JPH03140287A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To adapt the title recording paper to an ultrahigh speed machine by improving recording sensitivity without being accompanied by the generation of scumming by using base paper composed of a pulp composition containing a specific amount or more of regenerated pulp prepared using old paper as a raw material and characterized by that the measured value of the surface thereof due to a regular reflection type smoothness meter is specific. CONSTITUTION:Base paper compound of pulp composition containing 10wt.% or more of regenerated pulp and characterized by that the measured value of the surface thereof due to a regular reflection type smoothness meter is 8% or more under pressure of 20kg/cm<2> is used. The repulpable feedstock such as a non-printed high quality white, a ruled high quality white or creamy colored, a non-printed high quality creamy colored, a card, a non- printed intermediate quality white a non-printed denatured white, a printed high quality imitation, a printed colored high quality including art, a Kent, a non-printed art, a color printed intermediate quality, a color printed denatured, a news, a magazine, etc., papers can be employed. The regenerated pulp is treated by a beater in the front process of a papermaking machine and lowered to about 30-150ml in Canadian Standard Freeness before use. In the surface smoothing treatment of the base paper, it is effective to use a super calender or gloss calender constituted of a metal roll and an elastic roll according to an on-machine or off-machine system.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a thermal recording paper, and particularly to a thermal recording paper that has a recording sensitivity that is sufficiently applicable to ultra-high-speed machines without causing background stains.

"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 brings a recoloring substance into contact with heat to obtain a colored image. 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.

Furthermore, with the remarkable increase in the amount of information in recent years, development of high-speed machines (G11 machines) and even higher-speed machines (GIV machines) in the field of facsimile, for example, 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.

On the other hand, in recent years, paper, which is included in municipal waste, has received particular attention as well as resource protection. Furthermore, paper generated by households and offices is contributing to an increase in the amount of municipal waste. Therefore, it is desired to collect such waste paper and use it as a raw material.

``Problem to be solved by the invention'' However, conventional proposals have focused on improving the materials that make up 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 found that these drawbacks are largely caused by the characteristics of the base paper that makes up the thermal recording paper, especially the characteristics of the pulp that makes up the base paper. .

In other words, chemical pulp has traditionally been used as the pulp constituting base paper, but satisfactory results have not been obtained even after various adjustments to the beating conditions and paper-making conditions. When blended with recycled pulp (recycled pulp) and adjusted to a specific value for the smoothness of the base paper surface measured with a special smoothness meter, thermal recording paper using that base paper will suffer from surface stains. The present inventors have now completed the present invention by discovering that the recording sensitivity is significantly improved without any problems, and as a result, it is possible to easily obtain a heat-sensitive recording paper that is fully compatible with ultra-high-speed machines.

"Means for Solving the Problems" The present invention is characterized in that the total pulp composition contains 10% by weight or more of recycled pulp, and the measured value of the surface of the base paper with a specular reflection type smoothness meter is under a pressure condition of 20 kg/ci. This heat-sensitive recording paper is characterized by using a base paper having a content of 8% or more.

"Function" The thermal recording paper of the present invention uses a base paper containing 10% by weight or more of recycled pulp in the total pulp composition. In comparison, the compressive elastic modulus of the base paper is lower and its thermal conductivity is lower, so even if the recording sensitivity of the recording layer is increased enough to respond to the minute thermal energy from the recording head, the relationship between the recording head and the recording paper will deteriorate. Heat is concentrated at the contacts of
It is presumed that heat is difficult to conduct to areas other than the contact points, and as a result, highly sensitive recording is possible without causing background stains. Incidentally, if the recycled pulp is less than 10% by weight, a sufficient improvement effect cannot be expected.

Specific examples of raw materials for recycled pulp include top white, ruled white, cream top white, card, special white, medium white, imitation, colored clay, gent, white art, special top cut, special top cut, newspaper, and Ni. Examples include magazines, etc. (used paper standard quality specification table = compiled by the Used Paper Recycling Promotion Center). Regenerated pulp is generally obtained by appropriately combining a disintegration process, a rough selection process, a fine selection process, a deinking process, and a bleaching process. In the disintegration process, low concentration pulper, high concentration pulper, etc. are used, screens, cleaners, etc. are used in the rough selection process and fine selection process, and in the deinking process, flotation method, water washing method, compromise method, etc. selected based on quality.

Note that if the obtained recycled pulp is blended without being treated, there is a risk that the smoothness of the surface of the base paper and the paper strength of the base paper will decrease. Therefore, it is preferable to treat the untreated recycled pulp with a beating machine in the pre-process of the paper machine, and it is preferable to reduce the Canadian Standard freeness of untreated recycled pulp in the range of about 30 to 150 degrees. If the beating is less than 30 d, a sufficient smoothness improvement effect cannot be obtained, and if the beating is more than 150 d, the compressive modulus of the obtained base paper becomes high, and the desired effect of the present invention is not achieved. There is a risk that it will become small.

As the refining machine, a conical refiner, a single disc refiner, a double disc refiner, etc. are used, but in consideration of power, it is more preferable to use a double disc refiner.

In the thermal recording paper of the present invention, as described above, recycled pulp is
A base paper containing 20% by weight or more is used, and the surface of the base paper is measured using a specular reflection smoothness meter (measurement pressure: 20% by weight).
It is necessary to process so that the measured value in kg/cm"2 is 8% or more, more preferably 14% or more.

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 according to the detailed study results of the inventors, - It is not affected by the air permeability of the paper, unlike the Heck smoothness meter and Barker Printsurf, which are air leak type smoothness measuring instruments, and can provide measurement values that have an excellent correlation with the actual smoothness. Moreover, this specular reflection type smoothness meter (measurement pressure;
It has become clear that the desired effects of the present invention can be determined very appropriately from the measured values at 20 kg/cm''), and the present invention has been completed.

Incidentally, a specular reflection type smoothness meter (measurement pressure: 20 kg) on the surface of the base paper was used.
/cm2) is less than 8%, even if the base paper contains 10% by weight or more of recycled pulp, the contact between the recording paper and the recording head will be uneven, and the density of the recorded image will also decrease. Therefore, the desired effect of the present invention cannot be obtained.

For smoothing the surface of base paper, machine calenders consisting only of metal rolls installed at the rear of Fourdrinier or circular wire paper machines can also be used, but supercalendar gloss calenders consisting of metal rolls and elastic rolls can also be used. It is effective to use a soft calendar, etc., on-machine or off-machine.

As the metal roll, for example, a chilled roll, an alloy chilled roll, a steel roll, or a metal roll whose surface is plated with hard chromium, etc. are appropriately selected and used, and as an elastic roll, for example, natural rubber, styrene rubber, nitrile rubber, chloroform etc. are used. Various plastic resins such as Brene rubber, chlorosulfonated ethylene rubber, butyl rubber, polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, aromatic polyamide resin, polyimide resin, polyether resin, polyester resin, polycarbonate resin, cotton, and paper. An elastic roll made of , wool, Tetoron, nylon, or a mixture thereof is appropriately selected and used.

Note that, in terms of efficiency, on-machine smoothing treatment is preferable, and in this case, a calender composed of elastic rolls having a Shore D hardness of 42 to 98 degrees (ASTFI standard, D-2240) is particularly preferably used. Among these, elastic rolls made of urethane rubber, aromatic polyamide resin, a mixture of paper and wool, 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 preferred. 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 exhibit the desired effects of the present invention.

The elastic rolls described above are softer than ordinary elastic rolls and 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 various measures such as cooling from the outside, changing the diameter of the roll, and changing the thickness of the elastic body are adopted as appropriate.

On-machine super calenders and on-machine soft calenders, which are composed of metal rolls and elastic rolls, are published in Paper and Pulp Technology Times August 1985 issue (page 31) and in 1988.
It is introduced in the May issue (page 10), etc. Further, processing conditions are appropriately adjusted depending on the number of nips, nip linear pressure, machine speed, etc.

Note that it is also possible to smooth the base paper surface by using a Yankee dryer whose dryer surface is mirror-treated with hard chrome plating, etc., as the dryer of the paper machine, but in any case, regular reflection type smoothing of the base paper surface is possible. The measured value with a thermometer (measurement pressure: 20 kg/cm'') must be 8% or more.

A heat-sensitive recording layer is formed on the base paper thus obtained according to a conventional method, and various combinations of coloring substances can be used to form the recording layer. Specifically, the following are 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.
180°C compound, combination of 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-chlorohendiine, 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, and fatty acid polyhydric alcohols such as erythrinth, 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.

Described in Japanese Patent Publication No. 41-14511,
A combination in which various inorganic metal salts in the composition (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.

([) Combinations of heavy metal oxalates such as silver, lead, mercury, thorium oxalates and sulfur compounds such as Na-tetrathionate, sodium thiosulfate, thiourea.

(g) A combination of a ferric salt of a fatty acid, such as ferric stearate, and a four-mouth aromatic polyhydroxy compound of 3,4-dihydroxytetraphenylmethane.

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

(i) A combination of a noble metal salt of an organic acid such as silver hehenate 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.

(g) Combinations of organic acid lead salts such as lead caproate, lead pelargonate, and 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.

(e) Those that form oxazine dyes, such as a combination of resorcinol and a nitroso compound, 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)-
3-7(2-methylindol-3-yl)phthalide,
3. 3-bis(l,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3,3-bis(1
゜2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3
-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, etc. Allylmethane dye, 4,
4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2
, 4,5-1-lichlorophenylleucoolamine and other diphenylmethane dyes, benzoylleucomethylene blue, P-nitrobenzoylleucomethylene blue and other thiazine dyes, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, Spiro dyes such as 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo)spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine to B-anilino lactam, rhodamine (p-nitroanilino)lactam,
Lactam dyes such as rhodamine (O-chloroanilino)lactam, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 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- Dibenzylaminofluorane, 3-diethylamino-7-N-methyl-
N-benzylaminofluorane, 3-diethylamide,”
-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-(N-ethyl-P-toluidino)-6-methyl-7-phenylaminofluorane, 3 -(N-ethyl-p-toluidino)-6-methyl-7-(p-)luidino)fluoran, 3-diethylamino-6-methyl-7
-phenylaminofluorane, 3-dibutylamino-6
-Methyl-7-phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxyphenylamino)
Fluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyltwophenylaminofluoran, 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-6methyl-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-N -n-hexyl)amino-6-
Methyl-7-phenylaminofluorane, 3-(N-ethyl-N-β-ethylhexyl)amino-6-methyl-
7-phenylaminofluorane, 3-(N-ethyl-N
-tetrahydrofurfuryl)amino6-methyl-7-phenylaminofluorane 1. Fluoran dyes such as 3-(N-ethyl-N-cyclopentyl)amino-6-methyl-7-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-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, 2,2-bis(4-hydroxyphenyl)-4-methyl-pentane,
4.4'dihydroxydiphenyl sulfide, 4.4
'-Thiobis(6-tert-butyl-3-methylphenol L 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy- 4'-isopropoxydiphenyl sulfone, 4-hydroxy 3', 4'-1-rimethylene diphenyl sulfone, 4-hydroxy-3'4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone , 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'-trihydroxybenzophenone,
2.2', 4゜4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, 4-hydroxybenzoate, α-propyl fragrant, 4-hydroxybenzoic acid-
5ec~butyl, pentyl 4-hydroxybenzoate, 4
-Phenyl hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylfurovir 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-4-hydroxybenzoate -chlorobenzyl, 4
-Hydroxybenzoic acid - Phenolic compounds such as p-methoxybenzyl, novolac type phenolic resin, phenol polymer, benzoic acid, p-tertbutylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxy Benzoic acid, 3-cyclohexyl-
4-Hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3tert-butylsalicylic acid, 3,5-ditert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α -methylbenzyl)salicylic acid, 3-chloro5-(α~methylbenzyl)salicylic acid, 3-phenyl-
5-(α,α-dimethylbenzyl)salicylic acid, 3,5
- Aromatic carboxylic acids such as di-α-methylbenzyl salicylic acid, and their phenolic compounds; salts of aromatic carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; and other organic acidic substances. Note that, of course, two or more of these coloring agents can be used in combination as necessary.

The ratio of the basic dye and coloring agent to be used is appropriately selected depending on the type of basic dye and coloring agent used, and is not particularly limited, but is generally based on 100 parts by weight of the basic dye. 100-700 parts by weight, preferably 150-4
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 denzins and other 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. It is blended in an amount of about 2 to 40% by weight, preferably about 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 clay, 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, valmitic acid amide, coconut fatty acid amide, 2,2'-methylene bis(4
-methyl-6-tert-butylphenol), 4.4
'-Butylidenebis(6-tert-butyl-3-methylphenol), i,i,3-1-lis(2-methyl-
Hindered phenols such as 4-hydroxy-5tert-butylphenyl)butane L p-benzylbiphenyl, 1,2-bis(phenoxy)ethane, ■,2-bis(
Ethers such as 4-methylphenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 2-naphtholbenzyl ether, dibenzyl terephthalate, 1-
Esters such as hydroxy-2naphthoic acid phenyl ester, ultraviolet absorbers such as 2-(2'-hydroxy-5'-methylphenyl)hensitriazole, 2-hydroxy-4-benzyloxybenzophenone, and various known heat A fusible substance can also be used as a sensitizer.

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 coating liquid to be applied is not particularly limited, and is generally 2 to 12 g/n (preferably 3 g/n in terms of dry weight).
It is adjusted in the range of ~10g/%.

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" The present invention will be described in more detail with reference to Examples below, but it 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 (1) Preparation of base paper Regenerated pulp made from newspaper and having a freeness of 240Id was beaten in a double disc refiner to a freeness of 100-Id. To 10 parts of this recycled pulp, each was beaten to 500 ml of freeness and added 70 parts of BKP and NBK.
Talc was added to the pulp suspension obtained by blending 20 parts of P so that the ash content was 6%, and rosin size was added as a sizing agent at 1.4% based on the bone dry pulp.

After adjusting the PL+ of this pulp slurry to 4.6 with a sulfuric acid band, paper was made using a fourdrinier cylinder dryer paper machine, and 1.5 g of an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) was added to the pulp slurry. /rd, and processed with a machine calendar to give a basis weight of 40g/%.
, measured value with a specular reflection type smoothness meter (pressure condition 20 kg/c
A base paper for thermal recording paper having i) of 9% was obtained.

■ 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 obtained coating liquid was applied and dried on the base paper obtained in step ① above so that the coating amount after drying was 7 g/rd,
Further, the paper was subjected to supercalender treatment to obtain heat-sensitive recording paper.

The thus obtained thermal recording paper was printed at a head voltage of 1 using an ultra-high-speed thermal printer (up-i 03. manufactured by Sony).
Printing was performed at 5.5 volts for 6 ms during the pulse, and the image density was measured using a Macbeth densitometer, and the results are shown in the table. Also,
The background stain on the surface of the recording layer was visually determined and the results are listed in the table. The evaluation criteria were [◎...extremely excellent]. ○
...Some dirt is observed. x: Significant staining was observed].

Furthermore, the sharpness of the recorded images was visually judged and the results are also listed in the table. The evaluation criteria were [◎...extremely excellent]. O: good, ×: poor].

Example 2 Regenerated pulp made from imitation material and having a freeness of 400 d was refined in a double disc refiner to a freeness of 250 ml. To 10 parts of this recycled pulp, 70 parts of LBKP and NBKP beaten to a freeness of 5001d, respectively.
Talc was added to the pulp suspension obtained by blending 20 parts so that the ash content was 6%, and rosin size was added as a sizing agent at 1.4% based on the bone dry pulp.

After adjusting the pH of this pulp slurry to 466 with a sulfuric acid band, paper was made using a fourdrinier cylinder dryer paper machine, and an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) was added at 1.5 g/n. (size press so that the metal roll and elastic roll (Shore D hardness 91)
Processed with an on-machine calendar consisting of 1 tsubo
A base paper for thermal recording paper having a measurement value of 40 g/n (with a specular reflection type smoothness meter (pressure condition: 20 kg/cffl) of 16%) was obtained.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Example 3 Recycled pulp made from newspaper and having a freeness of 200 was beaten in a double-day flip inner to give a freeness of 100-. To 50 parts of this recycled pulp, 50 parts of freeness
Talc was added to the pulp suspension obtained by blending 50 parts of NBKI' beaten to 0d so that the ash content was 6%, and rosin size was added as a sizing agent at 1.4% based on the bone dry pulp. did.

After adjusting the pH of this pulp slurry to 4.6 with sulfuric acid band, paper was made using a fourdrinier cylinder dryer paper machine, and 1.5 g of an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) was added to the pulp slurry. /%, and processed with an on-machine calender consisting of a metal roll and an elastic roll (Shore D hardness 91 degrees) to a basis weight of 4.
0g/m, measured value with a specular reflection type smoothness meter (pressure condition 20
A base paper for thermosensitive recording paper having a kg/c+Il) of 18% was obtained.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Example 4 Regenerated pulp with a freeness of 420d made from white pulp was refined in a double disc refiner to a freeness of 300ml. Talc was added to the pulp suspension obtained by blending 90 parts of this recycled pulp with NBKPIO parts beaten to a freeness of 500 so that the paper content was 6%, and rosin size was added as a sizing agent to the bone-dry pulp. It was added at 1.4%.

After adjusting the pH of this pulp slurry to 4.6 with sulfuric acid band, paper was made using a long multi-cylinder cylinder dryer paper machine, and an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Tamago Cornstarch Co., Ltd.) was added at 1°5 g/ml. Size pressed to a size of m, and processed with an on-machine calendar consisting of a metal roll and an elastic roll (Shore D hardness: 87 degrees) to a size of tsubo ff.
A base paper for thermal recording paper was obtained which had a value of 140 g/rrf and a value measured with a specular reflection type smoothness meter (pressure condition 20 kg/c+fl) of 16%.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Example 5 A recycled pulp with a freeness of 500 d made from white pulp was refined in a double disc refiner to obtain a freeness of 420 d. To 80 parts of this recycled pulp, 50 parts of freeness
Talc was added to the pulp suspension obtained by blending 20 parts of NBKP beaten to 0- so that the paper component was 6%, and rosin size was added as a sizing agent at 1.4% based on the bone dry pulp. .

After adjusting the pH of this pulp slurry to 4.6 with sulfuric acid band, paper was made using a long multi-cylinder cylinder dryer paper machine, and 1.5 g/min of an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Tamago Cornstarch Co., Ltd.) was added to the pulp slurry. rd, size press the metal roll and elastic roll (Shore D hardness 78
Processed with an on-machine calendar consisting of
A base paper for thermal recording paper was obtained which had a J40 g/rd and a value measured with a specular reflection type smoothness meter (pressure condition 20 kg/r:d) of 10%.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Example 6 Freeness made from newspapers 200 ml of recycled pulp was refined in a double disc refiner to obtain 150 m2 of freeness. 10 parts of this recycled pulp were each beaten to a freeness of 500rn1.
Ground calcium carbonate (trade name: Softon 120) is added to the pulp suspension obtained by blending 0 parts of
0, manufactured by Bihoku Hanka Co., Ltd.) was added so that the paper component was 6%, and sulfuric acid was added at 0.5% based on the bone dry pulp.
Cationic starch (trade name, CATO-F, manufactured by Tamago National Co., Ltd.) was added at 0.5% to the bone-dry pulp, and alkyl ketene dimer (trade name, SP) was added as a neutral sizing agent.
K 90, manufactured by Arayo Kagaku Co., Ltd.) at 0.2% for absolute dry pulp.
%, paper was made using a long-length multi-tube cylinder dryer paper machine, and an aqueous solution of oxidized starch (trade name: Ace A, manufactured by Tamago Cornstarch Co., Ltd.) was size-pressed to 1.5 g/nf, and a metal roll was added. Processed with an on-machine calendar consisting of an elastic roll (Shore D hardness 91 degrees), the basis weight was 40 g/rd, and the value measured with a specular reflection type smoothness meter (pressure condition 20 kg/cJ) was 5% per month. A certain base paper for thermal recording paper was obtained.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Example 7 Regenerated pulp with a freeness of 550 - made from ruled paper as a raw material was refined in a double disc refiner to a freeness of 430 txl. To 50 parts of this recycled pulp, each was beaten to 500 ml of freeness, 30 parts of BKP, 30 parts of NB
Talc was added to the pulp suspension obtained by blending 20 parts of KP so that the paper component was 6%, and rosin size was added as a sizing agent at 1.4% based on the bone dry pulp.

After adjusting the pH of this pulp slurry to 4.6 with a sulfuric acid band, it was made into paper using a round-mesh monotube Yankee dryer paper machine, and the basis weight was 40 g/rrf, as measured by a regular reflection type smoothness meter (
A base paper for thermal recording paper was obtained in which the pressure conditions (20 kg/cffl) were 30% on the cast side and 10% on the back side.

A thermosensitive recording paper was prepared in the same manner as in Example I except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Comparative Example'1 LBKP each beaten to freeness 500 ml
A base paper for thermosensitive recording paper was obtained in the same manner as in Example 1, except that bulpus benzigone consisting of 80 parts of N B K P and 20 parts of N B K P was used. The measurement value of this base paper using a specular reflection type smoothness meter (pressure conditions: 20 kg/cm2) is 9%.
Met.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

Comparative Example 2 Freeness 240 ml of recycled pulp made from newspaper was refined in a double disc refiner to obtain a freeness of 100-. To 15 parts of this recycled pulp, 65 parts of LBKP and NBKP beaten to a freeness of 500, respectively.
A base paper for thermosensitive recording paper was obtained in the same manner as in Example 1, except that a pulp suspension obtained by blending 20 parts of the above was used.

Measured value of this base paper with a specular reflection type smoothness meter (pressure conditions: 2
0 kg/cm2) was 7%.

A thermosensitive recording paper was prepared in the same manner as in Example 1 except that this base paper was used, and a performance comparison test was conducted, and the results are shown in the table.

As is clear from the results in Table "Effect J," all of the thermal recording papers obtained in the Examples of the present invention produced recorded images with clear and excellent image density without causing background stains. .

Claims (2)

[Claims] (1) The total pulp composition contains 10% by weight or more of recycled pulp made from waste paper, and the value measured with a specular reflection type smoothness meter on the surface of the base paper is 8% or more at a pressure of 20 kg/cm^2 A thermal recording paper characterized by using a base paper that is (2) The heat-sensitive recording paper according to claim (1), wherein the recycled pulp is pulp whose Canadian Standard freeness has been lowered in the range of 30 to 150 ml by beating treatment in a pre-process of the paper machine.