JPS59145189A - Heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To enhance stability of a ground part and reliability of images, by using a calcium salt of hydroxynaphthoic acid as a color developing substance, in a heat-sensitive recording material comprising a leuco dye and a color developing substance. CONSTITUTION:A calcium salt of hydroxynaphthoic acid such as calcium 2- hydroxy-3-naphtoate is used as a color developing substance, and it is applied onto a base such as a paper or a synthetic paper together with a known leuco dye, particularly preferably a fluoran compound of the formula (wherein each of R1, R2 is a lower alkyl group or a cycloalkyl group, and R1 and R2 may combine with each other to constitute a nitrogen-containing heterocyclic group) and a binder, followed by drying. The leuco dye, the color developing substance and the binder as used in quantities of 5-30wt%, 40-80wt% and 2-20wt%, respectively. Other than the calcium salt of hydroxynaphthoic acid, a known pnenolic substance or the like may be used as the color developing substance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to improvements in heat-sensitive recording materials containing leuco dyes as color formers.

[Prior art]

Thermosensitive recording materials generally have a thermosensitive coloring layer containing a thermochromic composition as a main component on a support such as paper, synthetic paper, or plastic film. A colored image can be obtained by heating. Compared to other recording materials, this type of recording material does not require complicated processing such as development and fixing, can produce records in a short time using relatively simple equipment, and generates less noise and pollutes the environment. Due to its low cost, it is used not only for copying books and documents, but also as a recording material in a wide range of applications such as computers, facsimiles, ticket vending machines, labels, and recorders. Thermal color-forming compositions used in such heat-sensitive recording materials generally contain a co-dye consisting of a color former and a color developer that causes the color former to develop color when heated. Conventionally, organic acids and phenolic substances have been used. A recording material that combines a color forming agent and a color developing substance has the advantage that the resulting image has a particularly clear color tone, has a high background whiteness, and has excellent light fastness. , is widely used.

However, on the other hand, images with this recording material may lose contrast due to color development or discoloration due to contact with organic solvents, plasticizers, oils and fats, and the reliability of the images may be reduced. It is also true that this is insufficient. In particular, phenolic substances such as bisphenol A have the property of decolorizing images when they come into contact with lamp films such as polyvinyl chloride.
This has become a problem recently. On the other hand, Tokko Showa 5'5-1
When a metal-containing compound as disclosed in Publication No. 195 is used as a color developer, good image reliability can generally be obtained, but in this case, The drawback is that the coloring in the areas is too thick, which is impractical because it ultimately leads to a decrease in contrast.

〔the purpose〕

The object of the present invention is to provide a heat-sensitive recording material with improved image reliability, and more specifically, to provide a thermal recording material with improved image reliability, in which the image area and the background area are stable even when they come into contact with oils and fats, plasticizers, organic solvents, etc. The object of the present invention is to provide a heat-sensitive recording material with significantly improved properties.

〔composition〕

According to the present invention, in a heat-sensitive recording material containing a leuco dye and a color developing substance that causes the leuco dye to develop color when heated,
A heat-sensitive recording material is provided, wherein the color developing substance is a calcium salt of hydroxynaphthoic acids.

In the present invention, various types of hydroxy are used as color developing substances such as calcium salt of synapthoic acid, and specific examples of such substances include calcium 2-hydroxy-3-naphthoate, 1-bromo-2-hydroxy- Calcium 3-naphthoate, Calcium 1-chloro-2-hydroxy-3-naphthoate, Calcium 1-hydroxy-2-naphthoate, Calcium 2-hydroxy-1-naphthoate, 6-chloro-2-
Examples include calcium hydroxy-3-naphthoate, but are not limited to these, of course.

The leuco dyes used in the present invention include those commonly used in this type of heat-sensitive recording material, such as triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based leuco dyes. A fluoran compound represented by the following general formula is used.

In wiping, R1 and R2 may be the same or different and represent a lower alkyl group such as methinepeethyl, propyl, butyl, amyl, etc., as well as a cycloalkyl group such as cyclohexyl group, and R1 and R2 may be the same or different. (can be bonded to each other to form a nitrogen-containing heterocyclic group, such as pyrrolidine, piperidine, etc.) Specific examples of the above-mentioned fluoran compounds include, for example, 3
-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-
Examples include methyl-7-anilinofluorane, tei-diethylamino-6-methyl-7-anilinofluorane, and 3-(N-methyl-N-?amylamino)-6-R7-anilinofluorane.

In the present invention, a calcium salt of hydroxynaphthoic acids is used as a color developer. However, as long as this does not particularly impede the purpose of the present invention, this may be a phenolic substance that has been commonly used as a color developer. Examples of such phenolic substances include 4.4-impropylidene bisphenol and 4.4-impropylidene bisphenol.
'-isopropyritine bis(0-methylphenol), 4.4'-secondary-butyritene bisphenol, 4.4'-isopropyritine bis(2-tert-butylphenol), 4.4'-cyclohexylidene diphenol 4.4'
-isopropyritine bis()-chlorophenol), 2.2'-methylenebis(4-methyl-6-tert-butylphenol), 2.2'-methylenebis(4-ethyl-6-tert-butylphenol), 4.4 '-Butylidene bis(6-tert-butyl-
m-cresol), 4'-thiobis(6-tert-butyl-m-cresol), haloxybenzoic acid impropinobe p-oxybenzoic acid isobutinohe p-ocybenzoic acid ff hensyl, p-oxybenzoic acid cyclohexyl, Examples include neopentylcatechol butylphenone p-oxybenzoate, propyl protocatechuate (ester), benzyl protocatechuate, propyl gallate, and stearyl gallate.

The heat-sensitive coloring layer may contain a binder, a filler, a surfactant, a lubricant, and the like. In this case, binders include water-soluble resins such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, imbutylene/maleic anhydride copolymer alkali salts, as well as polyurethane, styrene/butadiene copolymers, polyacrylic esters, etc. latex can be used. As the filler, in addition to inorganic materials such as calcium carbonate, silica, titanium oxide, aluminum hydroxide, clay, and Merck, organic fillers made of fine particles of urea-formalin resin 1, polystyrene, etc. can be used. As the lubricant, in addition to higher fatty acids, their esters, amides, and metal salts, various wax-like substances can be used.

In order to produce the heat-sensitive recording material of the present invention, an aqueous solution containing a leuco dye, a color developer and a binder as main components may be coated on a support such as paper or synthetic paper and dried.

The amounts of the leuco dye, color developer and binder used are 5 to 30% by weight, 0 to 80% by weight, and 2 to 20% by weight, respectively. The amount of the heat-sensitive coloring layer to be formed is preferably about 2 to 10 degrees centigrade.

〔effect〕

The heat-sensitive recording material of the present invention uses a calcium salt of hydroxynaphthoic acids as a color developer, and therefore has significantly improved image reliability. However, there is hardly any background coloring, and there is no problem of decoloring of the colored image. Utilizing these characteristics, the heat-sensitive recording material of the present invention can be used in various fields, such as facsimiles, various measuring instruments, etc., as well as being used as recording paper.
It is advantageously applied as magnetic ticket paper, label sheet, etc.

〔Example〕

Examples are shown below. Note that parts and units are parts by weight and parts by weight, respectively. In addition, the canned liquid was pulverized and dispersed using a ball mill so that the average particle size of the particles contained therein was 5 μm or less.

Example [Liquid A] Leuco dye for clothing-1 10 parts water
,. , 7 [Liquid B] Urine malformalin resin fine particles 20 parts stearic acid amide 15 parts zinc stearate
511 Polyvinyl alcohol top 10 aqueous solution 40rr water
150 [Liquid C] Color developing substance shown in Table 1 15 parts Polyvinyl alcohol 10% aqueous solution 15n water
[Liquid A], [Liquid B+], and [Liquid C] obtained in the above manner were uniformly stirred and mixed, and the dry adhesion amount of the dye was 0.5 ii'/ A thermosensitive recording paper was obtained by coating with Labosod so that the temperature became 1.

Table 1 shows specific combinations of leuco dyes and color developing substances used to create each heat-sensitive recording material.

Next, various tests shown below were conducted on each of the heat-sensitive recording materials obtained above, and the results are shown in Table 2.

Color development property: The color development area was measured using a Macbeth densitometer when color was developed at 140C using a thermal gradient tester, and the value was indicated as Dmax. Further, the density of the background portion in this case was expressed as Dmin.

Oil resistance: Cottonseed oil was applied to the image area and background area of a heat-colored sample, and the condition of the image area and background area after being left at 40C for one day was visually compared with that before the test. .

Plasticizer resistance・・・Plasticizer (dioctyl adipate) is applied to the image area and background area of a thermally colored sample, and the condition of the image area and background area after being left at room temperature for one day is checked before the test. Visual comparison was made with that of

In addition, in Table 2, the symbols shown as evaluation criteria for oil resistance and plasticizer resistance mean the following.

◎・・・・・・No change at all ○・・・・・・Almost no change △・・・・・・Slight change×・・・・・・Big change '' means a decrease in density (decolorization) in the image area and an increase in density (color development) in the background area.

Table 2 As can be seen from the above results, the product of the present invention has almost no decolorization of the image or coloration of the background due to oil, plasticizer, etc., and its image reliability is higher than that of the conventional technology. It can be seen that there has been a significant improvement.

Patent applicant Ricoh Co., Ltd. Representative Patent Attorney Toshiaki Ikeura

Claims (2)

[Claims] (1) In a heat-sensitive recording material having a heat-sensitive coloring layer containing a normally colorless or light-colored leuco dye and a color-developing substance that causes the leuco dye to develop color when heated, the color-developing substance is calcium of hydroxynaphthoic acids. A heat-sensitive recording material characterized by being salt. (2) The heat-sensitive recording material according to claim 1, wherein the leuco dye is a fluoran compound represented by the following general formula. (In the formula, R1 and R1 may be the same or different, each represents lower alkyl or cycloalkyl, and R1
and horses can combine with each other to form nitrogen-containing heterocycles)