JPS6353093A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To ensure excellent properties for close contact with a thermal head and record a high-quality image with favorable gradation reproduction properties, by providing a water base thermal recording layer on the surface of a raw paper having a delamination strength measured according to Tappi RC-308 not higher than a specified value and an optical contact rate of the surface on which to provide the recording layer at least a specified value. CONSTITUTION:A raw paper having a delamination strength measured according to Tappi RC-308 of not more than 0.200ftlb/in<2>, preferably, not more than 0.150 ftlb/in<2> is selectively used. The optical contact ratio (measured after 1min from the pressing of a paper to a prism under the condition of 5kg/cm<2>) of the surface of the raw paper on which to provide a thermal recording layer is set to be at least 6%, preferably, at least 7%. A leuco dye based thermal recording layer or the like is used on the surface of the raw paper.

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 can clearly record a recorded image with gradation.

``Prior Art'' Thermosensitive recording paper, which forms recorded images using physical and chemical changes in substances caused by thermal energy, is well known.
Coupled with advances in recording equipment, it has come to be used not only as a recording medium for facsimiles 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 hard copies of images are required is increasing, and conventional methods such as instant film and dry silver Paper was used, but 44p recording paper was relatively cheap;
And record it! ,'? Since A-type devices are compact and easy to maintain, demand in this field is rapidly increasing.

``Problems to be Solved by the Invention'' However, many images displayed on a CRT screen are rich in gradation, and conventional thermal recording paper does not necessarily provide a satisfactory recorded image.

Therefore, methods have been proposed to improve the smoothness of the recording paper surface in order to improve the contact between the thermal head and the recording paper surface, but in the case of images with gradation, it is difficult to express halftones. Since the output of the thermal head is extremely low, it is not possible to obtain a recorded image with clear gradation simply by improving the surface smoothness.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems by providing a thermal head that has excellent adhesion with a thermal head, resulting in good gradation image reproducibility and high-quality recorded images. The purpose is to provide recording paper.

As a result of intensive research on the adhesion between the thermal head and the surface of the recording paper, the present inventors have found that the adhesion between the thermal head and the surface of the recording paper is determined not only by the smoothness of the surface of the recording paper, but also by its cushioning properties and the surface of the recording paper. We found that it is greatly influenced by flexibility. In other words, when the surface of the recording paper comes into contact with the thermal head due to the pressure of the platen roll, if the recording paper is hard and has poor cushioning properties even if it is smooth, the contact with the thermal head, which has various shapes, will be uneven. ,
As a result, only low-quality recorded images with non-uniform color development can be obtained.

The cushioning properties and surface flexibility of recording paper are largely dependent on the properties of the base paper, so as a result of repeated and intensive research into base paper for thermal recording paper, we found that the cushioning properties and surface flexibility of recording paper The axial fiber bonding force, i.e. r
It was found that the delamination strength was significantly affected. Then, they discovered that by selectively using base papers with specific delamination strength and surface smoothness, it was possible to obtain thermal recording paper that had excellent gradation image reproducibility and produced high-quality recorded images, and completed the present invention. I ended up doing it.

``Means for Solving Problems'' The present invention has an interlayer peel strength of 0.200 ft1b/in2 or less measured according to Tappi RC-308, and an optical contact ratio of the surface on which the recording layer is provided (5 kg/in2). cu
The value measured 1 minute after pressing the paper against the prism at t) is 6
This heat-sensitive recording paper is characterized in that an aqueous heat-sensitive recording layer is provided on the surface of a base paper having a water-based heat-sensitive recording layer of at least 50%.

"Function" The thermal recording paper of the present invention has the following properties (Tappi RC).
-308, base paper with an interlayer peel strength of 0.200 ft1b/in2 or less, more preferably 0.150 ft1b/in2 or less, as measured by an internal bond impact tester manufactured by Nidowin, etc., is selectively used. It is used.

The delamination strength of base paper used for general coated paper is 0.
A base paper having a peel strength of 250 ft1b/in2 or less, which is considerably weaker than those of the present invention, is selected and used.

Further, the surface smoothness of the base paper used in the present invention is preferably as high as possible, but it is necessary that the optical contact ratio of at least the surface on which the heat-sensitive recording layer is provided is 6% or more, more preferably 7% or more.

The optical contact ratio is a value optically measured as the contact area ratio of paper pressed against a prism, and is suitable in principle to express the adhesion between the thermal head and the thermal paper. In the thermal recording paper of the present invention, which aims at clear reproduction of gradation images,
The lower the pressure of pressing the paper on the prism surface, the better the relationship with the recorded image quality. Therefore, the conditions for pressurizing the paper against the prism were 5 kg/Cl11, and after 1 minute of pressurization, The measured value was taken as the optical contact rate. The measuring device used is, for example, a "regular reflection type smoothness meter" manufactured by Toyo Seiki Seisakusho.

The base paper having the above-mentioned specific delamination strength and optical contact rate used in the present invention is achieved mainly by adjusting the type of pulp used and the surface treatment conditions such as size press applied to the base paper.

The most important factor in the type of pulp is its fiber morphology, and the weight average fiber length (FS-100 manufactured by KAJAANI)
By using pulp with a diameter (measured value) of 0.7 mm or less, a base paper with desirable cushioning properties and smoothness can be obtained. The proportion of such pulp used is 70 to 100 of the total pulp.
It is desirable that the fiber length is about % by weight, and it is necessary to prepare the mixed pulp so that the weight average fiber length does not exceed 0.8 m.

In addition, when surface treatment is applied to base paper using a size press, etc., the amount of solid content adhered to is 1 g/m or less, preferably 0°8 g/m.
Desirable cushioning properties, flexibility, and even smoothness of the base paper can be obtained by adjusting the amount to be 0.5 g/m or less, most preferably 0.5 g/m or less.

For general coated paper, the amount of solid content deposited on the base paper by size press etc. is 1 g/lri or more, and if surface strength is particularly required, it is treated to 3 g/m or more, but this As mentioned above, the base paper of the invention is subjected to only a very small amount of treatment, and in some cases, completely untreated base paper is used.

As for the composition of the surface treatment liquid for size press, etc., conventionally used oxidized starch, polyvinyl alcohol, acrylic binder, styrene surface sizing agent, etc. are appropriately used alone or in combination.

In order to improve the contact between the recording paper surface and the thermal head, it is a desirable embodiment to adjust the orientation of the base paper, and the width-to-vertical ratio (Y/T ratio) of the base paper tension is 60.
% or more.

The base paper used in the thermal recording paper of the present invention is not particularly limited in other preparations, paper making conditions, surface treatment conditions, etc., as long as it has the specific glabella peel strength and optical contact rate as described above. For example, by providing a coating layer of oil-absorbing pigments such as silicon oxide, calcined kaolin, light calcium carbonate, etc. on the surface of the base paper, the uniformity of the base paper surface, cushioning properties, heat retention ability, etc. are improved. It is also possible to improve

In the heat-sensitive recording paper of the present invention, a heat-sensitive recording layer is formed on the surface of the base paper having a specific interlayer peel strength and optical contact rate adjusted in this way. Various heat-sensitive recording layers such as a heat-sensitive recording layer, a photofixable diazo heat-sensitive recording layer, and a metal salt type heat-sensitive recording layer can be appropriately selected and used.

The most commonly used leuco dye-based heat-sensitive recording layer, which is 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 color developer. However, 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-di,methylindol-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-
Triallyl such as bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, etc. Methane dye, 4.4
'-Bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N2,4
．． Diphenylmethane dyes such as 5-trichlorophenylleucoauramine, benzoylleucomethylene blue,
Thiazine dyes such as p-nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-
Spiro dyes such as ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, Lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (0-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran,
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-7N-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)fluoran, 3-diethylamino-6-methyl-7-phenylaminofluoran, 3-dibutylamino-6-methyl-7-phenylaminofluoran, 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-(0
-chlorophenylamino)fluoran, 3-dibutylamino-7-(0-chlorophenylamino)fluoran,
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-1so-amyl)amino-6-methyl-7-
Phenylaminofluorane, 3-(N-methyl-N-n
-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
Examples include fluoran dyes such as -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.

The color developer used in combination with the above-mentioned basic dyes is not particularly limited, and should have the property of liquefying, vaporizing, or dissolving when the temperature rises, and the property of causing coloration upon contact with the above-mentioned basic dyes. Various color developers are used.

Typical specific examples include 4-tert-butylphenol, α-naphthol, β-naphthol, 4-7 cetylphenol, 4-tert-octylphenol, 4.
4'-5ec-butylidenediphenol, 4-phenylphenol, 4.4'-dihydroxy-diphenylmethane, 4.4'-isopropylidenediphenol, hydroquinone, 4.4'-cyclohexylidenediphenol, 4.4' -dihydroxydiphenyl sulfide,
4.4'-thiobis(6tert-butyl-3-methylphenol), 4.4'-dihydroxydiphenyl sulfon, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2.4-dihydroxyhensiphenone, 2,4 .4'-1-dihydroxyhensiphenone, 2.2', 4.4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, 4
-propyl hydroxybenzoate, 5ec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, 4-
Chlorophenyl hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 4-hydroxybenztiHp-chlorobenzyl, p-methoxybenzyl 4-hydroxybenzoate, novolac type phenolic resin, phenol polymer, etc. Phenolic compound, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-5e
e -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-
Benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3.5-di-tert-butylsalicylic acid, 3
- Aromatic carboxylic acids such as phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3゜5-di-α-methylbenzylsalicylic acid, and these phenolic compounds,
Examples include organic acidic substances such as salts of aromatic carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel.

The ratio of the basic dye to the color developer is generally about 100 to 700 parts by weight, preferably about 150 to 400 parts by weight, per 100 parts by weight of the dye. Of course, two or more of these color developers may be used in combination as necessary.

Coating liquids containing these materials are generally prepared by using water as a dispersion medium and dispersing dyes and color developers together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand grinder. Ru.

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/butadiene copolymer emulsion, etc. account for 2 to 40% by weight of the total solids, preferably 5% by weight. ~
25% by weight is used.

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

In addition, to improve the adhesion of residue to the recording head and further whiten the sticky heat-sensitive recording layer, we use kaolin, clay, talc, etc.
Inorganic pigments such as calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay 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, etc. may be added to prevent the recording layer from sticking when it comes into contact with the recording head.

Furthermore, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, valmitic acid amide, 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), 4.4'
-Hindered phenols such as butylidene bis(6-t-butyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 2-(2 '-hydroxy-5'-methylphenyl)-benzotriazole, 2-hydroxy-4
- Ultraviolet absorbers such as benzyloxybenzophenone and various known thermofusible substances can also be used together.

In the thermal recording paper 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, in the method of applying a heat-sensitive coating liquid to the above-mentioned specific base paper, an appropriate application device such as an air knife coater or a blade coater is used.

Furthermore, the amount of coating liquid to be applied is not particularly limited, and is generally 2 to 12 g/m in terms of dry weight, preferably 3 to 12 g/m.
10g/n? It is prepared within the range of.

Furthermore, it is possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, and various known techniques in the field of heat-sensitive recording paper can be added.

"Example" 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.

Further, unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight, respectively.

Examples 1-5. Comparative Example 1 90 parts of LBKP with a weight average fiber length of 0.65 mm and a part of NBKPIO with a weight average fiber length of 1.901 m were beaten to a Canadian Standard Freeness of 450 cc, and 1.5 parts of rosin, 3.0 parts of sulfate band, A base paper having a basis weight of 45 g/m was made using a long-length paper machine with the addition of 6 parts of talc. This base paper was subjected to a size press treatment with a size press liquid having the composition shown in Table 1 so that the solid adhesion amount was as shown in Table 1 to obtain a base paper for thermal recording.

Comparative Example 2 65 parts of LBKP with a weight average fiber length of 0.65 m and 35 parts of NBKP with a weight average fiber length of 1.901 m were mixed with Canadian
A base paper was made in the same manner as in Example 1 except that the pulp obtained by beating to a standard freeness of 450 cc was used, and a size press liquid having the composition as shown in Table 1 was applied to this base paper in the first step. A base paper for heat-sensitive recording was prepared by size press treatment to obtain the solid adhesion amount as shown in the table.

Comparative Example 3 Example 1 except that a valve obtained by beating 80 parts of Ryu's LBKP with a weight average fiber length of 0.77 and 20 parts of On+ NBKP with a weight average fiber length of 1.9 to Canadian Standard Freeness of 450 cc was used. A base paper is made in the same manner as above, and this base paper is subjected to a size press treatment with a size press liquid having a composition as shown in Table 1 so that the solid adhesion amount is as shown in Table 1. It was used as the base paper.

The eight types of base paper obtained in this way were calendered,
The thermosensitive base papers were finished to the tightness as shown in Table 1 and had the interlayer peel strength and optical contact ratio as shown in Table 1, respectively.

200 parts of 4,4'-isopropylidenediphenol and 3-(N-methyl-N-is) were added to this heat-sensitive base paper.

-Amyl)amino-6-methyl-7-phenylaminofluorane 30 parts with an average particle size of 1 to 3 μm
% polyvinyl alcohol as a binder in the aqueous dispersion (
200 parts of a 15% aqueous solution of PVA-110 (manufactured by Kuraray), 30 parts of silicon oxide as a pigment, 15 parts of calcium carbonate,
200 parts of zinc stearate as a lubricant, other antifoaming agents,
A coating solution with a concentration of 28% prepared by adding a fluorescent dye, a dispersant, etc. was coated with a Mayer bar so that the dry weight was 6.5 g/rrr, and the paper was treated with a super calender to make heat-sensitive recording paper. .

The eight types of heat-sensitive recording paper thus obtained were recorded using a video printer LjP-103 manufactured by Sony ■, and the reproducibility of gradation images was visually judged [5-point scale = 5 (good) to 1 (bad).
] The recorded image quality is listed in Table 1.

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

Claims (1)

[Claims] The delamination strength measured according to TappiRC-308 is 0.200 ftlb/in^2 or less, and the optical contact rate of the surface on which the recording layer is provided (pressing the paper against the prism at 5 kg/cm^2 for 1 minute) 1. A heat-sensitive recording paper, characterized in that a heat-sensitive recording layer is provided on the surface of a base paper having a heat-sensitive recording layer (value measured later) of 6% or more.