JPH04164684A - Preparation of thermal recording sheet - Google Patents

Abstract

PURPOSE:To stably prepare a thermal recording sheet having no whiteness or smoothness irregularity on the surface of its recording layer and excellent in high speed recording aptitude over a long time by passing the recording sheet through the pressure nip formed between a specific elastic roll and a metal roll so that the surface of the recording layer thereof comes into contact with the surface of the metal roll to apply smoothing treatment to the recording layer. CONSTITUTION:In preparing a thermal recording sheet, the recording sheet is passed through the pressure nip formed between an elastic roll finished so that the thickness of the elastic layer thereof is 7-20mm and cooled so that the surface temp. thereof is 10-40C and a metal roll so that the surface of the recording layer thereof comes into contact with the surface of the metal roll to be subjected to smoothing treatment. When the thickness of the elastic layer is less than 7mm, the heat generated in the elastic layer of the roll can be transmitted to the iron core of the roll within a short time but the surface of the sheet is excessively subjected to smoothing treatment and the contact area with a recording head increases and the contamination of the head is generated. When said thickness exceeds 20mm, the heat generated in the elastic layer can not be transmitted to the iron core and the thermal deterioration due to heat generation or the generation of abnormal sound is brought about.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a high-quality heat-sensitive recording sheet.

(Prior Art) In the thermal recording method, a thermal recording head (hereinafter simply referred to as head) is generally heated in response to an input signal, and the color forming agent on the recording sheet in contact with the head is brought into molten contact with the color forming agent to form a color. It is a recording method that obtains images, has a recording speed commensurate with the amount of information in the band that can be carried over telephone lines, is a primary coloring system that does not require developing or fixing processes, and has extremely low wear on the head, making it suitable for printers, It is rapidly being applied to information devices such as facsimiles.

In particular, with the remarkable increase in the amount of information in recent years, there has been a shift from the early so-called low-speed machines (recording time for one A4 page in about 6 minutes) to high-speed machines (about 1 minute) to even higher ultra-high-speed machines (
(approximately 3 seconds) are also being put into practical use. As the speed of such recording devices increases, various improvements have been made to the recording sheets used therein.

Smoothening the surface of the recording layer is one of these, and is being considered as an important countermeasure in terms of improving the contact between the head and the surface of the recording layer and facilitating heat transfer.

However, when a high-speed heat-sensitive recording sheet with a recording layer whose composition is formulated to increase recording sensitivity is processed with a normal supercalender or various smoothing devices built into a coater, the surface of the recording layer becomes highly smooth. However, unnecessary white unevenness occurs over the entire surface of the recording layer, resulting in a recording layer with significantly reduced whiteness.

Therefore, at present, it is necessary to perform a light surface treatment at the expense of smoothness, or to perform a smoothing treatment at the expense of the whiteness of the surface of the recording layer.

In view of the above-mentioned current situation, the present inventors have conducted extensive research in order to develop a method for appropriately smoothing the surface of the recording layer without causing white unevenness. In particular, as a result of comprehensive studies on the structure and material of the rolls that make up the pressure nip of the smoothing device, operating conditions, and even the composition of the recording layer, we found that By using an elastic roll made of woolen paper with a Shore D hardness of 42 to 69 degrees, which has a softness that was completely unimaginable with conventional pressure smoothing devices, high-speed recording is possible without white unevenness on the surface of the recording layer. It has been found that it is possible to smoothen the surface of a recording layer having the following properties.

However, using such an elastic roll.

When performing smoothing treatment, if the nip linear pressure is not applied uniformly across the width of the elastic roll and the distribution is slightly uneven, the fibers that make up the elastic body may shift or twist. Over a short period of time, thermal deterioration due to heat generation and generation of abnormal noises may occur, and in some cases, carbonization may even progress to the point where the roll becomes black and scorched, making the roll unusable. Moreover,
During this time, undesirable white unevenness or smoothness unevenness occurs on the surface of the recording layer of the heat-sensitive recording sheet treated with this roll, which may result in a defective product.

(Problems to be Solved by the Invention) The present invention provides a method for stably producing a heat-sensitive recording sheet over a long period of time that has no white unevenness or smooth unevenness on the surface of the recording layer and has excellent high-speed recording suitability. It is something to do.

(Means for Solving the Problems) The present invention provides an elastic roll and a metal roll that are finished so that the elastic layer has a thickness of 7 to 20 days and are cooled so that the surface temperature thereof is in the range of 10 to 40°C. The present invention provides a method for producing a heat-sensitive recording sheet, characterized in that the sheet is passed through a pressure nip formed by the above method so that the surface of the recording layer comes into contact with the surface of a metal roll, and then subjected to a smoothing treatment.

(Function) The method for producing a heat-sensitive recording sheet of the present invention will be explained in more detail.

The method for producing a heat-sensitive recording sheet of the present invention comprises an elastic roll whose elastic layer is finished to have a thickness in a specific range and whose surface temperature is cooled to a specific range, and a metal roll. The paper is passed through the pressure nip so that the surface of the recording layer comes into contact with the surface of the metal roll, and is smoothed.

The elastic roll used in this manufacturing method preferably has a thickness of 1 nm so that the elastic layer of the roll has a thickness of 7 to 201 nm.
0 to 18 cranes, and on the surface of the roll
It is cooled from the inside to a temperature in the range of ~40°C.

By the way, the reason why the thickness of the elastic layer of the roll is limited to a specific range of 7 to 20 m as mentioned above is that the thickness of the elastic layer of the roll is limited to a specific range that is much thinner than in the conventional case. By limiting the heat generated inside the elastic layer of the roll to the roll iron core cooled by cooling water, it is possible to transfer the heat generated inside the elastic layer of the roll to the roll iron core cooled by cooling water. Therefore, the elastic body does not undergo thermal deterioration due to heat generation, or abnormal noise is not generated.

Incidentally, if the thickness of the elastic layer of the obtained elastic roll is smaller than 7n, the heat generated inside the elastic layer of the roll cannot be transferred to the cooled roll iron core in a short time. However, the surface of the sheet must be excessively smoothed, and as a result, the contact area with the recording head increases, causing staining of the head and making it unusable.

On the other hand, when the thickness exceeds 20 mm, the surface of the sheet can be sufficiently smoothed, but the heat generated inside the elastic layer of the roll can be reduced by cooling the iron core in a short period of time. As a result, thermal deterioration due to heat generation and abnormal noise occur.

In addition, since the elastic roll used in the method of the present invention is a soft roll, it easily generates heat (the heat generation phenomenon causes the physical properties of the elastic body to become unstable, and in extreme cases, the elastic body itself accumulates). The heat generated may even cause melting damage.

Therefore, a refrigerant is introduced into the inside of the roll to cool the roll to a temperature in the range of 10 to 40°C on the surface thereof, and various measures such as cooling from the outside can be adopted as appropriate.

The elastic layer of the elastic roll is not particularly limited as long as the hardness falls within the specified range below, and examples include natural rubber, styrene rubber, nitrile rubber, chloroprene rubber, chlorosulfonated ethylene rubber, butyl rubber, and polysulfide rubber. , rubbers such as silicone rubber, fluorine rubber, and urethane rubber, and various plastic resins such as incyanate-based heat-resistant resins.

Note that when an elastic roll having an elastic layer made of rubber, plastic resin, or a combination thereof is used, the life of the roll becomes longer and the desired effects of the present invention can be efficiently obtained, so this embodiment is a preferred embodiment of the present invention. This is one of the embodiments.

In addition, the Shore D hardness of the elastic layer (ASTM standard, D-2
240) is softer than 70 degrees, an excessive nip line pressure is required to obtain sufficient surface smoothness, and as a result, the life of the elastic body itself is significantly shortened. However, with an elastic roll harder than 85 degrees, it is difficult to effectively prevent a decrease in whiteness, so the Shore D hardness of the elastic roll is 70 to 85 degrees, preferably 75 to 8.
It is adjusted to a range of 0 degrees.

In the method of the present invention, the metal rolls forming the pressure nip with the specific elastic roll are not particularly limited, and include chilled rolls used in normal smoothing processing equipment such as super calenders and gloss calenders; A chilled alloy roll, a steel roll, a metal roll whose surface is plated with hard chrome, etc. are appropriately selected and used. The form of the pressurizing device, the number of pressurizing nips, etc. are also adjusted as appropriate in accordance with ordinary smoothing processing devices.

Then, a heat-sensitive recording sheet is passed through this pressure nip so that the surface of the recording layer contacts the surface of the metal roll, and the surface of the recording layer is smoothed. It is appropriately adjusted depending on the hardness of the elastic roll, the type of recording sheet, and various other processing conditions such as speed, number of nips, and temperature conditions.

It is desirable to adjust the nip linear pressure within the range of 30 to 300 kg/am; if it is lower than 30 kg/cx, even if a relatively hard elastic roll is used, it will not be possible to record under operational conditions that prevent the occurrence of color unevenness. Defects in sheet thickness, etc. may occur,
It becomes difficult to obtain satisfactory high-speed recording aptitude. In addition, if the weight exceeds 300 kg/aa, even if a particularly soft elastic roll is used, it becomes difficult to prevent a decrease in whiteness and excessive smoothness, and the heat generation phenomenon of the elastic roll itself increases significantly. Stable operation becomes impossible.

With the method of the present invention, even if the recording layer is composed of a composition with increased recording sensitivity suitable for high-speed recording, the surface of the recording layer can be smoothed without reducing whiteness or causing unnecessary uneven color development or uneven smoothness. As a result, a heat-sensitive recording sheet with improved suitability for high-speed recording can be obtained extremely efficiently.

The reason why such excellent effects can be obtained is not necessarily clear, but by using an elastic roll finished so that the thickness of the elastic layer is 7 to 20 mm,
Because the pressure nip is as wide as 5 tl, the distribution of local nip pressure across the width of the nip is completely different from that of conventional super calendars, and as a result, unnecessary uneven coloring can be effectively prevented. Moreover, it is presumed that an appropriate smoothing effect on the surface of the recording layer is produced.

Therefore, according to the method of the present invention, it is possible to process a heat-sensitive recording sheet having a recording layer having a composition with significantly increased recording sensitivity as described above. 35% by weight or less, more preferably 2
It is also possible to smoothen the recording layer with a content of 5% by weight or less.

The heat-sensitive recording sheet to be smoothed by the method of the present invention is not particularly limited, but generally a heat-sensitive coating liquid containing a coloring agent consisting of a colorless or light-colored basic dye, a coloring agent, and a binder is used. A recording sheet coated on a support is used.

Examples of colorless to light-colored basic dyes include 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-dimethylindole-3-yl) yl)-6-dimethylaminophthalide, 3,3-bis(9-nitylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3-bis(2-
phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(l
triallylmethane dyes such as -methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'-bis-
Dimethylaminobenzhydrylbenzyl ether, N-
Diphenylmethane dyes such as halophenyl leuco auramine and N-2,4,5-trichlorophenyl leuco auramine, thiazine dyes such as benzoyl leucomethylene blue and p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3 -Ethyl-
Spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran,
Spiro dyes such as 3-methyl-naphtho-(6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (0
-lactam dyes such as 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
-Simethylfluorane, 3-(N-ethyl-p-)luidino)-7-methylfluorane, 3-diethylamino-
7-N-acetyl-N-methylaminofluorane, 3-
diethylamino-7-N-methylaminofluorane, 3
-diethylamino-7-dibenzylaminofluorane,
3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-(N-
Ethyl-p-)luidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-)luidino)fluorane,
3-diethylamino-6-methyl-7-phenylaminofluorane, 3-dibutylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7-(
2-Carbomethoxy-phenylamino)fluorane, 3
-(N-cyclohexyl-N-methylamino)-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)fluorane, 3-dibutylamino-7-(
o-chlorophenylamino)fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3-(N-methyl-Nn-amyl)amino-6
-Methyl-7-phenylaminofluorane, 3-(N-
Ethyl-N-n-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-N-n-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 Examples include fluoran dyes such as -N-cyclopentyl)amino-6-methyl-7-phenylaminofluoran.

In addition, various organic color developers that develop color upon contact with basic dyes are known, such as 4-tert-butylphenol, α-naphthol, β-naphthol, 4-acetylphenol, 4-tert-octylphenol. , 4
．． 4'-5ec-butylidene diphenol, 4-phenylphenol, 4,4'-dihydroxy-diphenylmethane, 4.4" isopropylidene diphenol, hydroquinone, 4.4'-cyclohexylidene diphenol, 4°4'- (1,3-dimethylbutylidene)bisphenol, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(6-tert-butyl-
3-methylphenol), 4.4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4 -hydroxy-3',4'-)
Rimethylene diphenyl sulfone, 4-hydroxy-3'
, 4'-tetramethylene diphenyl sulfone, 3.4-
Dihydroxy-41-methyldiphenylsulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 1
, 3-di(2-(4-hydroxyphenyl)-2-propyl)benzene, hydroquinone monobenzyl ether,
bis(4-hydroxyphenyl) vinegar M butyl ester,
4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2.4.4'-)dihydroxybenzophenone, 2. 2', 4. 4'-tetrahydroxyhensiphenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-
5ec-butyl hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate,
Benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate,
Phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-4-hydroxybenzoate
-Chlorobenzyl, 4-hydroxybenzoin ft1. -p
- Phenolic compounds such as methoxybenzyl, novolac type phenolic resins, phenol polymers, benzoic acid, p
-tert-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-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl) Aromatic carboxylic acids such as salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3.5-di-α-methylbenzylsalicylic acid, and organic acidic substances such as these phenolic compounds, salts of aromatic carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel.

Further, examples of organic thermofusible substances suitably blended into the heat-sensitive recording layer include stearamide, methylene bisamide stearate, oleic acid amide, palmitic acid amide,
Fatty acid amide such as coconut fatty acid amide, 2,2'-methylenebis(4-methyl 6-tert-butylphenol)
, 4,4'-butylidene bis(6-tert-butyl-
3-methylphenol), 1,1.3-1-lis(2-
Hindered phenols such as methyl-4-hydroxy-5-tert-butylphenyl)butane, p-hensylbiphenyl, 1,2-bis(phenoxy)ethane, 1.
Ethers such as 2-bis(4-methylphenoxy)ethane, 1.2-bis(3-methylphenoxy)ethane, 2-naphtholhensylniter, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid phenyl ester, etc. esters, 2-(2'-hydroxy-5'-
Examples include ultraviolet absorbers such as methylphenyl)benzotriazole and 2-hydroxy-4-benzyloxyhensiphenone.

The usage ratio of the basic colorless dye and the color developer in the recording layer is generally about 1 to 50 parts by weight, preferably about 1 to 10 parts by weight, per 1 part by weight of the basic colorless dye, to form the recording layer. In addition to the basic colorless dye and developer, the coating liquid contains adhesive components such as starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose,
Gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer salt, ethylene/acrylic acid copolymer salt, styrene/acrylic acid copolymer salt, natural Rubber emulsion, styrene/butadiene copolymer emulsion, acrylonitrile/butadiene copolymer emulsion, methyl methacrylate/butadiene copolymer emulsion, polychloroprene emulsion, vinyl acetate emulsion, ethylene/vinyl acetate emulsion, etc. are added.

In addition, as pigment components, for example, diatomaceous earth, calcined diatomaceous earth, kaolin, calcined kaolin, white carbon, magnesium carbonate, calcium carbonate, zinc oxide, aluminum oxide, titanium oxide, silicon oxide, aluminum hydroxide, barium acid, zinc sulfate, Inorganic pigments such as talc, clay, and calcined clay, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea/formalin resin filler, raw starch granules, etc. may be added, but are of course limited to these exemplified substances. It is also possible to use two or more types together if necessary.

Furthermore, various other auxiliary agents can be added to the recording layer coating solution, such as sodium dioctyl sulfosuccinate, sodium dodecylhenzenesulfonate, sodium lauryl alcohol sulfate, alginate, fatty acid metal. Examples include dispersants such as salts, various heat-fusible substances as described above, antifoaming agents, fluorescent dyes, and colored dyes.

The method of forming the recording layer is not particularly limited either, and examples include a method of applying a recording layer forming coating liquid onto a support using an appropriate coating device such as an air knife coater, a blade coater, a bar coater, a gravure coater, a multilayer coater, etc. and drying it. formed by.

The amount of coating liquid to be applied is also not particularly limited, and is generally about 2 to 12 g/rd in terms of dry weight, preferably 3 to 10 g/rd.
It is adjusted within a range of about %.

The support is not particularly limited, and may include papers such as high-quality paper, base paper made with a Yankee machine, single-sided glossy base paper, double-sided glossy base paper, cast coated paper, art paper, coated paper, medium-quality coated paper, and synthetic fibers. Paper, synthetic resin film, etc. are used as appropriate.

Further, various known techniques in the field of heat-sensitive recording materials can be added, such as providing an overcoat layer on the recording layer for the purpose of protecting the recording layer, or providing an undercoat layer or a backing layer on the support.

"Examples" The present invention will be described in more detail with reference to Examples below, but it is of course not limited to these Examples. Further, unless otherwise specified, parts and % in the examples represent "parts by weight" and "% by weight", respectively.

[Fine pulverization treatment of basic dye dispersion]

100 parts of 3-(N-ethyl-1so-pentyl)amino-6-methyl-7-ayurinofluorane 300 parts of rosebenzylbiphenyl 400 parts of a 2% aqueous solution of polyvinyl alcohol and a 2% aqueous solution of methylcellulose 1 part of dioctyl sodium sulfosuccinate Prepare an aqueous dispersion of a basic dye consisting of a conical ball mill (trade name: COBA
LL-MILL (manufactured by FRYMA in Switzerland) with circumferential speed of 15m
A basic dye aqueous dispersion was prepared by wet milling at a flow rate of 72 kg/hr and a flow rate of 72 kg/hr.

[Preparation of coating liquid for thermal recording paper]

Bisphenol A (manufactured by Mitsui Toatsu) 300 parts, water 450 parts
parts, 455 parts of an aqueous solution containing 5 parts of methyl cellulose,
Color developer dispersion 905.5 with an average particle size of 2.0 μm obtained by stirring and pulverizing 0.5 parts of sodium dioctyl sulfosuccinate
1,000 parts of a 10% aqueous solution of methyl methacrylate/acrylamide copolymer and 100 parts of amorphous silicon oxide were thoroughly mixed with a propeller mixer, and then 30 parts of a 30% aqueous dispersion of zinc stearate was added. A coating liquid for heat-sensitive recording paper was prepared by adding and stirring 826 parts of the basic dye aqueous dispersion obtained in the above method.

[Manufacture of thermal recording paper]

A 35 parts aqueous dispersion consisting of 100 parts of amorphous silicon oxide, 10 parts of styrene-butadiene copolymer latex (solid content), and 2 parts of carboxymethyl cellulose (solid content) was coated on a base paper of 50 g/rd using a blade coater. The coating was applied and dried so that the coating amount after drying was 7 g/m.

On this coated surface, the above-mentioned coating liquid for heat-sensitive recording paper was applied and dried using a blade coater so that the coating amount after drying was 3.5 g/tri.

(Example 1) The surface of a roll made of isocyanate-based heat-resistant resin was polished with a grinder so that the thickness of the elastic layer was 13 degrees, thereby obtaining an elastic roll having a Shore D hardness of 78 degrees.

Using a two-stage super calendar consisting of the obtained elastic roll and a chilled steel swimming roll with an outer diameter of 300 mm, the nip linear pressure was 70 kg/cm and the speed was 500 m/cm.
Under conditions of 10 minutes, the thermal recording paper was passed through the elastic roll so that the surface of the recording layer was in contact with the metal roll surface while internally cooling the elastic roll so that the surface temperature did not exceed 20°C. Obtained.

(Example-2) In Example-1, except that an elastic roll with an elastic layer thickness of 19°C was used and internal cooling was performed so that the surface temperature of the elastic roll did not exceed 15°C. A thermosensitive recording paper was obtained in the same manner as in Example-1.

(Example 3) Example 1 except that an elastic roll with an elastic layer thickness of 8N was used and the process was performed while internally cooling the elastic roll so that the surface temperature did not exceed 12°C. A thermosensitive recording paper was obtained in the same manner as in -1.

(Example-4) The same procedure as in Example-1 was carried out, except that the elastic layer was made of rubber and the elastic roll was cooled internally so that the surface temperature did not exceed 15°C. A thermosensitive recording paper was obtained.

(Example-5) In Example-4, an elastic roll with an elastic layer thickness of 8N was used, and the process was performed while internally cooling the elastic roll so that the surface temperature did not exceed 12°C. A thermosensitive recording paper was obtained in the same manner as in Example 4.

(Comparative Example-1) In Example-1, an elastic roll having an elastic layer made of woolen paper with a thickness of 80 nm and a Shore D hardness of 81 degrees was used, and the internal temperature was adjusted so that the surface temperature of the roll did not exceed 30°C. A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the recording paper was cooled.

(Comparative Example-2) In Comparative Example-1, an elastic roll was used in which the elastic layer was made of urethane rubber with a thickness of 30 degrees and the Job-D hardness was 80 degrees, and the surface temperature of the roll was made to not exceed 43 degrees Celsius. A thermosensitive recording paper was obtained in the same manner as in Comparative Example 1, except that the nip linear pressure was 80 kg/am while internal cooling was performed.

Seven types of heat-sensitive recording papers thus obtained were subjected to comparative tests for Bekk smoothness and whiteness of the surface of the recording layer, print density, image quality, and capri (mottle).

We also compared the occurrence of torsion in the elastic body and the abnormal noise generated during operation, and the results, including the overall judgment, are shown in a separate table.

Please note that the print density is determined by a commercially available thermal facsimile (product name:
The color density of the recorded image recorded using a NEFAX-2 (manufactured by NEC Corporation) was measured using a Macbeth densitometer (manufactured by Macbeth Corporation, RD).
-100R type).

Moreover, the whiteness was measured using a Hunter whiteness meter.

Regarding the image quality, the degree of printing unevenness in the halftone part of the above print was visually judged, and the degree of fogging (mottle) was visually judged by the degree of partial decrease in whiteness on the paper surface.

The evaluation criteria for image quality, capri (7 torr), occurrence of twisting in the elastic body, occurrence of abnormal noise during operation, and overall judgment are as follows.

1: Extremely excellent 2: Excellent 3; Fair 4: Slightly inferior 5: Extremely inferior [Effect] According to the method for producing a heat-sensitive recording sheet of the present invention, as is clear from the results in the table, Heat-sensitive recording sheets of excellent quality can be produced stably over a long period of time without unnecessary color unevenness or smoothness unevenness during smoothing treatment, which tends to occur when producing using soft elastic rolls. Stable operation was possible with no twisting or abnormal noise.

Claims (3)

[Claims] (1) The recording layer is placed in a pressure nip formed by an elastic roll and a metal roll, which are finished so that the thickness of the elastic layer is 7 to 20 mm and are cooled so that the surface temperature is in the range of 10 to 40°C. A method for producing a heat-sensitive recording sheet, which comprises passing the sheet so that its surface is in contact with a metal roll surface and subjecting it to a smoothing treatment. (2) The method for producing a heat-sensitive recording sheet according to claim (1), wherein rubber, plastic resin, or a combination thereof is used as the elastic layer. (3) Shore D hardness of the elastic layer (ASTM standard, D-2
240) is 70 to 85 degrees, the method for producing a heat-sensitive recording sheet according to claim 1.