JP2008265267A - Polypropylene film for thermal stencil printing, and thermal stencil printing base sheet consisting of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene film having an excellent perforation suitability for thermal stencil printing and a thermal stencil printing base sheet consisting of the same. <P>SOLUTION: The polypropylene film of 1.5 to 3.5 μm thickness for thermal stencil printing consists of a polypropylene resin (A) having a melting point of 156°C or higher. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement of a thermoplastic resin base material used for a heat-sensitive stencil sheet that enables stencil printing by melting and punching a part of a resin thin film with thermal energy.

  Stencil printing is a technique for transferring ink or the like to printing paper through holes formed in a base sheet. In thermal stencil printing, a porous support layer made of natural cellulose fibers and / or synthetic resin fibers and a thermoplastic resin group are used. A laminated body joined with a material is used as a printing substrate, and a specific portion of the thermoplastic resin substrate is perforated using an appropriately selected heat source to form a printing pattern (Patent Document 1). Here, as the heat source, pulsed radiation of visible light to infrared light, thermal head, irradiation of beam rays such as laser light, and the like have been proposed. In order to print precise images, characters, etc., it is required to reduce the shape and size of the heat source, but since the amount of heat generated is also small, the thermoplastic resin base is required for reliable perforation. It is considered important that the energy required for the material to start flowing is small. Therefore, the improvement of the material has been intensively studied, and a stretched thermoplastic resin film is a thermoplastic resin film obtained by stretching a synthetic resin film such as polyethylene, polypropylene, polyvinyl chloride, etc., and has a thickness of 10 μm. The following films have been proposed to be preferably used (Patent Document 2). Among these, for polypropylene films, polypropylene copolymer films have been proposed as heat sensitive stencil films. (Patent Document 3). A technique for irradiating an electron beam has also been proposed for a polypropylene system (Patent Document 4). However, since a very thin film is inferior in the efficiency of electron beam irradiation, there is a limitation in cost in practical use. .

  Furthermore, in order to obtain sufficient perforation properties, many proposals have been made for improved techniques for using a polyester film as the heat-sensitive film (Patent Documents 5 to 9). Currently, polyester films are widely used as heat-sensitive stencil paper. Yes.

However, in the case of a polyester-based copolymer, there is a problem that wrinkles are likely to occur while being thin and capable of being thinned.
Japanese Patent Publication No.41-7623 Japanese Patent Publication No.54-33117 Japanese Patent Publication No.47-1184 Japanese Patent Publication No. 5-30637 JP 60-48398 A JP-A-60-85996 JP-A-62-149496 JP 2002-127628 A JP 2006-249439 A

  The present invention proposes a polypropylene film and a heat-sensitive stencil sheet comprising this polypropylene film, which can be made ultra-thin by using a specific polypropylene film and has excellent punchability for heat-sensitive stencil printing.

In order to solve the above problems, the present invention
(1) A heat-sensitive stencil polypropylene film comprising a polypropylene resin (A) having a melting point of 156 ° C. or higher and a thickness of 1.5 to 3.5 μm,
(2) The polypropylene film for heat-sensitive stencil as described in (1) above, wherein the polypropylene resin (A) contains polypropylene having a long-chain branched structure,
(3) The polypropylene film for heat-sensitive stencil according to (1) or (2) above, wherein the surface glossiness of at least one side is 100 to 140%,
(4) The polypropylene film for heat-sensitive stencil according to any one of (1) to (3), wherein the ten-point average roughness (Rz) of at least one surface is 0.20 to 1.2 μm,
(5) A heat-sensitive stencil sheet in which a porous support layer and the heat-sensitive stencil polypropylene film according to any one of (1) to (4) are joined is proposed.

The polypropylene film for heat-sensitive stencil of the present invention and the heat-sensitive stencil sheet comprising the same are made of a polypropylene resin (A) having a specific melting point and adopting a polypropylene film having a specific thickness,
1. Despite being an ultra-thin film, it has excellent rigidity, so it has excellent processing suitability such as laminating, high yield during base paper manufacturing, and high quality uniformity.
2. It has excellent properties and effects such as heat-sensitive stencil paper that does not easily wrinkle and prints finely.

  Hereinafter, the present invention will be described in detail together with preferred embodiments.

  It is important that the polypropylene resin (A) constituting the polypropylene film for heat-sensitive stencil of the present invention has a melting point of 156 ° C., preferably 159 ° C. or higher, particularly preferably 162 ° C. or higher. The reason why only the lower limit of the melting point is defined in the present invention is that a polypropylene resin having a high melting point, that is, high crystallinity, is suitable for film thinning and has been found to be more preferable. That is, from the viewpoint of improving the sensitivity of the stencil sheet, which is the object of the present invention, it is preferable that the crystallinity is low as described above, and it can be said that this is contrary to the object from this point of view. It is directly connected and the handling property is remarkably impaired. In other words, although the present inventors have a trade-off relationship between film thinning and low crystallization, which are requirements for high sensitivity, thinning that can be achieved by increasing crystallinity contributes greatly to improving sensitivity. As a result, the present invention has been found.

  Accordingly, a highly crystalline polypropylene resin is preferably used in the present invention. However, the upper limit depends on the current production technology of polypropylene resin, and the upper limit of the melting point of commercially available polypropylene is around 167 ° C. is there.

  In order to make the melting point of the polypropylene resin (A) in the above range, it is exemplified as a preferable method to increase the stereoregularity of the polypropylene. That is, it is preferable to use a polypropylene having an isotactic pentad fraction (mmmm) of 95% or more expressed by a meso chain of five monomer units of polypropylene having an isotactic structure. By carrying out like this, (mmmm) of polypropylene resin (A) can be controlled to 90% or more, preferably 92% or more. Such a polypropylene resin can be produced using, for example, a Ziegler-Natta catalyst or a metallocene catalyst.

  Furthermore, it is preferable that the polypropylene resin (A) contains polypropylene having a long-chain branched structure (hereinafter referred to as XPP).

  In XPP, it is difficult to obtain a long-chain branched structure by a normal propylene polymerization reaction, so once polypropylene (linear) is produced, a cross-linking reaction by electron beam irradiation or a chemical cross-linking reaction by peroxide is used. By doing so, a long chain branched structure can be obtained. At this time, in order to smoothly perform the crosslinking reaction, a comonomer can be appropriately copolymerized, for example, by introducing a monomer unit having an unsaturated group in the molecular chain of polypropylene. The molecular weight of the side chain of the long-chain branched structure obtained in this way cannot be defined unconditionally, but contains branched-chain polypropylene having a structure in which several hundred units or more of propylene chains are added.

  Such a polypropylene was developed as a high melt tension polypropylene “HMS-PP” for the purpose of improving the melt tension of the polypropylene resin containing it and improving the sheet moldability or for the production of a foamed polypropylene sheet. It is on the market.

Specifically, “HMS-PP” (PF-814) manufactured by Basell, and “HMS-PP” (WB130HMS, etc.) manufactured by Borealis are exemplified. The characteristic of high melt tension polypropylene is the relationship between melt tension (MS) and melt flow rate (MFR) when measured at 230 ° C. (1)
log (MS)> − 0.56 · log (MFR) +0.74 (1)
(However, MS: melt tension (cN) measured at 230 ° C., MFR: melt flow rate (g / 10 min))
It is preferable to satisfy.

  Moreover, the high melt tension polypropylene having such a long-chain branched structure has a higher crystallization temperature than ordinary polypropylene because the polypropylene itself having a long-chain branched structure has a strong crystal nucleating agent action. Specifically, the melt crystallization temperature of a normal polypropylene homopolymer is about 100 to 110 ° C., whereas when the polypropylene having a long chain branched structure is contained, the melt crystallization temperature is 115 to 130 ° C. To rise. Such a high crystallization temperature means that the solidification after melting and perforation by heat is fast, which is a more preferable characteristic for obtaining a higher-definition printed matter.

  The polypropylene resin (A) constituting the film of the present invention preferably contains a branched polypropylene having the above characteristics. Specifically, it can be obtained by appropriately mixing high melt tension polypropylene having the above-mentioned characteristics and ordinary polypropylene, but in order to make the melt crystallization temperature in the above-mentioned range, the content of XPP must be polypropylene resin. It is preferable that it is 0.1 weight% or more with respect to (A), More preferably, it is 0.3 weight% or more. Further, if the content of XPP is too large, the stretchability may be impaired, and it is preferably 5% by weight or less, more preferably 3% by weight or less.

  Of course, the polypropylene resin (A) may be copolymerized with α-olefin such as ethylene, butene-1, hexene-1, and 4-methylpentene-1 as long as the object of the present invention is not violated. Further, poly α-olefins such as high density polyethylene, low density polyethylene, linear low density polyethylene, polybutene 1, and poly-4-methylpentene 1 may be added.

  Among these, polybutene-1 may form a eutectic with polypropylene, and if it is in a small amount, it can be largely compatible without disturbing the crystallinity, and the sensitivity can be improved. The amount added is preferably 5% by weight or less, and preferably 0.5 to 3% by weight, since the sensitivity can be improved without greatly reducing the rigidity.

  Further, it may contain a known heat stabilizer, antioxidant, chlorine scavenger, organic and / or inorganic slip agent, antistatic agent, etc., as long as it does not contradict this purpose. Among these, the inorganic slip agent may cause foreign matters to cause defects, and in producing a thin film, there is a high possibility of causing breakage in the stretching process and errors in the punching process. It is desirable not to add as much as possible. In addition, examples of the chlorine scavenger include so-called metal soaps such as calcium stearate and inorganic hydrotalcites, but metal soaps are not so good in thermal stability, and form foreign matters in the melting process. There is a fear. On the other hand, since the inorganic type is originally a particle, there is a possibility that the stability of the film forming process and the piercing property may be hindered as described above. Because of the advantages and disadvantages, the amount of metal soap added is preferably 200 ppm (weight basis) or less, particularly preferably 100 ppm (weight basis) or less, and hydrotalcites are 100 ppm (weight basis) or less. More preferably, it is preferably set to 50 ppm (weight basis) or less. For this reason, it is desirable to reduce the amount of residual chlorine in the polypropylene resin as much as possible, and it is preferably 15 ppm (weight basis) or less, particularly preferably 10 ppm (weight basis) or less.

  Examples of the antistatic agent used in the film of the present invention include polyhydric alcohol fatty acid partial esters, alkyl dialkanolamine compounds, alkyldialkylbetaine type amphoteric surfactants, and the like. ˜1% by weight.

  The film of the present invention is obtained by biaxially stretching a polypropylene resin having the above properties to a film thickness of 1.5 to 3.5 μm, preferably 1.5 to 3 μm.

  If the film thickness is less than 1.5 μm, it is difficult to stably form a film, and even if it is obtained, it is inferior in rigidity and difficult to handle. On the other hand, when it exceeds 3.5 μm, the sensitivity characteristic may be impaired.

  The surface glossiness of at least one surface of the film of the present invention is preferably 100 to 140%, more preferably 110 to 130%. Here, the gloss is an index that reflects the glossiness of the surface, but the glossiness is an index that reflects the surface roughness. As the surface is roughened, the glossiness decreases and the gloss also decreases. On the other hand, the smoother the surface, the higher the gloss. Accordingly, when the gloss is low and the surface is rough, the film becomes slippery, and it is difficult to obtain a well-rolled film roll, and the processing suitability may deteriorate. On the other hand, when the gloss is high and the surface is smooth, the yield may be lowered due to problems such as poor sliding and wrinkles or film sticking and blocking.

  Further, as the surface roughness of the film of the present invention, the ten-point average roughness (Rz) of at least one surface is preferably 0.2 to 1.2 μm, more preferably 0.3 to 1.0 μm. is there. These preferable ten-point average roughness values are preferably satisfied on both sides (both sides) of the film. When Rz exceeds 1.2 μm and the surface is rough, the film becomes slippery, and it is difficult to obtain a well-rolled film roll and the processing suitability may be lowered. On the other hand, when Rz is less than 0.2 μm and the surface is smooth, the yield may decrease due to problems such as poor sliding and wrinkles or film sticking and blocking.

  In order to obtain such a gloss value and a surface roughness Rz value, it is possible to add incompatible components (polymer, particles, etc.) to polypropylene and stretch the film. It is not suitable for production, and there is a tendency that perforation errors increase when the obtained film is used as a heat-sensitive stencil. In the present invention, a preferable method is that the cooling temperature is in the range of 80 to 120 ° C. in the melt extrusion sheet forming step of the resin containing the polypropylene resin having a long chain branched structure. As a result, β-type spherulites are formed together with α-type spherulites in the cooling sheet, and surface irregularities are formed when the β-type spherulites transition to α-type in the stretching process. Obtainable. The gloss control can be appropriately controlled by the content of the long-chain branched structure and the casting temperature. Since the polypropylene having a long chain branched structure has an action as a β crystal nucleating agent for inducing β crystals, the surface can be effectively roughened. An example of a method for further controlling the gloss is a method in which a nucleating agent that selectively forms β-type crystals is added to the resin.

  In addition, it is preferable to increase the surface wetting tension on at least one side of the film of the present invention in order to improve the adhesion to the porous substrate. The surface wetting tension is preferably 35 to 52 mN / m, more preferably 38 to 50 mN / m. If the wetting tension is too low, the adhesiveness may be lowered. On the other hand, if the wetting tension is too high, blocking may occur when the film is wound into a roll. In order to obtain such surface wetting tension, a method of introducing a polar group on the surface by using corona discharge treatment, plasma treatment, flame treatment or the like is preferable. In particular, corona discharge treatment is advantageous in terms of cost and is preferably used.

  The film of the present invention has the above properties, but it is necessary that at least one side is bonded to the porous support layer in order to use it as a heat-sensitive stencil sheet.

  The porous support layer is required to be easy to impregnate and move the ink while maintaining the film strength as the stencil paper, and is preferably a porous body made of natural cellulose fibers and / or synthetic resin fibers. In joining the porous support layer and the film of the present invention, a polyester-based, polyurethane-based, or acrylic adhesive is appropriately used.

  Subsequently, the manufacturing method of this invention film is demonstrated.

  The film of the present invention is produced by a biaxial stretching method, but may be any method such as a tenter method or a tubular (bubble) method. Among these, the tenter method is preferable because the thickness unevenness and flatness are improved. The tenter method further includes a simultaneous biaxial stretching method and a sequential biaxial stretching method, and any method may be used. Hereinafter, a method for obtaining the film of the present invention by sequential biaxial stretching will be described, but the present invention is not limited thereto.

  T-type in which ordinary polypropylene and high melt tension polypropylene containing a long-chain branched structure are pellet-blended, melt-kneaded at 230 to 270 ° C. using an extruder, and foreign matters in the resin are removed by a polymer filter It is led to a slit die and melt extruded into a sheet. Of course, not depending on the pellet blend, it may be melt-blended in advance, or a polypropylene resin pellet containing a high melt tension polypropylene having a long-chain branched structure produced using a graft reaction or the like is obtained, You may melt-extrude with an extruder.

  Next, the molten sheet is cooled and solidified while closely contacting with an air pressure on a cooling drum controlled at 80 to 120 ° C. Here, if the temperature of the cooling drum is less than 80 ° C., the surface of the biaxially stretched film may be too smooth and winding may be difficult. On the other hand, if the temperature is too high, crystallization is slowed, the line speed has to be reduced, and the economy may be deteriorated.

  Next, the cooled and solidified sheet is preheated by a plurality of heated metal rolls, the sheet temperature is increased to 135 to 155 ° C., preferably 140 to 150 ° C., and 3 to 3 between a pair of rolls having a difference in peripheral speed. The film is stretched 7 times, preferably 4 to 6 times in the longitudinal direction to form a uniaxially stretched film. Next, both ends in the width direction of the uniaxially stretched film are held by clips, guided to a heating oven, preheated to 150 to 170 ° C., and then stretched 7 to 12 times, preferably 8 to 11 times in the width direction, to form a biaxially stretched film. And annealing at 140 to 160 ° C. while allowing 0 to 20% relaxation in the width direction. After trimming both edge portions of the biaxially stretched film thus obtained, if necessary, after surface treatment such as corona discharge treatment, flame treatment, ozone treatment, etc., it is wound into a roll. The wound film is subjected to an aging treatment in an atmosphere of 20 to 40 ° C. and then cut into a product width suitable for bonding to a porous support.

  The heat-sensitive stencil sheet can be obtained by bonding the polypropylene film roll obtained as described above and a porous support using an adhesive. At this time, the adhesive may be applied to either the film of the present invention or the porous support, but since the film is usually thin and inferior in rigidity, it is technically difficult to apply uniformly. It is preferable to apply it to a porous support and attach it to a film. After the polypropylene film and the porous support are bonded together, the solvent is removed in a hot air oven, and the adhesive is dried and solidified, and then wound.

  Next, measurement methods and evaluation methods used in the examples of the present invention will be described.

(1) Glossiness (%)
According to JIS K-7105 (1981), the average value of five data measured under the conditions of an incident angle of 60 ° and a light receiving angle of 60 ° using a digital variable angle gloss meter UGV-5D manufactured by Suga Test Instruments Co., Ltd. It was.

(2) Film thickness (μm)
The thickness of the micrometer method was measured according to 7.4.1.1 of JIS C-2330 (2001).

(3) Melting point (Tm), melt crystallization temperature (Tmc) (° C)
Using an RDC220 differential scanning calorimeter manufactured by Seiko Co., Ltd., five measurements were performed under the following conditions, and the average values of the remaining three points excluding the maximum and minimum two points were defined as Tm and Tmc.

<Sample preparation>
4 ± 1 mg as a specimen is sealed in an aluminum pan for measurement.

<Measurement>
The film is melted / recrystallized / remelted in the following steps (a) → (b) → (c).

(A) Melting (1st Run): 30 ° C. → 280 ° C. (heating rate 20 ° C./min)
(B) Recrystallization: Hold at 280 ° C. for 5 minutes and then cool to 30 ° C. at 20 ° C./min. (C) Remelt (2nd Run): 30 ° C. → 280 ° C. (heating rate 20 ° C./min)
At this time, the endothermic peak temperature accompanying melting observed at 2nd Run is defined as Tm, and when there are a plurality of peak values, the peak having the largest peak area is employed as Tm.

  For Tmc, the exothermic peak temperature accompanying crystallization observed during recrystallization is defined as Tmc, and when there are a plurality of peak values, the peak having the largest peak area is employed as Tmc.

(4) Intrinsic viscosity ([η])
0.1 mg of a sample was dissolved in 100 ml of tetralin at 135 ° C., and this solution was measured using a viscometer in a constant temperature bath at 135 ° C., and the intrinsic viscosity [η] was determined from the specific viscosity S according to the following formula (unit: : Dl / g).

[Η] = (S / 0.1) × (1 + 0.22 × S)
(5) Centerline average roughness (Ra) and ten-point average roughness (Rz)
Measured according to JIS B-0601 (1982) using a “non-contact three-dimensional fine shape measuring instrument (ET-30HK)” and “three-dimensional roughness analyzer (MODEL SPA-11)” manufactured by Kosaka Laboratory Ltd. . The number of measurements was 3, and the average value was used.

  The detailed conditions are as follows.

    Measurement surface treatment: Aluminum was vacuum-deposited on the measurement surface to obtain a non-contact method.

Measurement length: 1mm
Horizontal magnification: 200 times Vertical magnification: 20,000 times Cut off: 0.25 mm
Width direction feed speed: 0.1 mm / sec Length direction feed pitch: 10 μm
Number of feeds in the length direction: 20 times (6) Slip coefficient The slip coefficient is obtained from the friction force observed when two films are slid by the following method.

<Sample preparation>
A film sample (width 75 mm × length 100 mm) cut into a strip shape is aged in a hot air oven at 50 ° C. for 3 hours, and then conditioned in an atmosphere of 23 ° C. and relative humidity 65% for 12 hours or more.
<Measurement of friction force>
Next, the two sheets are overlapped, and a load (weight 200 g, bottom area 65 mm × 65 mm square) is placed thereon, and one film is drawn in the longitudinal direction of the strip (take-off speed: 150 mm / min). Measure the force with a slip tester.

The frictional force is classified into a static frictional force observed at a critical point where the film starts to slide and a dynamic frictional force observed during take-up. In the present invention, the latter dynamic frictional force R (g) is read from the chart,
Slip coefficient = R (g) / 200 (g)
And This measurement is repeated 5 times, and the average value is obtained.

  If the slip coefficient exceeds 1.0, wrinkles are likely to occur, which may impair handling properties during winding and laminating.

(7) Wetting tension Measured according to JIS K 6768 (1999) using a mixed liquid of formamide and ethylene glycol monoether (unit: mN / m).

(8) Perforation sensitivity Perforation sensitivity was evaluated as an evaluation of printing characteristics of polypropylene as a thermal printing base paper. A polypropylene film was bonded to a porous support (Japanese paper) to prepare a base paper, and a character image was made with a thermal head at an applied energy of 0.09 mJ and 0.12 mJ. The perforation state of the image portion was observed with a microscope from the polypropylene film side of the plate-making base paper, and the perforation sensitivity was evaluated by the following items.

    (Double-circle): The predetermined | prescribed perforation was performed reliably and was favorable.

    ○: There was a part where a predetermined perforation could not be obtained.

    Δ: There were portions where predetermined perforations could not be obtained.

    X: No predetermined perforation is obtained.

(9) Film Formation Method Biaxial stretching was performed by the following film formation method to obtain a film sample.

  The prepared polypropylene pellets were melt-extruded from a tandem extruder having a screw diameter of 90 mmφ / 90 mmφ at 245 ° C. and cooled and solidified on a cooling drum set at 95 ° C. to obtain an unstretched sheet. Next, the unstretched sheet is sequentially heated with four metal rolls, the film temperature is raised to a predetermined temperature, the film is stretched at a predetermined magnification in the longitudinal direction between a pair of stretching rolls, The both ends of the uniaxially stretched film were gripped and led to a hot air oven. The uniaxially stretched film was preheated to a predetermined temperature in a hot air oven, then stretched 9 times in the width direction, and then heat-set at 150 ° C. while allowing 5% relaxation in the width direction.

  The biaxially stretched film thus obtained was subjected to corona discharge treatment on the side opposite to the drum surface after exiting the hot air oven, and the film-forming edge held by the clip was removed and wound into a roll. . The roll was left to stand at room temperature for 1 day, then slit and wound up as a product roll.

Example 1
As a polypropylene resin, 97% by weight of Borealis HB300BF and 3% by weight of Basell HMS-PP PF814 were chip-blended, and led to an extruder according to the film forming method described in (7), on a 95 ° C. cooling drum. Made into a sheet. Next, the film was stretched 4.5 times at 145 ° C. in the longitudinal direction and 9 times at 158 ° C. in the width direction. After biaxial stretching, corona discharge treatment was performed to obtain a wetting tension of 41 mN / m. The thickness of the obtained film was 1.7 μm.

  The biaxially stretched polypropylene film thus obtained was bonded to Japanese paper, and the printing characteristics were evaluated. As a result, the perforation sensitivity was good.

(Example 2)
As a polypropylene resin, 95% by weight of HC318BF manufactured by Borealis and 5% by weight of HMS-PP PF814 manufactured by Basell were chip-blended and led to an extruder. The stretching conditions were 4.8 times at 143 ° C. in the longitudinal direction and 9 times at 156 ° C. in the width direction. The corona discharge treatment was 48 mN / m. Except for the above, the procedure was the same as in Example 1. The film thickness obtained was 3.2 μm.

  The results of the printing property evaluation were excellent although slightly inferior to Example 1.

(Example 3)
As a polypropylene resin, 94% by weight of Borealis HB300BF, 3% by weight of HMS-PP PF814 manufactured by Basell, and 3% by weight of polybutene-1 (BL4000 manufactured by Mitsui Chemicals, Inc.) were used in a chip blend. As stretching conditions, the film was stretched 4.8 times at 145 ° C. in the longitudinal direction and 9 times at 156 ° C. in the width direction. After biaxial stretching, a corona discharge treatment was applied to obtain a wet tension of 43 mN / m. Except for the above, the procedure was the same as in Example 1. The thickness of the obtained film was 2.2 μm.

  As a result of evaluating the printing characteristics, the perforation sensitivity was good.

(Comparative Example 1)
A film having a film thickness of 4 μm was obtained using the same film forming conditions as in Example 1. The perforation sensitivity was inferior as shown in Table 1.

Example 4
In Example 1, 100% by weight of HB300BF was formed without adding PF814. Although the product wound up in a roll shape had a tendency to block between the film layers and could not be stably unwound, the perforation sensitivity was good.

(Comparative Example 2)
As a polypropylene resin, an ethylene propylene copolymer resin composed of 98% by weight of propylene and 2% by weight of ethylene was used, and 3% by weight of PF814 was added to 97% by weight of the chip to obtain a biaxially stretched film. However, since a film of 5 μm or less cannot be stably obtained, the thickness is set to 6 μm.

  The printability of the film thus obtained was evaluated, but it was not only wrinkled when bonded to the porous support, but also had poor perforation sensitivity.

Tm: melting point Tmc: melt crystallization temperature [η]: limiting viscosity

Claims (5)

A heat-sensitive stencil polypropylene film having a melting point of 156 ° C. or higher and a polypropylene resin (A) having a thickness of 1.5 to 3.5 μm. The polypropylene film for heat-sensitive stencils according to claim 1, wherein the polypropylene resin (A) contains polypropylene having a long-chain branched structure. The polypropylene film for heat-sensitive stencil according to claim 1 or 2, wherein at least one surface has a surface glossiness of 100 to 140%. The polypropylene film for heat-sensitive stencils according to any one of claims 1 to 3, wherein the ten-point average roughness (Rz) of at least one surface is 0.20 to 1.2 µm. A heat-sensitive stencil sheet obtained by bonding a porous support layer and the polypropylene film for heat-sensitive stencil according to any one of claims 1 to 4.