JP2011005801A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium which has high development sensitivity and superior contrast in a printed portion and can hardly let head scums adhere thereto.SOLUTION: The thermal recording medium includes on its support body, a heat sensitive recording layer containing at least colorless or light-colored electron-donating leuco dye and electron-accepting developing agent. The thermal layer contains cellulose nanofiber so that high color sensitivity is achieved, and head scums are hardly attached thereon, and in addition, high contrast is obtained in the printed portion.

Description

  The present invention relates to a heat-sensitive recording material that obtains a recorded image by utilizing a coloring reaction between an electron-donating leuco dye and an electron-accepting developer.

  The heat-sensitive recording material contains a colorless or light-colored electron-donating leuco dye (hereinafter referred to as “dye”) and an electron-accepting developer (hereinafter referred to as “developer”) such as a phenolic compound. After grinding and dispersing into fine particles, both are mixed, and a coating solution obtained by adding a binder, filler, sensitivity improver, lubricant and other auxiliaries to paper, synthetic paper, film, plastic, etc. A recorded image can be obtained by developing a color by an instantaneous chemical reaction by heating such as a thermal head, hot stamp, thermal pen, laser beam or the like. This thermal recording medium is widely used in facsimiles, computer terminal printers, automatic ticket vending machines, measuring recorders, etc., and for various tickets, receipts, labels, bank ATMs, It is also used for gas and electricity meter readings and for cash vouchers such as car betting tickets. Since fine particles are melted (dissolved) by heat and cause a chemical reaction, the molten material adheres to the thermal head (head residue), resulting in printing failure, or the molten material is lost after cooling and solidification, causing misidentification. In order to prevent this, a pigment having high oil absorption is used for the thermosensitive coloring layer (Patent Documents 1 and 2).

JP 2001-026181 JP 2006-272828 A

However, the most commonly used silica as a highly oil-absorbing pigment has a refractive index of about 1.30 to 1.35, and is usually used as a binder or coloring material (refractive index of 1) used in a thermosensitive coloring layer. The refractive index difference is large (about .50), light scattering occurs, and the contrast of printed characters and barcodes is lowered, which may cause misperception and reading failure.
Accordingly, an object of the present invention is to provide a heat-sensitive recording material that has high color development sensitivity and is difficult to adhere to head debris, and that has an excellent contrast in a printing portion.

The said subject was achieved by containing a cellulose nanofiber in a thermosensitive recording layer.
That is, the present invention is a heat-sensitive recording material provided with a heat-sensitive recording layer comprising at least a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and the heat-sensitive recording layer is formed of cellulose. A thermal recording material comprising nanofibers.

  According to the present invention, it is possible to obtain a heat-sensitive recording material having high color development sensitivity and being difficult to adhere to head debris, and having excellent print section contrast.

Embodiments of the present invention will be described below.
The heat-sensitive recording material of the present invention is a heat-sensitive recording material provided with a heat-sensitive recording layer containing at least a colorless or light-colored electron-donating leuco dye and an electron-accepting developer as a coating layer on a support, The heat-sensitive recording layer contains cellulose nanofibers.

  The heat-sensitive recording material is usually formed by laminating an under layer, a heat-sensitive recording layer, and a protective layer in this order as a coating layer on a support. Of these, coating layers other than the heat-sensitive recording layer may be omitted, and an intermediate layer may be provided between the heat-sensitive recording layer and the protective layer.

  The cellulose nanofibers used in the present invention have a width of 0.5 to 20 nm and a length of about 0.1 to 15 μm obtained by defibration (miniaturization) of a cellulosic raw material by chemical treatment or mechanical treatment.

  As a method for producing cellulose nanofibers used in the present invention, a cellulose raw material such as finely divided cellulose oxidized by a catalyst is defibrated by a high-pressure homogenizer (cellulose nanofibers obtained by chemical treatment), a cellulose raw material Examples of the suspension obtained by defibration and classification using glass or zirconia beads as a grinding medium (cellulose nanofibers by mechanical treatment) can be exemplified, and the method is not limited to these production methods. However, it is particularly preferable to use cellulose nanofibers produced by performing an oxidation treatment with a catalyst from the viewpoint of improving the strength of the heat-sensitive recording layer of the heat-sensitive recording material.

  In the present invention, cellulose nanofibers obtained by chemical treatment include (1) an oxidant in the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides and mixtures thereof. Using cellulose nanofibers obtained by a method comprising a step of preparing oxidized cellulose, (2) a step of wet atomization of the oxidized cellulose to form nanofibers, and using the cellulose nanofibers produced by this method, This is preferable from the viewpoints of color development (particularly, contrast between the printed portion and the white paper portion) and head residue.

  The cellulose raw material used as the raw material of the cellulose nanofiber of the present invention is not particularly limited, and kraft pulp or sulfite pulp derived from various woods, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer or a mill, or the like. Microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis can be used. In addition, plants such as kenaf, hemp, rice, bagasse and bamboo can also be used. Among these, when bleached kraft pulp, bleached sulfite pulp, powdered cellulose, and microcrystalline cellulose powder are used, it is easy to handle and has a relatively low viscosity (2% (w / v) B-type viscosity of 500% in aqueous dispersion). Cellulose nanofibers of about ˜2000 mPa · s) can be efficiently produced, and powdered cellulose and microcrystalline cellulose powder are more preferable.

Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline part of wood pulp by acid hydrolysis and then pulverizing and sieving. The degree of polymerization of cellulose in the powdered cellulose is preferably about 100 to 500, the degree of crystallinity of the powdered cellulose by X-ray diffraction is preferably 70 to 90%, and the volume average particle size by a laser diffraction type particle size distribution measuring device. Is preferably 100 μm or less, more preferably 50 μm or less. When the volume average particle size is 100 μm or less, a cellulose nanofiber dispersion having excellent fluidity can be obtained. As the powdered cellulose used in the present invention, for example, a fixed particle size in the form of a rod shaft produced by a method of purifying and drying an undegraded residue obtained after acid hydrolysis of a selected pulp, pulverizing and sieving. it may be a crystalline cellulose powder having a distribution, (manufactured by Nippon Paper Chemicals Co.) KC flock ^R, Ceolus ^TM (manufactured by Asahi Kasei Chemicals Corporation), a commercially available product may be used, such as Avicel ^R (FMC Corp.) .

（式１中、Ｒ¹〜Ｒ⁴は同一又は異なる炭素数１〜４程度のアルキル基を示す。）
式１で表される化合物のうち、２，２，６，６−テトラメチル−１−ピペリジン−Ｎ−オキシラジカル（以下、ＴＥＭＰＯと称する）、及び４−ヒドロキシ−２，２，６，６−テトラメチル−１−ピペリジン−Ｎ−オキシラジカル（以下、４−ヒドロキシＴＥＭＰＯと称する）を発生する化合物が好ましい。また、ＴＥＭＰＯ又は４−ヒドロキシＴＥＭＰＯから得られる誘導体も好ましく用いることができ、特に、４−ヒドロキシＴＥＭＰＯの誘導体が最も好ましく用いることができる。４−ヒドロキシＴＥＭＰＯ誘導体としては、４−ヒドロキシＴＥＭＰＯの水酸基を、炭素数４以下の直鎖或いは分岐状炭素鎖を有するアルコールでエーテル化して得られる誘導体か、あるいは、カルボン酸又はスルホン酸でエステル化して得られる誘導体が好ましい。４−ヒドロキシＴＥＭＰＯをエーテル化する際には、炭素数が４以下のアルコールを用いれば、アルコール中の飽和、不飽和結合の有無に関わらず、得られる誘導体が水溶性となり、酸化触媒として良好に機能する４−ヒドロキシＴＥＭＰＯ誘導体を得ることができる。 As the N-oxyl compound used for oxidizing the cellulosic raw material, any compound can be used as long as it promotes the target oxidation reaction. For example, the N-oxyl compound used in the present invention includes a substance represented by the following general formula (Formula 1).

(In Formula 1, R ^{1 to} R ⁴ represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Among the compounds represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO), and 4-hydroxy-2,2,6,6- A compound that generates a tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as 4-hydroxy TEMPO) is preferable. Moreover, the derivative | guide_body obtained from TEMPO or 4-hydroxy TEMPO can also be used preferably, and the derivative | guide_body of 4-hydroxy TEMPO can be used most preferably especially. The 4-hydroxy TEMPO derivative is a derivative obtained by etherifying the hydroxyl group of 4-hydroxy TEMPO with an alcohol having a linear or branched carbon chain having 4 or less carbon atoms, or esterified with carboxylic acid or sulfonic acid. The derivatives obtained are preferred. When 4-hydroxy TEMPO is etherified, if an alcohol having 4 or less carbon atoms is used, the resulting derivative becomes water-soluble regardless of the presence or absence of saturated or unsaturated bonds in the alcohol, making it an excellent oxidation catalyst. A functional 4-hydroxy TEMPO derivative can be obtained.

（式２〜４中、Ｒは炭素数４以下の直鎖又は分岐状炭素鎖である。）
さらに、下記式５で表されるＮ−オキシル化合物のラジカル、すなわち、アザアダマンタン型ニトロキシラジカルも、短時間で、均一なセルロースナノファイバーを製造できるため、特に好ましい。

（式５中、Ｒ⁵及びＲ⁶は、同一又は異なる水素又はＣ₁〜Ｃ₆の直鎖若しくは分岐鎖アルキル基を示す。） セルロース系原料を酸化する際に用いるＴＥＭＰＯや４−ヒドロキシルＴＥＭＰＯ誘導体などのＮ−オキシル化合物の量は、セルロース系原料をナノファイバー化できる触媒量であれば特に制限されない。例えば、絶乾１ｇのセルロース系原料に対して、０．０１〜１０ｍｍｏｌ、好ましくは０．０１〜１ｍｍｏｌ、さらに好ましくは０．０５〜５ｍｍｏｌ程度である。 Examples of the 4-hydroxy TEMPO derivative include compounds of the following formulas 2 to 4.

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, a radical of an N-oxyl compound represented by the following formula 5, that is, an azaadamantane type nitroxy radical, is particularly preferred because it can produce uniform cellulose nanofibers in a short time.

(In the formula 5, R ⁵ and R ⁶ are the same or. Shows different hydrogen or straight-chain or branched-chain alkyl group of C ₁ -C ₆₎ TEMPO or 4-hydroxy TEMPO derivative used in oxidizing the cellulosic material The amount of the N-oxyl compound, such as, is not particularly limited as long as it is a catalyst amount capable of converting the cellulose-based material into nanofibers. For example, it is about 0.01 to 10 mmol, preferably about 0.01 to 1 mmol, and more preferably about 0.05 to 5 mmol with respect to 1 g of an absolutely dry cellulosic material.

  As the bromide or iodide used in oxidizing the cellulosic raw material, a compound that can be dissociated and ionized in water, such as an alkali metal bromide or an alkali metal iodide, can be used. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. For example, it is about 0.1 to 100 mmol, preferably about 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol, with respect to 1 g of cellulosic raw material.

  As the oxidizing agent used for oxidizing the cellulosic raw material, the target oxidation reaction such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide can be promoted. Any oxidizing agent can be used as long as it is an oxidizing agent. Among these, from the viewpoint of production cost, sodium hypochlorite, which is the most widely used in industrial processes and has a low environmental load, is particularly suitable. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. For example, it is about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of cellulosic raw material.

  As described above, the oxidation of the cellulose-based raw material in the present invention is the presence of a compound selected from the group consisting of (1) N-oxyl compounds such as 4-hydroxy TEMPO derivatives and (2) bromides, iodides and mixtures thereof. Below, it is characterized by oxidizing a cellulosic raw material in water using an oxidizing agent such as sodium hypochlorite. This method has a feature that the oxidation reaction of the cellulosic raw material can proceed smoothly and efficiently even under mild conditions. Therefore, the reaction temperature may be about 15 to 30 ° C. In addition, since a carboxyl group produces | generates in a cellulose with progress of reaction, the fall of pH of a reaction liquid is recognized. In order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11, by adding an alkaline solution such as an aqueous sodium hydroxide solution.

  As described above, in the presence of (1) N-oxyl compound and (2) bromide, iodide, or a mixture thereof, an oxidized cellulose material obtained using an oxidizing agent is treated with wet fine particles. Cellulose nanofibers can be produced by fibrillation and defibration. As the wet atomization treatment, for example, a mixing / stirring and emulsifying / dispersing device such as a high-speed shear mixer or a high-pressure homogenizer can be used alone or in combination of two or more. In particular, when wet atomization is performed using an ultrahigh pressure homogenizer that enables a pressure of 100 MPa or more, preferably 120 MPa or more, more preferably 140 MPa or more, a relatively low viscosity (2% (w / v) aqueous dispersion Cellulose nanofibers having a B-type viscosity of about 500 to 2000 mPa · s) can be efficiently produced, which is preferable.

The cellulose nanofiber of the present invention is 0.5 mmol / g or more, preferably 0.9 mmol / g or more, more preferably 1.2 mmol / g or more, as the amount of carboxyl groups in 1 g of completely dried cellulose nanofiber. This is desirable because it results in a uniform dispersion. The amount of carboxyl groups in cellulose nanofibers was prepared by adding 60 ml of a 0.5% by weight slurry of cellulose nanofibers, adding 0.1M hydrochloric acid aqueous solution to pH 2.5, and then dropping 0.05N sodium hydroxide aqueous solution dropwise. Then, the electrical conductivity is measured until the pH reaches 11, and can be calculated from the amount of sodium hydroxide (a) consumed in the weak acid neutralization stage where the change in electrical conductivity is gradual, using the following equation. .
Amount of carboxyl group [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp mass [g]

In the present invention, the B-type viscosity (60 rpm, 20 ° C.) in a concentration of 2% (w / v) of cellulose nanofiber (that is, 2 g of cellulose nanofiber (dry mass) is contained in 100 ml of dispersion) is 500. An aqueous dispersion of cellulose nanofibers having a viscosity of ˜7000 mPa · s, preferably 500 to 2,000 mPa · s is desirable because it can be suitably used as a coating material. A relatively low B-type viscosity in a 2% (w / v) aqueous dispersion of cellulose nanofibers is preferred because it is easy to handle when preparing a coating, and specifically, 500 to 2000 mPa · s. The degree is preferable, about 500 to 1500 mPa · s is more preferable, and about 500 to 1000 mPa · s is more preferable.
The B-type viscosity of the aqueous dispersion of cellulose nanofibers of the present invention can be measured by a known method. For example, it can be measured using a VICOMETER TV-10 viscometer manufactured by Toki Sangyo.

  In the present invention, (1) a step of preparing cellulose oxidized with an oxidizing agent in the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides and mixtures thereof, (2) The width and length of cellulose nanofibers obtained by a method comprising the step of wet atomization of oxidized cellulose to form nanofibers can be controlled by the oxidation treatment time, wet atomization treatment time or treatment pressure. it can. Further, the viscosity of the cellulose nanofiber dispersion can be controlled by the oxidation treatment time, the wet atomization treatment time or the treatment pressure, and the carboxy amount can be adjusted by changing the oxidation treatment conditions.

  In the present invention, by containing cellulose nanofibers in the heat-sensitive recording layer, excellent color developability (particularly the contrast between the printed portion and the white paper portion) is obtained, and the printed portion is not white (does not cause white blur). The reason is presumed as follows.

  In addition to high transparency, cellulose nanofibers have a refractive index of 1.49 at room temperature and are generally used as binders for protective layers such as polyvinyl alcohol (refractive index 1.49) and acrylic resins (refractive index). Since it is close to 1.49), light scattering hardly occurs in the thermosensitive recording layer. As a result, it is estimated that a heat-sensitive recording material having high contrast and no white blur is obtained. In addition, the inclusion of cellulose nanofibers forms appropriate gaps in the heat-sensitive recording layer. Coloring materials such as dyes and developers melted by the heat applied from the thermal head enter these gaps and adhere to the thermal head. In order to prevent this, it is presumed that the running performance of the printer is improved.

  In the present invention, by using cellulose nanofibers produced by subjecting the heat-sensitive recording layer to an oxidation treatment with a catalyst, the strength of the heat-sensitive recording layer is improved and appropriate voids are formed in the heat-sensitive recording layer. This is because cellulose nanofibers produced by oxidation treatment with a catalyst are in a state where carboxyl groups or aldehyde groups are introduced at a high density on the surface, and these carboxyl groups or aldehyde groups are contained in the thermosensitive recording layer. It is thought that this is because the pigment and binder to be bonded chemically.

In the present invention, in order to obtain high contrast, it is preferable to use cellulose nanofibers having a width of 0.5 to 20 nm and a length of 0.1 to 15 μm, and a width of 2 to 5 nm and a length of 1 More preferably, ˜5 μm cellulose nanofibers are used.
When the length of the cellulose nanofiber is 1 μm or less, gaps (voids) capable of absorbing the melt in the heat-sensitive recording layer are reduced, and head debris is likely to occur. On the other hand, when the thickness exceeds 15 μm, there is a risk that color development sensitivity and image quality may be deteriorated when printing is performed by a thermal printer. In order to obtain good coating layer strength, the carboxy content of the cellulose nanofiber is preferably 0.3 to 5 mmol / g, and more preferably 0.8 to 2 mmol / g.

  In the present invention, cellulose nanofibers and a water-soluble polymer such as starch, polyvinyl alcohol, methylcellulose, and carboxymethylcellulose, and a binder such as a synthetic resin emulsion such as a styrene / butadiene copolymer and an acrylic acid copolymer are formed on the heat-sensitive recording layer. It is preferable to contain, and it is particularly preferable to contain a binder having a refractive index of 1.48 to 1.50 such as polyvinyl alcohol or acrylic resin having a refractive index close to that of cellulose.

  In the heat-sensitive recording layer of the present invention, the content of the pigment (including cellulose nanofibers) and the binder is about 20 to 300 parts by weight in terms of solid content with respect to 100 parts by weight of the pigment (including cellulose nanofibers). Is desirable. The cellulose nanofiber content is desirably 50 parts by weight or more with respect to 100 parts by weight of the total pigment (including cellulose nanofibers).

Regarding the coating amount of each layer, the protective layer is usually about 1 to 5 g / m ² , the thermosensitive recording layer is usually about ² to 12 g / m ² , and the undercoat layer is usually about 1 to 20 g / m ² .

  Next, various materials used in the present invention are exemplified, but it is necessary to include not only the thermosensitive coloring layer but also a protective layer, a thermosensitive recording layer, an undercoat layer and the like as long as the desired effects on the above problems are not impaired. It can also be used for each coating layer provided according to the above.

As the dye used in the heat-sensitive recording material of the present invention, any of those known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and is not particularly limited, but includes a triphenylmethane compound, a fluoran compound. Compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored basic colorless dyes are shown below. These basic colorless dyes may be used alone or in combination of two or more.
<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino -6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino- 7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-n-dipentylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl- N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7- Nirinofuruoran, 3-cyclohexylamino-6-chloro-fluoran

<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 4-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam, 3,6 -Bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylamino) Phenyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane, bis- [2, 2,2′2′-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  As the developer used in the present invention, any known developer in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and is not particularly limited. For example, activated clay, attapulgite, colloidal silica Inorganic inorganic substances such as aluminum silicate, 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4 , 4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone, 4-Hydroxy-4′-n-propoxydiphenyls Hong, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4'-methyl Phenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, bis (p -Hydroxyphenyl) butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′- Hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydroxy) Phenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert-octylphenol), International Publication WO97 No. 16420, a phenolic compound such as a diphenylsulfone cross-linking compound, an international publication WO 02/0812229 or JP 2002-301873, a phenolic compound, an international publication WO 02/098774 or WO 03/029017 Phenol novolac type condensation compositions, urea urethane compounds described in International Publication WO 00/14058 or JP 2000-143611, thiourea compounds such as N, N′-di-m-chlorophenylthiourea, p-chlorobenzoic acid, Stearyl gallate Bis [4- (n-octyloxycarbonylamino) salicylate zinc] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] Salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid aromatic carboxylic acid, and zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc. of these aromatic carboxylic acids Examples thereof include a salt with a polyvalent metal salt, an antipyrine complex of zinc thiocyanate, and a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid. These developers can be used alone or in combination of two or more. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  In addition, a conventionally known sensitizer can be used as long as it does not inhibit the desired effect. Examples of such a sensitizer include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montanic acid wax, and polyethylene. Wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, Shu Dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1 , 4-Diethoxynaphthalene, 1-hydroxy-2-naphthoic acid Nyl ester, o-xylene-bis- (phenyl ether), 4- (m-methylphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2- Examples include, but are not limited to, di (3-methylphenoxy) ethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate and phenyl p-toluenesulfonate. It is not something. These sensitizers may be used alone or in combination of two or more.

  The type and amount of the dye, developer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. About 0.5 to 10 parts of developer and 0.5 to 10 parts of pigment are used for 1 part, and the binder is suitably about 5 to 25% in the solid content of the heat-sensitive recording layer.

  The binder used in the present invention includes fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and olefin-modified. Polyvinyl alcohol, nitrile modified polyvinyl alcohol, pyrrolidone modified polyvinyl alcohol, silicone modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer and Cell like ethyl cellulose, acetyl cellulose Derivatives, casein, arabic gum, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyral, polystyrose and copolymers thereof Polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumaro resin and the like can be exemplified. These polymer substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., and are used in the state of being emulsified or pasted in water or other media to achieve the required quality. It can also be used in combination.

  Examples of the pigment used in the present invention include kaolin, (calcined) kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, and silica. It is not limited to these.

  Examples of the crosslinking agent used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, chloride chloride Examples include ferric iron, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.

Examples of the lubricant used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.
Further, in the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol) is used as an image stabilizer exhibiting an oil resistance effect of a recorded image and the like within a range that does not hinder a desired effect on the above problems. ), 2,2′-di-t-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) Butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4-benzyloxy-4 ′-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, etc. Can also be added.
In addition, benzophenone and triazole ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.
In addition, a dispersant, an antifoaming agent, an antioxidant, a fluorescent dye, and the like can be used.

  Binders, crosslinking agents, pigments, and the like can be used for each coating layer provided as necessary, including a protective layer, a heat-sensitive recording layer, an undercoat layer, and the like as long as the effects of the present invention are not impaired. .

  The type and amount of the dye, developer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. 1 part of developer 0.5 to 10 parts of pigment, 0.5 to 20 parts of pigment, about 0.1 to 10 parts of sensitizer, about 0.01 to 10 parts by weight of stabilizer, other components 0 0.01 to 10 parts by weight are used.

  Dye, developer, and materials to be added as necessary are finely pulverized to a particle size of several microns or less by a pulverizer such as a ball mill, attritor or sand glider or an appropriate emulsifying device. Various additive materials are added to form a coating solution. As a solvent used in the coating liquid, water or alcohol can be used, and the solid content is about 20 to 40% by weight.

  By applying the coating liquid having the above composition to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired thermal recording material can be obtained. Moreover, you may use the composite sheet which combined these as a support body. Dye, developer, and materials to be added as needed are finely pulverized to a particle size of several microns or less with a pulverizer such as a ball mill, attritor or sand glider or an appropriate emulsifier, and depending on the binder and purpose. Various additive materials are added to form a coating solution. Water or alcohol can be used as the solvent used in the paint, and its solid content is about 20 to 40%. Further, the means for applying is not particularly limited, and can be applied according to well-known conventional techniques. For example, various coaters such as an air knife coater, rod blade coater, vent blade coater, bevel blade coater, roll coater, curtain coater, etc. The provided off-machine coating machine or on-machine coating machine is appropriately selected and used. The heat-sensitive recording material of the present invention can further be provided with an under layer comprising a filler and a binder between the support and the heat-sensitive recording material for the purpose of increasing the color development sensitivity. It is also possible to correct the curl by providing a backcoat layer on the opposite side of the support from the thermosensitive recording layer. Further, various known techniques in the heat-sensitive recording material field, such as supercalendering after the application of each layer, can be added as appropriate.

  The following examples illustrate the invention but are not intended to limit the invention.

  The heat-sensitive recording material of the present invention will be described below with reference to examples. In the description, parts and% indicate parts by weight and% by weight, respectively. Each layer coating solution was prepared by stirring and dispersing various solutions, dispersions, or coating solutions of the following composition.

[Preparation of cellulose nanofiber]
15 g of powdered cellulose (manufactured by Nippon Paper Chemical Co., Ltd., particle size: 24 μm) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma Aldrich) and 755 mg (7 mmol) of sodium bromide were dissolved, Stir until the powdered cellulose is uniformly dispersed. After adding 50 ml of sodium hypochlorite aqueous solution (effective chlorine 5%) to the reaction system, the pH was adjusted to 10.3 with 0.5N hydrochloric acid aqueous solution, and the oxidation reaction was started. During the decreasing reaction, the pH in the system was adjusted to pH 10 by successively adding a 0.5N aqueous sodium hydroxide solution. After reacting for 2 hours, oxidized powdered cellulose was separated by centrifugal operation (6000 rpm, 30 minutes, 20 ° C.) and sufficiently washed with water to obtain oxidized powdered cellulose. A 2% (w / v) slurry of oxidized powdered cellulose was treated with a mixer at 12,000 rpm for 15 minutes, and the powdered cellulose slurry was further treated with an ultra-high pressure homogenizer (pressure 140 MPa), and the following transparent A cellulose nanofiber dispersion was obtained.
In addition, the width | variety and length of a cellulose nanofiber are randomly extracted from the photograph of the cellulose nanofiber image | photographed with the electron microscope (100 pieces), and are the measured average values.
-Cellulose nanofiber 1: Width 2.1 nm, Length 1.5 μm Solid content 2%
Cellulose nanofiber 2: width 4.9 nm, length 4.8 μm, solid content 2%

[Under layer coating solution]
Calcined kaolin (manufactured by Engelhard, trade name: Ansilex 93, average particle size 3 μm) 30% dispersion 100 parts Styrene-butadiene copolymer latex (solid content 48%) 40 parts Completely saponified polyvinyl alcohol (PVA117) 10% Aqueous solution 30 parts Water 160 parts

The developer dispersion liquid (A liquid), leuco dye dispersion liquid (B liquid), and sensitizer dispersion liquid (C liquid) having the following composition are separately separated with a sand grinder until the average particle diameter becomes 0.5 μm. Wet grinding was performed.
Liquid A (developer dispersion)
4-Hydroxy-4′-isopropoxydiphenyl sulfone (Nippon Soda Co., Ltd., D8)
6.0 parts polyvinyl alcohol 10% aqueous solution 18.8 parts water 11.2 parts Liquid B (dye dispersion)
3-Dibutylamino-6-methyl-7-anilinofluorane (Yamada Chemical Co., Ltd., ODB-2) 2.0 parts Polyvinyl alcohol 10% aqueous solution 4.6 parts Water 2.6 parts C solution (sensitizer dispersion) liquid)
Dibenzyl oxalate 6.0 parts Polyvinyl alcohol 10% aqueous solution 18.8 parts Water 11.2 parts

Subsequently, the dispersion liquid was mixed at the following ratio to prepare a coating liquid for the heat-sensitive recording layer.
[Thermosensitive recording layer coating solution 1]
Liquid A (developer dispersion) 36.0 parts Liquid B (dye dispersion) 13.8 parts Liquid C (sensitizer dispersion) 36.0 parts Carboxyl group-modified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA-KL318) ) 10% aqueous solution 25 parts Cellulose nanofiber 1 2% dispersion 150 parts [thermal recording layer coating liquid 2]
Liquid A (developer dispersion) 36.0 parts Liquid B (dye dispersion) 13.8 parts Liquid C (sensitizer dispersion) 36.0 parts Carboxyl group-modified polyvinyl alcohol (PVA-KL318) 10% aqueous solution 25 parts Silica (Mizusawa Chemical Co., Ltd., trade name: Mizukasil P603) 30% dispersion 10 parts

[Example 1]
The under layer coating solution was applied to one side of a support (60 g / m ² base paper) and then dried to obtain an under coated paper having a coating amount of 10.0 g / m ² . Next, the thermal recording layer coating solution 1 was applied on the under layer so as to have a coating amount of 4.0 g / m ² and dried. This sheet was processed with a super calendar so that the Beck smoothness was 400 seconds to prepare a heat-sensitive recording material.
[Example 2]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the cellulose nanofiber 2 was used.
[Example 3]
A thermosensitive recording material was prepared in the same manner as in Example 1 except that the 10% aqueous solution of carboxy-modified polyvinyl alcohol of Example 1 was changed to a 10% solution of acrylic emulsion (trade name: Barrier Star B1000, manufactured by Mitsui Chemicals, Inc.).
[Example 4]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the cellulose nanofiber content in the protective layer coating solution of Example 1 was changed to 100 parts.

[Comparative Example 1]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the heat-sensitive recording layer coating solution 2 was used.
[Comparative Example 2]
A thermosensitive recording material was produced in the same manner as in Example 1 except that the cellulose nanofibers of Example 1 were changed to aluminum hydroxide (manufactured by Martinsberg, trade name: Martin Fin OL).
[Comparative Example 3]
A thermosensitive recording material was produced in the same manner as in Example 1 except that the cellulose nanofibers of Example 1 were changed to kaolin (trade name: Capim CC, manufactured by Capim).

The following evaluation was performed about the heat-sensitive recording material obtained above.
<Evaluation of color development sensitivity>
About the produced thermal recording body, it printed with the applied energy of 0.42 mJ / dot using the thermal recording paper printing test machine (The Okura Electric TH-PMD, the Kyocera thermal head was mounted | worn). The recording density of the recording part was measured and evaluated with a Macbeth densitometer (RD-914).
The larger the value, the higher the color sensitivity and the better the contrast.
<Image quality evaluation>
The solid print portion was visually evaluated.
○: Printed in clear black ×: The whole is blurred
<Head residue evaluation>
The produced thermal recording medium was subjected to checkered printing (for 100 labels, printing length of about 4 m) with a thermal label printer (IPEMZ manufactured by ISIDA), and the thermal head portion and printed matter after printing were visually evaluated.
○: There is almost no accumulation of head residue on the thermal head.
Δ: Head debris accumulates on the thermal head, but no printing failure occurs.
X: Head debris accumulates on the thermal head and printing failure occurs.
<Printability>
Under a 0 ° C. environment, 100 mm solid printing was performed with a thermal handy terminal printer <Canon HT1800>, and the printed matter was visually evaluated.
○: No white spots in the printed part ×: Several white spots in the printed part

The results are shown in Table 1.

Claims (1)

A heat-sensitive recording material provided with a heat-sensitive recording layer containing at least a colorless or light-colored electron-donating leuco dye and an electron-accepting color developer on a support, and the cellulose nanofibers are contained in the heat-sensitive recording layer A heat-sensitive recording material characterized by