JP2002264516A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium which is free of a flaw of the surface even when recording is made by a thick film thermal head and free from peeling. of a film face, of an image part in particular, when it is used as a large-sized block copy film and which curls little and suits a block copy film. SOLUTION: In the thermal recording medium constituted by forming on a substrate a thermal recording layer containing at least a leuco dye, a developer and a binding agent resin, the binding agent resin contains a polyvinyl acetal and a urethane modified copolymer polyester having a polymerization degree of 850 or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium, and more particularly, to an underlay film for plate making, particularly flexographic printing, utilizing a color development reaction between an electron-donating coloring compound and an electron-accepting compound. The present invention relates to a heat-sensitive recording medium useful as an underprint film.

[0002]

2. Description of the Related Art Thermosensitive recording media are generally paper, synthetic paper,
On a support such as a plastic film, a thermosensitive recording layer mainly composed of a thermochromic composition is provided.
A colored image can be obtained by heating with a hot pen, laser light, or the like. Compared with other recording materials, this type of recording material can record in a shorter time with a relatively simple apparatus without performing complicated processing such as development and fixing, and can generate noise and reduce environmental problems. It is used for copying books and documents due to its advantages such as low pollution and low cost, and is widely used as a versatile recording medium such as electronic calculators, facsimile machines, ticket vending machines, labels and recorders.

A thermochromic composition used in such a recording medium is generally an electron-donating color compound (color former).
And an electron-accepting compound (developing agent) that causes the coloring agent to develop color when heated. Examples of the coloring agent include colorless or pale-colored leuco dyes having a lactone, lactam or spiropyran ring. As the agent, various acidic substances, for example, organic acids and phenolic substances are used.

[0004] In recent years, as the heat-sensitive recording medium has replaced other conventional recording methods, and as demand has increased, there has been an increasing demand for improved quality of the heat-sensitive recording medium used in this heat-sensitive recording method. As one example, there is a demand for a thermal recording medium used as an underlay film for plate making of printing.

[0005] As a heat-sensitive recording medium useful as an underprint, there is one disclosed in JP-A-5-14859. This is a solvent that dissolves the color former and the binder resin, and finely disperses the organic acid, which is a developer that is hardly soluble or insoluble in this solvent, and mixes and disperses the dispersion with the dissolved binder resin and the color former. After applying the coating solution obtained on a transparent support, the surface of the heat-sensitive recording layer having fine irregularities generated is filled with a protective layer mainly composed of resin,
It is stated that a transparent thermosensitive recording medium having high transparency is formed.

[0006] JP-A-09-175021 and JP-A-09-175028 disclose, as a thermosensitive recording medium suitable for an underlay film, an ultraviolet curable resin, There is disclosed a thermosensitive recording medium provided with a resin obtained by copolymerizing a silicon component in a graft or block shape, a cross-linking agent reactive with the resin, and an overlayer containing an inorganic or organic filler.

[0007] Such a thermosensitive recording medium is generally recorded by a thermal head. However, when recording is performed by a thick film type thermal head, fine irregularities on the surface of the thermal head and the surface of the thermal head during heating are reduced. Due to thermal deformation, scratch marks may appear on the recorded image, which may be undesirable in appearance. When recording with a thin-film thermal head, the scars described above are unlikely to appear, but the recording surface is smoothed by heat and pressure and has high smoothness. When used as a substrate, the adhesiveness between the underlaying film and the photosensitive resin was too good during plate-making, and air bleeding between them was insufficient, which hindered plate-making.

Japanese Unexamined Patent Application Publication No. 11-277905 discloses an underlay film for flexographic printing in which a protective layer (mat layer) mainly composed of an ultraviolet curable resin or an electron beam curable resin and a filler is formed on a heat-sensitive recording layer. Is disclosed. The over layer (mat layer) carries a filler having an average particle size of 3 μm or more on a strong coating film made of an ultraviolet curable resin, so that the surface after recording by the thermal head is smoothed by the heat and pressure of the thermal head. Instead, it is possible to maintain a rough state.

However, in this thermosensitive recording medium, the binding strength of the recording layer may not be sufficient. For example, when used as a large underlay film such as A0 or more, the film may break due to handling. From where I did
A problem such as peeling of the film surface sometimes occurred. The peeling of the film surface is caused by the image recording portion (coloring portion)
May be particularly noticeable.

As means for improving the binding property of the recording layer and the adhesiveness between the recording layer and the support, Japanese Patent Application Laid-Open No. 10-297102 discloses a recording layer containing polyester urethane as a binder resin. Is disclosed. However, since the polyester resin generally has a low softening point, the thermal deformation of the recording layer during thermal recording is large, and it may be difficult to maintain the surface roughness after recording for use as an underlay film for flexographic printing. JP-A-11-058968 discloses a heat-sensitive recording medium containing polyvinyl acetal having a degree of polymerization of 850 or more as a binder resin for the recording layer. In this case, the heat-sensitive recording medium has curl. There was a problem of being big.

[0011]

SUMMARY OF THE INVENTION The present invention solves such a conventional problem and has no surface damage even when recorded by a thick-film thermal head. It is an object of the present invention to provide a thermosensitive recording medium suitable for an underlay film having a small curl and having no surface peeling, particularly, no image part peeling.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies focusing on a binder resin, and as a result, have completed the present invention.

That is, according to the present invention, on a support,
In a heat-sensitive recording medium having a heat-sensitive recording layer containing at least a leuco dye and a binder resin, the binder resin contains polyvinyl acetal having a polymerization degree of 850 or more and a urethane-modified copolymerized polyester. And a thermal recording medium characterized by the following.

The present invention provides the following (i) to (i)
Described above. (I) A thermosensitive recording medium in which the urethane-modified copolymer is at least 30% by weight based on the total amount of the polyvinyl acetal and the urethane-modified copolymer. (Ii) the glass transition point of the polyvinyl acetal is 1
A thermosensitive recording medium having a temperature of 00 ° C. or higher. (Iii) A thermosensitive recording medium in which the polyvinyl acetal is polyvinyl acetoacetal. (Iv) A thermosensitive recording medium in which a protective layer is formed on the thermosensitive recording layer, and 50% by weight or more of the total solid content of the protective layer is an ultraviolet curable resin. (V) A thermosensitive recording medium in which 5 to 10% by weight of the total solid content of the protective layer is a filler having an average particle size of 3 to 10 μm. (Vi) A thermosensitive recording medium wherein the photopolymerization initiator of the ultraviolet curable resin is an α-aminoketone photopolymerization initiator. (Vii) A thermosensitive recording medium wherein the developer used in the thermosensitive recording layer is a compound represented by the following general formula (1) or (2).

[0015]

Embedded image [In the formula (1), R represents a linear alkyl group having 16 to 24 carbon atoms. ]

[0016]

Embedded image [In the formula (2), R ′ represents a straight-chain alkyl group having 13 to 23 carbon atoms. (Viii) A thermosensitive recording medium in which the thickness of the support is 100 μm or less.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive recording layer of the heat-sensitive recording medium of the present invention is prepared by applying a coating solution containing at least a leuco dye, a color developer and a binder resin soluble in an organic solvent onto a support, followed by drying. It is formed by doing.

The leuco dye used in the present invention is a compound having an electron donating property and used alone or as a mixture of two or more. However, it is a colorless or pale color dye precursor itself, and is not particularly limited. Without known, conventionally known, for example, triphenylmethanephthalide type, triallylmethane type, fluoran type, phenothiian type, thioferoran type, xanthene type, indophthalyl type, spiropyran type, azaphthalide type, chromenopyrazole System, methine system, rhodamine anilinolactam system, rhodamine lactam system, quinazoline system, diazoxanthene system, bislactone system and the like are preferably used.

As a specific example, 2-anilino-3-
Methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6- (di-n-butylamino) fluoran, 2-anilino-3-methyl-6- (Nn-propyl-N-methylamino) Fluoran, 2-anilino-3
-Methyl-6- (N-isopropyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (N
-Isobutyl-N-methylamino) fluoran, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluoran, 2-anilino-3-methyl-6
-(N-sec-butyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluoran, 2-anilino-3-
Methyl-6- (N-iso-amyl-N-ethylamino) fluoran, 2-anilino-3-methyl-6- (N
-N-propyl-N-isopropylamino) fluoran, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluoran, 2-anilino-
3-methyl-6- (N-ethyl-p-toluidino) fluoran, 2-anilino-3-methyl-6- (N-methyl-p-toluidino) fluoran, 2- (m-trichloromethylanilino) -3 -Methyl-6-diethylaminofluoran, 2- (m-trifluoromethylanilino) -3
-Methyl-6-diethylaminofluoran, 2- (m-
Trifluoromethylanilino) -3-methyl-6- (N-
Cyclohexyl-N-methylamino) fluoran, 2-
(2,4-dimethylanilino) -3-methyl-6-diethylaminofluoran, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-ethylanilino) fluoran, 2- (N- Methyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluoran, 2-anilino-6- (Nn-hexyl-N-ethylamino) fluoran, 2- (o-chloroanilino )-
6-diethylaminofluoran, 2- (o-bromoanilino) -6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran, 2-
(O-fluoroanilino) -6-dibutylaminofluoran, 2- (o-chlorophenylamino) -6-ethylamino-7-methylfluoran 2- (m-trifluoromethylanilino) -6-diethylaminofluoran, 2-
(P-acetylanilino) -6- (Nn-amyl-N
-N-butylamino) fluoran, 2-benzylamino-6- (N-ethyl-p-toluidino) fluoran, 2
-Benzylamino-6- (N-methyl-2,4-dimethylanilino) fluoran, 2-benzylamino-6-
(N-ethyl-2,4-dimethylanilino) fluoran, 2-dibenzylamino-6- (N-methyl-p-toluidino) fluoran, 2-dibenzylamino-6
(N-ethyl-p-toluidino) fluoran, 2- (di-p-methylbenzylamino) -6- (N-ethyl-p
-Toluidino) fluoran, 2- (α-phenylethylamino) -6- (N-ethyl-p-toluidino) fluoran, 2-methylamino-6- (N-methylanilino)
Fluoran, 2-methylamino-6- (N-ethylanilino) fluoran, 2-methylamino-6- (N-propylanilino) fluoran, 2-ethylamino-6
(N-methyl-p-toluidino) fluoran, 2-methylamino-6- (N-methyl-2,4-dimethylanilino) fluoran, 2-ethylamino-6- (N-methyl-2,4-dimethyl Anilino) fluoran, 2-dimethylamino-6- (N-methylanilino) fluoran, 2
-Dimethylamino-6- (N-ethylanilino) fluoran, 2-diethylamino-6- (N-methyl-p-toluidino) fluoran, 2-diethylamino-6- (N
-Ethyl-p-toluidino) fluoran, 2-dipropylamino-6- (N-methylanilino) fluoran, 2
-Dipropylamino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-methylanilino) fluoran, 2-amino-6- (N-ethylanilino) fluoran, 2-amino-6- (N-propyl Anilino) fluoran, 2-amino-6- (N-methyl-p-toluidino) fluoran, 2-amino-6- (N-ethyl-p
-Toluidino) fluoran, 2-amino-6- (N-propyl-p-toluidino) fluoran, 2-amino-6
-(N-methyl-p-ethylanilino) fluoran, 2
-Amino-6- (N-ethyl-p-ethylanilino) fluoran, 2-amino-6- (N-propyl-p-ethylanilino) fluoran, 2-amino-6- (N-methyl-2,4-dimethylaniline) Rino) fluorane, 2-amino-6- (N-ethyl-2,4-dimethylanilino) fluoran, 2-amino-6- (N-propyl-2,4-
Dimethylanilino) fluoran, 2-amino-6- (N
-Methyl-p-chloroanilino) fluoran, 2-amino-6- (N-ethyl-p-chloroanilino) fluoran, 2-amino-6- (N-propyl-p-chloroanilino) fluoran, 2,3-dimethyl-6 -Dimethylaminofluoran, 3-methyl-6- (N-ethyl-p-
Toluidino) fluoran, 2-chloro-6-diethylaminofluoran, 2-bromo-6-diethylaminofluoran, 2-chloro-6-dipropylaminofluoran, 3-chloro-6-cyclohexylaminofluoran, 3-bromo -6-cyclohexylaminofluoran, 2-chloro-6- (N-ethyl-N-isoamylamino) fluoran, 2-chloro-3-methyl-6-diethylaminofluoran, 2-anilino-3-chloro-6
-Diethylaminofluoran, 2- (o-chloroanilino) -3-chloro-6-cyclohexylaminofluoran, 2- (m-trifluoromethylanilino) -3-chloro-6-diethylaminofluoran, 2- (2 , 3-Dichloroanilino) -3-chloro-6-diethylaminofluoran, 1,2-benzo-6-diethylaminofluoran, 1,2-benzo-6- (N-ethyl-N-isoamylamino) fluoran, 1, 2-benzo-6-dibutylaminofluoran, 1,2-benzo-6- (N-ethyl-N-cyclohexylamino) fluoran, 1,2-
Benzo-6- (N-ethyl-toluidino) fluoran,
2-anilino-3-methyl-6- (N-2-ethoxypropyl-N-ethylamino) fluoran, 2- (p-chloroanilino) -6- (Nn-octylamino) fluoran, 2- (p- Chloranilino) -6- (Nn-
(Partimylamino) fluoran, 2- (p-chloroanilino) -6- (di-n-octylamino) fluoran,
2-benzoylamino-6- (N-ethyl-p-toluidino) fluoran, 2- (o-methoxybenzoylamino) -6- (N-ethyl-p-toluidino) fluoran, 2-dibenzylamino-4-methyl -6-diethylaminofluoran, 2-dibenzylamino-4-methoxy-6- (N-methyl-p-toluidino) fluoran,
2-dibenzylamino-4-methyl-6- (N-ethyl-p-toluidino) fluoran, 2- (α-phenylethylamino) -4-methyl-6-diethylaminofluoran, 2- (p-toluidino) -3- (t-butyl)-
6- (N-methyl-p-toluidino) fluoran, 2-
(O-methoxycarbonylanilino) -6-diethylaminofluoran, 2-acetylamino-6- (N-methyl-p-toluidino) fluoran, 3-diethylamino-6- (m-trifluoromethylanilino) fluoran, 4-methoxy-6- (N-ethyl-p-toluidino) fluoran, 2-ethoxyethylamino-3-chloro-6-dibutylaminofluoran, 2-dibenzylamino-4-chloro-6- (N-ethyl -P-toluidino) fluoran, 2- (α-phenylethylamino)-
4-chloro-6-diethylaminofluoran, 2- (N
-Benzyl-p-trifluoromethylanilino) -4-chloro-6-diethylaminofluoran, 2-anilino-
3-methyl-6-pyrrolidinofluoran, 2-anilino-3-chloro-6-pyrrolidinofluoran, 2-anilino-3-methyl-6- (N-ethyl-N-tetrahydrofurfurylamino) fluoran, 2-mesidino-4 ',
5'-benzo-6-diethylaminofluoran, 2-
(M-trifluoromethylanilino) -3-methyl-6-
Pyrrolidinofluoran, 2- (α-naphthylamino)-
3,4-benzo-4'-bromo-6- (N-benzyl-
N-cyclohexylamino) fluoran, 2-piperidino-6-diethylaminofluoran, 2- (Nn-propyl-p-trifluoromethylanilino) -6-morpholinofluoran, 2- (di-Np -Chlorophenyl-methylamino) -6-pyrrolidinofluoran, 2-
(Nn-propyl-m-trifluoromethylanilino)
-6-morpholinofluoran, 1,2-benzo-6-
(N-ethyl-Nn-octylamino) fluoran,
1,2-benzo-6-diallylaminofluoran,
2-benzo-6- (N-ethoxyethyl-N-ethylamino) fluoran, benzoleucomethylene blue, 2-
[3,6-bis (diethylamino)]-6- (o-chloroanilino) xanthylbenzoate lactam, 2- [3
6-bis (diethylamino)]-9- (o-chloroanilino) xanthylbenzoate lactam, 3,3-bis (p
-Dimethylaminophenyl) phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, (also known as crystal violet lactone)
3,3-bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3- (2-
Methoxy-4-dimethylaminophenyl) -3- (2-
(Hydroxy-4,5-dichlorophenyl) phthalide, 3
-(2-hydroxy-4-dimethylaminophenyl)-
3- (2-methoxy-5-chlorophenyl) phthalide,
3- (2-hydroxy-4-dimethoxyaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide, 3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5 -Nitrophenyl) phthalide, 3- (2-hydroxy-4-diethylaminophenyl) -3- (2-methoxy-5-methylphenyl)
Phthalide, 3,6-bis (dimethylamino) fluorenespiro (9,3 ′)-6′-dimethylaminophthalide,
6'-chloro-8'-methoxy-benzoindolino-spiropyran, 6'-bromo-2'-methoxy-benzoindolino-spiropyran and the like can be mentioned.

Since the heat-sensitive recording medium of the present invention is intended mainly for use as an underlay film, the leuco dye has a high absorbance in the photosensitive region of the plate material, that is, in the ultraviolet region at the time of color development. Are preferably used.

The developer used in the present invention is an electron-accepting compound, and various conventionally known electron-accepting developers can be used. An electron-accepting developer containing a long-chain alkyl group in a molecule disclosed in JP-A-124360 or the like.

For example, an organic phosphoric acid compound having an aliphatic group having 12 or more carbon atoms, an aliphatic carboxylic acid compound, a phenol compound or a metal salt of a mercaptoacetic acid having an aliphatic group having 10 to 18 carbon atoms or a metal salt of 5 to 5 carbon atoms. And alkyl esters of caffeic acid having an alkyl group of 8, and acidic phosphate esters having an aliphatic group having 16 or more carbon atoms. The aliphatic group includes a linear or branched alkyl group and alkenyl group, and may have a substituent such as a halogen, an alkoxy group, and an ester.

In the present invention, the above general formula (1) or (2)
When an alkylphosphon oxide represented by is used as a developer, a thermosensitive recording medium with less background fog is obtained,
Particularly preferred.

[0024]

Embedded image [In the formula (1), R represents a linear alkyl group having 16 to 24 carbon atoms. ]

[0025]

Embedded image [In the formula (2), R ′ represents a straight-chain alkyl group having 13 to 23 carbon atoms. ]

Specific examples of the alkylphosphonic acid compound represented by the general formula (1) include, for example, dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid,
Docosylphosphonic acid, tetracosylphosphonic acid, hexacosylphosphonic acid, octacosylphosphonic acid and the like. Examples of the α-hydroxyalkylphosphonic acid represented by the general formula (2) include α-hydroxydodecylphosphonic acid, α-hydroxytetradecylphosphonic acid,
α-hydroxyhexadecylphosphonic acid, α-hydroxyoctadecylphosphonic acid, α-hydroxyeicosylphosphonic acid, α-hydroxydocosylphosphonic acid, α-
And hydroxytetracosylphosphonic acid.

The present invention is characterized in that the binder resin used for the heat-sensitive recording layer contains both polyvinyl acetal having a degree of polymerization of 850 or more and urethane-modified copolymerized polyester.

The polyvinyl acetal is represented by the general formula (3), and is known as a product such as denka butyral (manufactured by Denki Kagaku Kogyo Co., Ltd.), Eslek B and Eslek K (manufactured by Sekisui Chemical Co., Ltd.). It is. Among these, those having a degree of polymerization of 850 or more include denkabutyral # 4000-2 and denkabutyral # 5000-A.
(Manufactured by Denki Kagaku Kogyo), S-LEC BX-1, S-LEC BX-5Z, S-LEC KS-3Z (Sekisui Chemical)
And the like.

[0029]

Embedded image [In the formula (3), R represents CH ₃ , C ₃ H ₇ , l, m, and n represent mol%, and the condition of l + m + n = 100 is satisfied. ]

In the present invention, the urethane-modified copolyester used together with the polyvinyl acetal having a degree of polymerization of 850 or more is an elastomer having a urethane bond in a molecular chain, and is usually composed of a polybasic acid having two or more carboxyl groups and a polybasic acid having two or more carboxyl groups. A saturated polyester obtained by a condensation reaction with a polyhydric alcohol can be obtained by reacting an organic diisocyanate with a chain extender, and examples include Byron UR (manufactured by Toyobo).

Polymerization degree 850 used for binder resin
As for the ratio of the polyvinyl acetal and the urethane-modified copolymerized polyester, it is preferable that at least 30% by weight of the total of both is the urethane-modified copolymerized polyester. In this case, a thermosensitive recording medium with less curl can be obtained.

In the present invention, the peeling of the film surface is improved by using both a polyvinyl acetal having a degree of polymerization of 850 or more and a urethane-modified copolymerized polyester as a binder, but the glass transition point (T
When g) is 100 ° C. or higher, the peeling of the recording portion (coloring portion) is significantly improved. Further, among polyvinyl acetal compounds, polyvinyl acetoacetal is particularly preferable in view of compatibility with the urethane-modified copolymerized polyester. Examples of the polyvinyl acetoacetal include, for example, Eslek KS-3z (manufactured by Sekisui Chemical).

In the present invention, if necessary, various known organic solvent-soluble resins other than polyvinyl acetal and urethane-modified copolymerized polyester can be mixed and used. Examples of resins having a hydroxyl group or a carboxyl group include, for example, cellulose derivatives such as ethyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate, and epoxy resins.

In the heat-sensitive recording layer, a filler commonly used in conventional heat-sensitive recording paper or the like can be appropriately selected and added.
Specific examples thereof include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide zinc oxide, barium sulfate, kaolin, talc, surface-treated inorganic fillers such as calcium carbonate and silica, urea formalin resin, Organic fillers such as styrene / methacrylic acid copolymer, polystyrene, silicone resin and fluororesin can be used.

The heat-sensitive recording layer comprises a binder resin dissolved in an organic solvent, a developer which is hardly soluble or insoluble in the solvent, and a fine filler, if necessary, are finely dispersed, and the color former is dissolved in the dispersion. The obtained coating solution is applied on a film and dried. The coating method is not particularly limited, and may be a conventional coating method. The thickness of the heat-sensitive recording layer is
Although it depends on the composition of the recording layer and the use of the heat-sensitive recording medium, 1 to 5
It is about 0 μm, preferably about 1 to 20 μm. In addition, various additives used in ordinary thermosensitive recording paper can be added to the recording layer coating liquid, if necessary, for the purpose of improving coatability or recording characteristics.

Since the protective layer is directly exposed to heat and pressure in thermal head recording, it needs to have sufficient heat resistance and mechanical strength. Curable resins are preferred. Here, the ultraviolet curable resin and the electron beam curable resin refer to monomers and prepolymers that undergo a polymerization reaction by ultraviolet irradiation or electron beam irradiation, and specific examples of such photopolymerizable monomers and prepolymers. Examples include the following monomers and prepolymers.

Examples of the prepolymer include (a) aliphatic, alicyclic, and araliphatic polyhydric alcohols having 2 to 6 valences and poly (meth) acrylates of polyalkylene glycols;
(B) aliphatic, alicyclic, araliphatic, aromatic poly (meth) acrylates of polyhydric alcohols obtained by adding alkylene oxide to dihydric to hexavalent polyhydric alcohols; (c)
Poly (meth) acryloyloxyalkyl phosphate; (d) polyester poly (meth) acrylate;
(E) epoxy poly (meth) acrylate; (f) polyurethane poly (meth) acrylate; (g) polyamide polymeth) acrylate; (h) polysiloxane poly (meth) acrylate; (i) side chains and / or ends. (Meth) Low molecular weight vinyl or diene polymers having an acryloyloxy group; (j) modified oligoester (meth) acrylates described in the above (a) to (i).

Examples of the monomer include (a) a carboxyl group-containing monomer represented by an ethylenically unsaturated mono- or polycarboxylic acid and a carboxylic acid group-containing monomer such as an alkali metal salt, an ammonium salt and an amine salt thereof. Monomer;
(B) amide group-containing monomers represented by vinyl lactams such as ethylenically unsaturated (meth) acrylamide or alkyl-substituted (meth) acrylamide, N-vinylpyrrolidone; (c) aliphatic or aromatic vinyl sulfone Sulfonic acid group-containing monomers represented by acids, and sulfonic acid group-containing monomers such as alkali metal salts, ammonium salts, and amine salts thereof; and (d) hydroxyl group-containing monomers represented by ethylenically unsaturated ethers. (E) Amino group-containing monomer such as dimethylaminoethyl (meth) acrylate-2-vinylpyridine; (f) Quaternary ammonium base-containing monomer; (g) Alkyl of ethylenically unsaturated carboxylic acid Esters; (h) nitrile group-containing monomers such as (meth) acrylonitrile; (i) styrene; (j) vinyl acetate, (meth) allyl acetate What ethylenically unsaturated esters of saturated alcohols; (k) mono (meth) acrylates of alkylene oxide addition polymer of compounds containing active hydrogen;
(L) an ester group-containing bifunctional monomer represented by a diester of a polybasic acid and an unsaturated alcohol; (m) a diester of an alkylene oxide addition polymer of a compound containing active hydrogen and (meth) acrylic acid (N) bisacrylamide such as N, N-methylenebisacrylamide; (o) bifunctional monomer such as divinylbenzene, divinylethylene glycol, divinylsulfone, divinylether, divinylketone; p) an ester group-containing polyfunctional monomer represented by a polyester of a polycarboxylic acid and an unsaturated alcohol; (q) a polyester of an alkylene oxide addition polymer of a compound containing an active hydrogen and (meth) acrylic acid. And polyfunctional unsaturated monomers such as (r) trivinylbenzene. In addition, a monomer and a prepolymer can also use 2 or more types together.

In the case of an ultraviolet curable resin, a photopolymerization initiator is required together with these monomers or prepolymers. Specific examples include, for example, thioxanthone, benzoin, benzoin alkyl ether xanthone, dimethylxanthone, benzophenone, anthracene, 2,2
-Diethoxyacetophenone, benzyldimethylketal, benzyldiphenyldisulfide, anthraquinone, 1-chloroanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, N, N '
-Tetraethyl-4,4'-diaminobenzophenone,
One or more of 1,1-dichloroacetophenone and the like are appropriately blended. The amount of the polymerization initiator used is desirably 0.1 to 10% by weight, preferably 0.5 to 5% by weight, in the photopolymerizable monomer or prepolymer.

A particularly preferred photopolymerization initiator in the present invention is α
-Aminoketones, for example, 2-methyl-1-
[4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone (Irgacure 907) and the like. By including this photopolymerization initiator, the curability of the protective layer can be improved, so that a stronger protective layer can be formed. This has the effect of increasing the barrier properties of precipitation.

The protective layer of the heat-sensitive recording medium of the present invention is formed by adding the above-mentioned ultraviolet curable resin and, if necessary, other thermoplastic resin, thermosetting resin, inorganic or organic filler, lubricant and the like to an organic solvent. A coating material prepared by dissolving or dispersing is applied and formed on the heat-sensitive recording layer. The content of the ultraviolet curable resin or the electron beam curable resin is preferably higher from the viewpoint of heat resistance and mechanical strength, but the content of the ultraviolet curable resin or the electron beam When more than 50% of a minute
It is possible to suppress the formation of fine irregularities on the surface of the thermal head when recording is performed by the thick-film type thermal head and the occurrence of scar-like marks on the recorded image due to thermal deformation of the surface during heating.

When the thermosensitive recording medium of the present invention is used for flexographic plate making, the content of the ultraviolet curable resin or the electron beam curable resin is 50% or more and the average particle size is 3 to 10 μm.
Is preferably contained in an amount of 5 to 10% by weight of the total solid content of the protective layer. In this case, the surface of the protective layer after recording is not smoothed, and when used as an underprint, air bleeding property when it is brought into close contact with a plate material (photosensitive resin) is ensured.

There is no particular limitation on the coating method of the protective layer, and the coating can be performed by a conventionally known method. The preferable amount of the protective layer to be applied is 0.2 to 20 g / m ² , more preferably 0.5 to 10 g / m ² . 1 to 8μ in thickness
m, preferably 2 to 4 μm. If the amount of the protective layer adhered is too small, the function of the protective layer such as storage stability and head matching of the recording medium will be insufficient, and if it is too large, the thermal sensitivity of the recording medium will decrease, which is disadvantageous in cost.

In the heat-sensitive recording medium of the present invention, the back layer is provided on the surface opposite to the heat-sensitive layer, such as an undercoat layer between the substrate and the heat-sensitive recording layer, or an intermediate layer between the heat-sensitive recording layer and the protective layer. Etc. can be provided as needed.

The support used in the present invention is not particularly limited, and it can be used according to the purpose such as paper, synthetic paper, plastic film and the like. The thickness of the support can be appropriately selected according to the purpose of use of the heat-sensitive recording medium. However, when the support is used as a large-format (for example, A0 plate or more) underlay film, the film breaks during handling of the film, In some cases, the film surface may be peeled therefrom. To prevent this, a thicker film is preferable.On the other hand, a thicker support increases the cost or makes it difficult to finish a roll-shaped product. . The thermal recording medium of the present invention can provide an underlay film in which the film surface does not peel off when handled in a large format, even if the support is 100 μm or less.

[0046]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, "parts" means parts by weight.

(Solution A) Denka Butyral # 5000-A (manufactured by Denki Kagaku Kogyo Co., Ltd.) 10 parts (polymerization degree 2000, Tg = 90 ° C.) 40 parts octadecylphosphonic acid 150 parts methyl ethyl ketone 150 parts toluene 100 parts Dispersed to 0.3 μm to obtain solution (A).

(Solution B) ESREC BX-1 (manufactured by Sekisui Chemical) 10 parts (degree of polymerization 1700, Tg = 86 ° C.) 40 parts octadecylphosphonic acid 150 parts methyl ethyl ketone 150 parts toluene 100 parts To obtain solution (B).

(Solution C) Esrec KS-3z (manufactured by Sekisui Chemical) 10 parts (degree of polymerization 2000, Tg = 110 ° C.) 40 parts octadecylphosphonic acid 150 parts methyl ethyl ketone 150 parts toluene 100 parts To obtain a liquid (C).

(D solution) Denka butyral # 3000-2 (manufactured by Denki Kagaku Kogyo Co., Ltd.) 10 parts (degree of polymerization 700, Tg = 72 ° C.) 40 parts octadecylphosphonic acid 150 parts methyl ethyl ketone 150 parts toluene 100 parts It was dispersed to 0.3 μm to obtain a liquid (D).

(E liquid) UV curable resin (Dainippon Ink Chemical, V-9057, solid content: 75%) 50 parts Cured acrylic particles (Soken Chemical, MX-500) 3 parts Ethyl p-dimethylaminobenzoate 0.75 Part ethyl acetate 25 parts The above composition was sufficiently stirred and mixed to obtain a liquid (E).

(Solution F) Ester acrylate ultraviolet curable resin (Dainippon Ink Chemical, C4-782) 50 parts Cured acrylic particles (Soken Chemical, MX-500) 5.5 parts α-aminoketone photopolymerization initiator ( Ciba-Geigy, Irgacure 907) 0.5 part Ethyl acetate 60 parts The above composition was sufficiently stirred and mixed to obtain a liquid (F).

(Solution G) The following composition was ground and dispersed by a ball mill to a particle size of 0.3 μm. Urethane acrylate UV curable resin (Dainippon Ink and Chemicals Unidick C7-157, solid content 75%) 13.3 parts Silicon-modified polyvinyl butyral (Dainichi Seika, SP-712, solid content 12.5%) 20 parts Kaolin ( Engelhard, UW-90) 10 parts Methyl ethyl ketone 80 parts Toluene 20 parts Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.
(Solid content: 75%) was added by 3.3 parts to obtain a liquid (G).

Example 1 Urethane-modified copolymerized polyester solution (Toyobo, Byron UR-3200) 10 parts A liquid 90 parts 2-anilino-3-methyl-6-diethylaminofluorane 4 parts Methyl ethyl ketone 20 parts Toluene 20 parts The above composition liquid Was sufficiently stirred and mixed to obtain a recording layer liquid. 10
0 μm thick PET film (Dupont, Melinex 7)
05) This recording layer liquid was applied and dried to a thickness of 14 μm.
After the heat-sensitive recording layer was provided, solution E was applied onto the recording layer, dried, and then irradiated with ultraviolet rays to form a protective layer, thereby producing a heat-sensitive recording medium.

Example 2 A heat-sensitive recording medium was produced in the same manner as in Example 1 except that Liquid B was used instead of Liquid A.

Example 3 A heat-sensitive recording medium was produced in the same manner as in Example 1 except that Liquid C was used instead of Liquid A.

Example 4 A thermosensitive recording medium was produced in the same manner as in Example 3, except that the urethane-modified copolymerized polyester solution Byron UR-8300 was used instead of Byron UR-3200.

Example 5 A thermosensitive recording medium was produced in the same manner as in Example 3 except that the solution F was used instead of the solution E.

Comparative Example 1 A heat-sensitive recording medium was produced in the same manner as in Example 3 except that Liquid G was used instead of Liquid E.

Comparative Example 2 Liquid D 90 parts 2-anilino-3-methyl-6-diethylaminofluoran 4 parts Denkabutyral # 3000-2 10% MEK solution 30 parts Toluene 20 parts The above composition liquids were thoroughly stirred and mixed. And a recording layer liquid. 10
0 μm thick PET film (Dupont, Melinex 7)
05), this recording layer liquid was applied and dried to provide a heat-sensitive recording layer having a thickness of 14 μm. Then, solution E was applied on the recording layer, dried, and then irradiated with ultraviolet rays to form a protective layer. Was prepared.

Comparative Example 3 Solution C 90 parts 2-anilino-3-methyl-6-diethylaminofluoran 4 parts ESREC KS-3Z 5% MEK solution 60 parts The above composition liquid was sufficiently stirred and mixed, and mixed with a recording layer liquid. did. 10
0 μm thick PET film (Dupont, Melinex 7)
05), this recording layer liquid was applied and dried to provide a heat-sensitive recording layer having a thickness of 14 μm. Then, solution E was applied on the recording layer, dried, and then irradiated with ultraviolet rays to form a protective layer. Was prepared.

[Evaluation of Thermal Recording Medium] Film peeling The prepared thermal recording medium was placed at 90 ° C. with the coated surface outside.
The state of peeling of the film surface when bent was evaluated. In addition, a thermal plotter T
Solid printing was performed by P-4910, and the same evaluation was performed. Table 1 shows the results. The evaluation levels are as shown in Table 2.

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[Table 1]

[0064]

[Table 2]

Printing Scratches The produced heat-sensitive recording medium was replaced with OYO Intermengen.
Solid printing was performed using a thermal plotter XE-4200 manufactured by ts (using a thick film thermal head), and the presence or absence of scratches on the printed surface was observed. Table 3 shows the results.

[0066]

[Table 3]

Curl The produced heat-sensitive recording medium is cut into A4 size plates,
It was left in an environment of 3 ° C. and 50% Rh for 24 hours, and the heights of the four corners were measured and averaged. Table 4 shows the results.

[0068]

[Table 4]

[0069]

According to the present invention, the surface is not damaged even when recorded by a thick film thermal head, and when used as a large format underlay film, the film surface does not peel off, and particularly, the image portion does not peel off. A thermal recording medium suitable for an underlay film having a small curl is provided, and the contribution to the thermal recording field is extremely large.

Claims (9)

[Claims] 1. A heat-sensitive recording medium comprising a support and a heat-sensitive recording layer containing at least a leuco dye, a color developer and a binder resin, wherein the binder resin is made of polyvinyl having a polymerization degree of 850 or more. A thermosensitive recording medium comprising an acetal and a urethane-modified copolymerized polyester. 2. The heat-sensitive recording medium according to claim 1, wherein the urethane-modified copolyester is at least 30% by weight based on the total amount of the polyvinyl acetal and the urethane-modified copolyester. 3. The heat-sensitive recording medium according to claim 1, wherein the glass transition point of the polyvinyl acetal is 100 ° C. or higher. 4. The heat-sensitive recording medium according to claim 1, wherein the polyvinyl acetal is polyvinyl acetoacetal. 5. The thermosensitive recording according to claim 1, wherein a protective layer is formed on the thermosensitive recording layer, and 50% by weight or more of the total solid content of the protective layer is an ultraviolet curable resin. Medium. 6. 5 to 10% by weight of the total solids of the protective layer
Is a filler having an average particle size of 3 to 10 μm.
5. The heat-sensitive recording medium according to any one of 4. 7. The photopolymerization initiator of the ultraviolet curable resin,
The heat-sensitive recording medium according to claim 5, which is an α-aminoketone-based photopolymerization initiator. 8. The heat-sensitive recording medium according to claim 1, wherein the developer used in the heat-sensitive recording layer is a compound represented by the following general formula (1) or (2). Embedded image [In the formula (1), R represents a linear alkyl group having 16 to 24 carbon atoms. ] [In the formula (2), R ′ represents a straight-chain alkyl group having 13 to 23 carbon atoms. ] 9. The heat-sensitive recording medium according to claim 1, wherein said support has a thickness of 100 μm or less.