JPS58158289A - Composition for heat-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To obtain a composition having excellent thermal respondence of recording and excellent color intensity and free of color disappearance even under high-temperature and high-moist conditions and also in the presence of plasticizer from a low-melting mixture composed of a leuco dye and a mixture selected from specific benzyl paraoxybenzoates as developers. CONSTITUTION:A composition for a heat-sensitive recording sheet is composed of a colorless or light-color leuco dye and a substance having a developing function. As for the substances constituting the developer, a mixture having a low melting point (80-120 deg.C), selected from benzyl esters of paraoxy benzoic acid, e.g., benzyl esters (A) (nucleus halogen or lower alkylsubstituted benzyl ester, etc.), aryl esters (B) (phenyl ester, etc.), or lower alkyl esters (C) (propyl ester, etc.) is used. The preferred amount of the developer used is 3-10pts.wt. on the basis of 1pt.wt. leuco dye.

Description

[Detailed description of the invention] TECHNICAL FIELD The present invention relates to an improved composition for a kanji sickle sheet.

Generally, heat-sensitive recording sheets are produced by grinding and dispersing a colorless or light-colored leuco dye and a color developer into fine particles, then mixing the mixture, adding a binder, filler, sensitivity enhancer, lubricant, and other auxiliary agents. The resulting coating liquid is applied to a support such as paper or film, and records are created by coloring through an instantaneous chemical reaction upon heating. In this case, various vivid hues can be obtained by selecting the type of colorless dye.

These thermal recording sheets are used in a wide range of fields, including thermal pen type recording paper for various medical and industrial measuring instruments, thermal printer recording paper for computer terminals and calculators, thermal ticketing for automatic ticket vending machines, and facsimile recording paper. Application development is underway.

In recent years, thermal heads of color recording apparatuses have become capable of high-density and high-speed recording. For example, the recording speed has been increased to 2 to 4 times or more than the conventional technology. As a result, the thermal energy of thermal heads is becoming smaller and smaller, and the heat-sensitive recording sheets used therein are also required to have sufficient color sensitivity to obtain clear color recordings with a small amount of heat. For this purpose, it is necessary for the color developer to melt with a small amount of heat and cause a coloring reaction, and it is desired that coloring occurs at a temperature of 70 to 120°C. However, the melting point of leuco dyes having structures such as lactone, lactam, and spiropyran used in thermosensitive recording sheets is usually 160 to 240°C, and no stable dyes that melt at such low temperatures have been found.

On the other hand, many phenolic compounds are known as color developers in combination with leuco dyes, but bisphenol A (melting point 1
56 to 158°G), and is currently the most widely used in terms of quality stability, price, and availability. However, bisphenol A has the disadvantage of a high thermal coloring temperature. Phenolic substances with a low melting point, such as 4-tert-butylphenol (melting point 94-99°C),
When -valent phenols such as α-naphtho-) I/(melting point 95 to 96°C) and β-naphthol (melting point 119 to 122°C) are used, the storage stability and stability of the heat-sensitive recording sheet deteriorate. Not only does the skin gradually develop color even at room temperature, but it also has a strong so-called phenol odor, making it impractical.

If the color forming material itself has a high melting point (or a low melting point), if a third substance is allowed to coexist and the third substance melts, thereby dissolving the color forming material, it is possible to cause a color reaction even at low temperatures. It has been proposed to add heat-melting substances with low melting points, such as various waxes, fatty acid amides, alkylated biphenyls, substituted biphenylalkanes, coumarin compounds, and diphenylamines, as sensitizers or melting point depressants. In the method of adding a sensitizer, it is necessary to melt the sensitizer before the color reaction begins, so the thermal response to minute amounts of heat is sufficient for high-speed dynamic recording in a short period of time. There are disadvantages such as not being able to obtain

Recently, paraoxybenzoic acid benzyl ester has been developed as a color developer, and the defects observed in conventional color developers have been significantly improved. As a result, it has become possible to obtain a heat-sensitive recording sheet having extremely excellent properties for practical use. However, there is a drawback that the obtained records tend to fade, especially in hot and humid conditions such as summer.

The present inventors possessed the advantages of the paraoxybenzoic acid benzyl ester color developer and conducted various studies to improve the disadvantages thereof, and as a result, the present invention was completed.

The present invention uses a colorless or light-colored leuco dye, a benzyl ester and/or an aryl ester which may have a substituent of paraoxybenzoic acid as a color developer, and a known triphenylmethane-phthalide-based leuco dye. , fluorane series, phenothiazine series, indolylphthalide series,
Spiropyran-based, rhodamine lactam-based, triphenylmethane-based, azaphthalide-based, chromenoindole-based, and triase/based agents are used.

The benzyl ester of paraoxybenzoic acid (A) constituting the color developer is a benzyl ester.

Aryl esters (B) such as nuclear halogen or lower alkyl substituted benzyl esters include phenyl esters, naphthyl esters, nuclear halogens, lower alkyl or lower alkoxy substituted phenyl or naphthyl esters, lower alkyl esters (C) include methyl, Examples include ethyl, propyl, butyl, amyl, and hexyl esters.

(Use an ester mixture selected from group (Al and/or group (B) and optionally group (C10). The type of ester and the ratio of combined use are selected as appropriate depending on the performance required for the recording sheet and the melting point of the ester. However, it is generally preferred that the melting point of the mixture is between 80 and 120°C, and those that melt instantly are particularly preferred.

According to the present invention, a color developer having a desired melting point can be obtained by combining only substances having color developing ability without using a melting point depressing agent that does not have color developing ability. That is, it does not use an inert melting point lowering agent (it has excellent thermoresponse, develops a high concentration of color, and does not cause mechanical troubles such as streaks of lees adhering to the thermal head or ghosting).

Furthermore, the storage stability of records after color development, which has been a drawback of benzyl paraoxybenzoic acid ester, is improved. The reason may be as follows. Regarding the mechanism of color development between leuco dyes and phenolic substances, there is a prevailing theory that the lactone ring of the leuco dye is cleaved by acid and the color is developed, but in addition to this, charge transfer interactions between the dye and the color developer also come into play. It is believed that In that case, close contact between dye and developer molecules is required. According to this, it is easy to understand not only the reason for color development but also the reason for decolorization. That is, when paraoxybenzoic acid be/zyl ester is used alone as a color developer, after color development, crystals are precipitated in the color development area, and the color disappears with O accompanied by a so-called whitening phenomenon. The reason for this is probably that the intermolecular force between the benzyl esters is stronger than the charge transfer force between the dye and any of the benzyl esters, and the benzyl ester is extracted from the colored complex, causing recrystallization. It is effective to mix substances with similar structures in order to weaken intermolecular forces and reduce the tendency to crystallize. The phenomenon of melting point depression due to eutectic is a specific example. In the present invention, by mixing a plurality of paraoxybenzoic acid esters, a composition having an arbitrary melting point is created, and the crystallization tendency of each ester is weakened, resulting in improved coloring performance,
A composition for a heat-sensitive recording sheet having excellent storage performance can be obtained.

The color developer used in the present invention may be different from conventionally used bisphenol A% pp' (
It can also be used in combination with phenols or organic acids such as 1=-methyl-hexylidene) diphenol, para-tert-butylphenol, para-phenylphenol, Novo2c resin and May enol resin. The color developer and color-forming colorless dye are atomized using a grinder such as a ball mill, attritor, or sand grinder, or a suitable emulsifying device, and various additive materials are added depending on the purpose to form a coating liquid.

This coating solution usually contains binders such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, starch, styrene-maleic anhydride copolymer, vinyl acetate maleic anhydride copolymer, and styrene-butadiene copolymer. , as well as inorganic or organic fillers such as kaolin, calcined kaolin, diatomaceous earth, talc, titanium, calcium carbonate, magnesium carbonate, and aluminum hydroxide, as well as excipients such as fatty acid metal salts, waxes, etc. lubricants, benzophenol-based or triazole-based ultraviolet absorbers, water-resistant agents such as glyoxal, dispersants, antifoaming agents, etc. can be used. By applying this coating liquid to paper and various films, the desired heat-sensitive recording sheet can be obtained.

The amount of the color developer and the amounts of other various components used in the present invention are determined according to the required performance and recording suitability, and are not particularly limited. 3 to 10 parts of the filler and 1 to 20 parts of the filler are used, and the binder is suitably used in an amount of 10 to 20% based on the total solid content.

When the composition of the present invention is used, the thermal response and color intensity of the recording are extremely excellent, and the recording does not fade even under high temperature and humidity or in the presence of a plasticizer (because a good background record can be obtained,
A heat-sensitive recording sheet that is extremely superior to conventional methods can be obtained.

Experimental Example 1 Paraoxybenzoic acid benzyl ester (melting point 111°C)
and paraoxybenzoic acid n-propyl ester (melting point 98
℃) were mixed in various proportions and the melting points were measured. The results are shown in FIG. 78-1 by mixing two types of esters
Compositions with any melting point in the range of 11°C are obtained.

Experimental Example 2 Three types of esters of roseoxybenzoic acid, namely phenyl ester (melting point 179°C), benzyl ester, and
N-propyl esters were mixed in various proportions and the melting points were measured. The results are shown in FIG. By mixing three types of esters, a composition having an arbitrary melting point in the range of 100 to 120°C can be obtained.

Parts in the following examples mean parts by weight.

Example 1 Solution A (dye dispersion) 6-(N-cyclohexyl-N-methyl 2.0 parts thylamino)-methi/-7-anilitofluorane 10% polyvinyl alcohol aqueous solution 4,
6 parts water
2.5 parts Solution B (color developer dispersion) Color developer shown in Table 1 6.0 parts 1
0% polyvinyl alcohol aqueous solution 30.0
Part: Grind and mix each liquid having the above composition using a ball mill.

Next, 1.0 part of liquid A and 4.0 parts of liquid B were mixed to prepare a coating liquid, and this coating liquid was applied to high-quality paper using a wire bar (coating amount: 7.5.9 parts m2). The color density of the obtained thermosensitive recording sheet at each temperature was measured. The results are shown in Table 1. In the table, Compound I means phenyl paraoxybenzoate, Compound ① means benzyl paraoxybenzoate, and Compound Uchika means propyl paraoxybenzoate. As is clear from this formation, the composition of the present invention has excellent recording thermal response and color density.

Table 1 * Y value was measured using a dichroic meter, P = 1.911-
The color density P was determined from the formula 1o Y.

Example 2 A recording sheet obtained in the same manner as in Example 1 was colored under predetermined conditions, and its storage stability under high temperature and humidity (40°C, 90% relative humidity) was investigated. The results are shown in Table 2. Second
As is clear from the table, the composition of the present invention has excellent recording stability even under high temperature and high humidity.
.

斡：○ means almost no change. □ ×: Crystals precipitate white or discolor in spots.

Example 3 A recording sheet obtained in the same manner as in Example 1 was coated with a plasticizer-containing polyvinyl chloride sheet, and 10 g/c was coated at 40°C.
After applying a pressure of m2, the stability of the recording was examined. The results are shown in Table 3.

As is clear from Table 3, the stability of the compositions of the invention against plasticizers is very good.

Table 3 *: Color development temperature is 150℃ for this example, all other examples are 1
20℃.

**: O has almost no change.

× indicates that the crystals are white (precipitated or discolored in spots).

Example 4 Solution A (dye dispersion) Crystal violet lactone 2.0 parts 1
0% polyvinyl alcohol aqueous solution 4.6 parts water
2
．． 5 parts Liquid B (color developer dispersion) Color developer shown in Table 4 6.0 parts 1
30.0 parts of 0% polyvinyl alcohol aqueous solution The can liquid having the above composition was ground and mixed in a ball mill. Next, prepare a coating liquid by mixing 1.0 parts of liquid A and 4.0 parts of liquid B, and apply this coating liquid to high-quality paper using a wire bar (coating amount: 7.
．． 5. F/ff! 2). The obtained heat-sensitive recording sheet was colored under specified conditions, and then heated under high temperature and humidity (40°C, relative humidity 90%).
) was investigated for storage stability. The results are shown in Table 4. For O 2 crystal violet lactone, when paraoxybenzoic acid ester alone was used as a color developer, the color was significantly erased. However, it is known that when two types of esters are used in combination, discoloration is suppressed and storage stability is greatly improved.

Section 4 Table *; Color development temperature is 150°C in this example, and 120°C in other examples.

**No change for 20.

×: Crystals precipitate white or fade in spots.

Example 5 Using a recording sheet obtained in the same manner as in Example 4, Example 6
The stability against plasticizers was investigated using the same method as above. The results are shown in Table 5. It is known that the stability against plasticizers is significantly improved by incorporating esters.

Table 5 *: Coloring temperature is 150℃ in this example only. Other examples are 120°C0 There is no change in $$20.

× is mottled discoloration.

Example 6 A thermosensitive recording sheet was obtained under the same conditions as in Example 1, except that 4.6 parts of a 10% hydroxyethyl cellulose aqueous solution was used instead of the 10% polyvinyl alcohol aqueous solution in Liquid A (dye dispersion) in Example 1. . The stability of the surface of this recording sheet under high temperature and humidity conditions (40° C., relative humidity 90%) was investigated. The results are shown in Table 6. As is clear from Table 6, the ester mixture of the present invention:
Like benzyl paraoxybenzoic acid ester and phenyl ester, it shows good texture and no fogging is observed.

On the other hand, in the case of bisphenol A, the texture is poor and the fogging on the texture increases after storage.

Table 6 For Δ, no background fogging was observed.

Example 7 A thermosensitive recording sheet was obtained under the same conditions as in Example 4 except that a 10% hydroxyethyl cellulose aqueous solution 4-6'flJ was used instead of the 10% polyvinyl alcohol aqueous solution in the A liquid (dye dispersion) in Example 4. Ta. About this recording sheet Under high temperature and humidity (40℃, relative humidity 90%)
), the stability of the scalp was investigated. The results are shown in Table 7.

As is clear from Table 7, the ester mixture of the present invention exhibits good skin texture similar to benzyl paraoxybenzoate and phenyl ester, and no fogging is observed.

On the other hand, when converted to bisphenol, the texture is poor, and after storage, there is severe fogging of the texture.

For $20, there is no visible skin fogging at all.

× indicates severe background fogging.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the mixing ratio of two types of esters of roseoxybenzoic acid and their melting points, and Figure 2 is a graph showing the relationship between the mixing ratio of six types of esters and their melting points. has the following meanings: NPF: Haloxybenzoic acid propyl ester B
ZE: haloxybenzoic acid benzyl ester poB-p
h: paraoxybenzoic acid phenyl ester I:
POB-Ph + BZE H: Same as above 10 NPE (10%) ■: Same as above 10 NPF (20%) %1 Figure NPE BZE
BZE # it th/running hyung kudzu 2 times 0 20 40 60 80 100BZ
E's Judou I Komu

Claims (1)

[Claims] 1. Contains a colorless or light-colored leuco dye and a low melting point mixture selected from benzyl esters and/or aryl esters that may have a substituent of paraoxybenzoic acid as a color developer. A characterized composition for heat-sensitive recording sheets. 2. Contains a colorless or light-colored leuco dye and a low melting point mixture selected from benzyl esters and/or aryl esters having substituents of paraoxybenzoic acid as a color developer and alkyl esters of paraoxybenzoic acid. A composition for a heat-sensitive recording sheet characterized by: