JPH04125190A - Film for thermosensitive screen base paper - Google Patents

Abstract

PURPOSE:To enable a film for thermosensitive screen base paper to be obtained by a small curl and by staining a thermal head little even in many times processing by a method wherein a shrinkage percentage at a specific temperature is regulated. CONSTITUTION:A biaxial oriented film consisting of thermoplastic resin shall be 0.5-3.5mum its thickness, not less than 1.5% shrinkage percentage at 150 deg.C and not more than 0.20% shrinkage percentage at 70 deg.C. Further, the thermoplastic resin should preferably be aromatic polyester and a face aromatic refraction index of the biaxial oriented film shall be 1.485 or higher and lower than 1.500.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a film for heat-sensitive stencil paper, and more specifically to a heat-sensitive stencil plate that does not curl, has high sensitivity, is free from head stains, and is capable of high-quality plate making and printing. The present invention relates to a film that can be formed by bonding a base paper to a porous support.

[Prior Art] Heat-sensitive stencil printing usually uses a base paper in which an ink-permeable porous support and a hot-melt perforated film are bonded directly or via an adhesive, and desired characters are printed on the film of this base paper. , create a plate by thermally perforating the figure and topography,
This plate is used for printing, and the method for producing this plate is digital plate making using a thermal head (hereinafter referred to as T
H method) and a method of irradiating with infrared rays or xenon flash light (hereinafter abbreviated as flash method) are already known.

In particular, the TH method has advantages over electrostatic copying (PPC), such as lower printing costs when printing a large number of sheets, and the ability to print at crystal speed, and is rapidly becoming popular in offices, schools, etc. are doing.

On the other hand, as a method for laminating a hot-melt perforated film and an ink-permeable porous support, there are conventional laminating methods such as dry laminating and wet laminating, as well as methods described in Japanese Patent Publication No. 55-47997. It is known to use a laminating method etc.

The base paper produced in this manner tends to curl inward on the film side due to lamination conditions or changes in temperature and humidity during storage. If the curl becomes large, handling and conveyance of the base paper within the stencil printing machine become poor, leading to troubles such as base paper jamming, which becomes a major problem. In particular, recently, films with improved perforation sensitivity, such as films with improved perforation by increasing the shrinkage rate at 150°C, have been developed for the purpose of high-speed platemaking, low-energy platemaking, and high resolution.
Japanese Unexamined Patent Publication No. 63-312192) has been proposed, but in this case, although the perforation sensitivity is improved, the conventional lamination method has the drawback that the amount of shrinkage during lamination is large, resulting in large curling of the base paper.

As a method for reducing the curl of base paper, a method has been proposed in which, for example, an ink-permeable porous support is stretched by applying tension, and then a film is layered and bonded to the support (Japanese Unexamined Patent Publication No. 1-156096).

Although this method produces good curling immediately after the base paper is manufactured, curling occurs if there is a large change in temperature and humidity during storage.

In particular, in order to reduce drilling energy, the film thickness has recently been reduced to 1
It is extremely thin at ~3 μm, and the tension when bonding it together is extremely delicate, making it difficult to employ as a continuous mass production technology for base paper.

Furthermore, in the TH method, since the film is instantaneously melted and perforated using a high-temperature thermal head, there is a problem in that a sticking phenomenon occurs between the thermal head and the film. In this case, even if a small portion of the heat generating element of the head melts, unlike the flash method, the head (heat generating part) and the film are constantly moving relative to each other, so it may cause serious damage as mentioned above. problems occur.

As a method to prevent this, it has been proposed to form a release layer by coating the film surface with a surfactant, silicone oil layer, etc.
Japanese Patent Publication No. Sho BO-97891).

Formation of a release layer is effective in preventing heat fusion to the head, but if the adhesion between the film and the release layer is insufficient, the release layer will peel off and adhere to the head in the form of scum. In this case, although the sticking phenomenon does not occur, if the plate is made many times, the amount of deposits on the head will increase, and the heat transfer to the film will decrease, resulting in a decrease in perforation, resulting in problems such as a decrease in print density or image clarity. arise.

[Objective] The object of the present invention is to provide a film for thermal stencil paper that has good perforation sensitivity, has little curling even under various temperature and humidity conditions, and has little thermal head staining even during multiple plate making. be.

[Structure] According to the present invention, the object of the present invention is to provide a biaxially stretched film made of a thermoplastic resin and having a thickness of 0.5 to 3.5 μ4, and having a shrinkage rate of 0.20 at 70°C. % or less and a shrinkage rate at 150° C. of 1.5% or more.

Examples of the thermoplastic resin in the present invention include vinyl chloride resins, vinylidene chloride copolymer resins, polypropylene resins, and polyester resins, among which polyester resins are preferred.

The polyester resin is not particularly limited as long as it has an ester bond as its main skeleton, but typical examples include terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, a, β- Screw(
Aromatic dicarboxylic acids such as 2-chlorophenoquine)ethane-4,4°-dicarboxylic acid, pentasodium sulfoisophthalic acid, or aliphatic dicarboxylic acids such as sebacic acid, adipic acid, dodecadionic acid, etc., on the other hand as the diol component. ethylene glycol, diethylene glycol, l,
Mention may be made of polyesters with 4-butanediol, polyethylene glycol, polytetramethylene glycol, etc., and mixtures thereof. Among these, aromatic polyesters are particularly preferred.

A biaxially stretched film made of thermoplastic resin has a thickness of 0.
．． It is necessary to have a thickness of 5 to 3.5 μm, preferably 1.0 to 2.5 μm. If the thickness of the film is too thin, the perforation accuracy will decrease, and it will be easy to see unclear and dark areas.
If the blade is too thick, it is not preferable because it may cause printing defects or uneven thickness.

The biaxially stretched film in the present invention further needs to have a shrinkage rate at 150° C. of 1.5% or more, preferably 2% or more. If this shrinkage rate is small, the heat-sensitive perforation properties of the film will deteriorate, which is not preferable. On the other hand, if this shrinkage rate is too large, the base paper will curl with the film side facing inward. Therefore, it is necessary to consider the balance between the shrinkage rate at 150°C and the shrinkage rate at 70°C, but it is preferable to keep it to 5% or less.

The biaxially stretched film of the present invention is characterized by maintaining a shrinkage rate at 150°C of 1.5% or more, preferably 2% or more, and a shrinkage rate of 0.20% or less at 70°C.
Preferably, it is 0.15% or less. As a result, the occurrence of curling can be significantly reduced without reducing the heat-sensitive perforation properties of the film, to a level that does not pose a problem in practical use.

The relationship between the shrinkage rate and curl of a biaxially stretched film at 70°C is considered as follows.

Base paper is usually manufactured by laminating a film to a porous support such as porous tissue paper or gauze using an adhesive, and then coating a release layer on the film. In the drying step, heat treatment is performed, usually at 00 to 80°C. The shrinkage of the film under these processing conditions acts as shrinkage stress on the film side of the base paper, causing curling. Therefore, to prevent curling, the temperature of the film should be 70°C.
It is effective to reduce the shrinkage rate in .

For example, in the case of polyethylene terephthalate film 7
A temperature of 0° C. is near the polymer glass transition temperature, so the shrinkage rate at 70° C. depends on the residual stress inherent in the film. Therefore, when a film is stored for a long period of time, this shrinkage rate tends to decrease, but this requires a large storage space industrially, so the shrinkage rate at 70°C is reduced at the film manufacturing stage. It needs to be made smaller.

The biaxially stretched film can be produced by a method known in the art, except for performing the treatment to develop the film properties described above. For example, aromatic polyester is sufficiently dried at a predetermined temperature, then fed to an extruder, extruded from a die onto a rotating cooling drum in a molten state, and the film-like melt is brought into close contact with the drum and rapidly solidified to form an unstretched film. Then, a method is usually used in which the unstretched film is subjected to biaxial stretching and heat setting treatment to obtain a biaxially stretched film. Preferred examples of the biaxial stretching method include a sequential biaxial stretching method and a multistage stretching method in which the film is sequentially stretched biaxially and then stretched again in the longitudinal direction. The stretching ratio is usually 2.5 to 5 times in each of the longitudinal and lateral directions. Further, heat setting is usually carried out at a temperature of 100 to 250°C with a relaxation rate of 20% or less.

Adjustment of shrinkage rate at 150°C of biaxially stretched film is as follows:
For example, as described in JP-A-63-31292, this can be done by adjusting the heat treatment conditions after biaxial stretching. The shrinkage rate can be increased by relaxing the heat treatment conditions, and for example, the shrinkage rate can be increased by lowering the heat treatment temperature. However, if this temperature is lowered, the shrinkage rate at 70°C will inevitably increase.

The method of reducing the shrinkage rate at 70°C while maintaining the shrinkage rate at 150°C to 1.5% or higher is to increase the tension when winding the film or to take it back after the heat treatment process after biaxial stretching. A method of adjusting tension etc. is particularly effective. By reducing these tensions, the shrinkage rate at 70°C can be reduced.

In order to impart further curl reduction properties to the biaxially stretched film of the present invention, in addition to the above-mentioned shrinkage rate characteristics, especially in the polyester film, the refractive index in the plane direction (hereinafter sometimes abbreviated as nz) must be increased to 1. .485 or more 1.5
It is preferably less than 0.00, more preferably 1.487 or more and less than 1.500.

The reason why this in-plane refractive index contributes to curl reduction is considered as follows.

In addition to the above-mentioned thermal contraction, the difference in humidity expansion between the porous support and the film is considered to be a factor causing curling. For example, paper commonly used as a porous support has a humidity expansion coefficient of lXl.
On the other hand, the humidity expansion coefficient of a film such as a polyester film with a thickness of 2.5 μl is approximately 10×lO°6RH, and the stencil paper made by laminating the two has a humidity expansion coefficient difference of about 0' to 7XIO-'%RH. Therefore, it can be said that there is an inherent factor that causes the film to curl under high humidity.

However, for boat fishing, the paper is much thicker than the film, so the difference in humidity expansion alone will not cause curling, but if the shrinkage rate of the film at 70°C is large, curling will occur due to the synergistic effect. It is thought that the

The in-plane refractive index (nz) of the film becomes relatively large when the longitudinal and transverse orientations of the biaxially stretched film are reduced. It is understood that by reducing the orientation in the vertical and horizontal directions, the humidity expansion coefficient increases, and as a result, the difference between the humidity expansion coefficient and the paper humidity expansion coefficient becomes smaller, making it difficult for curling to occur.

However, if the in-plane refractive index (nz) is greater than 1,500, the mechanical strength of the film decreases and becomes insufficient, and problems such as poor handling properties occur, which is not preferable.

The in-plane refractive index (nz) of the biaxially stretched film is 1.485.
Setting it to less than 1,500 is effective in reducing curl, but at the same time it has the advantage of improving the adhesion between the film and the release layer. This improvement in adhesion reduces the amount of debris that accumulates on the head, and even when making and printing a large number of sheets, there is no decrease in print density or smearing, and the same clear image as at the beginning of plate making and printing can be obtained.

In order to improve the adhesion to the porous support, the film for heat-sensitive stencil paper of the present invention has air on the surface of the film.
Corona discharge treatment may be performed in a carbon dioxide or nitrogen gas atmosphere. Further, other adhesion-promoting treatments may be applied.

Furthermore, this film may contain organic or inorganic additives to improve slipperiness.

The porous support to which the above-mentioned film is bonded is not particularly limited, but may include Japanese paper, Kyugucho paper, synthetic fiber paper,
Typical examples include various woven fabrics and nonwoven fabrics. Furthermore, the weight of the porous support used is not particularly limited, but is usually 2 to 20 g/m', preferably 5 to 20 g/m'.
15g/■2 culm size is used. In addition, when using a mesh-like sheet, it is recommended to use one woven with fibers with a thickness of 20 to 60 μm, and the grid spacing is 20 μm.
It is preferable to use one with a diameter of 250 μm.

The adhesive used to bond the film of the present invention and the porous support is not particularly limited, but typical examples include vinyl acetate resin, acrylic resin, urethane resin, and polyester resin. I can do it.

[Example] Hereinafter, the present invention will be further explained with reference to Examples. In addition,
The properties in the examples were measured by the following method.

■) Shrinkage rate of the film Sample the film into a leg-width strip, mark it with a constant pressure #i (usually 10 cm), and then hold it in an oven heated to the following predetermined temperature for a predetermined time, Thereafter, the temperature was returned to room temperature, the distance between the marks was determined as -Fl, and the shrinkage rate was calculated from the following formula.

[However, intersection: distance between marks before heating and holding 51=pressure between marks after heating and holding M] (a) Shrinkage rate at 150°C It was determined at a heating temperature of 150°C and a heating and holding time of 30 minutes.

(a) Shrinkage rate at 70℃ It was determined at a heating temperature of 70° C. and a heating holding time of 60 minutes.

2) Refractive index in the plane direction The refractive index in the plane direction of the film was measured using an Atsabe refractometer manufactured by Atago ■ and a sodium lamp as the light source.

3) Mail-order properties A reverse plate test was conducted on the base paper in a high-humidity environment with a relative humidity of 70% or more, and the transportability was evaluated using the following criteria.

Transportability evaluation criteria: ◎: Almost no curls, good mail order ○: Slight curls, but mail order ×: Large curls, high degree of mail order trouble △: Between Q and × 4) Dirt on the thermal head Thermal stencil printing equipment (Nibribo 1-5S88 manufactured by Ricoh)
In 0), after 1000 plates were made using a ``Funatsuri'' character manuscript, the state of adhesion of the bulk material on the thermal head was evaluated visually or with a microscope using the following criteria.

Head dirt evaluation criteria ○: Almost no head dirt △ Head dirt is slightly present °C) 0.62
After thoroughly drying the polyethylene terephthalate, it was melted and extruded into a sheet using an extruder, and rapidly solidified using an electrostatic casting method to form an amorphous sheet. Stretched 3.7 to 3.9 times in the transverse direction,
Further, heat treatment was performed at 200-230''C for about 1.5 seconds to obtain a biaxially stretched film with a thickness of 2.0 μm and the physical properties shown in Table 1.

Next, a base paper for heat-sensitive stenciling was prepared by pasting the Flume with Tetron 0 gauze. The properties of this base paper are shown in Table 1.

As is clear from Table 1, the film of Example 1.2 makes it possible to obtain a thermal stencil paper with less curl and no head stains.

[Effects of the Invention] The film of the present invention reduces or prevents the occurrence of curling, which is a problem when handling high-sensitivity thermal stencil paper, and has excellent perforation sensitivity with less head staining even during multiple plate making. , image quality thermal stencil paper can be produced.

Claims (2)

[Claims] (1) A biaxially stretched film made of a thermoplastic resin with a thickness of 0.5 to 3.5 μm and a shrinkage rate of 0 at 70°C.
．． 20% or less, and the shrinkage rate at 150°C is 1
．． A film for heat-sensitive stencil paper, characterized in that the content is 5% or more. (2) The film for heat-sensitive stencil paper according to claim (1), wherein the thermoplastic resin is an aromatic polyester, and the film has an in-plane refractive index of 1,485 or more and less than 1,500.