6-methyl-
7-phenylaminofluorane, 3-(N-ethyl-N
-isoamyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-methyl-Nn-hexyl)
amino-6-methyl-7-phenylaminofluorane,
3-(N-ethyl-Nn-hexyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N-β-ethylhexyl)amino-6-methyl-7-
Phenylaminofluorane, 3-(N-ethyl-N-tetrahydrofurfuryl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N-cyclopentyl)amino-6-methyl-7- Fluoran dyes such as phenylaminofluorane. Of course, the dyes are not limited to these dyes, and two or more types of dyes can be used in combination.

Furthermore, various compounds are known as coloring agents used in combination with the above-mentioned basic dyes, for example, the following are exemplified.

4-tert-butylphenol, α-naphthol, β
-naphthol, 4-acetylphenol, 4-ter
t-octylphenol, 4.4'-5ec-butylidene diphenol, 4-phenylphenol, 4.4'-
Dihydroxy-diphenylmethane, 4゜4'-isopropylidenediphenol, hydroquinone, 4,4'-cyclohexylidenediphenol, 4.4'-(1,3
-dimethylbutylidene)bisphenol, 2,2-bis(4-hydroxyphenyl)-4-methyl-penkune,
4.4'-dihydroxydiphenyl sulfide, 4.
4'-thiobis(6tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone,
4-hydroxy-4'-methoxydiphenyl sulfone,
4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-3', 4'-trimethylene diphenyl sulfone, 4-hydroxy-3', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4' -methyldiphenylsulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 1,3-di(2
-(4-hydroxyphenyl)-2-propyl]benzene, hydroquinone monobenzyl ether, bis(4-hydroxyphenyl)acetic acid butyl ester, 4-hydroxybenzophenone, 2゜4-dihydroxybenzophenone, 2,4.4'-tri Hydroxybenzophenone, 2
．． 2', 4゜4'-tetrahydroxybenzophenone,
Dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-5
ec-butyl, pentyl 4-hydroxybenzoate, 4-
Phenyl hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, P-chloro 4-hydroxybenzoate benzyl, 4-
Phenolic compounds such as hydroxybenzoic acid-ρ-methoxybenzyl, novolac type phenolic resin, phenol polymer, benzoic acid, p-Lert-butylbenzoic acid,
Trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4
-Hydroxybenzoic acid, 3.5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3.5-di-L
er t-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid ,3
, 5-di-α-methylbenzyl salicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, aluminum, etc.
Organic acidic substances such as salts with polyvalent metals such as calcium, titanium, manganese, tin, and nickel. Note that, of course, two or more of these coloring agents can be used in combination as necessary.

The usage ratio of the basic dye and coloring agent is appropriately selected depending on the type of basic dye and coloring agent used, and is not particularly limited. 100 to 700 parts by weight, preferably 150 to 4 parts by weight
About 0.00 parts by weight of coloring agent is used.

Preparation of coating liquids containing these generally uses water as a dispersion medium,
It is prepared by dispersing the dye and coloring agent together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand mill.

Such coating liquids usually contain starches and binders as binders.
Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene/maleic anhydride copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, etc. have a total solid content. 2 to 40% by weight, preferably 5 to 25% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid.
Examples include dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salts, other antifoaming agents, fluorescent dyes, and coloring dyes.

Furthermore, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined resin, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay may be added to improve the adhesion of residue to the recording head. Further, a dispersion or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. may be added to prevent sticking from contact with a recording device or a recording head.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide, 2,2'-methylene bis(4
-methyl-6-tert-butylphenol), 4.4
'-Butylidenebis(6tert-butyl-3-methylphenol), 1.1.3-tris(2-methyl-4-
Hindered phenols such as hydroxy-5-tert-butylphenyl)butane, p-benzylbiphenyl,
1.2-bis(phenoxy)ethane, 1.2-bis(4
Ethers such as -methylphenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, and 2-naphtholbenzyl ether; esters such as dibenzyl terephthalate and 1-hydroxy-2-naphthoic acid phenyl ester [2-( Ultraviolet absorbers such as 2'-hydroxy-51-methylphenyl)benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, and various known thermofusible substances can also be used together as sensitizers.

In the method of the present invention, the method of forming the recording layer is not particularly limited, and can be formed according to conventionally well-known and commonly used techniques. For example, a suitable coating device such as an air knife coater, a blade coater, a bar coater, a gravure coater, a curtain coater, etc. can be used to apply a coating liquid for a heat-sensitive recording layer onto a base paper.

Further, the amount of the coating liquid to be applied is not particularly limited, and is generally adjusted within the range of 2 to 12 g/rrf, preferably 3 to 10 g/rd in terms of dry weight.

It is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, etc. A protective layer may be provided on the back side of the base paper, or an undercoat layer may be provided between the base paper and the heat-sensitive recording layer. Of course, it is also possible to provide a heat-sensitive recording paper, and further, various known techniques in the field of heat-sensitive recording paper manufacturing, such as applying adhesive processing, can be added.

``Example J'' The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Note that parts and % in the examples indicate parts by weight and % by weight, respectively, unless otherwise specified.

Example 1 ■ Preparation of base paper An on-machine soft calender with a pressure nip consisting of a metal roll with a diameter of 420M with a hard chrome-plated surface and an elastic roll with a Shore D hardness of 78 degrees and a diameter of 400A+m was used to produce a regular reflective smooth paper. A flattening process (nip pressure 80 kg/rrr) of angry abrasive paper (40 g/rrr) with a measurement value (pressure condition 20 kg/cffl) using a thermometer of 8% was performed.
c+++) I. A base paper for heat-sensitive recording paper having a specular reflection type smoothness of 20% was prepared.

■ Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-phenylaminofluorane 10 parts Methyl cellulose 5% aqueous solution 20 parts water
10 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

■ Preparation of liquid B Bisphenol A 30 parts Methyl cellulose 5% aqueous solution 70 parts water
20 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

■ Preparation of thermal recording paper 40 parts of liquid A, 80 parts of liquid B, silicon oxide pigment (oil absorption: 1
80 m1/100 g), 100 parts of a 20% oxidized starch aqueous solution, and 70 parts of water were stirred and mixed to prepare a coating liquid for thermal recording. The resulting coating liquid was applied and dried on the base paper obtained in step (1) above so that the coated amount after drying was 7 g/rd, and then supercalendered to obtain heat-sensitive recording paper.

Example 2 Shore D elastic roll of on-machine soft calender
Change to an elastic roll with a hardness of 87 degrees and set the nip pressure to 160 k.
A base paper for heat-sensitive recording paper having a specular reflection type smoothness of 18% was prepared in the same manner as in Example 1, except that the smoothness was changed to g/cm.

Comparative Example I A base paper for heat-sensitive recording paper having a specular reflection type smoothness of 12% was prepared using a regular machine calender consisting of a combination of chilled rolls instead of an on-machine soft calender, and the following procedure was repeated in the same manner as in Example 1. A thermosensitive recording paper was obtained.

Comparative Example 2 Niff pressure of on-machine soft calender Okg/c
A base paper for thermal recording paper having a specular reflection type smoothness of 7% was prepared in the same manner as in Example 2, except that m was used, and thermal recording paper was obtained in the same manner as in Example 2.

The four types of thermal recording paper thus obtained were printed using an ultra-high-speed thermal printer (UP-103, manufactured by Sony Corporation) at a head voltage of 15.5 volts and a pulse width of 6 ms, and the image density was measured using a Macbeth densitometer. It was measured and the results are shown in the table.

In addition, background stains on the surface of the recording layer were visually determined and the results are also listed in the table. The evaluation criteria were [◎...extremely excellent]. Δ: Slight stains are observed. x: Significant staining was observed].

Table "Effects" As is clear from the results in the table, all of the thermal recording papers of the present invention did not cause background staining (exhibited excellent image density).

Patent applicant: Kanzaki Paper Co., Ltd.

Claims (5)

[Claims] (1) Use a metal roll and a Shore D hardness of 42 to 98 degrees (ASTM standard,
A method for producing base paper for thermosensitive recording paper, characterized in that the paper is flattened by passing the paper through a pressure nip constituted by an elastic roll having the following properties: D-2240). (2) The manufacturing method according to claim 1, wherein the elastic roll has a Shore D hardness of 70 to 95 degrees. (3) The manufacturing method according to claim (1), wherein the metal roll is heated to at least 80°C or higher. (4) The manufacturing method according to claim (1), wherein the pressure nip is a pressure nip of an on-machine soft calender. (5) The manufacturing method according to claim (1), wherein the base paper is flattened so that the measured value with a specular reflection type smoothness meter is 14% or more.