JP2000289354A - Heat-sensitive recording film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a heat-sensitive recording film of superior surface smoothness used for providing sufficient image density and resolution. SOLUTION: A heat-sensitive recording film is a void-containing film containing a number of voids inside, and its apparent specific gravity is 1.3 or less and its central line surface roughness is 0.3 mm or less, and a heat- sensitive acceptive layer is formed at least on one face of the void-containing polyester film, and the average light moving distance is set as 0.15 mm or shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording film having excellent recording sensitivity.

[0002]

2. Description of the Related Art As a conventional thermal transfer image receiving sheet, there is known a natural paper or a sheet having a recording layer formed on the surface of natural paper. However, in this method, only those having insufficient surface smoothness can be obtained. On the other hand, in order to improve the smoothness of the image receiving sheet, a thin polypropylene synthetic paper and natural paper are bonded together or a thick polypropylene synthetic paper is used as a base material, and a recording layer is formed on these surfaces. Those provided are widely used. This is because polypropylene-based synthetic paper has a surface smoothness that cannot be obtained with natural paper, and also has an appropriate cushioning property. By having an appropriate cushioning property, uniform and sufficient contact can be made between the heating head / transfer ribbon / image receiving sheet during thermal transfer, and a uniform and high-density printed matter can be obtained. . However, when polypropylene-based synthetic paper is used as the base material, the polypropylene-based synthetic paper is extremely easily plastically deformed and has poor flexibility. And there is a serious disadvantage that the quality of the printed matter is significantly impaired. On the other hand, a method using a polyester-based void-containing film instead of the polypropylene-based synthetic paper has been proposed. However, a polyester-based void-containing film generally has higher rigidity than a polypropylene-based synthetic paper and has insufficient cushioning properties.
Therefore, in order to obtain an image density equivalent to that obtained by using a polyester-based synthetic paper using a polyester-based void-containing film, it is necessary to increase the void content in order to ensure cushioning. Further, the definition of the image is required together with the image density. This is because even finer images need to be seen clearly without blurring. For image density, it is better that the dots of the printer constituting the image are large, but this reduces the sharpness. Therefore, the dot size has an optimum value. However, no matter how much the dots are controlled to the optimum value, a clearer image cannot be obtained unless the optical dot gain due to the light diffusion inside the image receiving paper and the image receiving film occurs as much as possible.
This has not been well controlled in conventional image receiving films.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a heat-sensitive recording film which has the above-mentioned disadvantages of the prior art, namely, excellent surface smoothness and sufficient image density and resolution.

[0004]

The present invention relates to a void-containing polyester film containing a large number of voids therein, which has an apparent specific gravity of 1.3 or less and a center line average surface roughness of 0.3 mm. A heat-sensitive recording film, wherein a heat-sensitive receiving layer is provided on at least one surface of the following void-containing polyester film, and the average light moving distance is 0.15 mm or less.

[0005] The polyester in the present invention is obtained by mixing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol and neopentyl glycol. It is a polyester produced by condensation. These polyesters may be prepared by directly reacting an aromatic dicarboxylic acid and a glycol, or by subjecting an alkyl ester of the aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Can be produced by a method such as polycondensation. Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of the third component. In any case, in the present invention, a polyester having an ethylene terephthalate unit, a butylene terephthalate unit or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. .

The thermoplastic resin incompatible with the polyester used in the present invention is optional, and is not particularly limited as long as it is incompatible with the polyester. The cavity derived from the thermoplastic resin incompatible with the polyester means that a cavity exists around the thermoplastic resin, and can be confirmed by, for example, a cross-sectional photograph of the film by an electron microscope. Specific examples include polystyrene-based resins, polyolefin-based resins, polyacryl-based resins, polycarbonate resins, polysulfone-based resins, and cellulose-based resins. In particular, polystyrene resins or polyolefin resins such as polymethylpentene and polypropylene are preferably used.

However, more preferred thermoplastic resins incompatible with polyester include, for example, the following. That is, the thermoplastic resin incompatible with the polyester contains at least a polystyrene resin, a polymethylpentene resin, and a polypropylene resin, and contains a polystyrene resin content (a weight%) and a polymethylpentene resin. The amount (b weight%) and the content of the polypropylene resin (c weight%) are as follows: 0.01 ≦ a / (b + c) ≦ 1, c / b ≦ 1, 3 ≦
It is most preferable to satisfy a + b + c ≦ 20, which is suitable for increasing the void ratio and improving the folding wrinkle resistance.

[0008] Here, the polystyrene resin refers to a thermoplastic resin having a polystyrene structure as a basic component, and includes other components in addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene. Modified resins graft- or block-copolymerized, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of these polystyrene-based resins with thermoplastic resins, such as polyphenylene ether, are also included.

[0009] The polymethylpentene resin is 8
0 mol% or more, preferably 90 mol% or more, is a polymer having units derived from 4-methylpentene-1, and other components include ethylene units, propylene units,
Derived units derived from butene-1 unit, 3-methylbutene-1 and the like are exemplified. The melt flow rate of such polymethylpentene is preferably 200 g / 10 min or less, more preferably 30 g / 10 min or less. This is because if the melt flow rate exceeds 200 g / 10 minutes, it is difficult to obtain the effect of reducing the weight of the film.

The polypropylene resin in the present invention also includes modified resins obtained by grafting or block copolymerizing other components in addition to homopolymers such as isotactic polypropylene and syndiotactic polypropylene. Further, as the presence state of the polypropylene resin in the present invention, the above polypropylene resin may be used separately from the polymethylpentene, or a propylene unit may be used as a copolymer component in the polymethylpentene resin. The introduced one may be used.

The mixing amount of these void-forming agents, that is, the thermoplastic resin incompatible with the polyester, to the polyester varies depending on the desired amount of voids, but is in the range of 3 to 20% by weight based on the whole film. And more preferably 5 to 18% by weight. And 3
If the amount is less than the weight percentage, there is a limit to increasing the amount of cavities generated. Conversely, if the content is 20% by weight or more, the stretchability of the film is significantly impaired, and the heat resistance, strength, and stiffness are impaired.

Further, in order to improve the concealing property and the like, inorganic or organic particles may be added to the film in the polyester or in the incompatible resin, if necessary. Particles that can be added include silica, kaolinite, talc,
Examples thereof include, but are not particularly limited to, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, zinc sulfide, and organic white pigment.

The void-containing polyester film of the present invention has an apparent specific gravity of 1.3 or less, preferably 1.2 or less.
More preferably, it must be 1.1 or less. And
If the apparent specific gravity is larger than 1.3, the amount of cavities existing in the film is too small, and a sufficient image density cannot be obtained during thermal transfer printing. On the other hand, the lower limit of the apparent specific gravity is not limited, but is preferably 0.7 or more, and more preferably 0.8 or more, in order to secure the breaking wrinkle resistance.

The void-containing polyester film of the present invention has a center line average surface roughness of 0.3 μm or less, preferably 0.25 μm or less, more preferably 0.2 μm or less, more preferably 0.1 μm or less. It is 15 μm or less. If it exceeds 0.3 μm, the surface smoothness of the film surface will be impaired, and it will be difficult to obtain uniform adhesion between the thermal head and the recording film during thermal recording, and the image density will be extremely reduced. In addition, the thermal transfer image becomes rough, and the print quality is greatly reduced.

Further, in the heat-sensitive recording film of the present invention, the average light moving distance inside the film must be 0.15 mm or less, preferably 0.13 mm or less, more preferably 0.10 mm or less. If the average light moving distance exceeds 0.15 mm, the printed image will be inferior in sharpness and the image will be blurred, which is not preferable.

This average light moving distance can be usually obtained from MTF which is an index indicating the high resolution of the photographic material. A Probability Description of the Yule-Niel
senEffect II: The Impact of Halftone Geometry (Jou
rnal of Imaging Science and Technology pp637, volu
me 41, 1997) experimentally states that the MTF and the average light travel distance have a relationship of Equation 1.

(Equation 1) That is, if the MTF of each frequency is obtained, this kp is obtained. However, the MTF is usually calculated from the reflected light density of screens with different line widths and intervals (spatial frequency) placed on paper or recording film or printed directly, or the spatial frequency changes continuously. From the light having a sinusoidal function distribution using the reflection density. However, this method only requires relatively low frequencies. In particular, when kp is obtained from paper or a recording film, the error becomes very large.Therefore, the kp obtained from the method of the embodiment described later and the sharpness of the printed matter on the paper or the recording film are relatively small. Think of it as a good match.

The uniform biaxially oriented film will be described in detail by exemplifying means for achieving the above average light moving distance. Although not limited to the following method, the following method is desirable. First, the average particle size is 0.1 ~
A polyester layer (skin layer) containing fine voids derived from fine particles of 3 μm is provided on the core layer (A layer). 0.
If it is 1 μm or less or exceeds 3 μm, the average light moving distance cannot be within the preferred range of the present invention even if the amount of addition is increased.

The particles that can be added to the skin layer may be inorganic particles or organic particles, and are not particularly limited. For example, titanium dioxide, calcium carbonate, barium sulfate, zinc sulfide, Examples include silicon dioxide, aluminum oxide, talc, and kaolin.
These particles may be subjected to a surface treatment as necessary. Examples of the treating agent include, but are not limited to, aluminum oxide, silicon dioxide, zinc oxide, silicon-based resin, siloxane-based resin, fluorine-based resin, silane coupling agent and titanate coupling agent, polyol and polyvinylpyridine. Not something.

Among them, particularly preferred particles include titanium oxide fine particles and / or zinc sulfide fine particles. The titanium oxide fine particles may be either anatase type or rutile type. Further, the particle surface may be subjected to an inorganic treatment such as alumina or silica, or may be subjected to a silicon-based or alcohol-based organic treatment.

The concentration of the fine particles added to the skin layer is arbitrary, but is preferably 20 to 50% by weight. When the addition amount is less than 10%, it is difficult to reduce the average light moving distance to 0.15 mm or less.
On the other hand, when it exceeds 50%, the smoothness of the film surface is rapidly deteriorated and the quality of the image is lowered.

Further, a coloring agent, a light-proofing agent, a fluorescent agent, an antistatic agent and the like can be added to the skin layer as needed.

Further, the thickness of the skin layer is preferably 1 to 20 μm and less than 30% of the total thickness of the film. If the thickness of the skin layer is less than 1 μm, the variation in the concentration of fine particles per surface area of the film becomes large, so that the image density becomes uneven and the printed matter tends to give a rough impression. On the other hand, even if the skin layer is formed with a thickness exceeding 20 μm, the effect of improving the image density cannot be obtained and is meaningless. Furthermore, the skin layer thickness is 30 times
%, The stretchability of the whole film tends to be remarkably reduced, which is not preferable for securing stable industrial productivity.

The average light moving distance can be controlled by the amount and type of particles in the skin layer and the core layer, the amount of cavities, the thickness ratio, and the like. Considering other parameters and productivity, as an example, when titanium oxide is used for the skin layer, the added amount is 20 to 40% by weight, the thickness of the skin layer is 5 to 25% of the entire thickness, Specific gravity is 0.75
A value of about 1.05 seems to be good. However, in the present invention, the raw materials can be changed without being limited to this method.

The method of producing the void-containing polyester film of the present invention is optional, and is not particularly limited. For example, it can be produced as follows. First, as a method of joining the skin layer to the film surface,
It is most preferable to adopt a co-extrusion method in which the resins of the layer A and the layer B are supplied to different extruders, then laminated in a molten state and extruded from the same die.

The unstretched sheet thus obtained is further stretched between rolls having different speeds (roll stretching), stretched by gripping and expanding with clips (tenter stretching), or stretched by air pressure. (Inflation stretching) and the like are subjected to biaxial orientation treatment. By performing the orientation treatment, interfacial separation occurs between the polyester / incompatible resin and between the polyester / fine particles, and many fine cavities are developed. Therefore, the conditions for stretching and orienting the unstretched sheet are closely related to the formation of cavities. Hereinafter, the stretching / orienting conditions will be described by taking as an example a sequential biaxial stretching method most preferably used, particularly a method of stretching an unstretched sheet in the longitudinal direction and then in the width direction.

First, the first-stage longitudinal stretching step is the most important process for forming many fine cavities inside the film. In longitudinal stretching, stretching is performed between two or many rolls having different peripheral speeds. As the heating means at this time,
A method using a heating roll or a method using a non-contact heating method may be used, or both may be used. Among these, the most preferred stretching method is a method using both roll heating and non-contact heating. In this case, the film is first preheated to 50 ° C. to a temperature equal to or lower than the glass transition point of the polyester using a heating roll, and then the front and back sides of the film are heated by independent infrared heaters of a control system. At this time,
The skin layer surface is heated to a lower temperature, and the insufficient heat is compensated for by infrared heating from the opposite surface. Thus, it is extremely important to heat and stretch the film front and back to different temperatures. The method of providing a temperature difference with a non-contact heating device is only one preferable example, and the same effect can be obtained by another method, for example, a method of sandwiching a film between rolls having different temperatures and heating. In any case, the heating of the entire film is mainly performed from the anti-skin layer side to supply a sufficient amount of heat enough to uniformly stretch the film, and the skin layer surface is stretched at a lower temperature. This is an important point for forming a large number of cavities derived from inorganic fine particles.

Next, the uniaxially stretched film thus obtained is introduced into a tenter and stretched 2.5 to 5 times in the width direction. The preferred stretching temperature at this time is 100 ° C to 2 ° C.
00 ° C. The biaxially stretched film thus obtained is subjected to a heat treatment as necessary. The heat treatment is preferably performed in a tenter, and the melting point of the polyester is Tm-50.
It is preferable to carry out in the range of ° C. to Tm.

As a method for providing a coating layer, a commonly used method such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, a reverse roll coating method, etc. Applicable. As the step of applying, any method such as a method of applying before stretching the film, a method of applying after longitudinal stretching, and a method of applying to the surface of the film after the orientation treatment is possible.

By using the thus obtained film of the present invention as a support for a heat-sensitive recording material and providing a heat-sensitive recording layer on the support, the heat-sensitive recording material of the present invention can be obtained. The heat-sensitive recording layer contains a known color former and a color former.

As the combination of the color former and the color former, any combination can be used as long as they come into contact with each other to cause a color reaction. For example, a colorless or pale white basic dye and an inorganic or organic acidic substance can be used. Or combinations of higher fatty acid metal salts such as ferric stearate with phenols such as gallic acid, and combinations of diazonium compounds with couplers and basic substances. Can be.

Various types of the colorless or light-colored basic dyes are known, for example, 3.3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p- Dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3-
(1,2-dimethylindol-3-yl) phthalide,
3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, , 3-Bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -6-dimethylaminophthalide, 3,3 Screw (2-
Phenylindol-3-yl) -6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1
-Methylpyrrol-3-yl) -6-dimethylaminophthalide and other triallylmethane dyes, 4,4-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucouramine, N-2.4 Diphenylmethane dyes such as 1,5-trichlorophenylleuco auramine, thiazine dyes such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue;
3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3
-Spiro dyes such as methyl-naphtho- (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B anilinolactam, rhodamine- (p-nitriloanilino) lactam, rhodamine-
Lactam dyes such as (o-chloroanilino) lactam,
3-dimethylamino-7-methoxyfluoran, 3-dimethylamido-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6,7
-Dimethylfluoran, 3- (N-ethyl-p-toluidino) -7-methylfluorane, 3-diethylamino-
7-N-acetyl-N-methylaminofluoran, 3-
Diethylamino-7-N-methylaminofluoran, 3
-Diethylamino-7-N-methylaminofluoran,
3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-N-methyl-N-benzylaminofluoran, 3-diethylamino-7-N-chloroethyl-N-methylaminofluoran, 3-diethylamino- 7-N-diethylaminofluoran, 3-
(N-ethyl-p-toluidino) -6-methyl-7-phenylaminofluoran, 3- (N-cyclopentyl-
N-ethylamino) -6-methyl-7-anilinofluoran, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluoran, 3-diethylamino-6-methyl- 7-phenylaminofluoran,
3-diethylamino-7- (2-carbomethoxyphenylamino) fluoran, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-phenylaminofluoran, 3- (N-cyclohexyl-N-methyl amino)
-6-methyl-7-phenylaminofluoran, 3-piperidino-6-methyl-7-phenylaminofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 3-diethylamino-7- (o -Chlorophenylamino) fluoran, 3-dibutylamino-7-
(O-chlorophenylamino) fluoran, 3-virolidino-6-methyl-7-p-butylphenylfluoran, 3-N-methyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluoran, 3 And fluoran dyes such as -N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluoran.

Various inorganic or organic acidic substances which are colored as basic dyes are also known. Examples of the inorganic acidic substances include activated clay, acidic clay, atabalgit, bentonite, colloidal silica, aluminum silicate and the like. As an example, as an organic acidic substance, 4-t
tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2,2′-methylenebis (4-methyl-6-ter
t-isobutylphenol), 4,4′-isopropylidenebis (2-tert-butylphenol),
4'-sec-butylidene diphenol, 4-phenylphenol, 4,4'-isopropylidene diphenol (bisphenol A), 2,2'-methylenebis (4-
Phenolic compounds such as chlorophenol), hydroquinone, 4,4'-cyclohexylidenediphenol, benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolak-type phenolic resins, and phenolic polymers; Acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid ,
Salicylic acid, 3-isopropylsalicylic acid, 3-ter
t-butylsalicylic acid, 3-benzylsalicylic acid, 3-
(Α-methylbenzyl) salicylic acid, 3,5-di-te
rt-butylsalicylic acid, 3-phenyl-5- (α, α
-Dimethylbenzyl) salicylic acid, aromatic carboxylic acids such as 3,5-di-α-methylbenzylsalicylic acid, and the phenolic compounds and aromatic carboxylic acids and, for example, zinc, magnesium, aluminum, calcium, titanium, manganese, tin, Examples thereof include salts with polyvalent metals such as nickel.

Each of these basic dyes (color formers) and color formers may be used alone, or two or more may be used in combination as needed. The use ratio of the color former and the color former is appropriately selected according to the type of the color former and the color former to be used, and is not particularly limited. In general, it is based on 1 part by weight of the color former. The color former is used in an amount of 1 to 20 parts by weight, preferably about 2 to 10 parts by weight.

The coating liquid containing these color formers and color formers is generally prepared by mixing a basic dye (color former) and a color former by stirring with a water mill, an attritor, a sand mill or the like and using a pulverizer using water as a dispersion medium. It is adjusted by, for example, dispersing uniformly or separately.

The coating solution contains starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt,
Styrene / maleic anhydride copolymer salt, ethylene / acrylic copolymer salt, styrene / butadiene copolymer emulsion, urea resin, melanin resin, amide resin, etc. 5-2
About 5% by weight is contained.

Further, various auxiliaries can be added to the coating liquid as needed, for example, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, sodium salt of fatty acid, metal salt of fatty acid And the like, a benzophenone-based ultraviolet absorber and the like, an antifoaming agent, a fluorescent paint, a coloring paint, a conductive substance, and the like are appropriately added.

If necessary, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, stearic amide, methylene bisamide stearate, oleic amide, palmitic amide, palm fatty acid Fatty acid amides such as amides, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and the like Hindered phenols, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2-hydroxy-
UV absorbers such as 4-benzyloxybenzophenone,
1,2-di (3-methylfechinosi) ethane, 1,2-
Diphenokiethane, 1-phenoxy-2- (4-methylfechinosi) ethane, terephthalic acid dimethyl ester,
Dibutyl terephthalate, dibenzyl terephthalate, p-benzyl-biphenyl, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene,
Esters such as 1-hydroxynaphthoic acid phenyl ester, and various known heat-fusible substances and inorganic materials such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica, and activated clay. Pigments can also be added.

In the heat-sensitive recording material of the present invention, the method for forming the heat-sensitive recording layer is not particularly limited.
For example, it is formed by a method of applying and drying a coating liquid by air knife coating, blade coating, or the like. Also, the amount of the coating liquid applied is not particularly limited, and is usually adjusted in a range of about ² to 50 g / m ² in terms of dry weight. The heat-sensitive recording layer of the present invention may be either one color or multicolor.

In the present invention, it is preferable to provide an intermediate layer between the heat-sensitive recording layer and the support polyester film.

The intermediate layer is formed by applying a solution, emulsion or dispersion of a polymer material containing at least one kind of polyester resin, polyacrylic resin, polyurethane resin and vinylidene chloride resin on the polyester film surface. Is done.

The polyester resin of the intermediate layer is formed from a dibasic acid and glycol, and is soluble, emulsified or dispersed in water. As the polyester resin, for example, a dibasic acid is a dicarboxylic acid containing 50 to 0.5 mol% of the total dicarboxylic acid and a sulfonic acid group, and a polyester copolymer obtained by copolymerizing these two dicarboxylic acid components and a glycol component. It is a polymer. Examples of the sulfonic acid metal salt-containing dicarboxylic acids include metals such as sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and 5- (4-sulfophenoxy) isophthalic acid. Salts are mentioned, and particularly preferred are metal salts of 5-sodium sulfoisophthalic acid and sodium sulfoterephthalic acid. These sulfonic acid metal-containing dicarboxylic acids in the copolymer are present in an amount of 50 to 0.5 mol%, preferably 2 to 0.5 mol%, based on the total dicarboxylic acid components.
When the content exceeds 50 mol%, the water resistance of the copolymer decreases even if the dispersibility in water is improved. The dispersibility of the polyester copolymer in water is
Although it depends on the copolymer composition, the type and amount of the water-soluble organic compound, etc., the smaller the amount of the dicarboxylic acid component containing a metal sulfonic acid salt, the better, as long as the dispersibility in water is not impaired. As the normal dicarboxylic acid containing no sulfonic acid metal salt, aromatic, aliphatic and alicyclic dicarboxylic acids are used. As aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, orthophthalic acid,
2,6-naphthalenedicarboxylic acid and the like can be mentioned. These aromatic dicarboxylic acids are preferably at least 40 mol% of the total dicarboxylic acid components, and are preferably at least 40 mol%.
If it is less than this, the mechanical strength and the water resistance of the polyester copolymer decrease. Examples of the aliphatic and alicyclic dicarboxylic acids include succinic acid, adipic acid, sebacic acid, 1.3-cyclopentanedicarboxylic acid, 1.2-cyclohexanedicarboxylic acid, 1.3-cyclohexanedicarboxylic acid, and 1.
4-cyclohexanedicarboxylic acid and the like. When these non-aromatic dicarboxylic acid components are added, the adhesive performance may be improved in some cases, but generally, the mechanical strength and water resistance of the polyester copolymer deteriorate. On the other hand, as the glycol component to be reacted with the dicarboxylic acid mixture,
Aliphatic glycol having 2 or more carbon atoms, and 6 to 1 carbon atoms
Two alicyclic glycols, and a mixture of both,
For example, ethylene glycol, 1.2-propylene glycol, 1.3-propanediol, 1.4-butanediol, neopentyl glycol, 1.6-hexanediol, 1.2-cyclohexanedimethanol, 1.4
-Cyclohexanedimethanol, p-xylene glycol, diethylene glycol, triethylene glycol,
Examples include polyethylene glycol and polytetramethylene glycol. The polyester copolymer is obtained by ordinary melt polycondensation. That is, a direct esterification method in which the above-mentioned dicarboxylic acid component is directly reacted with a glycol component to distill water to form an ester, followed by polycondensation, or a reaction of a dimethyl ester of a dicarboxylic acid component with a glycol component to give methyl alcohol Is obtained by a transesterification method in which is subjected to transesterification by distilling off and then polycondensation. In addition, a polymer can be obtained by solution polycondensation or interfacial polycondensation. At the time of melt polycondensation, an antioxidant, a slipping agent, inorganic fine particles, an antistatic agent and the like can be added as required. The above-mentioned polyether such as polyethylene glycol can be added by melt blending during melt polycondensation or after polymerization.

Examples of the polyurethane resin include (1) a compound having two or more active hydrogen atoms in the molecule, (2) an organic polyisocyanate having two or more isocyanate groups in the molecule, or (3) a compound having two or more active hydrogen atoms in the molecule. And a chain extender having at least two active hydrogen atoms, and a compound having a terminal isocyanate group.

The compound (1) is generally known as having two or more hydroxyl groups at the terminal or in the molecule.
Those containing a carboxylic acid, amino group or meltcapto group, and particularly preferred are polyether polyol, polyester polyol and polyether ester polyol. Examples of polyether polyols include compounds obtained by polymerizing alkylene oxides such as ethylene oxide and propylene oxide, or compounds obtained by polymerizing styrene oxide and epichlorohydrin, or random copolymerization, block copolymerization, or addition polymerization to a polyhydric alcohol. And the like. Polyester polyols and polyetherester polyols mainly include linear or branched compounds, such as succinic acid, adipic acid, phthalic acid and maleic anhydride, and polyvalent saturated and unsaturated carboxylic anhydrides. , Ethylene glycol, diethylene glycol, 1.4-butanediol, neopentyl glycol, 1.6-hexanediol and polyvalent saturated and unsaturated alcohols such as trimethylolpropane, relatively low molecular weight polyethylene glycol, polypropylene glycol And polyalkylene ether glycols or a mixture of these alcohols. Further, polyester polyols include polyesters obtained from lactone and hydroxy acid, and polyether ester polyols include polyether esters obtained by adding ethylene oxide or propylene oxide to polyesters produced in advance. .

As the organic polyisocyanate (2), isomers of toluylene diisocyanate, 4,4 ′
-Aromatic diisocyanates such as diphenylmethane diisocyanate; aromatic aliphatic diisocyanates such as xylylene diisocyanate; aliphatic diisocyanates such as isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; Polyisocyanates added in advance with methylolpropane or the like are included.

The chain extender having at least two active hydrogens of the above (3) includes ethylene glycol, diethylene glycol, 1,4-butanediol and 1,6-
Glycols such as hexanediol, polyhydric alcohols such as glycerin, trimethylolpropane and pentaerythritol, diamines such as ethylenediamine, hexamethylenediamine and piperazine, aminoalcohols such as monoethanolamine and diethanolamine, and thiols such as thiodiethyleneglycol Examples include diglycols and water.

The polyacrylic resin is obtained by polymerizing monomers other than acrylic acid or a derivative thereof and, if necessary, acrylic acid (derivative) having a vinyl group. The monomers used include acrylic acid, methacrylic acid (hereinafter, acrylic acid and / or methacrylic acid are referred to as (meth) acrylic acid), and lower alkyl esters of (meth) acrylic acid (eg, methyl, ethyl, Propyl, butyl, amyl, hexyl, heptyl, octyl, 2-ethylhexyl ester), methyl (meth) acrylate, hydroxymethyl (meth) acrylate,
Examples include styrene, glycidyl (meth) acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate.

The sensitivity of the heat-sensitive recording material can be improved by including organic or inorganic particles in the intermediate layer. Such inorganic particles include titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate,
Examples include aluminum oxide, zeolite, kaolin, and talc, and examples of the organic particles include cross-linked styrene and cross-linked acryl. Particularly preferred are calcium carbonate, barium sulfate, and more preferably titanium dioxide. In the present invention, it is preferable that the intermediate layer comprises a binder composed of a polyester resin and a polyacryl resin, and organic or inorganic particles, and a weight ratio of the binder / particles is 2/8 to 6/4. Is preferable from the viewpoint of print density.

The thus obtained void-containing polyester film for thermal recording has excellent image clarity with respect to the film. To prepare a thermal transfer image-receiving sheet using the void-containing polyester film of the present invention, a recording layer for receiving ink or a diffusible (sublimable) dye migrating from the thermal transfer ink sheet is formed on the film surface. do it. In this case, the recording layer may be formed directly on the film, or may be formed via an undercoat layer such as an easy-adhesion layer, a whiteness improving layer, or an antistatic layer.

The heat-sensitive recording film of the present invention may be used alone as a substrate, or may be used in combination with another substrate. Other substrates that can be combined include, but are not limited to, natural paper, various synthetic resin films, woven fabrics, and nonwoven fabrics. Alternatively, the surface opposite to the surface on which the receiving layer is formed may be subjected to an adhesive treatment to be used as a heat-sensitive recordable adhesive label.

The heat-sensitive recording film thus obtained is excellent in surface smoothness, sufficient image density and resolution, and excellent in folding wrinkle resistance as compared with those conventionally proposed. Ideal for thermal recording.

Next, examples of the present invention and comparative examples will be described. The measurement / evaluation method used in the present invention will be described below. 1) Apparent specific gravity A film was cut out accurately into a square of 10 cm × 10 cm, and its thickness was measured at 50 points to obtain an average thickness t (unit: μm).
Ask for. Next, the weight of the sample is measured up to 0.1 mg and is referred to as w (unit: g). Then, the apparent specific gravity was calculated by the following equation. Apparent specific gravity (-) = (w / t) x 10000

2) Center line average surface roughness According to JIS-B601-1982, using a Surfcom 300A type surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.), stylus diameter 2 μm, stylus pressure 30 m
g, measurement pressure 30 mg, cut-off 0.8 mm, measurement length 2.5 mm, and the center line average surface roughness was measured.

3) Thickness of skin layer The cut surface of the film was observed and observed with an electron microscope.

4) Average light moving distance kp inside the film A dot screen is placed on the film, and the reflectance of the film portion at each dot area ratio is measured. The reflectance with respect to the area ratio is plotted, and the value of kp is determined by Equation 2 and the least squares method so that the minimum value is obtained. The value of kp at that time is defined as the average light moving distance. The measuring instrument, conditions, etc. are as follows. Screen: A in photographic emulsion on transparent polyester
M halftone created at 65 dpi. Dot area ratio should be at least every 10% from 0 to 100% and 95
Use%. Measurement device: Edmund Scientific Infiviver video microscope to CCD camera (Sony XC-7
8) Import the image. At this time, the magnification is set so that the width is 2 mm on a 14-inch television monitor. The image is decomposed into 512 × 384 pixels, and the reflectance distribution at each point (based on the aluminum oxide white plate) is obtained. The reflectance having the largest number of points is defined as the reflectance Rp of this sample, and plotted against each dot area ratio F. The image analysis software is IMAGELAB (Werner Frei As
sociates), but other software may be used as long as the function is satisfied.

(Equation 2) The value of A is determined by Imaging Science (author JCDain).
ty et al., published in Academic Press), pp. 244, calculates the MTF of a 100 μm-thick polyester film containing 5% titanium oxide (TA-300, manufactured by Fuji Titanium Co., Ltd.). , Kp when it most approximates the equation 1 by the least square method. Using this kp, the minimum value of A in the above-described method using the screen was 0.810, which was adopted. Samples are stacked on each other so that Rp is not substantially affected by the pedestal.

5) Evaluation of Recorded Image Quality A recorded image obtained by recording with a practical video printer (product: UP-103, manufactured by Sony Corporation) was measured by a Macbeth densitometer (product: RD-914, manufactured by Macbeth). The following evaluation was performed on the recording portion where the recording density was around 0.6 at that time. Dot analyzer (Product: DA-200
0, manufactured by Kanzaki Paper Co., Ltd.)
The white paper part was ternarized, and the ratio of the high density part was counted.

Example 1 (Adjustment of cavity forming agent) Melt flow rate as raw material
20% by weight of a 1.7 polystyrene resin (TOPOLEX 570-57U manufactured by Mitsui Toatsu Co., Ltd.) and a melt flow rate of 1.7
Polypropylene resin (Noblene manufactured by Mitsui Toatsu Co., Ltd.)
FO-50F) 20 wt% and melt flow rate 8 polymethylpentene resin (TPX, manufactured by Mitsui Petrochemical Co., Ltd.)
DX-845) 60% by weight of pellets were mixed, supplied to a twin-screw extruder, and sufficiently kneaded to prepare a cavity-forming agent.

(Preparation of Master Pellets Containing Fine Particles) 50% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.64 and 50% by weight of anatase type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm (electron microscopic method)
% By weight is supplied to a vent-type twin-screw extruder and preliminarily kneaded, and then the molten polymer is continuously supplied to a vent-type single-screw kneader and kneaded to contain fine particles (titanium oxide). The master pellet was prepared. Subsequently, 10% by weight of the cavity-forming agent obtained by the above method, 5% by weight of master pellets containing fine particles (titanium oxide) and an intrinsic viscosity of 0.1% were used.
The polyethylene terephthalate resin of No. 62 was mixed with pellets in an amount of 85% by weight and vacuum-dried to obtain a raw material for the film constituting the layer A. On the other hand, 30% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 70% by weight of the above-mentioned master pellets containing fine particles (titanium oxide) were mixed and vacuum-dried to obtain a raw material for a film constituting the B layer.

(Preparation of Unstretched Film) Next, the raw materials of the film constituting each layer were supplied to separate extruders, and the layer B was joined to one surface of the layer A in a molten state using a feed block. At this time, the discharge amount ratio of the A layer and the B layer was controlled to 93: 7 volume ratio using a gear pump.
Then, it was extruded onto a cooling drum adjusted to 30 ° C. by using a T-die to prepare an unstretched sheet having a thickness of about 600 μm. At this time, extrusion was performed so that the layer B side was a non-drum surface and the layer A side was a drum surface.

(Preparation of Biaxially Stretched Film) The obtained unstretched sheet is uniformly heated to 65 ° C. using a heating roll,
The speed is regulated (2 m / min) by sandwiching the film between a metal roll whose temperature is controlled to 65 ° C. and a rubber roll whose temperature is not controlled,
Similarly, it was stretched 3.4 times with a high-speed roll (metal roll was controlled at a temperature of 30 ° C., and a rubber roll was not controlled) whose speed was regulated (6.8 m / min). At this time, the two sets of rolls whose speeds were regulated were installed in parallel so that the interval between the speed regulation points was 25 cm, and they were arranged so that the B surface (non-drum surface) side was in contact with the rubber roll surface. In addition, an infrared heater having a gold reflection film at the center of the nip roll (rated 20
(W / cm) was placed opposite to both surfaces of the film (a distance of 1 cm from the film surface), the layer A surface was heated at 100% of the rated current, and the layer B surface was heated at 60% of the rated. The uniaxially stretched film thus obtained is guided to a tenter, heated to 140 ° C., stretched transversely 3.7 times, and fixed in width.
Heat treatment was performed at 220 ° C. for 5 seconds, and relaxation was further performed at 220 ° C. in the width direction by 4% to obtain a 75 μm-thick void-containing polyester film.

An intermediate layer was provided on one side of this film as follows. That is, the following solution was prepared and coated on one surface of the above film at a coating amount of about 0.05 g / m ² : water-dispersed polyester resin (Vylonal MD-16 manufactured by Toyobo Co., Ltd.): 0.9 g Acrylic resin (ethyl acrylate / methyl methacrylate / hydroxy methacrylate / glycidyl methacrylate / sodium vinyl sulfonate = 45/45/6/2/2 (% by weight)
1g blocked isocyanate (Elastron BN- manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
11) ... 0.2 g zinc borofluoride (manufactured by Hashimoto Chemical Co., Ltd.)
10% by weight solution: 0.002 g 4: 6 solution of isopropyl alcohol and water: 25.892 g Average particle size 0.02
Immediately after application of 2 g of titanium dioxide having a thickness of 2 μm, it was dried at 80 ° C. for 2 minutes and at 130 ° C. for 30 seconds. The solid content after coating was approximately 5/5 of binder / particle.

Further, on this intermediate layer, a coating solution prepared as follows was applied so that the coating amount after drying was 1 g / m ^2, and a heat-sensitive recording layer was provided: Solution A preparation 3- ( N-ethyl-N-isoamylamino)-
6-methyl-7-phenylaminofluorane: 10 parts by weight Dibenzyl terephthalate: 20 parts by weight Methyl cellulose 5% aqueous solution: 20 parts by weight Water: 40 parts by weight This composition was ground by a sand mill until the average particle diameter became 3 μm. . Solution B Preparation 4,4'-isopropylidene diphenol ... 3
0 parts by weight methylcellulose 5% aqueous solution 40 parts by weight water
20 parts by weight This composition was sand-milled to have an average particle size of 3 μm.
m. 90 parts by weight of solution A, 90 parts by weight of solution B, silicon oxide pigment (trade name: Mizukasil P-527, average particle diameter: 1.
8 μm, oil absorption: 180 cc / 100 g, manufactured by Mizusawa Chemical Co., Ltd.) 30 parts by weight, 10% aqueous polyvinyl alcohol solution 3
00 parts by weight and 28 parts by weight of water were mixed and stirred to obtain a coating liquid. Thus, a heat-sensitive recording film was obtained.

Example 2 In Example 1, the thickness of the film was changed to B / A / B = 5/9.
A thermosensitive recording film was obtained in the same manner as in Example 1 except that the thickness was changed to 0/5 μm.

Comparative Example 1 The procedure of Example 1 was repeated except that 84% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 16% by weight of a master pellet containing fine particles (titanium oxide) were mixed and vacuum-dried as the raw material of the layer B. A recording film was obtained in the same manner as in Example 1.

Comparative Example 2 A recording film was obtained in the same manner as in Example 1 except that the thickness of the film was changed to 18/18.

Comparative Example 3 Vacuum dried 88% by weight of polyethylene terephthalate chips having an intrinsic viscosity of 0.62, 2% by weight of polyethylene glycol flakes having a molecular weight of 4000 and polymethylpentene pellets having a melt flow rate of 180 (TPX, manufactured by Mitsui Petrochemical Co., Ltd.) DX-820) 10 wt% was added and mixed to obtain a raw material for a film constituting the layer A. on the other hand,
In the same manner as in Example 1, a master pellet containing fine particles (calcium carbonate) containing 30% by weight of calcium carbonate particles (manufactured by Bihoku Powder Co., Ltd., Softon) having an average particle diameter of 1.2 μm (electron microscopic method) was prepared. This master pellet 45
% By weight and 55% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, followed by vacuum drying to obtain a raw material for a film constituting the B layer. The raw materials of the film constituting each layer were supplied to separate extruders, and the B layer was bonded to both sides of the A layer using a feed block. In the subsequent steps, the film was stretched 3.5 times at 98 ° C according to a conventional method.
The film was transversely stretched by 3.2 times at a temperature of 220 ° C. and then heat-treated at a temperature of 220 ° C. to obtain a void-containing polyester film. Otherwise, Example 1
In the same manner as in the above, a heat-sensitive recording film was obtained.

Comparative Example 3 As raw materials for the film constituting the layer A, 10% by weight of a master pellet containing fine particles (titanium oxide) subjected to vacuum drying, 83% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 subjected to vacuum drying, and a melt were used. Flow rate 1.
A recording film was obtained in the same manner as in Example 1 except that 7% by weight of a polystyrene resin (TOPOLEX 570-57U manufactured by Mitsui Toatsu Co., Ltd.) was mixed in a pellet.

Example 3 A thermosensitive method was performed in the same manner as in Example 1 except that zinc sulfide fine particles having an average particle diameter of 0.3 μm (electron microscopic method) were used as the fine particle-containing master pellets used in the layer B instead of the titanium oxide particles. A recording film was obtained. In addition, the same raw material as that of Example 1 was used for the material of the layer A.

Example 4 The discharge ratio of the A layer and the B layer was changed to 85 to 15 by volume,
Layer B1 (non-drum surface) / layer A / layer B2 (drum surface) in the same manner as in Example 1 except that the discharge amount of layer B is equally divided into two to form layer B on both sides of layer A. An unstretched sheet having the structure was prepared. The subsequent stretching and heat treatment steps were performed in exactly the same manner as in Example 1 to obtain a thermosensitive recording film.

Example 5 As raw materials for the layer B, 40% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, 50% by weight of master pellets containing fine particles (titanium oxide) used in Example 1, and master pellets containing a fluorescent brightener (Eastman OB in polyethylene terephthalate resin with intrinsic viscosity of 0.62
-1 (2% by weight) was mixed with pellets and vacuum-dried. Except for this, an unstretched film was prepared in exactly the same manner as in Example 1. The obtained unstretched sheet was uniformly heated to 83 ° C.
The speed is controlled (2 m / min) by sandwiching the film between a metal roll and a non-heated rubber roll whose temperature is controlled to ℃, and the speed is similarly controlled (6.8 m / min). Rubber roll temperature is not controlled)
Stretched 3.4 times. At this time, the two sets of rolls whose speeds were regulated were installed in parallel so that the interval between the speed regulation points was 25 cm, and they were arranged so that the B surface (non-drum surface) side was in contact with the rubber roll surface. In this example, the film was heated only by the roll heating without using the auxiliary heating device.
The uniaxially stretched film thus obtained is guided to a tenter, heated to 130 ° C., stretched 3.5 times in a transverse direction, fixed in width, subjected to a heat treatment at 220 ° C. for 5 seconds, and further heated at 220 ° C. in the width direction. A heat-sensitive recording film was obtained in the same manner as in Example 1 except that a polyester film containing cavities was relaxed by 4%.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

The present invention is an excellent heat-sensitive recording film having excellent surface smoothness and sufficient image density and resolution.

Continued on the front page F-term (reference) 2H111 AA26 AA27 CA03 CA25 CA30 4F100 AA11A AA21A AK01A AK07A AK08A AK12A AK41A AK41B BA02 BA44 DE01A DJ00A EH17 EJ37A GB90 JA13A JA20A JB16A JD14BJ00 JD14BJ00

Claims (8)

[Claims] 1. A void-containing polyester film containing a large number of voids therein, wherein the apparent specific gravity is 1.3 or less and the center line average surface roughness is 0.3 mm or less. A heat-sensitive recording layer provided on at least one side thereof, and having an average light moving distance of 0.15 mm or less. 2. The void-containing polyester film according to claim 1, which is derived from a microvoid-containing polyester layer (skin layer) comprising fine particles having an average particle size of 0.1 to 5 μm and a thermoplastic resin incompatible with polyester. A heat-sensitive recording film comprising a film (core layer) containing voids inside the film, which is laminated. 3. The heat-sensitive recording film according to claim 2, wherein the thickness of the skin layer of the void-containing polyester film is 1 to 20 μm and 3% or more and less than 30% of the total thickness of the film. 4. A heat-sensitive recording film, wherein the fine particles added to the skin layer according to claim 2 are titanium oxide. 5. A heat-sensitive recording film, wherein the fine particles added to the skin layer according to claim 2 are zinc sulfide. 6. A thermoplastic resin incompatible with polyester containing at least a polystyrene resin, a polymethylpentene resin and a polypropylene resin, wherein the polystyrene resin content (a weight%) and the polymethylpentene resin 6. The method according to claim 1, wherein the content of the resin (b weight%) and the content of the polypropylene resin (c weight%) satisfy the following relationship. Any thermal recording film. 0.01 ≦ a / (b + c) ≦ 1 c / b ≦ 13 3 ≦ a + b + c ≦ 20 7. A heat-sensitive recording film according to any one of claims 1 to 6, wherein the base material is a polyester-based film having at least one axis oriented therein and containing fine voids therein. 8. The heat-sensitive recording film according to claim 1, wherein the ink receiving layer contains at least a polyester resin.