JPH04278392A - Thermal recording receiving sheet base material - Google Patents

Abstract

PURPOSE:To also ensure good flexibility while easily obtaining high whiteness by using a polyester film wherein a surface air leakage index, heat conductivity and whiteness are respectively specific values in a thermal recording receiving sheet base material and setting the cushion factor thereof to a specific value. CONSTITUTION:A receiving sheet base material contains a polyester film wherein a surface air leakage index is 1000-30000sec or less, heat conductivity is (0.5X10<-4>)-(3X10<-4>)cal/cm.s. deg.C and whiteness is 70% or more and the cushion factor thereof is set to 10% or more. The polyester film contains fine air bubbles and the surface wetting tension thereof is 40dyn/cm or more and the apparent specific gravity thereof is 0.5-1.2. Further, the polyester film contains 2-25wt.% of polyolefin and is biaxially stretched.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving sheet substrate for heat-sensitive recording. More specifically, sheets whose surfaces are coated with heat-sensitive coloring dyes and then heat-sensitively colored by a heat-sensitive head, such as sheets for thermal paper, heat-sensitive labels, and cards that heat-sensitively display balances on the surface. It is related to the base material.

0002

2. Description of the Related Art A method of coating a substrate with a dye that develops color due to heat and performing recording using a head that generates heat is a well-known technique as disclosed in Japanese Patent Publication No. 45-14039. Paper is generally used as this base material, but films such as synthetic paper are also used.

0003

[Problems to be Solved by the Invention] However, when synthetic paper is used, it is sensitive to heat and curls occur due to local heating, making it impossible to raise the temperature of the head, resulting in poor color development. . In addition, polyester film is a heat-resistant film, but in order to make it white and opaque, it is necessary to add a large amount of pigment particles, which makes the film rigid. In addition, since the polyester film itself is relatively rigid, it has poor contact with the head and has the drawback of being susceptible to missing prints. Furthermore, since it has a higher thermal conductivity than paper, there is also the problem that heat escapes more easily, resulting in poor color development. Furthermore, when paper is used as the base material, the smoothness of the surface is not very good, so there is a problem that printing omissions are likely to occur.

[0004] In order to solve these problems, the present invention has a surface that is highly smooth and does not easily cause printing omissions, has a thermal conductivity within an appropriate range, is less likely to cause curling due to local heating, and prevents heat from escaping. The purpose of the present invention is to provide a receiving sheet base material for heat-sensitive recording which can prevent the coloring appropriately and sufficiently develop color, is highly flexible and can provide good contact with the head, and has sufficient whiteness. do.

[0005]

[Means for Solving the Problems] The heat-sensitive recording receiving sheet base material of the present invention which meets this purpose has a surface air leakage index of 1,000 to 30,000 seconds, and a thermal conductivity of 0.5× 10-4 or more 3 x 10-4 cal/cm・s
・Contains a polyester film with a whiteness of 70% or more at temperatures below 100°C and a cushioning ratio of 10% or more.

[0006] The polyester as used in the present invention is a polymer obtained by condensation polymerization from diol and dicarboxylic acid, and dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, Diols include ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, and the like. Specific examples include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, and polyethylene-2,6-naphthalenedicarboxylate. 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 copolymerization components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, and sebacic acid. , phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,
Examples include dicarboxylic acid components such as 5-sodium sulfoisophthalic acid.

[0008] Furthermore, various known additives such as antioxidants and antistatic agents may be added to the polyester. As the polyester used in the present invention, polyethylene terephthalate is preferable. Polyethylene terephthalate film is water resistant, durable,
It has excellent chemical resistance.

Conventionally, titanium oxide or the like has been added to whiten the above-mentioned polyester film, but as mentioned above, there is a problem in that the film becomes stiff (stiff), so it is difficult to obtain a film with high flexibility. things become difficult. In the present invention, whitening is achieved by containing fine air bubbles inside the film and scattering light with the air bubbles. As a result, as shown in the examples below, while obtaining high whiteness,
It achieves high flexibility (cushion ratio) that cannot be obtained with conventional films.

[0010] The formation of these fine bubbles is caused by the film base material,
For example, this can be achieved by finely dispersing an incompatible polymer with a high melting point in polyester and stretching it (for example, biaxial stretching). During stretching, voids (bubbles) are formed around the incompatible polymer particles, which scatter light, resulting in whitening and a high degree of whiteness. Incompatible polymers include poly-3-methylphthene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene,
Polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate,
It is a polymer with a melting point of 200°C or higher selected from polyvinyl fluoride, polychlorotrifluoroethylene, etc. Among these, polyolefins, particularly polymethylpentene, are preferred for polyester base materials.

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

In order to uniformly disperse incompatible polymers, it is effective to add a specific gravity lowering agent as a dispersion aid. A specific gravity lowering agent is a compound that has the effect of lowering the specific gravity, and only certain compounds have this effect. For example, for polyester, polyalkylene glycols such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, and polypropylene glycol, ethyleneoxide/propylenoxide copolymers, and even sodium dodecylbenzenesulfonate and alkylsulfonates are used. sodium salt,
Representative examples include glycerin monostearate and tetrabutylphosphonium para-aminobenzenesulfonate. In the case of the film of the present invention, polyalkylene glycols, especially polyethylene glycols, are particularly preferred. The amount added is preferably 0.1% by weight or more and 5% by weight or less. If it is too small, the effect of addition will be diminished, and if it is too large, the original properties of the film base material may be impaired. Such a specific gravity lowering agent can be added in advance to a film base polymer to prepare a master polymer (master chip).

As described above, since the white polyester film contains fine air bubbles, the apparent specific gravity of the polyester film is lower than that of a normal polyester film. If a specific gravity lowering agent is further added, the specific gravity will be further lowered. In other words, a white and light film can be obtained. In order to make this white polyester film lightweight while maintaining its mechanical properties as a heat-sensitive recording receptor sheet,
Apparent specific gravity is 0.5 or more and 1.2 or less, preferably 0.7
It is desirable that the value is 1.1 or less. The apparent specific gravity is
If it is less than 0.5, there are too many microbubbles and the strength of the film becomes too weak. On the other hand, if it is 1.2 or more, there are few microbubbles, the thermal conductivity does not decrease sufficiently, and the cushioning ratio is also low, making it impossible to perform high-quality printing.

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 layer A/layer B, or a three-layer structure of layer A/layer B/layer A. In this case, layer B is a layer containing microbubbles, and layer A is a polyester layer. With such a configuration, the B layer can obtain the target high whiteness and desired surface properties, while the A layer can maintain the desired mechanical properties (e.g., flexibility, strength) as a receiving sheet for heat-sensitive recording. be able to. Furthermore, when polyolefin is added to generate microbubbles, the wetting tension decreases, but the laminated structure as described above allows the wetting tension of at least one surface to be maintained at the same level as polyester.

As described above, in the base material of the present invention, the thermal conductivity is reduced and the cushioning ratio is increased by containing microbubbles inside the film. In addition, whitening is caused by microbubbles, regardless of the addition of pigments, so
There is no absorption of light by pigments, and high whiteness can be obtained.

The whiteness was determined to be 7 by the measuring method described below.
0% or more. Preferably it is 75% or more. When the whiteness is less than 70%, the contrast with the colored image is poor and a high-quality image cannot be obtained.

[0017] Furthermore, the cushioning ratio of the base material is 10% or more,
Preferably, it is necessary to set it to 15% or more. If the cushioning ratio is less than 10%, the head will hit hard,
Missing dots may occur.

Further, in the heat-sensitive recording receiving sheet of the present invention, the air wettability index of the surface of the white polyester film must be from 1,000 to 30,000 seconds, preferably from 5,000 to 28,000 seconds. Air wetness index is 10
If it is less than 0.00 seconds, the surface will be rough and dots will likely be missing in the print. In addition, color development is also poor because of poor adhesion to the head and insufficient heat transfer. In the case of 30,000 seconds or more, slippage becomes poor, handling properties such as winding are poor, and runnability in a printer is poor.

Furthermore, in the heat-sensitive recording receiving sheet of the present invention, the white polyester film has a thermal conductivity of 0.5.
x10-4 to 3 x 10-4 cal/cm・s・℃, preferably 0.8 x 10-4 to 2
x10-4 cal/cm・s・℃. When the thermal conductivity is 0.5×10 −4 cal/cm·s·°C or less, heat does not escape, so local heating occurs on only one side, causing curling and one-sided elongation. 3×10-4 cal/cm・
If the temperature is higher than s.degree. C., sufficient color development cannot be obtained because too much heat escapes.

Furthermore, in the heat-sensitive recording receiving sheet of the present invention, it is preferable that the wetting tension of the surface of the white polyester film is 40 dyn/cm or more. When the wetting tension is less than 40 dyn/cm, repellency is likely to occur during application of the heat-sensitive dye, and adhesion after application is also poor.

Next, a method for manufacturing the white polyester film used in the heat-sensitive recording receiving sheet of the present invention will be explained, but the method is not limited to this example. Polymethylpentene as an incompatible polymer and polyethylene glycol as a specific gravity lowering agent are mixed with polyethylene terephthalate, and the mixture is sufficiently mixed and dried to obtain 270-3
It is fed to extruder B heated to a temperature of 00°C. If necessary, polyethylene terephthalate containing inorganic additives such as CaCO3 is fed to extruder A in a conventional manner, and the polymer in layer A of the extruder is transferred to one side or one side of layer B in the T-die two-layer or three-layer nozzle. A/B or A/B/A on both surfaces
It may be laminated into two or three layers having the following structure. Here, in order to set the air leakage index on the surface of the base material to 1,000 to 30,000 seconds, it is preferable to make the dispersion diameter of the incompatible polymer small. As mentioned above, it is also preferable to have an A/B or A/B/A laminated structure consisting of the polyester layer A and the microbubble-containing layer B. If the dispersion diameter of the incompatible polymer is large, it is not preferable because the undulations will appear up to the surface of the A layer. In order to make the dispersion diameter of the incompatible polymer fine, it is preferable to apply high shear force within the extruder. The shear stress in the extruder is 105 dyn/cm2
, preferably 106 dyn/cm2 or more. To do this, extrude by increasing the rotational speed of the screw as high as possible. Further, it is preferable to use a method such as extrusion using a twin-screw extruder. It is also effective to attach a mixer to the tip of the extruder.

This molten sheet is cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 to 60°C, and the unstretched film is guided to a group of rolls heated to 80 to 120°C, and the longitudinal 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 ratio, it is preferable to have a structure containing microbubbles inside the film, and for this purpose, it is preferable to perform longitudinal stretching at the lowest possible temperature. It is preferable to carry out longitudinal stretching in the range of glass transition point +5°C to glass transition point +25°C. It is also preferable to longitudinally stretch the film by 1.2 to 2 times, then cool it once to below the glass transition point, and then heat it again and stretch it by 2 to 4 times, giving a total magnification of 2 to 5 times. . By doing this, the generation of fine bubbles is promoted,
This is preferable in order to obtain the desired thermal conductivity and cushioning rate. Furthermore, it is also preferable to perform a heat treatment before the transverse stretching and then perform the transverse stretching to achieve the object. Subsequently, the longitudinally stretched film is held at both ends with clips and introduced into a tenter, where it is laterally 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 both vertically and horizontally, and the area ratio (longitudinal stretching ratio x
The transverse stretching ratio) is preferably 6 to 20 times. If the area magnification is less than 6 times, the resulting film will have poor whiteness, while if it exceeds 20 times, it will tend to tear easily during stretching and the film formability will tend to be poor. In order to impart flatness and dimensional stability to the biaxially stretched film, it is heat-set at 150 to 230°C in a tenter, uniformly cooled slowly, and then cooled to room temperature and wound to obtain the film of the present invention. .

[Method for Measuring Physical Properties and Evaluating Effects] The methods for evaluating physical property values and evaluating effects of the present invention are as follows.

(1) Air Leakage Index Measured using an Oken type smoothness meter KT-5 (manufactured by Asahi Seiko Co., Ltd.).

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

(3) Whiteness Measure the color tristimulus values X, Y, and Z using a color difference meter ND-K68 (manufactured by Nippon Denshoku Kogyo Co., Ltd.). Whiteness (%) = 4 x (0.847 x It was determined as Z)-3×Y.

(4) A standard measuring tip (No.
．． 900030) and place it on the dial gauge stand (No. 7001DGS-M). If the thickness of each film is d50 and d500 when a load of 50g and 500g is applied to the dial gauge holding part, cushioning ratio (%) = (d50-d500)/d5
Set to 0.

(5) Wetting tension Measured according to JIS K-6768.

(6) Dye Adhesion After coating and drying a known heat-sensitive dye, a cellophane tape peeling test was conducted. ○: No abnormality in the coating film. Δ: Part of the coating film peels off. ×: The coating film peels off entirely.

(7) Printability After coating and drying a known heat-sensitive dye, printing was performed by sandwiching it between a thermal head and a platen at a pressure of about 4 kg/cm 2 . ○: Can print without any problems. Δ: Some dots are missing and the color density is decreased. ×: Missing dots and a large decrease in color density.

(8) Cut the apparent specific gravity film into a 100 x 100 mm square, and place it on a dial gauge (No. 2109-10 manufactured by Mitoyo Seisakusho) with a diameter of 10 mm.
The thickness is measured at a minimum of 10 points using a measuring element (No. 7002) of mm, and the average value d (μm) of the thickness is calculated. In addition, this film was weighed using a direct reading balance,
Read the weight w (g) to the nearest 10-4 g. At this time, apparent specific gravity = w/d x 100.

[0032]

EXAMPLES The present invention will be explained based on examples. Example 1 Using two extruders, polyethylene terephthalate chips and a master chip to which polyethylene glycol with a molecular weight of 4000 was added during polymerization of polyethylene terephthalate were vacuum-dried at 180°C for 3 hours, and then
89% by weight of polyethylene terephthalate, 1% by weight of polyethylene glycol, and 10% by weight of polymethylpentene were mixed and supplied to extruder 1 heated to 270 to 300°C. Further, polyethylene terephthalate chips to which 14% by weight of calcium carbonate particles ("Softon 3200" manufactured by Shiraishi Calcium) were added were vacuum dried as described above and then supplied to the extruder 2. Extruder 1, extruder 2
Extruder 1 is the inner layer, extruder 2 is the inner layer, and extruder 2 is the inner layer.
Coextrusion was performed to form a three-layer structure with the outer layer being formed into a sheet using a T-die. Further, this film was cooled and solidified in a cooling drum with a surface temperature of 25°C, and an unstretched film was obtained at 85 to 98°C.
The film was introduced into a group of rolls heated to 25° C., longitudinally stretched 3.6 times in the longitudinal direction, and cooled with a group of rolls heated at 25° C. to 50° C. Subsequently, the longitudinally stretched film was introduced into a tenter while holding both ends with clips, and was laterally stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130°C. After that, 23 in the tenter
The film was heat-set at 0° C., cooled uniformly, and then cooled to room temperature to obtain a film having a thickness of 100 μm. The laminated structure 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, only the polyethylene terephthalate chips were extruded from the extruder 2, and a film with a thickness of 100 μm was obtained in the same manner as in Example 2. The laminated structure 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, only extruder 1 was used to obtain a single film of the same raw material as that supplied to extruder 1. The physical properties of the obtained film are shown in Table 1.

Comparative Example 2 A master chip made of polyethylene terephthalate compounded with titanium dioxide particles and a polyethylene terephthalate chip were vacuum-dried at 180°C for 3 hours.
The titanium dioxide particles were mixed in an amount of 14% by weight, and a film with 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” manufactured by Shiraishi Calcium)
Chips of polyethylene terephthalate to which 14 wt. The physical properties of the obtained film are shown in Table 1.

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

[0038]

[Table 1]

[0039]

[Effects of the Invention] When using the receiving sheet for heat-sensitive recording of the present invention, a high degree of whiteness can be easily obtained, and even with a high degree of whiteness, the thermal conductivity is within the optimum range, so inconveniences such as curling can be prevented. Together with this, sufficient color development can be achieved. In addition, because the surface is smooth, printing is less likely to occur, and since there is no need to add pigments to obtain whiteness, it is highly flexible, hits the head well, and prints do not easily come off from this surface. In addition to preventing this, handling and running properties can be improved. Therefore, it is not possible to obtain with conventional synthetic paper.
A receiving sheet for heat-sensitive recording that is resistant to heat and exhibits good color development can be obtained, and a receiving sheet for heat-sensitive recording that has high whiteness and rich flexibility compared to conventional pigment-added films can be obtained.

Claims (8)

[Claims] [Claim 1] The base material has a surface air leakage index of 100.
0 or more and 30,000 seconds or less, and the thermal conductivity is 0.5×1
0-4 or more and 3 x 10-4 cal/cm・s・℃ or less,
A receiving sheet base material for heat-sensitive recording, comprising a polyester film having a whiteness of 70% or more and a cushioning ratio of 10% or more. 2. The receiving sheet substrate for heat-sensitive recording according to claim 1, wherein the polyester film contains fine air bubbles inside the film. 3. The receiving sheet substrate for heat-sensitive recording according to claim 1, wherein the surface wetting tension of the polyester film is 40 dyn/cm or more. 4. The polyester film has a layer A/
4. The method according to claim 2 or 3, wherein the layer has a two-layer structure of layer B or a three-layer structure of layer A/layer B/layer A, wherein the layer B is the fine bubble-containing layer and the layer A is a polyester layer. Receptive sheet base material for heat-sensitive recording. 5. The receiving sheet substrate for heat-sensitive recording according to claim 1, wherein the polyester film has an apparent specific gravity of 0.5 or more and 1.2 or less. 6. The receiving sheet substrate for heat-sensitive recording according to claim 1, wherein the polyester film contains polyester containing 2% by weight or more and 25% by weight or less of polyolefin and is biaxially stretched. 7. The receiving sheet substrate for heat-sensitive recording according to claim 6, wherein the polyolefin is polymethylpentene. 8. The receiving sheet substrate for heat-sensitive recording according to claim 6 or 7, wherein the polyester contains 0.1% by weight or more and 5% by weight or less of polyalkylene glycol and its derivatives.