JP2674342B2 - Receptive sheet base material for thermal recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a receiving sheet base material for thermal recording. More specifically, a sheet on which heat-sensitive coloring is performed by a heat-sensitive head by applying a heat-sensitive coloring dye to the surface, that is, a sheet for heat-sensitive paper, a heat-sensitive label, a card for heat-sensitively displaying balance, etc. on the surface. It relates to a substrate.

[0002]

2. Description of the Related Art A technique of applying a dye that develops color to heat on a substrate and recording with a head that generates heat is a technique known from JP-B-45-14039. Paper is generally used as the base material,
Films such as synthetic paper are also used.

[0003]

However, when synthetic paper is used, there is a problem in that the temperature of the head cannot be raised and the coloring is poor because it is weak against heat and curls due to local heating or the like. . Further, there is a polyester film as a heat resistant film, but it is necessary to add a large amount of pigment particles in order to make it white and opaque, and the film becomes rigid. Further, since the polyester film itself is relatively rigid, it has a drawback in that it does not hit the head easily and print defects easily occur. Further, since the thermal conductivity is higher than that of paper, there is a problem that heat easily escapes and color development is deteriorated. Furthermore, when paper is used as the base material, the smoothness of the surface is not so good, and there is a problem in that print omission easily occurs.

In order to solve such a problem, the present invention has a high surface smoothness, is less likely to cause print omission, has a thermal conductivity in an appropriate range, is less likely to cause curling due to local heating, and escapes heat. An object of the present invention is to provide a heat-sensitive receiving sheet base material for heat-sensitive recording, which is capable of appropriately preventing and sufficiently developing color, and which is rich in flexibility and can obtain good contact with a head, and has sufficient whiteness. To do.

[0005]

The heat-sensitive recording receiving sheet base material of the present invention for this purpose has an air leakage index of 1000 to 30,000 seconds on the surface of the base material, and a thermal conductivity of 0.5 ×. Includes a polyester film of 10 ^-4 or more and 3 × 10 ^-4 cal / cm · s · ° C. or less, whiteness of 70% or more , surface wetting tension of 40 dyn / cm or more , and a cushion ratio of 10
Consist of those that are greater than or equal to%.

The polyester referred to in the present invention is a polymer obtained by polycondensation of a diol and a dicarboxylic acid, and examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, And the diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specific examples thereof include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalene dicarboxylate. In the case of the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferred.

Of course, these polyesters may be homopolyesters or copolyesters, and examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol, adipic acid and sebacic acid. And dicarboxylic acid components such as phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid.

Further, various known additives such as antioxidants and antistatic agents may be added to the polyester. Polyethylene terephthalate is preferred as the polyester used in the present invention. Polyethylene terephthalate film is water resistant, durable,
It has excellent chemical resistance.

In order to whiten the above polyester film, titanium oxide or the like has been conventionally added. However, there is a problem that the film becomes rigid (rough) as described above, and a film having high flexibility is obtained. Becomes difficult.
In the present invention, fine bubbles are contained inside the film, and light is scattered by the bubbles to achieve whitening. With this, as shown in the examples described later, while obtaining high whiteness,
A high degree of flexibility (cushion rate), which cannot be obtained with conventional films, is achieved.

The formation of the fine bubbles is caused by the film base material,
For example, it is achieved by finely dispersing an incompatible polymer having a high melting point in polyester and stretching it (for example, biaxial stretching). During stretching, voids (air bubbles) are formed around the incompatible polymer particles, and this exerts a scattering effect on light, so that whitening occurs and high whiteness can be obtained. Incompatible polymer means polymethylpentene
Emissions, polyvinyl -t- butane, 1,4-trans - poly-2,3-dimethyl-butadiene, polyvinyl cyclohexane, polystyrene, polymethyl styrene, poly dimethylstyrene, poly-fluorostyrene, poly-2-methyl-4-fluorostyrene , Cellulose triacetate,
It is a polymer having a melting point of 200 ° C. or higher selected from cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene and the like. Among them, polyolefin, particularly polymethylpentene, is preferable for the polyester base material.

The amount of the incompatible polymer (for example, polyolefin) added is preferably 2% by weight or more and 25% by weight or less. If the amount is less than this, the effect of whitening will fade,
If the whiteness is too high, the mechanical properties such as strength of the film itself may be too low. It is preferable that the incompatible polymer is uniformly dispersed. Due to the uniform dispersion, bubbles are uniformly formed inside the film,
The degree of whitening becomes uniform.

In order to uniformly disperse the incompatible polymer, it is effective to add a low specific gravity agent as a dispersion aid.
The low specific gravity agent is a compound having an effect of reducing the specific gravity, and only the specific compound has the effect.
For example, for polyester, polyalkylene glycols such as polyethylene glycol, methoxy polyethylene glycol, polytetramethylene glycol, and polypropylene glycol, ethylenoxide / propylenoxide copolymers, and further sodium dodecylbenzenesulfonate and alkylsulfonates. Sodium salt,
Typical examples are glycerin monostearate and tetrabutylphosphonium paraaminobenzene sulfonate. In the case of the film of the present invention, polyalkylene glycol is preferable, and polyethylene glycol is particularly preferable. The addition amount is preferably from 0.1% by weight to 5% by weight. If it is too small, the effect of the addition will be weakened, and if it is too large, the original properties of the film base material may be impaired. Such a low specific gravity agent can be prepared as a master polymer (master chip) by previously adding it to the film base polymer.

As described above, since the white polyester film contains fine bubbles, the apparent specific gravity of the polyester film becomes lower than that of a normal polyester film. If a specific gravity lowering agent is further added, the specific gravity becomes lower. That is, a white and light film is obtained.
In order to reduce the weight of this white polyester film while maintaining the mechanical properties as a heat-sensitive recording receiving sheet,
Apparent specific gravity is 0.5 or more and 1.2 or less, preferably 0.7
It is desirable that it is 1.1 or less. Apparent specific gravity
If it is 0.5 or less, the amount of fine bubbles is too large and the strength of the film becomes too weak. On the other hand, when it is 1.2 or more, the number of fine bubbles is small, the thermal conductivity is not sufficiently lowered, and the cushion rate is low, so that high-quality printing cannot be performed.

The heat-sensitive recording receiving sheet of the present invention may have a laminated film structure. For example, it has a two-layer structure of A layer / B layer or a three-layer structure of A layer / B layer / A layer. In this case, the layer B is a layer containing fine bubbles and the layer A is a polyester layer. With such a structure, the B layer can obtain the target high whiteness and desired surface characteristics, while the A layer can maintain the desired mechanical properties (for example, flexibility and strength) as a heat-sensitive recording receiving sheet. be able to. When a polyolefin is added to generate fine bubbles, the wetting tension is lowered, but the wetting tension of at least one surface can be kept equal to that of polyester by the above-mentioned laminated structure.

As described above, in the base material of the present invention, the thermal conductivity is reduced and the cushion rate is increased by containing fine bubbles inside the film. In addition, because it is whitened by fine bubbles, regardless of pigment addition,
High whiteness can be obtained without light absorption by the pigment.

The whiteness is 7 according to the measuring method described later.
0% or more. It is preferably at least 75%. When the whiteness is less than 70%, the contrast with the colored image is poor and a high quality image cannot be obtained.

The cushion ratio of the base material is 10% or more,
It is necessary to set it to preferably 15% or more. When the cushion rate is less than 10%, the head is hard to hit,
Dot omission may occur.

In the heat-sensitive recording receiving sheet of the present invention, the air wetting index on the surface of the white polyester film needs to be 1,000 to 30,000 seconds, preferably 5,000 to 28,000 seconds. Air wetting index is 10
When the time is 00 seconds or less, the surface is rough and dot omission of printing is likely to occur. In addition, the adhesion to the head is poor and sufficient heat is not transferred, resulting in poor color development. When it is 30,000 seconds or more, slipping becomes poor, handleability such as winding is poor, and running property in the printer is poor.

Further, in the heat-sensitive recording receiving sheet of the present invention, the white polyester film has a thermal conductivity of 0.5.
It is necessary that the temperature is × 10 ^{-4 to} 3 × 10 ^-4 cal / cm · s · ° C, preferably 0.8 × 10 ^-4 to 2 × 10 ^-4 cal / cm.
・ S ・ ℃. Thermal conductivity is 0.5 × 10 ^-4 cal / cm ・
s ・ If the temperature is below ℃, heat will not escape, and only one side will be locally heated, causing curling and stretching. 3 x 10 ^-4
If the temperature is above cal / cm ・ s ・ ℃, the heat will escape too much.
Sufficient coloring cannot be obtained.

Further, in the heat-sensitive recording receiving sheet of the present invention, the wetting tension of the surface of the white polyester film must be 40 dyn / cm or more . If the wetting tension is less than 40 dyn / cm, cissing is likely to occur when the thermal dye is applied, and the adhesion after application is poor.

Next, the method for producing the white polyester film used in the heat-sensitive recording receiving sheet of the present invention will be described, but the present invention is not limited to such an example. Polymethylpentene as an incompatible polymer and polyethylene glycol as a low-density agent are mixed with polyethylene terephthalate, and they are thoroughly mixed and dried to give 270-3.
Feed to extruder B heated to a temperature of 00 ° C. If necessary, polyethylene terephthalate containing an inorganic additive such as CaCO ₃ is supplied to the extruder A by a conventional method, and the polymer of the extruder A layer is in one side of the B layer in the T die 2 layer or 3 layer die. Or, A / B or A / B / A that comes to both surface layers
You may laminate to 2 layers or 3 layers of the structure which becomes. Here, in order to set the air leakage index on the surface of the base material to 1000 to 30,000 seconds, it is preferable to make the dispersion diameter of the incompatible polymer fine. As described above, it is also preferable to have a laminated structure of A / B or A / B / A consisting of the polyester layer A and the fine bubble-containing layer B. However, even with such a laminated structure, the fine bubble-containing layer B When the dispersed diameter of the incompatible polymer is large, the waviness appears even on the surface of the A layer, which is not preferable. In order to make the dispersed diameter of the incompatible polymer fine, it is preferable to apply a high shearing force in the extruder. The shear stress in the extruder is preferably 10 ⁵ dyn / cm ² , and more preferably 10 ⁶ dyn / cm ² or more. For that purpose, the screw is pushed out with the rotation speed as high as possible. Further, it is preferable to employ a method such as extrusion using a twin-screw extruder. It is also effective to attach a mixer or the like to the tip of this extruder.

This melted sheet is adhered to the drum cooled at a drum surface temperature of 10 to 60 ° C. by electrostatic force to be cooled and solidified, and the unstretched film is guided to a roll group heated at 80 to 120 ° C. The film is longitudinally stretched 2.0 to 5.0 times in the direction and cooled with a roll group at 20 to 50 ° C. At this time, in order to obtain the desired thermal conductivity and cushioning rate, it is preferable to have a structure containing fine bubbles inside the film, for which purpose it is preferable to carry out longitudinal stretching at a temperature as low as possible. It is preferable to perform longitudinal stretching in the range of glass transition point + 5 ° C to glass transition point + 25 ° C. Further, it is also preferable to carry out longitudinal stretching of 1.2 to 2 times, then once to cool to below the glass transition point, then heat again and stretch 2 to 4 times, so that the total draw ratio is 2 to 5 times. . By doing so, the generation of fine bubbles is promoted, which is preferable in obtaining the desired thermal conductivity and cushioning rate. Further, it is also preferable to achieve the object by performing a heat treatment before the transverse stretching and then performing the transverse stretching. Then, the both ends of the longitudinally stretched film are guided to a tenter while holding both ends of the film with clips, and transversely stretched in a direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C. The stretching ratio is 2 to 5 times in each of the length and width, and the area ratio (longitudinal stretching ratio × horizontal stretching ratio) is preferably 6 to 20 times. If the area ratio is less than 6 times, the whiteness of the obtained film will be poor, and if it exceeds 20 times, tearing will tend to occur during stretching and the film-forming property will tend to be poor. In order to impart flatness and dimensional stability to the biaxially stretched film, heat setting is performed at 150 to 230 ° C. in a tenter, and after uniform slow cooling, it is cooled to room temperature to obtain the film of the present invention. .

[Measurement of Physical Properties and Evaluation Method of Effects] The evaluation method of physical properties and the evaluation method of effects of the present invention are as follows.

(1) Air Leakage Index The air leak index was measured using a Woken type smoothness meter KT-5 (manufactured by Asahi Seiko Co., Ltd.).

(2) Thermal conductivity The thermal conductivity was measured using a thermal conductivity measuring device TXP-400 (manufactured by Miki Engineering Co., Ltd.).

(3) Whiteness The color tristimulus values X, Y and Z were measured with a color difference meter ND-K68 (manufactured by Nippon Denshoku Industries Co., Ltd.), and whiteness (%) = 4 × (0.847 ×). Z) -3 × Y.

(4) Cushion rate A standard gauge (N
o. 900030) and set it on a dial gauge stand (No. 7001 DGS-M). When each thickness of the film when a load of 50g and 500g in the dial gauge holding part and d _50, d _500, cushion factor (%) = a _{(d 50 -d 500) / d} 50.

(5) Wetting tension It was measured according to JIS K-6768.

(6) Dye Adhesion Property A known heat-sensitive dye was applied and dried, and then a cellophane tape peeling test was conducted. ○: There is no abnormality in the coating film. Δ: Part of the coating film peels off. X: The coating film peels off as a whole.

(7) Printability After printing a known heat-sensitive dye and drying, printing was carried out by sandwiching it between a thermal head and a platen at a pressure of about 4 kg / cm ² . ◯: Printing is possible without abnormality. Δ: Some dots are missing and the color density is reduced. X: Dot missing and large decrease in color density.

(8) Apparent specific gravity The film is cut into 100 × 100 mm squares, and a dial gauge (No. 2109-10 manufactured by Mitoyo Seisakusho) has a diameter of 10 mm.
The thickness of at least 10 points is measured with the one with the stylus (No. 7002) attached, and the average value d (μm) of thickness is calculated. In addition, this film is weighed with a direct balance and the weight w (g) is read up to the unit of 10 ⁻⁴ g. At this time, apparent specific gravity = w / d × 100.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments. Example 1 Using two extruders, polyethylene terephthalate chips and a master chip to which polyethylene glycol having a molecular weight of 4000 was added at the time of polymerization of polyethylene terephthalate were vacuum dried at 180 ° C. for 3 hours, and then,
Polyethylene terephthalate (89% by weight), polyethylene glycol (1% by weight) and polymethylpentene (10% by weight) were mixed and supplied to the extruder 1 heated to 270 to 300 ° C. Further, a polyethylene terephthalate chip containing 14% by weight of calcium carbonate particles ("Softon 3200" manufactured by Shiraishi Calcium) was vacuum-dried as described above and then fed to the extruder 2. Extruder 1, Extruder 2
The raw materials are extruded from the respective extruders, and the extruder 1 is the inner layer and the extruder 2 is
Was coextruded into a three-layer structure having an outer layer and was formed into a sheet from a T die. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. is 85 to 98 ° C.
The film was guided to a roll group that was heated to 3, longitudinally stretched 3.6 times in the longitudinal direction, and cooled by a roll group at 25 ° C to 50 ° C. Then, the both ends of the longitudinally stretched film were introduced into a tenter while holding both ends of the film with clips, and laterally stretched 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. Then in the tenter 23
After heat fixing at 0 ° C. and uniform cooling, the film was cooled to room temperature to obtain a film having a winding thickness of 100 μm. The laminated constitution of the obtained film was 7/86/7 μm. The physical properties of the obtained film are shown in Table 1.

Example 2 In Example 1, a polyethylene terephthalate chip alone was extruded from the extruder 2 to obtain a film having a thickness of 100 μm in the same manner as in Example 2. The laminated constitution of the obtained film was 7/86/7 μm. The physical properties of the obtained film are shown in Table 1.

Comparative Example 1 In Example 1, a single film of the same raw material as that supplied to the extruder 1 was obtained by using only the extruder 1. The physical properties of the obtained film are shown in Table 1.

Comparative Example 2 A master chip obtained by compounding polyethylene terephthalate with titanium dioxide particles and a polyethylene terephthalate chip were vacuum dried at 180 ° C. for 3 hours, and then,
The titanium dioxide particles were mixed in an amount of 14% by weight, and a film having a thickness of 100 μm was obtained in the same manner as in Example 1. The physical properties of the obtained film are shown in Table 1.

Comparative Example 3 Calcium carbonate particles (“Softon 32 made by Shiraishi Calcium”
A polyethylene terephthalate chip containing 14% by weight of "00" average particle diameter 1 μm) was vacuum dried at 180 ° C. for 3 hours and then extruded from an extruder to obtain a film having a thickness of 100 μm in the same manner as in Example 1. The physical properties of the obtained film are shown in Table 1.

Comparative Example 4 A film having a thickness of 100 μm was obtained in the same manner as in Comparative Example 2 using “Softon 1800” having an average particle size of 4 μm made by Shiraishi Calcium as the calcium carbonate particles. The physical properties of the obtained film are shown in Table 1.

[0038]

[Table 1]

[0039]

With the heat-sensitive recording receiving sheet of the present invention, a high whiteness can be easily obtained, and even if the whiteness is high, the thermal conductivity is in the optimum range, so that problems such as curling can be prevented. Along with that, it is possible to sufficiently develop the color. In addition, the smoothness of the surface makes it difficult for print defects to occur, and since it does not require the addition of pigments to obtain whiteness, it is highly flexible and can easily hit the head. Can be prevented and handling and running can be improved. Therefore, it cannot be obtained with conventional synthetic paper,
A heat-sensitive receiving sheet for heat-sensitive recording which is resistant to heat and excellent in color development is obtained, and a heat-sensitive receiving sheet for heat-sensitive recording is obtained which has high whiteness and is more flexible than the conventional pigment-added film.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location // B29C 47/06 B41M 5/18 H (C08L 67/02 23:20) B29K 67:00 105: 04 B29L 7:00 9:00 C08L 67:02

Claims (7)

(57) [Claims] 1. The substrate has a surface air leakage index of 1000.
The above is 30,000 seconds or less, and the thermal conductivity is 0.5 × 10.
^-4 or more and 3 × 10 ^-4 cal / cm · s · ° C or less, whiteness 70%
As described above , a receiving sheet base material for heat-sensitive recording comprising a polyester film having a surface wetting tension of 40 dyn / cm or more and having a cushion rate of 10% or more. 2. The receiving sheet base material for heat-sensitive recording according to claim 1, wherein the polyester film contains fine air bubbles inside the film. 3. The polyester film comprises A layer / B
From a 2-layer structure of layers, or a 3-layer structure of A layer / B layer / A layer
And the B layer is the fine bubble-containing layer, and the A layer is
The heat-sensitive recording receiving sheet according to claim 2, which is a polyester layer.
Base material. 4. The apparent specific gravity of the polyester film
Is 0.5 or more and 1.2 or less.
The receiving sheet base material for heat-sensitive recording described therein. 5. The polyester film is polyester.
Includes 2 wt% or more and 25 wt% or less of polyolefin in tell
Any of claims 1 to 4, wherein the biaxial stretching is carried out.
The receiving sheet base material for heat-sensitive recording as described in (1). 6. The polyolefin is polymethylpente
6. The heat-sensitive recording receiving sheet base material according to claim 5. 7. A polyalkylene glycol as the polyester
Content of 0.1% by weight or more and 5% by weight or less
The receiving sheet base for heat-sensitive recording according to claim 5 or 6,
Wood.