JPH06135173A - Film for highly sensitive thermal printing stencil paper - Google Patents

Abstract

PURPOSE:To provide a film for highly sensitive thermal printing stencil paper which is excellent in perforation sensitivity and printing resolution. CONSTITUTION:In a biaxially oriented film of 0.5-4.0mum thickness consisting of a polyester copolymer wherein 50-80mol% of acid component is terephthalic acid, its 20-50mol% is isophthalic acid, and at least 40mol% of glycol component is 1,4-butanediol, a melting point of the film is 140-190 deg.C, the maximum value of heating contraction stress within a range of 60-140 deg.C exceeds 500g/mm<2>, and a thermal contraction coefficient at 100 deg.C is at least 20%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film for heat-sensitive stencil printing base paper. More specifically, the present invention relates to a film for high-sensitivity heat-sensitive stencil printing base paper, which has excellent perforation sensitivity and has excellent image resolution and density during printing.

[0002]

2. Description of the Related Art Conventionally, as a base paper for heat-sensitive stencil printing, a laminate of porous thin paper on a thermoplastic resin film such as polyester has been known, and a film used for such application. Is required to have the following characteristics. (1) The thermal perforation sensitivity is good. That is, it must have a sufficient heat shrinkage ratio that it can be melted with a small amount of heat and that a perforation of an appropriate size can be obtained so that an image at the time of printing becomes clear. (2) It should have strength and elastic modulus sufficient to withstand the work of laminating with porous thin paper and printing. Also, in such work, even if there is a heating step, the problem such as a remarkable curl of the base paper does not occur due to the influence of the heating step. (3) The gradation of thermal perforation is good. When used as a base paper, if the portion other than the portion to be perforated is melted due to the influence of the perforations in the periphery, the gradation of the printed image becomes inferior, which is not preferable. That is, it should have a thermal perforation property that allows a clear distinction between the perforated portion and the non-perforated portion.

In addition to these requirements, it is also required to have excellent handleability and productivity during film production and base paper production. Specifically, at the time of film production, the stretchability is good, troubles such as breakage do not occur, and the winding property and slitting property are also good, and wrinkles may occur during winding.
It is necessary not to cause winding deviation. Even when the base paper is prepared, it is necessary that the problems such as the unwinding of the film and the running of the film in the process do not occur.

Conventionally, a biaxially stretched film intended for a thermoplastic resin as a film used for such an application,
A film having improved printing characteristics by defining its thermal characteristics (Japanese Patent Laid-Open No. Sho 62-149496), a film having surface roughness and the number of protrusions (Japanese Patent Laid-Open No. Sho 63-2).
No. 27634), or a film having a specified heat shrinkage property (JP-A-62-282983, JP-A-63).
-160895, Japanese Patent Application Laid-Open No. 63-321192, Japanese Patent Application Laid-Open No. 3-30996) and the like have been proposed, but all of the above problems cannot be solved.

[0005]

The inventors of the present invention have made earnest studies in view of the above problems, and as a result, they are composed of a polyester having a specific composition, and the melting point, the heat shrinkage ratio, and the heat shrinkage stress satisfy the specific conditions. The inventors have found that an axially oriented film is suitable for use as a heat sensitive stencil printing base paper, and have completed the present invention.

That is, the gist of the present invention is that the acid component is 50 to 50%.
Biaxially oriented with a thickness of 0.5 to 4.0 μm, comprising a polyester copolymer in which 80 mol% is terephthalic acid, 20 to 50 mol% is isophthalic acid, and 40 mol% or more of the glycol component is 1,4-butanediol. A film having a melting point of 140 to 190 ° C. and a temperature of 60 to 140 ° C.
In the above range, the maximum value of the heat shrinkage stress exceeds 500 g / mm ² , and the heat shrinkage rate at 100 ° C. is 20% or more.

The present invention will be described in detail below. The polyester referred to in the present invention refers to a polyester composed of the above-mentioned dicarboxylic acid component and glycol component, but may be a copolymer containing other components. Examples of such copolymerizable components include dicarboxylic acids such as phthalic acid, 2,6-naphthalenedicarboxylic acid, sebacic acid and adipic acid, ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4
-Glycol components such as cyclohexanedimethanol,
And oxycarboxylic acids such as p-hydroxybenzoic acid.

As a method for obtaining such polyester,
A method in which a predetermined amount of a dicarboxylic acid component and a glycol component are charged at the time of polymerization and a desired polyester is obtained by copolymerization, or two or more kinds of copolymerized polyesters having different component ratios are blended and melt-kneaded to obtain a predetermined component amount. The method of adjusting so that it may become. When the terephthalic acid constituting the polyester used in the present invention is less than 50 mol% or the isophthalic acid exceeds 50 mol% in all the acid components, the shrinkage stress is insufficient and a perforation of a sufficient size is not formed. It cannot be obtained, and the density during printing is reduced. On the other hand, when the content of terephthalic acid exceeds 80 mol%, the melting point does not become sufficiently low, so that the perforation sensitivity decreases. When isophthalic acid is less than 20 mol%, the shrinkage stress is insufficient because the content of dicarboxylic acid components other than terephthalic acid and isophthalic acid is increased in order to reach a predetermined melting point, and
Isophthalic acid, which causes problems such as high film cost, is preferably 25 mol% or more based on all acid components.

On the other hand, when the content of 1,4-butanediol constituting the polyester used in the present invention is less than 40 mol% in the total glycol component, the crystallinity of the polymer is lowered and an appropriate shrinkage stress cannot be obtained. The melting point of the film of the present invention needs to be 140 to 190 ° C, preferably 140 to 180 ° C, more preferably 150 to 175.
It is in the range of ° C. When the melting point is higher than 190 ° C, the high level of perforation sensitivity, which is the object of the present invention, cannot be obtained.
If the temperature is lower than 40 ° C., the heat-resistant dimensional stability of the film deteriorates, curling occurs during the process of manufacturing the base paper or during storage of the base paper, and the gradation of the printed image becomes poor.

It should be noted that the polymer blend may sometimes obtain melting endothermic peaks at two or more points during DSC (differential calorimetry) measurement, but in the present invention, it is calculated from the lowest temperature peak (I). When the energy is 30% or more of the total energy calculated from all the melting peaks, the temperature at the apex of peak (I) is the melting point, and when the energy is less than 30%, the temperature at the apex of the peak with the highest melting energy. Is the melting point.

In the present invention, the maximum value of the heat shrinkage stress of the film in the range of 60 to 140 ° C. is 500 g /
It is necessary to exceed mm ² . If it is 500 g / mm ² or less, even if the melting point is low and the film is easily melted by heat, the force for expanding the holes at the time of perforation is insufficient and the film has a size large enough to obtain a clear image at the time of printing. It is not preferable because no perforation can be obtained. The maximum value of the heat shrinkage stress is preferably 550 g / mm ² or more, more preferably 600 g / mm ² or more and 1500 kg / m.
It is less than m ² . Further, the ratio of the heat shrinkage stress to the lateral direction and the longitudinal direction of the film (in the lateral direction / longitudinal direction) is preferably in the range of 0.7 to 3.0, and more preferably 1.1 to 2. The range is 5. When the value of this ratio is less than 0.7, that is, when the shrinkage stress is extremely large in the longitudinal direction, the printing durability during printing may be poor. On the other hand, when it exceeds 3.0, the uniformity of the perforated shape may be deteriorated, and the image density and resolution during printing may be poor.

In order to obtain a film having the above-mentioned melting point and heat shrinkage stress, it is preferable to use a material polymer having a certain degree of crystallinity. When a polyester having a very low crystallinity, for example, a large amount of a copolymer component is used, the melting point becomes low, but the heat shrinkage stress cannot be increased. As used herein, having a certain degree of crystallinity means that the polymer has a thickness of 200 after melting.
An amorphous sheet obtained by molding into a sheet having a size of μm and rapidly cooling is below the melting point or softening point of the polymer and is 1 or less.
Treat in an oven maintained at a temperature of 00 ° C or higher for 5 hours,
The change in haze value before and after the heat treatment is 2% or more.

In addition to these requirements, in the present invention, the shrinkage percentage of the film after treatment at 100 ° C. for 10 minutes needs to be 20% or more, preferably 30 to 80%. 20
If it is less than%, the perforation sensitivity becomes insufficient and the print-like image density decreases, which is not preferable. The film of the present invention improves the workability during the winding step during film production, the coating during base paper preparation, the laminating step and printing, or prevents fusion between the thermal head and the film during thermal perforation. Therefore, the surface is roughened and the film is provided with appropriate slipperiness. Specifically, in order to moderately roughen the surface, the film has an average particle size of 0.05 to 2.0.
0.01 to 2.0% by weight, and preferably 0.1 to 1.5% by weight, of fine particles of μm is contained. Examples of such fine particles include calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon oxide, titanium oxide, kaolin, talc, carbon. Examples thereof include black, silicon nitride, boron nitride, and crosslinked polymer fine powders described in JP-B-59-5216, but are not limited thereto. At this time, the fine particles to be mixed may be a single component, or two or more components may be used at the same time. When two or more components are used, it is necessary that the average particle size and the total content of them are within the ranges described above. When the average particle size is less than 0.05 μm or the content of fine particles is less than 0.01% by weight, roughening of the film surface is insufficient and sufficient effects cannot be obtained. Also,
If the average particle size exceeds 2.0 μm or if the content exceeds 2.0% by weight, the degree of roughening of the film surface is too large and uneven heat transfer occurs, resulting in non-uniform perforation. It is not preferable because the resolution is poor and the printing quality is impaired.

In the present invention, the method as described above is used.
Gives a film with a roughened surface, but perforations
Sometimes the melted part of the film sticks to the thermal head
It prevents the decrease in sensitivity due to
Fine particles to further satisfy the requirements for printing quality and printing quality.
It is preferable to use those having a sharp particle size distribution.
That is, in the present invention, the particles measured by the method described below
D of the diameter distribution_{twenty five}/ D ₇₅However, preferably 1.05
1.7, more preferably 1.1 to 1.5, particularly preferably
It is 1.2 to 1.4. d_{twenty five}/ D₇₅Exceeds 1.7
Then, the number of protrusions with a large spread increases, and
It is not preferable because the effect of the present invention cannot be obtained.
Further, in the present invention, the particles to be contained in the film
Spherical silica, synthetic calcium carbonate,
Of monodisperse as described in Japanese Laid-Open Patent Publication No. 2-194049.
It is possible to use one or more selected from crosslinked polymer fine powders.
Most preferred.

In the present invention, a film whose surface is appropriately roughened by the above-mentioned method is obtained, but in order to further satisfy workability, printing resolution and printing quality, the film surface is The center line average roughness (Ra) is preferably 0.01 to 0.4 μm, more preferably 0.02 to 0.3 μm, and the maximum height (Rt) of the film surface is 0. The thickness is preferably 4 to 3 μm, more preferably 0.5 to 2 μm, and it is desirable to appropriately select the conditions so as to fall within this range.

Since the film of the present invention is an extremely thin film, the tensile elastic modulus in both the longitudinal direction and the width direction of the film is usually 300 kg / mm ² or more, preferably 350.
When the content is at least kg / mm ² , handling workability and printing durability will be better. Next, a method for producing the polyester film of the present invention will be described. In the present invention, the polymer is supplied to a well-known melt extrusion apparatus typified by an extruder, and heated to a temperature equal to or higher than the melting point of the polymer to melt it. Next, the melted polymer is extruded from a slit die and rapidly cooled and solidified on a rotating cooling drum to a temperature not higher than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is necessary to enhance the adhesion between the sheet and the rotary cooling drum, and the electrostatic application adhesion method and / or the liquid coating adhesion method are preferably adopted in the present invention.

The electrostatic application contact method is usually a method in which a linear electrode is placed on the upper surface of the sheet in a direction orthogonal to the flow of the sheet, and a DC voltage of about 5 to 10 kV is applied to the electrode to statically apply the sheet. This is a method of applying an electric charge to improve the adhesion to the drum. In addition, the liquid application contact method is a method for improving the adhesion between the drum and the sheet by uniformly applying the liquid to the whole or part of the surface of the rotary cooling drum (for example, only the portions that contact both ends of the sheet). Is. In the present invention, both may be used together if necessary.

In the present invention, the sheet thus obtained is biaxially stretched to form a film. Specifically, the unstretched sheet is preferably 40 to 120 ° C, more preferably 40 to 110 ° C.
In a temperature range of 3.0 to 7 times, preferably 3.5 to 7 by a roll or tenter type stretching machine in one direction.
Stretch twice. Next, in the direction orthogonal to the first stage, preferably in the temperature range of 40 to 125 ° C., more preferably 40 to 110 ° C., 3.0 to 7 times, preferably 3.5 to 7 times, more preferably 4.0 to 10. The film is stretched 7 times to obtain a biaxially oriented film. A method in which unidirectional stretching is performed in two or more stages can be used, but in that case as well, it is desirable that the final stretching ratio falls within the above range. Also,
It is also possible to simultaneously biaxially stretch the unstretched sheet so that the area ratio becomes 10 to 40 times.

The film thus obtained may be heat-treated, and if necessary, may be stretched in the machine direction and / or the transverse direction before or after the heat treatment. In the present invention, in order to obtain a film having the above-mentioned heat shrinkage property, the stretching ratio is 15 times or more as an area ratio, the heat treatment after stretching is not substantially performed, or even if it is performed, 130 ° C. or less, and further, 110 ° C or less, heat treatment time is 1 second to 5
It is preferable that the film is stretched or fixed at a length of 30% or less per minute.

In the present invention, about 10% by weight or less of another polymer (for example, polyethylene, polystyrene, polycarbonate, polysulfone, polyphenylene sulfide, polyamide, polyimide, etc.) is contained with respect to the total amount of polyester used for film formation. You can
Further, if necessary, additives such as an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a dye and a pigment may be added.

The thus-obtained polyester film of the present invention has excellent thermal piercing property and has a resolution at the time of printing by laminating a predetermined porous thin paper with a known adhesive according to a conventional method. Also, the heat-sensitive stencil printing base paper having excellent gradation can be obtained.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. The physical property measuring methods used in the present invention are shown below.

(1) Average particle size of fine particles Centrifugal sedimentation type particle size distribution measuring device SA- manufactured by Shimadzu Corporation
For the sedimentation method based on Stokes' resistance law using CP3 type
Therefore, the size of the particles was measured. Grains obtained by measurement
50% cumulative (weight basis) in the equivalent spherical distribution of the child
Average particle size (d₅₀). Similarly, on the large particle side
25% value from d_{twenty five}, 75% value is d ₇₅And

(2) Vertical and horizontal average heat shrinkage ratio The sample was heat-treated in an oven kept at 100 ° C. in a tensionless state for 3 minutes, and the length of the sample before and after that was measured to calculate the heat shrinkage ratio by the following formula. did.

[0025]

[Equation 1] Five points were measured in the longitudinal direction and the transverse direction of the film, and an average value was obtained.

(3) Heat shrinkage stress The film is cut into a strip having a width of 10 mm, and one end is loaded.
Set to the detector chuck and the other to the fixed chuck
The distance between the chucks was 50 mm. Do not apply initial load
In that state, immerse the film in an oil bath at a predetermined temperature,
The stress value was measured 5 seconds after the start of immersion. Before soaking
Rum cross-sectional area to heat shrinkage stress (g / mm ²) Is calculated
It was Measured at 5 points in the film lengthwise and widthwise directions, and averaged
I asked. Measurement is in the range of 60 ℃ -140 ℃ every 10 ℃
The maximum of the measured values at the 9 points.
The maximum value.

(4) Melting point Differential calorimeter SSC580DS manufactured by Seiko Instruments Inc.
It measured using C20 type. The DSC measurement conditions are as follows. That is, 10 mg of the sample film is used for DSC
Set in the device and heat up at a rate of 10 ℃ / min to 0 ℃
The melting point was measured as the top of the melting endothermic peak.

(5) Center line average roughness (Ra) The average roughness was measured as follows using a surface roughness measuring device (SE-3F) manufactured by Kosaka Laboratory Ltd. That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-section curve in the direction of the center line, and the center line of the extracted portion is taken as the x-axis, and the direction of longitudinal magnification is taken as the y-axis. When represented by f (x), the value given by the following equation was represented by [μm]. The center line average roughness was represented by the average value of the center line average roughness of the extracted portions obtained from the 10 section curves obtained from the surface of the sample film. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08.
mm.

[0029]

[Equation 2]

(6) Maximum height (Rt) The extracted portion was sandwiched by two straight lines parallel to the center line of the extracted portion (2.5 mm) of the section curve obtained when the average roughness of the center line was measured. At this time, the distance between these two straight lines was measured in the direction of the longitudinal magnification of the sectional curve, and the value was taken as the maximum height (μm) of the extracted portion. The maximum height was obtained by calculating 10 cross-section curves from the surface of the sample film and expressing the average value of the maximum heights of the extracted portions obtained from these cross-section curves.

(7) Practical characteristics of heat-sensitive stencil printing base paper Washi paper was attached to the film to prepare base paper. The obtained base paper is applied with a thermal head at an applied energy of 0.0.
A character image and a 16-step gradation image were prepared at 9 mJ and 0.12 mJ. The perforated state of the gradation image area was observed with a microscope from the film side of the plate-making base paper, and the following items were evaluated.

(I) Perforation sensitivity: The predetermined perforation is surely performed, and the size of the perforation is sufficient, which is good. Δ: Practical use is possible, although there are rare cases where certain holes cannot be obtained or where the size of the holes is insufficient. × ... There are many portions where the predetermined perforation cannot be obtained, and the perforation size is insufficient, which is a practical problem. Moreover, the following characteristics were visually determined for the characters and images obtained by actually printing using a lithographic base paper and a lithograph AP7200 printing machine manufactured by Ideal Science Co., Ltd.

(Ii) Print quality ○ ... There is no unevenness in density or bleeding, and clear printing is possible.
Good. Δ: Slight unevenness in shade and bleeding were observed, and the image was slightly lacking in sharpness. × ... The unevenness of light and shade, bleeding, and blurring are clearly seen.

Example 1 70 parts of dimethyl terephthalate and 3 parts of dimethyl isophthalate
0 parts, 56 parts of 1,4-butanediol, and 0.0075 parts of tetrabutyl titanate were placed in a reactor, the reaction starting temperature was set to 150 ° C., the reaction temperature was gradually raised with the distillation of methanol, and after 3 hours, 210 The temperature was raised to ° C. Further, after reacting for 1 hour, the average particle size is 1.1μ.
0.2 part of spherical silica particles of m was added, and a polycondensation reaction was carried out by an ordinary method. In this reaction, the temperature was gradually increased and the pressure was gradually reduced from the atmospheric pressure, and after 2 hours, the temperature was changed to 260.
C. and the pressure was 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained copolyester (A) was 0.70.

Using the obtained copolyester (A) as a raw material, it is extruded in a sheet form from an extruder at 260 ° C., and rapidly cooled by a static cooling method using a rotary cooling drum whose surface temperature is set to 25 ° C. It was solidified to obtain a substantially amorphous sheet having a thickness of 35 μm. Then, the obtained sheet was stretched 4.0 times in the longitudinal direction at 60 ° C. and 4.4 times in the transverse direction at 70 ° C., and further heat-treated at 90 ° C. for 6 seconds to give a thickness of 1.8 μm.
m biaxially oriented film was produced.

Example 2 Also, 80 mol% of the acid component is terephthalic acid and 20 mol%
Is isophthalic acid, and the glycol component is ethylene glycol. A polyethylene terephthalate / isophthalate copolymer (B) having an intrinsic viscosity of 0.68 was produced. The copolymer (B) contained 0.5% by weight of monodisperse crosslinked polymer particles (main component styrene, divinylbenzene) having an average particle size of 0.6 μ.

A mixture of the copolymer (A) and the copolymer (B) produced in Example 1 at a weight ratio of 50/50 was used as a raw material in the same manner as in Example 1, and a thickness of 40 μm was substantially obtained. An amorphous sheet was obtained. 3. Obtained sheet at 70 ° C.
The film was simultaneously biaxially stretched 2 times × 4.2 times and heat-treated at 100 ° C. for 30 seconds under a constant length to obtain a biaxially oriented film having a thickness of 2.0 μm.

Comparative Example 1 The heat treatment temperature was 140 ° C., and 10% in the width direction during the heat treatment.
A biaxially oriented film having a thickness of 1.8 μm was obtained in the same manner as in Example 1 except that the relaxation was performed.

Comparative Example 2 A biaxially oriented film was obtained in the same manner as in Example 1 except that the polymer extrusion rate was adjusted to a thickness of 5.0 μm.

Comparative Example 3 A polyethylene terephthalate / isophthalate copolymer (C), in which 85 mol% of the acid component is terephthalic acid and 15 mol% is isophthalic acid, is used as a raw material, and a substantially amorphous sheet having a thickness of 40 μm is used. Got The obtained sheet was biaxially stretched and heat treated in the same manner as in Example 1 to have a thickness of 2.0 μm.
A biaxially oriented film of was obtained.

Comparative Example 4 A copolymerized polyester (D) having an acid component of terephthalic acid, 67 mol% of the glycol component of ethylene glycol and 33 mol% of 1,4-cyclohexanedimethanol as a raw material, and having a thickness of 45 μm, amorphous. A quality sheet was produced. The obtained sheet is vertically oriented at 85 ° C. for 2.9 times, and further 80 times.
Draw 1.3 times at 2 ℃ in 2 steps, then 90 ℃ in the transverse direction
And then heat-treated at 130 ° C. for 6 seconds to obtain a biaxially oriented film having a thickness of 2.4 μm.

The above-obtained film was adhered to a porous thin paper according to a conventional method to prepare a heat-sensitive stencil printing base paper, which was then imprinted. The physical properties and the imprinting characteristics of the film are summarized in Table 1 below.

[0043]

[Table 1]

The films of Examples 1 and 2 are excellent in handleability at the time of producing the film and at the time of making the base paper, and the base papers made by using them have excellent thermal perforation sensitivity, and thus exhibit good copy printing characteristics. It was a thing. On the other hand, in Comparative Examples 1 and 4, since the shrinkage stress was insufficient, Comparative Example 2 had an excessively large thickness, and Comparative Example 3 had a high melting point.

[0045]

The film for heat-sensitive stencil printing base paper of the present invention has good handleability and excellent heat perforation, resolution during printing, and print quality, and has a high industrial value.

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Claims (1)

[Claims] 1. A thickness 0 comprising a polyester copolymer in which 50 to 80 mol% of the acid component is terephthalic acid, 20 to 50 mol% is isophthalic acid, and 40 mol% or more of the glycol component is 1,4-butanediol. A biaxially oriented film of 0.5 to 4.0 μm, the melting point of the film being 140 to
High-sensitivity heat-sensitive stencil printing base paper characterized in that the maximum value of heat shrinkage stress in the range of 190 ° C and temperature of 60 to 140 ° C exceeds 500 g / mm ² , and the heat shrinkage rate at 100 ° C is 20% or more. Film.