JPS61237689A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To enhance reproducibility of dots and recorded density and prevent curling, by a method wherein a combination paper comprising at least three layers such that adjacent layers differ in internal bond strength and/or Cobb water absorbing capacity is used as a paper base, and a thermal color forming layer is provided thereon. CONSTITUTION:The combination paper as the paper base comprises at least three layers made by several units of wires, in which the adjacent paper layers preferably differ in internal bond strength (TAPPI RC-308) and/or Cobb water absorbing capacity (JIS P-8140). The internal bond strength of the outer layer is preferably 0.5-2.0kg.cm, and the Cobb water absorbing capacity thereof is preferably 10-25g/m<2>. Though the paper base is made from a wood pulp as a main material, it may be combinedly made from wood pulp and synthetic fibers or synthetic pulp, with addition of a size, a reinforcing agent, a fixing agent, a dye, a fluorescent dye, an antistatic agent or the like as required. A color forming agent may be any of those generally used for pressure-sensitive recording paper, thermal recording paper or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal recording paper on which recording is performed using a thermal head, a thermal pen, etc. More specifically, the present invention relates to a thermal recording paper on which recording is performed using a thermal head, a thermal pen, etc. The present invention relates to a thermal recording paper that does not cause piling to the head, has good dot reproducibility even in high-speed recording, and provides clear, high-density recording.

(Prior art) In recent years, facsimiles, printers, etc. have made remarkable progress.
In particular, a thermal recording method using a combination of a thermal head and a thermal recording paper coated with a colorless dye such as ristal violet lactone and a phenol compound, as described in Japanese Patent Publication No. 1996-2-1-032, has been applied to these devices. Widely adopted.

This thermal recording method has many advantages such as primary coloring on the recording paper, no development required, the recording device can be simplified, the cost of the recording paper and recording device is low, it is non-impact, and there is no noise. It established its position as a low-speed recording method. However, a major drawback of thermosensitive recording is that the recording speed is slower than other recording methods such as electrostatic recording, and at present it has not been adopted to the extent of high-speed recording.

In thermal recording, the most important reason why high-speed recording is not possible is that heat conduction between the thermal head and the thermal recording paper in contact with it is insufficient, and a sufficient recording density cannot be obtained. The thermal head, which is a collection of dot-shaped electrical resistance heating elements, generates heat in response to recording signals, melting and coloring the thermosensitive coloring layer in contact with the thermal head. In order to obtain clear and high-density recording, it is necessary to have good dot reproducibility, that is, the thermal head and thermosensitive coloring layer should be in close contact as much as possible, heat conduction should be efficient, and the dots should be fully compatible with high-speed recording signals. It is necessary that nine dots are formed on the thermosensitive coloring layer, completely colored, corresponding to the shape of the dot heating element of the thermal head. but,
At present, only a few percent of the heat generated by the thermal head is transferred to the thermosensitive coloring layer, and the efficiency of heat transfer is extremely low.

Several methods have been proposed for improving the smoothness of the thermosensitive coloring layer so that the thermal head and the thermosensitive coloring layer come into close contact as much as possible.

Japanese Patent Publication No. 62-20/4t2 describes that the surface of the heat-sensitive coloring layer is treated to a Bekk smoothness of -200 to 1000 seconds. The JP-A Akihiro//J Kojj issue has Bekk smoothness, which can only correspond to heat pulses of about -7 milliseconds for 200 to 1000 seconds, and heat sensitivity for high-speed recording of less than 1 millisecond. The surface of the coloring layer has a Beck smoothness of 1100.
It is stated that it is necessary to perform the smoothing process for more than a second.

If the Bekk smoothness is set to 1ioo seconds or more, multiple color fogs will occur due to the pressure, so please prepare the base paper beforehand.
The smoothness has been improved to a Bekk smoothness of 100 seconds or more to prevent color fogging. In JP-A-Shoz, 1-irtort, the surface roughness Ra of the surface of the heat-sensitive coloring layer is 2 μm or less, and the gloss level is 2! It is stated that it should be done below.

The smoothness of the heat-sensitive coloring layer is improved only by the above-mentioned prior art calender treatment such as a high-pressure mono ξ-calender, a machine calender, a cross calender, etc. for improving the smoothness. Calendering is performed on the base paper only, on the base paper and thermal paper, or on the thermal paper only.

Thermal paper whose smoothness has been improved through these calender treatments has an increased level of smoothness and recording density, which increases sticking and rolling. Keeping it to a level, recording @tomo and sticking, ) threat ring are appropriately balanced. The conventional techniques are not practical for high-speed recording in terms of recording density or recording stability, regardless of the level of smoothness.

Sticking is when the thermal head and thermosensitive coloring layer adhere to each other.
This is a phenomenon that causes peeling noise and a decrease in dot reproducibility. Piling is a phenomenon in which thermally molten material from the thermosensitive coloring layer accumulates on the thermal head, causing a decrease in recording density and dot reproducibility. , all of which are stable phenomena that interfere with nine records.

Another disadvantage of calendering thermal paper is that color fogging occurs due to pressure, and the density of the background portion of the recording paper increases.

On the other hand, there is currently a limit to the calendering of base paper due to the occurrence of so-called bulges, wrinkles, etc. due to uneven basis weight. As mentioned above, the smoothing of the heat-sensitive coloring layer and the improvement of recording density by calendering are inevitably limited, and a product that is sufficiently satisfactory for high-speed recording has not been obtained.

Thermal paper has a color-forming layer on one side, but has the disadvantage that curling tends to occur on the color-forming side when coloring occurs depending on the conditions of use.

(Object of the Invention) An object of the present invention is to provide a thermal paper that improves the above-mentioned drawbacks, that is, firstly, a thermal paper that has good dot reproducibility and high recording density. First, it is necessary to supply heat-sensitive recording paper that prevents curling toward the coloring side during coloring.

(Structure of the Invention) As a result of intensive research to improve these drawbacks, the present inventors have developed a composite paper of three or more types with different internal bonding strength and/or Cobb water absorption of adjacent paper layers. The object of the present invention has been achieved by using a paper support as a paper support and providing a heat-sensitive coloring layer on the paper support.

The laminated paper of the paper support used in the present invention is a laminated paper of two or more layers formed by wires of λ or more (a combination of circular mesh or a combination of circular mesh and fourdrinier). reed, internal bonding strength of adjacent paper layers (Tappi RC-j 0
1) and/or Cobb water absorption < JIS -
It is desirable that the values (specified in p-r la o) be different.

The internal bonding force defined in the present invention indicates the degree of compressibility in the thickness direction of paper, and the smaller the value, the higher the contact rate with the thermal head when used as thermal paper, and the higher the color recording density. will improve. On the other hand, the smaller the value, the weaker the stiffness (9) and the more likely curling will occur. Furthermore, the smaller the value of the Cobb water absorption defined in the present invention, the less deterioration of surface smoothness during application of a heat-sensitive coating liquid and the higher the color recording density. However, in order to reduce this value, a large amount of sizing agent is required, which tends to cause stains during the papermaking process, and is also disadvantageous in terms of cost. The present inventors have realized that by using a support made of three or more paper layers having different internal bonding strength and/or Cobb water absorption as described above, the color density,
We succeeded in obtaining a thermal paper with well-balanced curling properties.

The paper support used in the present invention is made mainly from wood pulp, but it is also possible to mix some synthetic fibers or synthetic fibers into the paper. As the wood/group, both coniferous wood and hardwood/e-wood can be used.
Hardwood pulp is preferred because it has short fibers and is easily smooth. , 1 water degree of e Rupu is -oo-zoo country (C, S, F)
is preferable, more preferably 3oo-1Ioocx::
It is. In addition, rosin, paraffin wax, higher fatty acid salt, alkenyl succinate, fatty acid anhydride, styrene maleic anhydride copolymer, alkyl ketene dimer, epoxidized fatty acid amide as a sizing agent, maleic anhydride copolymer as a softening agent. reaction products with polyalkylene polyamines, grade ammonium salts of higher fatty acids, polyacrylamide, starch, polyvinyl alcohol as paper strength agents.
, a melamine-formaldehyde condensate, gelatin, a fixing agent such as bandate sulfate, polyamide polyamine epichlorohydrin, dyes, fluorescent dyes, antistatic agents, etc. may be added as necessary.

Next, the heat-sensitive coating liquid used in the present invention will be described.

Generally, a heat-sensitive coating liquid is prepared by separately dispersing a color former and a color developer in a water-soluble polymer solution using means such as a ball mill. Taking a ball mill as an example, in order to obtain a finely divided color former or color developer, balls of different particle sizes are used in an appropriate mixing ratio, and this is achieved by dispersing them for a sufficient amount of time. be done. It is also effective to use a model sand mill (trade name: Dyno Mill).

The resulting dispersion of color former and color developer is mixed, and inorganic pigments, waxes, higher fatty acid amides, metal soap, and if necessary, ultraviolet absorbers, antioxidants, latex binders, etc. are added to form a coating liquid. shall be. There is no problem in adding these additives at the time of dispersion.

The coating liquid generally has a coating amount of 0.21/m2 as a coloring agent.
It is coated on the support so that the ratio is between 0.9 and 0.09/m2.

The color forming agent used in the present invention is not particularly limited as long as it is used in general pressure-sensitive recording paper, heat-sensitive recording paper, etc. Specific examples include (1) triarylmethane compounds such as 3.3-terbis(p-dimethylaminophenyl)-1-dimethylaminophthalide (crystal violet lactone);
, J-(p-dimethylaminophenyl)-j-(/, 2
-dimethylindol-3-yl)phthalide, 3-(p
-dimethylaminophenyl)-J-(J-phenylindol-3-yl)phthalide, 3,3-bis-(p-ethylcarbazol-3-yl)-3-dimethylaminophthalide, 3,3-bis- (2-phenylindole-3
-il)-! -dimethylaminophthalide, etc.; (2) Diphenylmethane compounds, such as ≠, ≠-bis-dimethylaminobenzhydrin benzyl ether, N-halophenylleucoolamine, N-2゜4Z, t-)I
(3) Xanthine compounds, such as rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamine-7-butylaminofluorane, 3-diethylamine /-7-(,2-10 Roanilino)
Fluoran, 3-diethylamino-t-methyl-7-anilinoIO-fluoran, 3-piperidino-t-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-ot-methyl-7-anilinofluorane, 3-
Diethylamino-2-chloro-7-(β-ethoxyethyl)aminofluorane, 3-diethylamino-4-chloro-7-(γ-chloropropyl)aminofluorane, 3
-diethylamine-O-chloro-7-anilinofluorane, J-N-cyclohexyl-N-methylamino-6-
Methyl-7-anilinofluorane, 3-diethylamine-7-phenylfluorane, etc.; (4) Thiazine compounds, such as benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue, etc.; (5) Spiro compounds, such as, Examples include 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho-(3-methquin-benzo)-spiropyran, and mixtures thereof. these are.

Determined by application and desired characteristics.

The color developer used in the present invention includes phenol derivatives,
Aromatic carboxylic acid derivatives are preferred, and bisphenols are particularly preferred. Specifically, phenols and p
-octylphenol, p-tert-'7'f-ruphenol, p-phenylphenol, λ, 2bis(1)-
hydroxy) furononξ, /, /-bis(1)-hydroxyphenyl)pentane, /, /-his(p-hydroxyphenyl)hexane, λ1.2-bis(p-hydroxyphenyl)hexane, /, / Examples include -bis(p-hydroxyphenyl)-coethylhexane, -, cobis(p-hydroxyphenyl-3,!-dichlorophenyl)pro/en, and the like.

Examples of aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, propyl p-hydroxybenzoate, 'p
-Butyl hydroxybenzoate, Hensyl p-hydroxybenzoate, 3. ! Examples of -di-α-methylbenzyl salicylic acid and carboxylic acid include polyvalent metal salts thereof.

These color developers may be added as a eutectic with a thermofusible substance with a low melting point in order to melt at a desired temperature and cause a color reaction, or the low melting point compound may be added to the surface of the color developer particles. It is preferable to add it in a fused state.

Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bisstearamide, and higher fatty acid esters.

Examples of metalstones include polyvalent metal salts of higher fatty acids, ie, zinc stearate, aluminum stearate, calcium stearate, zinc oleate, and the like.

Inorganic pigments include kaolin, calcined kaolin, talc,
Examples include waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, titanium oxide, and barium carbonate.

The oil absorption of these inorganic pigments is AOml/100? It is preferable that the average particle diameter is 3 μm or less. The oil-absorbing inorganic pigment is desirably blended into the recording layer in terms of dry weight j-jO weight, preferably io-hiro θ weight.

These are dispersed in a binder and applied. Water-soluble binders are generally used, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and imbutylene-maleic anhydride copolymer. Polyacrylic acid, starch derivative casein, gelatin, etc. can be produced.

In addition, in order to impart water resistance to these binders, water-resistant agents (gelling agents, cross-linking agents) may be added, or emulsions of hydrophobic polymers, specifically styrene-butadiene rubber latex, acrylic resin emulsions, etc. You can also add

The binder reacts in the recording layer in an amount of 10 to 30% by dry weight. Furthermore, auxiliary agents such as antifoaming agents, fluorescent dyes, and coloring dyes may be added to the coating liquid as appropriate.

The coating liquid for forming such a recording layer is a blade coating method,
Conventionally known coating methods such as air knife coating, gravure coating, roll coating, spray coating, dip coating, bar coating, and extrusion coating can be used.

The amount of the coating liquid forming the recording layer to be applied to the support is not limited, but is usually 3 to /If/m2 by dry weight,
Preferably it is in the range of + to /Of 7m2 I:).

(Effects of the Invention) The effects obtained by the thermal recording paper according to the present invention using three or more laminated papers with different internal bonding strength and/or Cobb water absorption of adjacent paper layers as a paper support are as follows. First, during recording, the contact area with the thermal head increases, resulting in high recording density and good dot reproducibility. Second, during recording, there is less curling on the coloring surface side, and recording without paper jams etc. can be obtained.

(Example) A three-layer laminated paper was made using a cylinder paper machine using paper stock tubes as shown in Table 7. The basis weight was adjusted to AOf/m2° and the thickness to 76μ using a machine calender.

In addition, the basis weight of each of the three layers was 2077 m2.

In addition, the paper stock used for the outer layer of Example 1 alone was tsubo@A O
Comparative Example 1 was a paper made with f//m2, and Comparative Example C was a paper made with only an intermediate layer. Similarly, the outer layer single stock of Example C is Comparative Example 3, the middle layer single stock is Comparative Example Hiroshi, the outer layer single stock of Example 3 is Comparative Example J, and the middle layer single stock is The paper material was designated as Comparative Example t.

Above, the example (4i-AJ) according to the present invention and the comparative example (
AP) A heat-sensitive coating liquid was applied to the support of the glue sample to obtain heat-sensitive recording paper. Next, thermal recording was performed on these thermal recording papers, and the recording density was measured. In addition, the state of curling immediately after recording was evaluated.

(The curling was evaluated based on the height of the four corners of the paper.) These results are shown in Table 2.

The method for producing the heat-sensitive coating liquid, the method for coating it, and the method for measuring the heat-sensitive recording density are shown below.

Manufacturing method of heat-sensitive coating liquid Crystal violet lactone aok<9woi.

polyvinyl alcohol (degree of saponification and degree of polymerization 100)
) The mixture was dispersed in a JOOI ball mill with an aqueous solution overnight. Similarly, the mixture was dispersed overnight in a 3001 ball mill together with λ9.2-bis(hydroxyphenyl)prono3ne λθKgf10qb polyvinyl alcohol aqueous solution. Both dispersions were mixed with crystal violet lactone and 2.
The ratio of Corbis(gu-hydroxyphenyl)propane is /
: Mix so that the j weight ik ratio is achieved, and then add the mixed liquid,
A slight amount of calcium carbonate of tKf was added to 20 kg and sufficiently dispersed to prepare a coating liquid.

How to apply heat-sensitive coating liquid: At/m solid content on one side of base paper using an air knife coater.
2, dried in a TO'C hot air dryer, and machine calendered.

Method for measuring thermal recording density Recording speed: 1 dot per λ milliseconds, recording density: j dots/■ in the main scanning direction, 6 dots/■ in the sub-scanning direction, and solid coloring was performed at a thermal head energy of 0 millijoules/2. Ta. The recording density was determined by measuring the reflection density at 610 nm.

From the results shown in Table 2, it is clear that the thermal recording paper according to the present invention has excellent properties in terms of color density and curling.

Patent applicant: Fuji Photo Film Co., Ltd. -λ O-

Claims (2)

[Claims] (1) In thermosensitive recording paper having a thermosensitive coloring layer on a paper support, the support has an internal bond strength (Tapp) of adjacent paper layers.
i Specified in RC-308) and/or Cobb water absorption (specified in JIS-P-8140)).
A thermal recording paper characterized by being made of laminated paper of more than one layer. (2) The internal bonding strength of the outer layer of the laminated paper is 0.5 to 2.
0Kg・cm, and Cobb water absorption is 10-25g
2. The thermal recording paper according to claim 1, wherein