JPH0635208B2 - Thermal recording paper - Google Patents

Description

The present invention relates to a heat-sensitive recording paper, and more particularly to a heat-sensitive recording paper capable of clearly recording a recorded image having gradation.

“Prior Art” Thermal recording paper, which forms a recorded image by utilizing the physical and chemical changes of a substance due to thermal energy, is well known.
Together with the progress of recording equipment, it has come to be used not only as a recording medium for fax machines and various computers but also in a wide range of fields.

For example, CRTs are widely used in fields such as new media-related equipment, medical equipment, and industrial measurement, but the number of cases in which a hard copy of the image is required is increasing. Although paper has been used, thermal recording paper is relatively inexpensive, and the recording equipment is compact and easy to maintain, so demand for such fields is rapidly increasing.

"Problems to be Solved by the Invention" However, many images displayed on the screen of a CRT are rich in gradation, and conventional thermal recording papers do not always provide satisfactory recording images.

Therefore, a method of improving the smoothness of the recording paper surface has been proposed in order to improve the adhesion between the thermal head and the recording paper surface. Since the output of the thermal head is extremely low, a recorded image with clear gradation cannot be obtained by simply improving the surface smoothness.

Therefore, in order to solve the above problems, an object of the present invention is to provide excellent adhesion to a thermal head, resulting in good reproducibility of a gradation image, and heat sensitivity for providing a high-quality recorded image. It is to provide recording paper.

The inventors of the present invention have particularly earnestly studied the adhesion between the thermal head and the recording paper surface. As a result, the adhesion between the thermal head and the recording paper surface is not only the smoothness of the recording paper surface, but also its cushioning property and surface. We have found that it depends greatly on flexibility. That is, when the surface of the recording paper comes into contact with the thermal head by pressing the platen roll, in the case of a hard recording paper with good smoothness but poor cushioning properties, contact with the thermal head having various shapes becomes uneven. ,
As a result, only low-quality recorded images with uneven color development can be obtained.

Since the cushioning properties and surface flexibility of recording paper are largely dependent on the properties of the base paper, as a result of repeated intensive research on the base paper for thermal recording paper, the cushioning properties and surface flexibility of the recording paper were It was found that the fiber bonding force in the axial direction, that is, "delamination strength" has a significant influence. Then, by selectively using a base paper having a specific delamination strength and surface smoothness, excellent reproducibility of a gradation image,
The inventors have found that a heat-sensitive recording paper giving a high-quality recorded image can be obtained, and completed the present invention.

`` Means for solving the problems '' The present invention is a thermal recording paper provided with a thermal recording layer on the raw paper made by a Fourdrinier cylinder paper machine, the raw paper has a weight average fiber length of 0.
70 to 100% by weight of pulp of 7 mm or less based on the total weight of pulp
Containing the surface treatment on the base paper with a solid content of 1 g / m ² or less, the delamination strength measured according to Tappi RC-308 is 0.200 ftlb / in ² or less, and the surface on which the recording layer is provided. Of which the optical contact rate (measured 1 minute after pressurizing the paper to the prism at 5 kg / cm ² ) is 6% or more, an aqueous heat-sensitive recording layer is provided on the surface of the base paper. It is recording paper.

"Function" In the thermosensitive recording paper of the present invention, the delamination strength measured by an internal bond impact tester manufactured by Edwin Co. in accordance with Tappi RC-308 as described above is 0.200f.
A base paper of tlb / in ² or less, more preferably 0.150 ftlb / in ² or less is selectively used.

Delamination strength of base paper used for general coated paper is 0.25
It is 0 ftlb / in ² or more, and in the present invention, a base paper having a considerably weaker delamination strength as compared with these is selectively used.

Further, the higher the surface smoothness of the base paper used in the present invention, the more preferable, but at least the optical contact ratio of the surface on which the heat-sensitive recording layer is provided needs to be 6% or more, and more preferably 7% or more.

The optical contact ratio is a value obtained by optically measuring the contact area ratio of the paper pressed onto the prism, and is suitable for expressing the adhesion between the thermal head and the thermal paper in principle. In the thermal recording paper of the present invention for the purpose of clear reproducibility of gradation images,
The lower the pressure of the paper against the prism surface, the better the relationship with the recorded image quality. Therefore, pressurize the paper against the prism at 5 kg / cm ² and measure the value after 1 minute of pressure. Was defined as the optical contact rate. As the measuring device, for example, a "regular reflection type smoothness meter" manufactured by Toyo Seiki Seisakusho Ltd. is used.

The base paper having the above-mentioned specific delamination strength and optical contact ratio used in the present invention is a papermaking machine using a Fourdrinier multi-cylinder paper machine, such as the type of pulp mainly used and the size press applied to the base paper. This is achieved by adjusting the surface treatment conditions.

The most important factor in the type of pulp is its fiber form, which provides desirable cushioning and smoothness by using pulp with a weight average fiber length (measured by KAJAANI FS-100) of 0.7 mm or less. You can get the original paper. The proportion of such pulp used is preferably about 70 to 100% by weight of the total pulp, and it is necessary to prepare such that the weight average fiber length of the mixed pulp does not exceed 0.8 mm.

In addition, the surface treatment of the base paper such as a size press is adjusted so that the amount of solid components attached is 1 g / m ² or less, preferably 0.8 g / m ² or less, and most preferably 0.5 g / m ² or less. As a result, the desired cushioning property, flexibility and smoothness of the base paper can be obtained. In general coated paper, etc., the amount of solid content adhered to the base paper by a size press or the like is 1 g / m ² or more, and especially when surface strength is required, 3 g / m ² or more is treated. As described above, the base paper of the invention can be treated in an extremely small amount, and in some cases, a completely unprocessed base paper is used.

As the composition of the surface treatment liquid for a size press or the like, conventionally used oxidized starch, polyvinyl alcohol, an acrylic binder, a styrene-based surface sizing agent, etc. may be used alone or as a mixture.

In order to further improve the contact property between the surface of the recording paper and the thermal head, it is a desirable embodiment to adjust the orientation of the base paper, and the aspect ratio (Y / T ratio) of the base paper tension is 60.
It is desirable to make the paper so that the content is at least%.

The base paper used in the heat-sensitive recording paper of the present invention is appropriately finished according to the prior art. For example, the base paper surface is provided with a coating layer of an oil absorbing pigment such as silicon oxide, calcined kaolin, and light calcium carbonate on the base paper surface. Uniformity of
It is also possible to improve the cushioning property and the heat retaining ability.

The heat-sensitive recording paper of the present invention has a heat-sensitive recording layer formed on the surface of the base paper having the specific delamination strength and optical contact ratio thus adjusted. The heat-sensitive recording layer may be a leuco dye-based material. Various heat-sensitive recording layers such as a heat-sensitive recording layer, a photo-fixing type diazo heat-sensitive recording layer and a metal salt type heat-sensitive recording layer can be appropriately selected and used.

The leuco dye-based heat-sensitive recording layer most commonly used and particularly effective as the heat-sensitive recording layer of the present invention utilizes a color reaction between a colorless or light-colored basic dye and an organic or inorganic developer. However, various kinds of such 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-ethylcarbazol-3-yl) -6-dimethylaminophthalide,
3,3-bis (2-phenylindol-3-yl)-
6-Dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6
-Triallylmethane dyes such as dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leukoauramine, N-2,4,5-trichlorophenylleucoaamine, etc. Diphenylmethane dyes, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and other thiazine dyes, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-
Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-
Spiro dyes such as dibenzopyran, 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-dibenzylaminofluorane, 3-diethylamino-7-N
-Methyl-N-benzylaminofluorane, 3-diethylamino-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-
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
-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-N
-N-amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-n-amyl) amino-6-methyl-7-phenylaminofluorane, 3
-(N-Ethyl-N-iso-amyl) 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-phenylamino Examples thereof include fluoran dyes such as fluoran. Of course, the dyes are not limited to these dyes, and two or more dyes may be used in combination.

The developer used in combination with the basic dye as described above is not particularly limited, and has a property of liquefying, evaporating or dissolving by an increase in temperature, and a property of causing coloration in contact with the basic dye. Various developers that have are used.

As a typical specific example, 4-tert-butylphenol,
α-naphthol, β-naphthol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec
-Butylidene diphenol, 4-phenylphenol,
4,4'-dihydroxy-diphenylmethane, 4,4 '
-Isopropylidenediphenol, hydroquinone,
4,4'-cyclohexylidene diphenol, 4,4 '
-Dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol),
4,4'-dihydroxydiphenyl sulfone, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,
4,4'-trihydroxybenzophenone, 2,2 ',
4,4'-Tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, 4-hydroxy. Pentyl benzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate,
Tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, -p-chlorobenzyl 4-hydroxybenzoate, p-methoxybenzyl 4-hydroxybenzoate. , Novolac type phenolic resin, phenolic compounds such as phenolic polymer,
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 Acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3- (α-
Methylbenzyl) salicylic acid, 3-chloro-5- (α-
Aromatic carboxylic acids such as methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5- (α, α-dimethylbenzyl) salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, And organic acid substances such as salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel.

The ratio of the basic dye to the developer is generally 100 to 700 parts by weight, preferably 150 to 400 parts by weight, based on 100 parts by weight of the dye. Of course, two or more kinds of these color developers are used in combination, if necessary.

The coating liquid containing them is generally prepared as a coating liquid by using water as a dispersion medium and dispersing the dye and the developer together or separately by a stirring / grinding machine such as a ball mill, an attritor or a sand glider. It

In such a coating liquid, starch is usually used as a binder,
Hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / butadiene copolymer emulsion and the like are 2 to 40% by weight of the total solid content, preferably 5%. ~
25% by weight is used.

Further, various auxiliary agents can be added to the coating liquid as needed. For example, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate,
Examples thereof include dispersants such as lauryl alcohol sulfate / sodium salt and fatty acid metal salt, defoaming agents, fluorescent dyes, and coloring dyes.

In addition, kaolin, clay, talc, in order to improve the adhesion of dust to the recording head and to make the thermal recording layer whiter,
Inorganic pigments such as calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay and the like can also be added. In addition, stearic acid, polyethylene,
Waxes such as dispersions or emulsions of carnauba wax, paraffin wax, calcium stearate, zinc stearate, ester wax and the like can be added so that the recording layer does not stick when contacting with the recording head.

Furthermore, fatty acid amides such as stearic acid amide, stearic acid methylenebisamide, oleic acid amide, palmitic acid amide, and coconut fatty acid amide, terephthalic acid dibenzyl ester, 1,2- Di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,
Hindered phenols such as 4'-butylidene bis (6-t-butyl-3-methylphenol) and 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2- An ultraviolet absorber such as (2'-hydroxy-5'-methylphenyl) -benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, and various known heat-fusible substances may be used in combination.

In the thermosensitive recording paper of the present invention, the method for forming the recording layer is not particularly limited, and the recording layer can be formed according to a conventionally known and commonly used technique. For example, in the method of applying the heat-sensitive coating liquid to the specific base paper, an appropriate coating device such as an air knife coater or a blade coater is used.

The coating amount of the coating liquid is also not particularly limited, and is generally ² to 12 g / m ² in dry weight, preferably 3 to
It is prepared in the range of 10 g / m ² .

Further, an overcoat layer can be provided on the recording layer for the purpose of protecting the recording layer, and various known techniques in the field of thermal recording paper can be added.

"Examples" Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Unless otherwise specified, parts and% in the examples represent parts by weight and% by weight, respectively.

Examples 1 to 5 and Comparative Example 1 90 parts of LBKP having a weight average fiber length of 0.65 mm and 10 parts of NBKP having a weight average fiber length of 1.90 mm were beaten to a Canadian Standard Freeness of 450 cc, 1.5 parts of rosin, 3.0 parts of sulfuric acid band, and 6 talc. Was added to prepare a base paper having a basis weight of 45 g / m ^{2 using} a Fourdrinier cylinder type paper machine equipped with a size press. A size press liquid having a composition as shown in Table 1 was subjected to size press treatment on this base paper so that the solid adhesion amount as shown in Table 1 was obtained to obtain a base paper for thermal recording.

Comparative Example 2 Base paper was prepared in the same manner as in Example 1 except that pulp obtained by beating 65 parts of LBKP having a weight average fiber length of 0.65 mm and 35 parts of NBKP having a weight average fiber length of 1.90 mm to a Canadian Standard Freeness of 450 cc was used. The base paper was subjected to size press treatment with a size press liquid having a composition as shown in Table 1 so as to have a solid adhesion amount as shown in Table 1 to obtain a base paper for thermal recording.

Comparative Example 3 A base paper was prepared in the same manner as in Example 1 except that 80 parts of LBKP having a weight average fiber length of 0.77 mm and 20 parts of NBKP having a weight average fiber length of 1.90 mm were beaten to a Canadian Standard Freeness of 450 cc. The base paper was subjected to size press treatment with a size press liquid having a composition as shown in Table 1 so as to have a solid adhesion amount as shown in Table 1 to obtain a base paper for thermal recording.

The eight types of base paper thus obtained were subjected to a calendar treatment,
A heat-sensitive base paper having a finish as shown in Table 1 and a delamination strength and an optical contact rate as shown in Table 1 was prepared.

200 parts of 4,4'-isopropylidenediphenol, 3- (N-methyl-N-iso-amyl) amino-6-methyl-7-phenylaminofluorane 10 were added to the heat-sensitive base paper.
Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., as a binder, was added to 0% of a 30% aqueous dispersion having an average particle diameter of 1 to 3 μm.
Prepared by adding 200 parts of a 15% aqueous solution of PVA-110), 30 parts of silicon oxide as a pigment, 15 parts of calcium carbonate, 200 parts of zinc stearate as a lubricant, other defoaming agents, fluorescent dyes, dispersants, etc. 28 % Coating solution was applied with a Mayer bar to a dry weight of 6.5 g / m ^2, and subjected to a super calender treatment to obtain a thermosensitive recording paper.

The eight types of thermal recording papers thus obtained were recorded by a video printer UP-103 manufactured by Sony Corporation, and the reproducibility of the gradation image was visually judged [5-point method: 5 (good) to 1 (bad)].
The recording image quality is shown in Table 1.

"Effect" As is clear from the results shown in Table 1, all of the thermal recording papers of the present invention exhibited extremely excellent gradation image reproducibility.

Claims (1)

[Claims] 1. A heat-sensitive recording paper comprising a base paper produced by a long-mesh multi-cylinder paper machine and provided with a heat-sensitive recording layer, wherein the base paper has a weight average fiber length of 0.7 mm or less and a pulp weight of 70 to 100 parts by weight based on the total weight of the pulp. %, The surface treatment on the base paper is composed of a solid content of 1 g / m ² or less, and the delamination strength measured according to Tappi RC-308 is 0.200 ftlb / in ² or less, and a recording layer is provided. Optical contact ratio of the surface (1 kg by pressing the paper on the prism at 5 kg / cm ²
A heat-sensitive recording paper having a heat-sensitive recording layer on the surface of a base paper having a value (measured after a minute) of 6% or more.