JP2000108542A - Manufacture of film for heat-sensitive stencil printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the surface roughing of a film from occurring during film casting and, enhance the extensibility by melt-extruding an L-lactic acid polymer in a sheetlike form and casting the extruded sheet by cooling on a casting drum through a water film and further, biaxially stretching an unoriented film obtained through the cooled casting. SOLUTION: An L-lactic acid polymer contains an L-polylactic acid, a lactic acid/hydroxycarboxylic acid copolymer and a mixture thereof, and is dried and supplied to an extruder to be melt-extruded in a sheetlike form. Next, when the molten sheet is set by cooling on a casting drum, it is essential to form a water film on the casting drum. A decomposition product generated from the polymer sticks to the casting drum and in turn, is adhesively transferred to a cast film to prevent the surface of the film from becoming roughed. In addition, the unstretched film is biaxially stretched. Thus it is possible to enhance the heat sensitivity of the film and thereby, prolong the service life of a thermal head and further, shorten time required for plate making.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-sensitive stencil film to be used as a heat-sensitive stencil printing base material perforated by a thermal head or the like.
More particularly, the present invention relates to a method for producing a heat-sensitive stencil film having a particularly high sensitivity.

[0002]

2. Description of the Related Art Conventionally, as heat-sensitive stencil printing base paper (hereinafter simply referred to as base paper), thermoplastic resin films such as polyester films and vinylidene chloride films have been used.
There is known a structure in which a porous support made of natural fiber, chemical fiber or synthetic fiber or a thin paper, nonwoven fabric, gauze or the like obtained by mixing them is bonded with an adhesive (for example, see Japanese Patent Application Laid-Open No. SHO 51-51). No. 2513, JP-A-57
182495).

[0003] In these base papers, a thermoplastic resin film is perforated by flash irradiation or infrared irradiation by a thermal head or a halogen lamp, a xenon lamp, a flash lamp or the like, or further by pulsed irradiation of a laser beam or the like, and a porous support is formed. It is used as a plate with ink permeability. Plate making method using thermal head
In this method, an original is read by an image sensor, converted into a digital signal, and an image corresponding to the original is perforated in a dot shape on a film portion of a base paper by a thermal head to perform plate making. In the plate making method using such a thermal head, it is necessary to reduce the energy supplied to the thermal head in order to suppress the damage of the thermal head and extend the service life. Is desired.

[0004] In order to improve the sensitivity, films having specified thermal characteristics of a biaxially stretched polyester film (JP-A-62-28988, JP-A-62-14).
9496)) and a film having specified heat shrink characteristics (Japanese Patent Application Laid-Open Nos. 62-282983 and 63-16).
No. 0895) has been proposed, but the sensitivity has been improved, but is insufficient, and further improvement has been desired.

In Japanese Patent Application Laid-Open No. 10-119453, a film made of an L-lactic acid polymer having a low melting point is used. In Japanese Patent Application Laid-Open Nos. 6-23836 and 7-205278, the stretching temperature, the stretching ratio, and the heat treatment temperature are set. Although the method for producing a specified polylactic acid stretched film is described, the film for heat-sensitive stencil printing of the present invention has a small film thickness, and the above-mentioned production method has a problem of poor stretchability due to film surface roughness or the like generated during casting. was there.

Further, the L-lactic acid polymer has a rigid and highly crystalline molecular structure, and has a high rigidity of the film. There was a problem.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a film for heat-sensitive stencil printing which has a stable stretchability without causing surface roughness of the film at the time of film casting and which cannot be realized by conventional base paper. The purpose is to do.

[0008]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies and as a result, have found that unstretched L-
The inventors have found that the above problem can be solved by biaxially stretching a lactic acid film, and have reached the present invention.

That is, the present invention is characterized in that an unstretched film obtained by melt-extruding an L-lactic acid polymer into a sheet and cooling-casting it on a casting drum via a water film is biaxially stretched. The present invention relates to a method for manufacturing a stencil printing film.

[0010]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the L-lactic acid polymer includes L-polylactic acid, lactic acid-hydroxycarboxylic acid copolymer, and a mixture thereof.

Lactic acids and hydroxycarboxylic acids are used as raw materials for the polymer. Lactic acids include L
-Lactic acid, D-lactic acid or mixtures thereof or lactide which is a cyclic dimer of lactic acid can be used. Lactic acids as raw materials are preferably used in various combinations so that the L-lactic acid content ratio in the obtained polymer is 75% or more.

Hydroxycarboxylic acids that can be used in combination with lactic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, and 5-hydroxyvaleric acid.
Examples thereof include hydroxyvaleric acid and 6-hydroxycaproic acid. Further, a cyclic ester intermediate of hydroxycarboxylic acid, for example, glycolide which is a dimer of glycolic acid and a cyclic ester of 6-hydroxycaproic acid can be used. . Also, ε-caprolactone can be used.
Furthermore, aliphatic dicarboxylic acids and glycols can be used in a small amount. Mixtures of lactic acids and hydroxycarboxylic acids as raw materials are preferably used in various combinations so that the L-lactic acid content in the obtained copolymer is 75% or more.

The L-lactic acid polymer can be obtained by directly dehydrating or polycondensing the above raw materials, or a cyclic dimer of the above lactic acids or hydroxycarboxylic acids, for example, lactide or glycolide,
Alternatively, it can be obtained by a method of subjecting a cyclic ester intermediate such as ε-caprolactone to ring-opening polymerization. In the case of production by direct dehydration polycondensation, the raw materials lactic acid or lactic acid and hydroxycarboxylic acid are preferably subjected to azeotropic dehydration condensation in the presence of an organic solvent, particularly a phenyl ether solvent, and particularly preferably azeotropic distillation. Polymerization is carried out by a method in which water is removed from the discharged solvent and the solvent in a substantially anhydrous state is returned to the reaction system, whereby a high molecular weight L-lactic acid polymer suitable for the present invention is obtained. The molecular weight of the L-lactic acid polymer is preferably a high molecular weight as long as moldability is possible, and more preferably 10,000 to 5,000,000.

The L-lactic acid polymer of the present invention may contain a flame retardant, an antioxidant, a plasticizer, an ultraviolet absorber, a pigment, a dye, and the like, if necessary.

Further, particles can be blended for imparting lubricity. As particles, for example, clay, mica, titanium oxide, calcium carbonate, kaolin, talc,
Examples thereof include inorganic particles such as wet or dry silica, alumina, and zirconia, and organic particles containing acrylic acid, styrene, and the like as constituent components. The particle amount is L
-0.05 to 10 parts by weight, preferably 0.1 to 3 parts by weight, per 100 parts by weight of lactic acid polymer. The average diameter of the particles is 0.01 to 3 μm
And more preferably 0.1 to 2 μm. Of course, a plurality of particles having different types and average diameters can be used in combination.

Next, the above polymer is dried as required, supplied to an extruder, and melt-extruded into a sheet using a T-type die or the like. After that, when the molten sheet is cooled and solidified on the casting drum, it is important that a water film is formed on the casting drum. Without the water film, the decomposed product generated from the polymer adheres to the casting drum, and the adhered decomposed product is transferred to the film, resulting in surface roughening of the film or the subsequent stretching process of the film. Problems such as surface defects and uneven stretching occur. However, the presence of the water film is preferable because these problems can be prevented.

Here, the coating amount of the water film formed on the casting drum is preferably 0.05 to 20 g / m ² , because the releasability and the flatness of the obtained film are improved. Preferably, 0.5 to 10 g
/ M ² . Here, the water film does not need to be formed uniformly on the drum, but may be discretely dispersed in the above range, and the water contains a surfactant or a solvent soluble in water. May be.

As a method of forming a water film on the casting drum, a method of applying water on a drum while oozing water from a porous roll, a method of blowing humidified air, and the like are possible. Further, it is preferable to form fine irregularities or cracks so that a uniform water film is formed on the casting drum. In this case, the surface roughness is
It is preferable that the thickness be in the range of 0.01 to 10 μm because the uniformity of the water film at the time of casting is improved.

If the temperature of the casting drum is too high, the water film is liable to evaporate, and a uniform water film cannot be formed, or the film may be boiled during casting to form a surface defect. Is particularly preferable, and the temperature range is particularly preferably from 10 to 30 ° C.

The unstretched film is subsequently subjected to biaxial stretching. The method of biaxial stretching may be any method, and examples include inflation simultaneous biaxial stretching, Stenter simultaneous biaxial stretching, and Stenter sequential biaxial stretching.

A particularly preferred stretching method is a sequential biaxial stretching method. In the case of the sequential biaxial stretching method, the stretching in the longitudinal direction is performed by an ordinary roll stretching machine including a plurality of heating roll groups having a difference in peripheral speed. The stretching temperature in the machine direction is preferably L
-Glass transition point (Tg) of lactic acid polymer-20 ° C to Tg
+ 20 ° C, more preferably Tg-10 ° C to Tg + 10 ° C
It is. When the stretching temperature is in this range, the film can be stretched without breaking during stretching or fibrillation of the film, which is preferable. The stretching ratio is preferably 1.5 to 10 times, more preferably 1.5 to 5.0 times, and still more preferably 1.5 to 4.0 times. It is preferable that the stretching ratio be in the above range because a film having a smooth surface and excellent sensitivity can be obtained.

The uniaxially stretched film thus obtained is guided to a tenter while holding both ends of the film with clips, and preferably the glass transition point (T) of the L-lactic acid polymer is obtained.
g) -20 ° C to Tg + 20 ° C, more preferably Tg-1
In the temperature range of 0 ° C. to Tg + 10 ° C., the film is stretched in the transverse direction preferably in the range of 1.5 to 10 times, more preferably in the range of 1.5 to 5.0 times, and still more preferably in the range of 1.5 to 4.0 times. .
It is preferable that the stretching temperature be in the above range, since a highly sensitive film aimed at by the present invention can be obtained without breaking during the stretching process. When the stretching ratio is in the above range, a film having a smooth surface and excellent sensitivity can be obtained. The film thus obtained is preferably subjected to a heat treatment at a temperature not exceeding 20 ° C. from the stretching temperature for 0.5 second or more. The heat treatment may be carried out in the same tenter as in the transverse stretching, or may be carried out in another tenter by releasing the film end once and re-gripping. In addition, the heat treatment may be performed under tension, or may be performed while relaxing in the lateral direction to improve thermal dimensional stability. However, since excessive relaxation significantly deteriorates the mechanical properties of the biaxially stretched film, the upper limit of the relaxation rate is 8%,
Preferably, it is kept at 5%.

The thickness of the biaxially stretched film of the present invention is determined by the appropriate sensitivity and the like required for the base paper, but is preferably 0.1 to 10 μm, more preferably 0.3 to 7 μm, Particularly preferably, it is 0.5 to 5 μm.

The biaxially stretched film of the present invention can be adhered to a porous support to form a base paper. The porous support is a porous material made of natural fibers, synthetic fibers, and the like that can transmit the printing ink and does not substantially undergo thermal deformation under heating conditions under which the film is perforated. A woven fabric or other porous body is used.

For the adhesion between the film and the porous support, there is used a method in which the film is adhered with an adhesive or the like under a condition that does not hinder the perforation suitability of the film or by heat. In addition, a method of obtaining a base paper at a stretch by thermocompression bonding and co-stretching a porous support such as a nonwoven fabric made of a thermoplastic polymer on a film in the process of manufacturing the film, the porous support serves as a reinforcing member, This is a particularly preferable method because the film is not broken and the film-forming stability is extremely excellent.

[0026]

[Measurement method of properties] (1) Glass transition point (Tg), melting point (Tm) Using a differential scanning calorimeter RDC220 type manufactured by Seiko Denshi Co., Ltd., 5 mg of a film sample was collected, and the temperature was raised from room temperature at a heating rate of 20 ° C. The melting point (Tm) was determined from the temperature of the endothermic peak when the temperature was raised at a rate of / m. Further, the glass transition temperature (Tg) is measured by raising the temperature of the film sample to 280 ° C., holding the film sample at 280 ° C. for 5 minutes, quenching with liquid nitrogen, and raising the temperature again from room temperature at a rate of 20 ° C./min. did.

(2) Application amount of water film on casting drum (g / m ² ) A water film is formed while rotating the casting drum at a predetermined line speed, and has an effective width of 100 mm and a diameter of 50 mmφ.
Using a mass roll (manufactured by Masuda Seisakusho Co., Ltd.), the wiping time is appropriately set so that the measurement area becomes 10 to 100 m ² , and the formed water film is completely wiped off. Next, the weight (W2 [g]) of the mass roll was measured and the initial weight (W1
[G]) and the measured area (S [m ² ]) are determined by the following equation.

The mass roll is kept in the measuring atmosphere for at least 6 hours to adjust the humidity.

Water film amount (g / m ² ) = (W 2 −W 1) / S (3) Dirt on Casting Drum L-lactic acid polymer is melt-extruded into a sheet using a T-type die or the like. The sheet was cooled and cast using a casting drum, and the state of the casting drum surface after 3 hours was visually observed. Observation was made on the contacting portion of the film.

○ The state is almost the same as when casting was started. × The state where the decomposed matter adhered and became white. (4) Sensitivity The stretched film was bonded to thin paper with an adhesive to form a base paper. The base paper was supplied to a printing machine lithograph (GR275) manufactured by Riso Kagaku Kogyo Co., Ltd. to make an A4 size black solid sheet with a side of 10 mm in a grid pattern over the entire surface. The energy supplied to the thermal head was 30 μJ per dot. The perforated part was observed at a magnification of 100 with a scanning electron microscope, and the area of the perforated part was measured. Measurement is 1 per field of view
The measurement was performed for 10 visual fields with 50 specimens.

Sensitivity: Those having an average value of 1400 × 10 ⁻¹² m ² or more, ◎ Average value of 1000 × 10 ⁻¹² m ² or more and 1400 × 10
What ^-12 is less than m ^2, ○ averages 500 × 10 ^-12 m ² or more 1000 × 10 ^-12
what is less than m ^2, △ average value what is less than 500 × 10 ^-12 m ^2, was ×. Regarding the sensitivity and the variation, ○, △, and Δ are practically used.

[0032]

Examples 1 to 3 L-polylactic acid having a weight average molecular weight of about 100,000 (melting point: 175 ° C.) was added to calcium carbonate having an average particle size of 1.0 μm.
The raw material to which 5% by weight was added was melt-extruded at 230 ° C., and was cast on a 25 ° C. casting drum where fine water droplets were formed by blowing high-humidity air with an ultrasonic humidifier to obtain an unstretched film. The thickness of the water film was as shown in Table 1. The film thickness of the obtained unstretched film was 12.5 μm. 65 ° C.
After preheating with a preheating roll heated to 65 ° C., the film was stretched 2.5 times in the length direction with a stretching roll heated to 65 ° C. Furthermore, it was sent to a tenter type stretching machine and stretched 2.5 times in the width direction at a preheating temperature of 65 ° C and a stretching temperature of 65 ° C. Further, the film was heat-treated at 70 ° C. for 5 seconds in a tenter to obtain a biaxially stretched film. The thickness of the stretched film was 2.0 μm.

The sensitivity of the base paper obtained by laminating the film with thin paper with an adhesive was ◎.

Example 4 An unstretched film was obtained by casting in the same manner as in Example 1 except that the added particles were 0.5% by weight of titanium oxide of 1.0 μm. The thickness of the water film was as shown in Table 1. The film thickness of the obtained unstretched film was 18 μm.
Met. The unstretched film was preheated by a preheating roll heated to 65 ° C., and then stretched 3.0 times in the length direction by a stretching roll heated to 70 ° C. Further, it was fed into a tenter type stretching machine and stretched 3.0 times in the width direction at a preheating temperature of 65 ° C and a stretching temperature of 70 ° C. 70 ° C inside the tenter
For 5 seconds to obtain a biaxially stretched film. The thickness of the stretched film was 2.0 μm.

The sensitivity of the base paper obtained by laminating the film with thin paper with an adhesive was ◎.

Example 5 An unstretched film was obtained by casting in the same manner as in Example 1 except that the added particles were changed to 0.5% by weight of 1.2 μm silicon oxide. The thickness of the water film was as shown in Table 1. The film thickness of the obtained unstretched film was 18 μm.
Met. The unstretched film was preheated by a preheating roll heated to 65 ° C., and then stretched 3.0 times in the length direction by a stretching roll heated to 70 ° C. Further, it was fed into a tenter type stretching machine and stretched 3.0 times in the width direction at a preheating temperature of 65 ° C and a stretching temperature of 70 ° C. 70 ° C inside the tenter
For 5 seconds to obtain a biaxially stretched film. The thickness of the stretched film was 2.0 μm. The sensitivity of the base paper obtained by laminating the film with thin paper with an adhesive was ◎.

Example 6 The unstretched film cast in Example 1 was fed to a tenter-type simultaneous biaxial stretching machine, and a preheating temperature of 65 ° C. and a stretching temperature of 6
The film was simultaneously stretched 2.5 times in the longitudinal direction and 2.5 times in the transverse direction at 5 ° C. Further, the film was heat-treated at 70 ° C. for 5 seconds in a tenter to obtain a biaxially stretched film. Stretched film thickness is 2.0
μm.

The sensitivity of the base paper obtained by laminating the film with thin paper with an adhesive was ◎.

Comparative Example 1 L-polylactic acid having a weight average molecular weight of about 100,000 (melting point: 175 ° C.) was mixed with calcium carbonate having an average particle size of 1.0 μm.
5% by weight of the raw material was melted and extruded at 230 ° C.
An unstretched film was obtained by casting on a casting drum at a temperature of 0 ° C. The film thickness of the obtained unstretched film was 12.5 μm. The unstretched film was preheated by a preheating roll heated to 65 ° C, and then stretched 2.5 times in the length direction by a stretching roll heated to 65 ° C. Further, the film was sent to a tenter type stretching machine, stretched 2.5 times in the width direction at a preheating temperature of 65 ° C. and a stretching temperature of 65 ° C., and was further subjected to a heat treatment at 70 ° C. for 5 seconds inside the tenter. Occurred frequently. A 2.0 μm thick film that was barely biaxially stretched had poor flatness of the film, and the surface of the film had roughness that could be visually confirmed. The sensitivity of the base paper obtained by laminating this film with thin paper and an adhesive was: X.

[Table 1]

[0040]

According to the present invention, an unstretched film obtained by melt-extruding an L-lactic acid polymer into a sheet and cooling-casting it on a casting drum via a water film is biaxially stretched to obtain a very high sensitivity. A method for producing a heat-sensitive stencil film, which can reduce the energy supplied to a thermal head of a printing press when it is used, thereby extending the life of the thermal head and shortening the time required for plate making.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H114 AB23 AB25 BA06 DA42 DA73 EA02 EA06 EA08 GA01 4F210 AA41 AB16 AE01 AG01 AR06 AR20 QA02 QA03 QC06 QW06

Claims (3)

[Claims] 1. A film for heat-sensitive stencil printing, characterized in that an unstretched film obtained by melt-extruding an L-lactic acid polymer into a sheet and cooling-casting it on a casting drum via a water film is biaxially stretched. Manufacturing method. 2. The method for producing a heat-sensitive stencil printing film according to claim 1, wherein a heat treatment is performed at a temperature not exceeding 20 ° C. from the stretching temperature after the biaxial stretching. 3. The method for producing a heat-sensitive stencil printing film according to claim 1, wherein the stretching ratio in the longitudinal or transverse direction is 1.5 to 10 in biaxial stretching. .