JPH082695B2 - Base paper for thermal recording paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a base paper as a support for thermal recording paper used as recording paper or barcode label paper for facsimiles, CAD, various measuring machines, etc. The present invention relates to a base paper for heat-sensitive recording paper, which is suitable for obtaining recording characteristics excellent in sensitivity and sharpness.

<Prior Art> In general, a thermosensitive recording paper having a thermosensitive recording layer mainly composed of a colorless or light-colored leuco dye and a color developer which reacts with a leuco dye to develop a color is disclosed in Japanese Patent Publication No. 45-14035. Has been widely used. A thermal printer or the like having a built-in thermal head is used for recording on this thermal recording paper, but such a thermal recording method does not generate noise at the time of recording as compared with other conventional recording methods. , No need for developing and fixing, maintenance free, relatively inexpensive and compact equipment, and very clear color development, computer output, facsimile, CAD, calculator, measuring instrument It is widely used as a paper for recorders and tickets for vending machines.

In recent years, recording devices such as facsimiles and bar code printers are becoming compact, energy-saving and high-speed, so that low-energy, high-density and high-precision images can be obtained for thermal recording paper. That is, there is an increasing demand for higher sensitivity. In order to achieve this high sensitivity, various studies have been made on the materials such as leuco dyes, developers and sensitizers used in the thermosensitive coloring layer. However, since the thermal recording method is a method in which recording is performed by heat transfer between a thermal head composed of a dot-shaped heating element and a thermal recording paper in contact with the thermal head, the quality of contact is a major factor that governs heat transfer efficiency. Is. In addition, in the field of heat-sensitive recording labels that require chemical resistance and water resistance, a protective layer is provided on the thermosensitive coloring layer in order to satisfy the above-mentioned required characteristics, and the heat transfer efficiency by the protective layer is improved. The decrease of the value is also a big obstacle to the improvement of the recording sensitivity.

As a means for improving the adhesiveness with the thermal head and effectively utilizing the thermal energy applied from the thermal head, for example, in Japanese Examined Patent Publication No. 52-20142, the surface of the thermal recording paper is beck smoothed by the method of a super calender. At 200-1
Although a method of surface treatment for 000 seconds is described, increasing the super calender treatment pressure causes pressure fog and development that causes the thermal recording head and thermal recording paper to adhere to each other at the time of recording, degrading image quality, so-called sticking. If it is weak on the contrary, the desired recording sensitivity cannot be obtained,
There are problems such as management of processing conditions and increase in manufacturing cost.

As mentioned above, the study for increasing the sensitivity of the thermal recording paper is as follows.
Various things have been carried out regarding the constitution of the thermosensitive color developing layer, surface treatment, etc., but at present it has not reached a sufficiently satisfactory level.

<Problems to be Solved by the Invention> The present invention has been made in view of the above circumstances, and improves the adhesiveness between a thermal head and a thermal recording paper in order to impart highly sensitive recording characteristics to the thermal recording paper. The present invention provides a base paper for thermal recording paper.

<Means for Solving the Problems> The present invention is a raw paper comprising an intermediate layer and surface layers laminated on both sides thereof, and has a density gradient so that the intermediate layer has a lower density than the surface layer. And the density of the intermediate layer is 0.35
The base paper for heat-sensitive recording paper is characterized in that it is ~ 0.75 g / cm ³ .

The base paper of the present invention has two functions: strength as a support of the thermosensitive recording layer in the thermosensitive recording paper and good adhesion to the thermosensitive recording head. In order to exert these two functions, the outer surface portion and the middle portion have different densities, that is, the paper has a density gradient in the thickness direction of the paper, and the middle portion has a lower density than the surface. Is an essential condition. The reason for providing such a difference in density is that the thermal recording paper must have a cushioning property such as sponge in order to improve the adhesion to the thermal head. In order for the paper to have such a cushioning property, it is achieved by providing a low-density, bulky structure.

Since the thermosensitive recording paper has a thermosensitive recording layer on the surface of the base paper that is the support, it has a density similar to that of ordinary coated paper with less penetration of the coating liquid (generally 0.8 to 1.2 g / cm ³ ).
Is required.

In order for the paper to have strength as a support, a low-density, high-bulk structure is not sufficient.

Therefore, in order to satisfy these, the structure has a low density to have a cushioning property in the center part, and the outer surface part has a density similar to that of a general coating paper, and it is suitable for coating a coating material and as a support. It is configured to have strength.

The central portion in the present invention means a portion of 30 to 70% when the thickness is expressed as 100% in the thickness direction of the paper, that is, a central portion in the range of 50% ± 20% which is the center of the thickness direction. This is the portion equivalent to 40%. The central portion of the present invention has a density of 0.35 to 0.75 g / cm ³ , preferably 0.45.
It is important to be ~ 0.65 g / cm ³ . Where the density is
If it is larger than 0.75, the adhesiveness with the thermal head, which is the object of the present invention, cannot be sufficiently obtained. Further, paper having a density of less than 0.35 is weak in strength, cannot be manufactured by the current paper machine, and is not suitable for practical use.

In order to produce the base paper of the present invention as described above, for example, by providing multiple cylinders in a cylinder paper machine and making a papermaking process, the layers are formed by separate forming devices, and the paper is dehydrated in the couch part, It can be performed by a process of pressing and drying. Further, it is also possible to provide a partition plate at the slicing section with a Fourdrinier paper machine and supply different raw materials to each partition for papermaking. In such a manufacturing method, the surface layer (both the front side and the back side), which is the outer surface of the multilayer (basically 3 layers), is used as the density of ordinary paper (generally 0.8 g / cm ³ or more). 0.35-0.
By preparing the raw materials so that the density becomes 75 g / cm ³ , it is possible to produce a paper having a target density. Here, as a method for preparing a raw material for obtaining a target density, for example, adjusting the beating degree, selecting the type of pulp raw material, adjusting with additives such as pigments, pulp concentration, raw material supply amount, etc. It can be appropriately performed by adjusting the conditions. It is also possible to prepare the base paper produced as described above by applying a generally used surface treatment such that the base paper is smoothed by, for example, a super calendar.

Raw materials used for the base paper of the present invention, as a main raw material,
Various fibrous materials such as wood pulp and synthetic pulp can be appropriately used, and pigments, dyes, starches, synthetic resins, various additives for papermaking and the like can be used as required. The raw material to be used may be the same or different for the surface layer and the intermediate layer as described above and can be appropriately selected. However, in order to prevent the curling of the paper due to changes in temperature and humidity, both outer surface parts are It is preferable to use the same raw material.

The thickness of the base paper for thermal recording paper of the present invention is practically 40
The thickness is generally 100 μm, but is not particularly limited.

The base paper for heat-sensitive recording paper of the present invention having the constitution as described above can be used as a heat-sensitive recording paper having high sensitivity and excellent sharpness by using this as a support and providing a heat-sensitive color forming layer on the support. It is possible.

Next, the heat-sensitive recording material used in the heat-sensitive recording paper using the base paper for heat-sensitive recording paper of the present invention as a support will be described.

The heat-sensitive coloring layer is mainly composed of a colorless or light-colored leuco dye and a color developing agent that develops the dye when heated. Typical leuco dyes used are crystal violet lactone and 3-diethylamino-7. -Chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-pyrrolidino-6-methyl- 7-anilinofluorane, 3-piperidino-6-methyl-7-
Anilinofluorane, 3-cyclohexylmethylamino-6-methyl-7-anilinofluorane, 3-ethylisoamylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (o-chloroanilino)
Fluoran, 3-dibutylamino-7- (o-chloroanilino) fluorane and the like are included, but are not limited thereto.

Further, as a color developer which reacts with the above leuco dye to develop a color, α-naphthol, β-naphthol, 4-t-butylphenol, 4-t-octylphenol, 4-phenylphenol, 2,2-bis- (p -Hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) butane, 4,4'-cyclohexylidene diphenol, 2,2-bis (2,5-dibromo-4-hydroxyphenyl) propane, 4 , 4'-isopropylidene bis (2-t
-Butylphenol), 2,2'-methylenebis (4-chlorophenol), 4,4'-sulfonyldiphenol,
4,4'-thiobisphenol, benzoic acid, salicylic acid,
There are, but not limited to, derivatives such as gallic acid.

Further, in order to improve recording sensitivity, various commonly used heat-fusible substances can be added, if necessary. Examples of the heat fusible substance include organic compounds having an appropriate melting point,
For example, higher fatty acid amides such as stearic acid amide, animal waxes such as beeswax and shellac wax, vegetable waxes such as carnauba wax, mineral waxes such as montan wax, waxes such as paraffin wax and microcrystalline wax, and higher fatty acids. Aromatic carboxylic acid esters such as higher fatty acid esters, dimethyl terephthalate and diphenyl phthalate, alkylnaphthalene derivatives, alkyldiphenyl derivatives and alkylterphenyl derivatives are used.

Inorganic and organic pigments as a conventional filler, for example, heavy and light calcium carbonate, aluminum hydroxide, titanium oxide, zinc oxide, barium sulfate, talc, clay, satin white, kaolinite, polyolefin particles, polystyrene particles. , Urea-formalin resin particles or the like to improve the sharpness of a color image, or zinc stearate, calcium stearate or the like, and a release agent such as a fluorine resin to improve the head matching property. it can.

In addition, various surface active agents, antifoaming agents, antioxidants, ultraviolet absorbers, etc. are added as necessary, and a binder for binding onto the support is further added to form a thermosensitive coloring layer coating. Adjusted. Examples of the binder include casein, gelatin, polyvinyl alcohol, polyvinylpyrrolidone, starch, modified starch, isobutylene-maleic anhydride resin, diisobutylene-maleic anhydride resin, styrene-
Maleic anhydride resin, polyacrylamide, modified polyacrylamide, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, further vinyl acetate, acrylic acid ester, vinyl chloride-vinyl acetate copolymer, emulsion such as SBR, NBR, latex or the like alone or Used as a mixture.

The preparation of the heat-sensitive color developing layer coating is generally carried out by grinding the leuco dye, the color developer, and the heat-fusible substance, which is optionally added, with a media-type wet disperser to an average particle size of 5 μm or less, preferably 3 μm or less. It is prepared by treating and adjusting it as a dispersion, and adding a binder, a filler and various additives in a predetermined amount.

The thermosensitive coloring layer coating material is a thermosensitive coloring layer formed by applying and drying the coating material on the base paper for thermosensitive recording paper of the present invention by a well-known and commonly used coating method such as air knife coating, roll coating, bar coating and blade coating. Formed as.

The base paper for thermosensitive recording paper of the present invention is not limited to a structure in which a thermosensitive coloring layer is directly provided on the base paper, but is also a structure in which an under layer and a thermosensitive coloring layer are sequentially provided on the base paper, or a thermosensitive coloring layer and a protective layer are sequentially provided. Even if the constitution or the like is adopted, it is possible to obtain the recording characteristics with sufficiently high sensitivity and excellent sharpness, and the layer constitution is not restricted in any way.

<Examples> Next, the present invention will be described with reference to Examples. In addition, all the parts showing the mixing ratio represent parts by weight.

Example 1 The following paper stock was used to make a paper by a three-layer papermaking process of a surface layer, an intermediate layer and a surface layer with a cylinder paper machine, and the surface was treated with a thermal calender (surface temperature 110 ° C). To prepare a base paper for thermal recording paper of the present invention. The cross-section electron micrograph of the prepared base paper showed that the density was high at the outer surface and low at the center, and the thickness was 65 μm (about 15 μm for each surface layer).
m, intermediate layer about 35 μm), smoothness 260 seconds, density of central part 0.6
It was ³ g / cm ³ .

[Surface layer]

NBKP 30 parts LBKP 70 parts Rosin size 0.5 parts Aluminum sulfate 2 parts (printing degree 48 ° SR) [Intermediate layer] LBKP 100 parts Cationic acrylamide 0.5 parts (beating degree 21 ° SR) Example 2 Surface layer in Example 1 A base paper for heat-sensitive recording paper of the present invention was produced in exactly the same manner as in Example 1 except that the stock having the following composition was used. The cross-section electron micrograph of the prepared base paper showed that the density was high in the outer surface part and low in the central part, and the thickness was 60 μm (about 15 μm for each surface layer).
m, middle layer about 30 μm), smoothness 230 seconds, center density 0.6
It was 2 g / cm ³ .

[Surface layer]

NBKP 30 parts LBKP 70 parts Clay 8 parts Alkyl ketene dimer 0.2 parts (beating degree of 45 ° SR) Example 3 Using a Fourdrinier paper machine using the following paper materials, a partition plate was provided in the slice part to form three layers. Paper was fed into the paper so that it was divided into a surface layer, an intermediate layer, and a surface layer. At this time, surface size coating was performed.

[Surface layer]

NBKP 50 parts LBKP 50 parts TiO ₂ 2 parts (beating degree 55 ° SR) [Intermediate layer] LBKP 100 parts Cationic acrylamide 1 part (beating degree 17 ° SR) The paper produced as described above is heated in a calender (surface temperature 11
Surface treatment was performed at 0 ° C.) to prepare a base paper for thermal recording paper of the present invention. The cross-section electron micrograph of the prepared base paper showed that the density was high at the outer surface and low at the center, and the thickness was 60 μm (the boundaries of the layers are not clear due to the mixture of paper materials, but the surface layers are different). About 10-15 μm, intermediate layer about 30-40 μm),
The smoothness was 230 seconds, and the center density was 0.48 g / cm ³ .

Comparative Example An image was prepared using a stock paper having the following composition by an ordinary Fourdrinier paper machine in which a partition plate was not provided in the slice portion. In addition,
At this time, surface size coating was performed.

The paper produced by the above is heated by a thermal calender (surface temperature 11
Surface treatment was performed at 0 ° C.) to prepare a base paper for thermal recording paper for comparison. The base paper produced had a thickness of 65 μm and a smoothness.
It had a density of 0.93 g / cm ³ for 250 seconds.

Next, a mixture having the following composition was dispersed using a sand mill to prepare dispersions [A] to [C].

Using the liquids [A] to [C] obtained as described above,
A thermosensitive color developing layer coating material having the following composition was prepared, and a dry coating amount of 6 g was applied onto the base paper for thermal recording paper prepared in Examples 1 to 3 and Comparative Example.
After coating and drying so as to be / m ² , the surface treatment was carried out with a super calender so that the Bekk smoothness was 300 seconds to prepare a thermal recording paper.

The thermal recording paper using the obtained base papers of Examples 1 to 3 and Comparative Example as a support was used in a thermal printer manufactured by Matsushita Electronic Components Co., Ltd. to have a power consumption of 0.5 w / dot and a scanning line density of 8 × 7.7 dots. / m
Printing was performed with m and a pulse width of 1.0 msec, and the printing density was measured with a Macbeth reflection densitometer RD-914. In addition, the reproducibility of the printed dots was visually determined, the image quality was evaluated, and the degree of pressure fog due to the calendar process was also determined. The results are shown in Table 1. From Table 1, all of the thermal recording papers using the base papers of Examples 1 to 3 showed high density and high precision printing quality and almost no pressure fog, but the thermal recording papers of Comparative Examples had low density. However, the image quality was inferior, and the soiling of the background due to pressure fog was severe. The recording papers of Examples had sufficient strength and good handling characteristics.

<Effects of the Invention> The base paper for heat-sensitive recording of the present invention has a low density at the center and has cushioning properties, and therefore, when used as a support for heat-sensitive recording paper, it has excellent adhesion to a heat-sensitive head and thermal efficiency. Therefore, high sensitivity characteristics can be obtained.

Claims (1)

[Claims] 1. A base paper comprising an intermediate layer and surface layers laminated on both sides thereof, wherein the intermediate layer has a density gradient such that the intermediate layer has a lower density than the surface layer, and the density of the intermediate layer. Is 0.35
Raw paper for thermal recording paper, characterized in that it is ~ 0.75 g / cm ³ .