JP2009214421A - Polypropylene film for heat-sensitive stencil, and heat-sensitive stencil sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene film having an excellent boring property for a heat-sensitive stencil, and to provide a heat-sensitive stencil sheet using the polypropylene film. <P>SOLUTION: This polypropylene film for heat-sensitive stencil is constituted by containing a polypropylene-based resin (C). The polypropylene-based resin (C) contains a polypropylene resin (A) of which the melting point is 156°C or higher, and a petroleum resin (B) of which the glass transition temperature is 50 to 120°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermoplastic resin substrate 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 laminate obtained by joining the materials 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.

  Here, as the heat source, pulsed radiation of visible light to infrared light, thermal head, irradiation of a beam of light such as laser light, and the like have been proposed. In order to print precise images and characters, it is required to reduce the shape and size of the heat source. However, since the amount of generated heat is also reduced, the thermoplastic resin substrate 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 film has been proposed to be preferably used (Patent Document 1). Among these, a polypropylene copolymer film has been proposed as a heat-sensitive stencil film for improving the perforation property. (Patent Document 2). A technique for irradiating an electron beam has also been proposed for a polypropylene system (Patent Document 3). However, a very thin film is inferior in the efficiency of irradiating an electron beam. .

  Furthermore, in order to obtain sufficient perforation properties, many proposals have been made for improved techniques using polyester film as the heat-sensitive film (Patent Documents 4 to 8). 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.54-33117 Japanese Examined 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

  An object of the present invention is to provide a polypropylene film having excellent piercing properties for a heat-sensitive stencil and a heat-sensitive stencil sheet comprising the same by using a specific polypropylene film.

To achieve the above object, the present invention is characterized by the following.
(1) A polypropylene film for thermal stencil containing a polypropylene resin (C) containing a polypropylene resin (A) and a petroleum resin (B) having a glass transition temperature of 50 to 120 ° C.
(2) The polypropylene film for heat-sensitive stencils according to (1) above, wherein the content of the petroleum resin (B) in the polypropylene resin (C) is 1 to 15% by mass.
(3) The polypropylene film for heat-sensitive stencil according to (1) or (2) above, wherein the polypropylene resin (A) has a melting point of 156 ° C. or higher.
(4) The polypropylene film for heat-sensitive stencils according to any one of (1) to (3), wherein the film thickness is 1.5 to 3.5 μm.
(5) The thermal stencil plate according to any one of (1) to (4) above, wherein the ratio a / b of the longitudinal heat shrinkage rate a and the transverse heat shrinkage rate b is 1.5 to 3.0 Polypropylene film.
(6) The polypropylene film for heat-sensitive stencils according to any one of the above (1) to (5), wherein the surface glossiness of at least one surface is 100 to 140%.
(7) A heat-sensitive stencil sheet obtained by bonding a porous support and the polypropylene film for heat-sensitive stencil according to any one of (1) to (6) above.

The polypropylene film for heat-sensitive stencil of the present invention and the heat-sensitive stencil sheet comprising the same are obtained by adding a petroleum resin to a polypropylene resin.
1. High-definition printing is possible because holes with excellent perforation and high uniformity are formed.
2. It has excellent properties and effects such as high film rigidity, heat-sensitive stencil paper that is less likely to wrinkle, and a beautifully finished print.

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

  The polypropylene film for heat-sensitive stencil of the present invention is composed of a polypropylene resin (C) containing a polypropylene resin (A) and a petroleum resin (B).

  First, the melting point of the polypropylene resin (A) is not particularly specified, but when the film thickness is thin, it is preferably 156 ° C. or more, more preferably 159 ° C. or more from the viewpoint of handling properties. Yes, and particularly preferably 162 ° C or higher. About an upper limit, it depends on the manufacturing technology of the present polypropylene resin, and the upper limit of melting | fusing point of the polypropylene which can be obtained industrially is around 167 degreeC.

  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 adversely affected. 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 content in the polypropylene resin (A) is preferably 5% by mass or less, and preferably 0.5 to 3% by mass, because the sensitivity can be improved without greatly reducing the rigidity.

  The petroleum resin (B) has a glass transition temperature of 50 to 120 ° C., and a plurality of resins having different glass transition temperatures in this range may be selected. Here, petroleum resins include aliphatic petroleum resins, alicyclic petroleum resins, aromatic petroleum resins, rosin esters, terpene resins, terpene phenol resins, and the like. Also included.

  Among these, at least one selected from the group of alicyclic petroleum resins and terpene resins is preferable because of excellent compatibility with the polypropylene resin, and in particular, a 5-membered ring such as norbornene and dicyclopentadiene and / or Alternatively, a resin containing a 6-membered ring structure is more preferable. Specifically, Marcaretz M890A, M845A (manufactured by Maruzen Petrochemical Co., Ltd.) and Oppera PR103J (manufactured by ExxonMobil) are exemplified.

  Since the resin having such a structure has a rigid cyclic structure and excellent compatibility with the amorphous part of polypropylene, the rigid structure constrains the movement of the amorphous part of the polypropylene, thereby reducing the film rigidity. In particular, in a thin film, handling properties can be improved. The content of the petroleum resin (B) in the polypropylene resin (C) is preferably 1 to 15% by mass, more preferably 2 to 12% by mass, and particularly preferably 3 to 10% by mass. is there. When the content of the petroleum resin (B) is less than 1% by mass, the piercing property is inferior, and when it exceeds 15% by mass, the solvent resistance may be deteriorated or blocking may occur.

  In addition, a known heat stabilizer, antioxidant, chlorine scavenger, organic and / or inorganic slip agent, antistatic agent and the like may be contained within a range not violating the object of the present invention. 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. Thus, since there are advantages and disadvantages, the content of the metal soap in the polypropylene resin is preferably 200 ppm (mass basis) or less, particularly preferably 100 ppm (mass basis) or less, and hydrotalcite is preferably 100 ppm (mass basis). (Mass basis) or less, more preferably 50 ppm (mass basis) or less. In order to reduce the content of these chlorine scavengers as much as possible, it is desirable to reduce the amount of residual chlorine in the polypropylene resin as much as possible, preferably 15 ppm (mass basis) or less, particularly preferably 10 ppm (mass 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. Is 0.01-1 mass%.

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

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

  In the film of the present invention, it is desirable that the heat shrinkage ratio in the vertical direction and the horizontal direction is balanced from the viewpoint of the roundness of the hole, and specifically, the ratio of the heat shrinkage ratio a in the vertical direction and the heat shrinkage ratio b in the horizontal direction. It is preferable that a / b is 1.5-3.0, More preferably, it is 1.5-2.0. If it is less than 1.5, it is difficult to form a film, and if it exceeds 3.0, the flatness of the hole increases, and the amount of ink transmitted tends to be not constant.

  Further, the 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 glossiness is an index reflecting the surface roughness, and the glossiness decreases as the surface is roughened. On the other hand, the glossiness increases as the surface becomes smoother. Accordingly, when the glossiness 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 glossiness is high and the surface is smooth, the yield may decrease due to problems such as poor sliding and wrinkles.

  In order to obtain such glossiness, it is preferable to add a small amount of an incompatible polymer-based additive to polypropylene, specifically, high-density polyethylene, poly-4-methylpentene 1, polystyrene, ethylene propylene. A rubber etc. are illustrated. Specifically, it is preferable to set the cooling temperature in the range of 80 to 120 ° C. in the melt extrusion sheeting step. 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, so that the desired glossiness is achieved. Can be obtained. An example of a method for further controlling the glossiness is a method in which a nucleating agent that selectively forms β-type crystals is added to the resin.

  Further, 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 bonding property with a porous support (porous substrate) described later, particularly the adhesion. The surface wetting tension is preferably 35 to 52 mN / m, more preferably 38 to 50 mN / m. If the wetting tension is less than 35 mN / m, the adhesion may be lowered. On the other hand, if the wetting tension is more than 52 mN / m, 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 surface is bonded to a porous support in order to use it as a heat-sensitive stencil sheet.

  The porous support is required to be easy to impregnate and move the ink while maintaining the film strength as a heat-sensitive stencil sheet, and is preferably a porous body made of natural cellulose fibers and / or synthetic resin fibers. In the bonding of the porous support and the film of the present invention, a polyester, polyurethane, or acrylic adhesive is generally used as appropriate, but other methods such as thermocompression bonding and extrusion lamination are used. Also good.

  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.

  Polypropylene resin (A) and petroleum resin (B) are melted and kneaded at 220 to 270 ° C. using an extruder, led to a T-shaped slit die from which foreign substances in the resin have been removed by a filter, and melt extruded into a sheet. . Of course, melt blending may be performed in advance without relying on pellet blending.

  Next, the melt-extruded sheet is cooled and solidified while being closely adhered by 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, when the temperature exceeds 120 ° C., crystallization is slowed down, and the line speed has to be lowered, which may deteriorate the economy.

  Next, the cooled and solidified sheet is preheated by a plurality of heated metal rolls, and the sheet temperature is increased to 135 to 155 ° C., preferably 140 to 150 ° C. The film is stretched 8 times, preferably 6 to 8 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 10 times in the width direction. 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 film obtained as described above and a porous support. As a joining method, thermocompression bonding, extrusion lamination, adhesion, or the like is preferably used. When bonding by bonding, 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. Since it is high, it is preferably applied to a porous support and bonded 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) Melting point (Tm) (° C)
Using an RDC220 differential scanning calorimeter manufactured by Seiko Co., Ltd., measurement was performed 5 times under the following conditions, and the average value of the remaining 3 points excluding 2 points of the maximum value and the minimum value was defined as Tm.

<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.

(2) Glass transition temperature (° C)
When a 5 mg sample was heated at a rate of 20 ° C./min in a nitrogen atmosphere in accordance with JIS K-7122 (1987) using a Seiko RDC220 differential scanning calorimeter, the secondary transition The change in specific heat associated with was determined as the glass transition temperature (Tg).

(3) Wetting tension Using a mixed liquid of formamide and ethylene glycol monoether, the wetting tension was measured according to JIS C-2330 (2001) 7.4.13 (unit: mN / m).

(4) 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.

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

(6) Heat shrinkage rate (%)
It measured according to 7.3 of JIS Z-1712 (1997).

(7) Perforation sensitivity The perforation sensitivity was evaluated as a printing characteristic evaluation as a thermal printing base paper. A polypropylene film was bonded to a porous support (Japanese paper) to produce 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 area was observed with a microscope from the polypropylene film side of the plate-making base paper, and the perforation sensitivity was evaluated according to the following items.

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

(8) Flatness The drilled state was observed in the same manner as in (7) above, the long diameter c and the short diameter d of the hole were measured, and (cd) / c was defined as the flatness.

(9) Corona treatment strength This is the electric power supplied per unit area of the film to be treated, and is represented by the following equation.

  Here, the area of the film represents the area of the film portion to be processed per minute.

Corona treatment strength (W · min / m ² ) = Power supply (W) / Processed film area (m ² / min)
(10) 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
The above-mentioned item (10), wherein 93% by mass of Borealis HB300BF (melting point 163 ° C.) as polypropylene resin (A) and 7% by mass of Oppera PR103J (glass transition temperature 70 ° C.) as petroleum resin (B) are chip-blended. In accordance with the film forming method, the film was led to an extruder and formed into a sheet on a 95 ° C. cooling drum. Next, the film was stretched 7 times at 140 ° C. in the longitudinal direction and 9 times at 158 ° C. in the width direction. After biaxial stretching, a corona discharge treatment was performed at a corona treatment strength of 8 W · min / m ² 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 and the flatness of the holes was as low as 0.20.

(Example 2)
90% by mass of Borealis HB300BF as polypropylene resin (A) and 10% by mass of Oppera PR103J as petroleum resin (B) were introduced into an extruder. The stretching conditions were 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 performed at a corona treatment strength of 15 W · min / m ² to obtain a wet tension of 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. The flatness was as low as 0.10.

(Example 3)
97% by mass of Borealis HB300BF as the polypropylene resin (A) and 3% by mass of Oppera PR103J as the petroleum resin (B) were used in a chip blend. As stretching conditions, the film was stretched 7.5 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 at a corona treatment strength of 9 W · min / m ² 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, it was excellent although it was slightly inferior to Example 1. The flatness was as low as 0.15.

Example 4
As a polypropylene resin (A), 84% by mass of HB300BF manufactured by Borealis and as a petroleum resin (B), 16% by mass of Oppera PR103J were used in a chip blend. As stretching conditions, the film was stretched 6.5 times at 142 ° C. in the longitudinal direction and 9 times at 156 ° C. in the width direction. After biaxial stretching, a corona discharge treatment was applied at a corona treatment strength of 12 W · min / m ² to obtain a wetting tension of 46 mN / m. Except for the above, the procedure was the same as in Example 1. The thickness of the obtained film was 2.0 μm.

  As a result of evaluating the printing characteristics, the perforation sensitivity was excellent. Further, although the flatness was a little higher at 0.23, the product wound up in a roll shape had a blocking tendency between the film layers.

(Example 5)
As a polypropylene resin (A), 91% by mass of HB300BF manufactured by Borealis and as a petroleum resin (B), 9% by mass of Oppera PR103J were used in a chip blend. As stretching conditions, the film was stretched 6.0 times at 144 ° C. in the longitudinal direction and 9 times at 156 ° C. in the width direction. After biaxial stretching, a corona discharge treatment was performed at a corona treatment strength of 15 W · min / m ² to obtain a wet tension of 48 mN / m. Except for the above, the procedure was the same as in Example 1. The thickness of the obtained film was 4.0 μm.

  As a result of evaluating printing characteristics, perforation sensitivity was slightly low. Also, the flatness was as high as 0.25.

(Comparative Example 1)
HB300BF was formed into a film at 100% by mass without adding petroleum resin. As stretching conditions, the film was stretched 5.5 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 performed at a corona treatment strength of 8 W · min / m ² to obtain a wetting tension of 41 N / m. Except for the above, the procedure was the same as in Example 1. The thickness of the obtained film was 2.5 μm.

  As a result of evaluating printing characteristics, perforation sensitivity was poor. The flatness was also high at 0.30.

  Tm: melting point

Claims (7)

A heat-sensitive stencil polypropylene film comprising a polypropylene resin (C) comprising a polypropylene resin (A) and a petroleum resin (B) having a glass transition temperature of 50 to 120 ° C. The polypropylene film for heat-sensitive stencils according to claim 1, wherein the content of the petroleum resin (B) in the polypropylene resin (C) is 1 to 15% by mass. The polypropylene film for heat-sensitive stencil according to claim 1 or 2, wherein the melting point of the polypropylene resin (A) is 156 ° C or higher. The polypropylene film for heat-sensitive stencils according to any one of claims 1 to 3, wherein the thickness is 1.5 to 3.5 µm. The heat-sensitive stencil polypropylene film according to any one of claims 1 to 4, wherein the ratio a / b of the longitudinal heat shrinkage rate a and the transverse heat shrinkage rate b is 1.5 to 3.0. The polypropylene film for heat-sensitive stencils according to any one of claims 1 to 5, wherein at least one surface has a surface glossiness of 100 to 140%. A heat-sensitive stencil sheet obtained by bonding a porous support and the polypropylene film for heat-sensitive stencil according to any one of claims 1 to 6.