JPH02307788A - Polyester film for thermally sensitive stencil paper - Google Patents

Abstract

PURPOSE:To ensure that the subject film has high perforation capability, high resolution during printing and superior resistance to wear or does not become curled during the use or storage of stencil paper by selecting the film with specific melting point and glass transition point and with a surface state and coefficient of thermal contraction which satisfy specific conditions. CONSTITUTION:The subject film is a biaxially oriented film consisting of a polyester compound with a melting point of 200 to 250 deg.C and a glass transition temperature of 70 deg.C or more. In addition, the film has a thickness of 0.5 to 6 mum, a surface curvature of 0.03 to 0.5 mum, and a coefficient of thermal contraction of 3 to 35% at least in one direction on the film surface after thermal processing at 150 deg.C for 3 minutes. Polyester has main acid component such as aromatic dicarboxylic acid and main glycol component such as alkylene glycol. The recommendable aromatic dicarboxylic acid is terephthalic acid and the recommendable alkylene glycol is ethylene glycol. The polyester compound is obtained by introducing a specific composition unit into polyester. For example, part of the telephthalic acid unit is used as the 2,6-naphthalene dicarboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polyester film for thermal stencil printing base paper. More specifically, the present invention relates to a film for heat-sensitive stencil printing base paper that has excellent perforation properties, resolution during printing, and printing durability, and does not curl during use or storage of the base paper.

[Prior Art and Problems to be Solved by the Invention] Conventionally, as a base paper for heat-sensitive stencil printing, one in which a thermoplastic resin film is laminated with porous thin paper is known.

The above thermoplastic resin film includes polyester,
Films made of various resins such as polyvinyl chloride and polypropylene are used, but the properties as a base paper for thermal stencil printing are significantly affected by the physical properties of these films, so various films are used according to the required properties.
Improvements are being attempted.

Films used for such purposes are required to have the following properties.

(1) Good thermal perforability. That is, it should melt with a small amount of heat and have a sufficient heat shrinkage rate to obtain perforations of appropriate size so that the image when printed is clear.

(2) The film must have sufficient strength and elastic modulus to withstand the work of laminating with porous thin paper and printing, and the film has good slipperiness so that the work can be carried out smoothly.

(3) Must be able to withstand organic solvents such as toluene and xylene used in printing inks for long periods of time. - In addition to these requirements, it is also necessary to have excellent productivity during film production. That is, it is necessary that the film has good stretchability and does not cause troubles such as breakage, and also has good winding and slitting properties so that it does not wrinkle or roll misaligned during winding.

Furthermore, after laminating with porous thin paper to form a base paper, it is necessary that the base paper does not curl due to dimensional changes in the film during storage or the like.

A two-wheel stretched film with improved printing properties made of a thermoplastic resin with specific thermal properties as a film conventionally used for such purposes (Japanese Patent Application Laid-open No. 149596/1983)
has been proposed, but it does not satisfy all of the above requirements.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventors have conducted intensive studies and found that a biaxially oriented film made of polyester having a specific melting point and glass transition point and whose surface state and heat shrinkage rate satisfy specific conditions is heat-sensitive. It was discovered that the film is suitable as a film for stencil printing base paper, and the present invention was completed.

That is, the gist of the present invention is a biaxially oriented film made of a polyester composition having a melting point of 200 to 250°C and a glass transition temperature of 70°C or higher, the film having a thickness of 0.5 to 6 μm, and a surface of Ra is 0.03~0.5tt
m, a polyester film for heat-sensitive stencil printing base paper, characterized in that the heat shrinkage rate after treatment at 150° C. for 3 minutes is 3 to 35% in at least one direction within the plane of the film.

The present invention will be explained in detail below.

The term "polyester" used in the present invention refers to a polyester containing an aromatic dicarboxylic acid as a main acid component and an alkylene glycol as a main glycol component. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, 2.6-
Examples include naphthalene dicarboxylic acid. In addition, alkylene glycols include ethylene glycol, tetramethylene glycol, neopentyl glycol, 1.4
-Cyclohexane dimetatool and the like.

The film of the present invention is composed of a polyester composition having the above-mentioned structure, and the melting point of the composition is 200 to 250°C, preferably 200 to 240°C, and the glass transition temperature is 70°C or higher, preferably 72 to 110°C. . If the melting point is less than 200°C, the film will lack heat resistance, so when used as a base paper for thermal stencil printing, it will suffer heat loss during perforation.
The redundant portions are perforated, causing a drop in resolution. On the other hand, if the melting point exceeds 250° C., the perforation property decreases, uneven perforation increases, and the printing quality deteriorates, which is not preferable. If the glass transition point is less than 70° C., the dimensional stability of the film decreases, so that the base paper curls after being processed into a base paper, which is not preferable. This phenomenon is particularly noticeable when stored in a high temperature place.

The polyester composition used in the present invention is characterized by a lower melting point and a higher glass transition temperature than normal ones, but such a polyester composition can be obtained by introducing a specific structural unit into polyester. I can do it. One or more types of such units may be used, but for example, a part of terephthalic acid units may be replaced by 2,6-naphthalene dicarboxylic acid units, or a part of ethylene glycol units may be replaced by 1,4-cyclohexane dimetatool. Methods include:

Methods for introducing such units include adding monomers that provide the respective structural units during polyester production and copolymerizing them, blending pomopolymers each composed of a single component, and blending copolymers. Examples include methods. Among them, preferably 85 mol% or more of ethylene terephthalate units, more preferably 95 mol%
A polyester containing mol% or more of ethylene naphthalate units, a polyester containing preferably 90 mol% or more, more preferably 95 mol% or more of ethylene naphthalate units, and/or 1.
Preferably 80 mol% or more, more preferably 90 mol% of 4-cyclohexylene dimethylene terephthalate units.
It is particularly preferable to use a blend composition with a polyester containing the above-mentioned components, from the viewpoint of manufacturing cost and the fact that problems such as fusion during drying of the polymer do not occur.

The thickness of the film of the present invention needs to be 0.5 to 6 μm, preferably 0.5 to 3 μm. The thinner the film, the shorter the heat transfer distance, and the less thermal energy required during perforation (this improves perforation and improves resolution and print quality during printing, but 0.
If the thickness is less than 5 μm, printing is likely to be unclear and uneven density will occur, and productivity and winding workability will deteriorate in film production. A film with a thickness exceeding 6 μm is not preferable because the perforation property deteriorates and unevenness occurs during printing.

Further, the film of the present invention needs to have a heat shrinkage rate within a certain range in order to uniformly and quickly perforate the film. That is, the heat shrinkage rate after treatment at 150° C. for 3 minutes must be in the range of 3 to 35% at least in one direction within the film plane. If the heating shrinkage rate is less than 3%,
The perforations are uneven and the resolution is poor. Also, the heating shrinkage rate is 35%.
Exceeding this is not preferable because the deformation around the perforations becomes significant and the print quality deteriorates due to fusion of the perforations. This value preferably ranges from 5 to 25%.

Another feature of the film of the present invention is that the center line average roughness (Ra) of the surface is within a specific range. In order to improve workability during film winding, coating, laminating processes, and printing, it is necessary to provide the film with appropriate slipperiness. For this purpose, a method of roughening the surface is adopted, but if the degree of roughening is too large, heat transfer becomes uneven and the perforations become uneven, resulting in poor resolution and impaired printing quality. Therefore, the Ra of the film of the present invention needs to be in the range of 0.03 to 0.5 μm,
Preferably it is in the range of 0.05 to 0.3 μm.

If Ra is less than 0.03 μw, workability will be poor, and if Ra is less than 0.5 μm
Exceeding this is not preferable as the resolution and print quality will be poor.

In order to provide such surface roughness, the following method may be adopted. That is, a method of blending a fine inert compound into the polymer used for film formation is preferably employed. Such methods include the so-called precipitated particle method, in which a phosphorus compound or the like is applied to a metal compound dissolved in the reaction system during polymer production to precipitate fine particles, and the extrusion process from the polymer production process to the extrusion process before film formation. In either step, a method in which inert inorganic or organic fine particles are blended with the polymer, a so-called additive particle method, is preferably used. Examples of inert fine particles used in the additive particle method include kaolin, talc, magnesium carbonate, calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, carbon blank, and Examples include, but are not limited to, crosslinked polymer fine powders as described in Japanese Patent Publication No. 59-5216. The average particle size of such inert fine particles is usually
Equal sphere diameter of 0.01 to 5 μm, preferably 0.1 to 3
μm range, and the amount added to the film is usually
It is selected from the range of 0.01 to 5% by weight, preferably 0.1 to 3% by weight. The inert fine particles blended at this time may be a single component, or two or more components may be used simultaneously. A method of simultaneously blending fine particles by the precipitated particle method and fine particles by the additive particle method is also preferably used.

The above-mentioned film surface has a number of protrusions with a protrusion height of 0.1 μm or more measured using a three-dimensional surface roughness meter, which will be described later, usually from 1000 to 12,000/1112, preferably 3.
The number of protrusions with a protrusion height of 0.4 μm or more is usually 20 to 2,000.
It is preferably in the range of 50 to 1000 pieces/112. When these requirements in addition to Ra are satisfied at the same time, workability, resolution during printing, and print quality are more highly satisfied.

Since the film of the present invention is produced as an extremely thin film, a decrease in strength is not preferable because handling efficiency deteriorates. In the present invention, it is preferable that the tensile modulus of the film in both the longitudinal and transverse directions is 300 kg/12 or more, preferably 400 kg/2 or more, as this provides better handling and printing durability.

Next, a method for manufacturing such a polyester film will be explained. In the present invention, a polymer is supplied to a well-known melt extrusion device such as an extruder, and heated to a temperature equal to or higher than the melting point of the polymer to melt it. Next, the molten polymer is extruded through a slit-shaped goo and rapidly cooled and solidified on a rotating cooling drum to a temperature below the glass transition temperature to obtain an unoriented sheet in a substantially amorphous state.

In this case, in order to improve the flatness of the sheet, it is necessary to increase the adhesion between the sheet and the rotating cooling drum, and in the present invention, an electrostatic application adhesion method and/or a liquid application adhesion method are preferably employed.

The electrostatic application adhesion method usually involves placing a linear electrode on the upper surface of the sheet in a direction perpendicular to the flow of the sheet.
In this method, a DC voltage of 0 kV is applied to impart an electrostatic charge to the sheet, thereby improving its adhesion to the drum. In addition, the liquid application adhesion method is a method that improves the adhesion between the drum and the sheet by uniformly applying a liquid to the entire or part of the surface of the rotating cooling drum (for example, only the parts that contact both ends of the sheet). be. In the present invention, both may be used in combination if necessary.

In the present invention, the sheet thus obtained is biaxially stretched to form a film.

Specifically speaking about the stretching conditions, the unstretched sheet is preferably heated at 60 to 120°C, more preferably 70 to 11°C.
It is stretched 2.5 to 7 times in one direction using a roll or tenter type stretching machine in a temperature range of 0"C. Next, it is stretched in a direction perpendicular to the first stage, preferably at 65 to 125C, more preferably at 75 to 125C. Stretching is performed 2.5 to 7 times in a temperature range of 115°C to obtain a biaxially oriented film.Also, a method of stretching in one direction in two or more stages can also be used, but in that case, the final stretching It is preferable that the magnification falls within the above range.Also, the area magnification of the unstretched sheet is 6 to 6.
It is also possible to carry out simultaneous biaxial stretching so that the stretching is 30 times.

The film thus obtained is preferably subjected to heat treatment, but it can also be stretched in the longitudinal and/or transverse directions before or after heat treatment, if necessary.

In the present invention, the heat shrinkage rate after treatment at 150°C for 3 minutes is small (3 to 25% in one direction within the film plane).
However, in order to achieve such a heat shrinkage rate, the heat treatment temperature is usually 100 to 200°C, preferably 120 to 1
The temperature is 80°C, and the heat treatment time is 1 second to 10 minutes. Such heat treatment may be carried out under limited shrinkage or elongation of the film within 20% or at a constant length, and may be carried out in two or more stages.

In addition, in the present invention, other polymers (for example, polyethylene, polystyrene, polycarbonate, polysulfone, polyethersulfone, polyphenylene sulfide, polyamide, polyimide, etc.) may be contained in an amount of about 10% by weight or less based on the total amount of polyester used for film formation. Good too. In addition, antioxidants, heat stabilizers, lubricants,
Additives such as antistatic agents, dyes, and pigments may be added.

The thus obtained polyester film of the present invention can be obtained by laminating predetermined porous thin paper using a conventional method to improve thermal perforability, resolution during printing,
It is possible to obtain an excellent base paper for heat-sensitive stencil printing, which has excellent printing durability and does not cause the problem of curling during use or storage of the base paper. - [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, the physical property measurement method in the following examples is shown below.

(1) Melting point and glass transition temperature Seiko Electronics Industries Co., Ltd. differential calorimeter 5SC580DS
Measurement was performed using C20 type. The DSC measurement conditions are as follows. That is, the sample film lOmj was set in a DSC device, melted and stored at a temperature of 300° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. Rapidly cooled sample from 0℃ to 10'C
/min, and the glass transition temperature (Tg) and melting point (Tm
) was measured. Tg is sensed as the D'SC curve bends due to a change in specific heat, and the baseline moves in parallel.

The intersection of the tangent to the baseline at a temperature below the bending point and the tangent at the point where the slope is maximum in the bent portion was defined as the starting point of bending, and this temperature was defined as Tg.

Moreover, Tm was measured as the peak temperature of endotherm due to melting.

(2) Heat shrinkage rate The sample was heat treated in an oven maintained at a temperature of 150° C. for 3 minutes without tension, and the length of the sample before and after was measured and calculated using the following formula.

Measurements were made at five points each in the vertical and horizontal directions of the film, and the average value of each was taken as the measured value.

(3) Center line average roughness) It was determined as follows using a surface roughness measuring machine (SE-3F) manufactured by Koita Research Institute. That is, the reference length I-(2,5+s
+i) is extracted, and the roughness curve y=f (
x), the value given by the following formula is [μm]
It is expressed as The center line average roughness is 1 from the sample film surface.
Zero cross-sectional curves were determined, and the average value of the center line average roughness of the sampled portion determined from these cross-sectional curves was expressed. still,
The tip radius of the stylus was 2 μM, the load was 30 mg, and the volume was 0.08 ml.

Three-dimensional surface roughness meter (SE-3AK) manufactured by Kazu Koita Laboratory Co., Ltd.
Using stylus tip radius of 5 μm, load of 30 mg, measurement length Q of 5 mm, sampling pinch of 1.0 μm, cutoff value of 0.25 mm, 1 magnification of 20,000 times, lateral magnification of 200 times, number of scans of 500 lines. The protrusion height and number of protrusions were measured under the following conditions. The protrusion height (X, μm) referred to here is,
The height of the point where the number of protrusions is maximum is taken as the 0 level, the height from this level is taken as the protrusion height, and the number of protrusions at each protrusion height (Y).

The relationship between number and size 2) was diagrammed and expressed as a distribution curve.

Protrusion height O, 1 μm or more and 0.4 μm or more,
It is expressed by the total number of protrusions corresponding to protrusions whose height exceeds 0.1 μm and 0.4 μm according to the above method.

(5) Mimeograph printing properties A base paper was prepared by laminating porous thin paper made of polyester to the obtained film. Using the base paper, characters and images printed using Risograph FX7200 manufactured by Riso Kagaku Kogyo Co., Ltd. as a plate making machine and AP7200 as a printing machine were visually judged and the following characteristics were evaluated.

i) Printing quality; ○... Good and clear printing with no uneven shading or bleeding.

△: Slight unevenness in shading and bleeding are observed, and the clarity is slightly lacking.

×: There is obvious unevenness in shading or bleeding.

ii) Rigidity resistance ○...Continuous printing of 2000 sheets or more is possible.

×: Only a few hundred sheets can be printed continuously.

(6) Create a base paper by laminating the curl characteristic film of the base paper with porous tissue paper,
The obtained base paper was stored under conditions of 50° C. and 60% RH for 7 days, and the state of curl was evaluated based on the following criteria.

○... is good with almost no curling.

△... Some curling occurs, but it can be used as base paper.

×: Significant curling makes it difficult to use as base paper.

Example 1 100 parts of dimethyl terephthalate, 6 parts of ethylene glycol
4 parts and 0.11 parts of calcium acetate hydrate were placed in a reactor, and a transesterification reaction was carried out.

That is, the reaction initiation temperature was set at 180°C, and as methanol was distilled off, the reaction temperature was gradually raised to 23°C.
The temperature was raised to 0°C to substantially complete the transesterification reaction.

Next, 0.07 part of triethyl phosphate was added, followed by 0.3 part of silica particles having an average particle size of 1.2 μm and 0.404 parts of antimony trioxide, and a polycondensation reaction was carried out by a conventional method. That is, the temperature was gradually increased and the pressure was gradually reduced from normal pressure, and after 2 hours, the temperature was reduced to 285°C.
The pressure was 0.3 mmHg.

The reaction was stopped 5 hours after the start of the reaction, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyethylene terephthalate was 0.66.

Similarly, using 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol as starting materials, 2.6-
produced naphthalate. However, silica particles were not added, and the temperature of the polycondensation reaction was raised to 290°C.

Next, 85 parts of the obtained polyethylene terephthalate,
15 parts of polyethylene-2,6-nuclate were mixed. This was extruded into a sheet form from an extruder at 290°C, and rapidly solidified using an electrostatic cooling method on a rotating cooling drum with a surface temperature of 40°C to form a substantially amorphous sheet with a thickness of 27 μm. Obtained.

Next, the obtained sheet was stretched 3.7 times in the machine direction at 88°C, 4.2 times in the transverse direction at 105°C, and further stretched 7 times at 140°C.
Heat treatment was performed for seconds to obtain a biaxially oriented film with a thickness of 1.8 μm.

Example 2 Using 97 parts of terephthalic acid, 3 parts of isophthalic acid, and 105 parts of 1°4-cyclohexane dimetatool as starting materials, 0.06 part of tetrabutyl titanate was added as a catalyst, and the mixture was heated and stirred to perform an esterification reaction. Subsequently, a polycondensation reaction was carried out to produce a poly 1,4-cyclohexylene dimethylene terephthalate copolymer having an intrinsic viscosity of 0.60. After this polymer was made into chips, solid phase polymerization was performed under a nitrogen stream to finally obtain a polymer having an intrinsic viscosity of 1.05.

10 parts of the obtained polymer and 20 parts used in Example 1
' and 90 parts of polyethylene terephthalate to obtain a biaxially oriented film having a thickness of 1.9 μm in the same manner as in Example 1.

Example 3 Using 94 parts of dimethyl terephthalate, 7.6 parts of dimethyl 2,6-naphthalene dicarboxylate, and 64 parts of ethylene glycol as starting materials, a transesterification reaction and a polycondensation reaction were carried out in the same manner as in Example 1. A polyethylene terephthalate naphthalate copolymer having a viscosity of 0.67 was obtained.

However, the added particles were spherical silica with an average particle diameter of 0.9 μm, and the amount added was 0.5% by weight based on the polymer.

Next, using the obtained polymer as a raw material, a biaxially oriented film with a thickness of 1.8 μm was obtained in the same manner as in Example 1.

Comparative Example 1 A biaxially oriented film with a thickness of 1.8 μm was obtained in the same manner as in Example 1, using the polyethylene terephthalate produced in Example 1 as a raw material, except that polyethylene-2,6-naphthalate was not mixed.

Comparative Example 2 A polyethylene terephthalate sehacate copolymer containing 15 mol % of sebacic acid was produced in the same manner as in Example 1. The added particles were silica particles with an average particle diameter of 1.2 μm, and the amount added was 0.3% by weight based on the polymer. The intrinsic viscosity of the polymer was 0.69.

Next, using the obtained polymer as a raw material, a biaxially oriented film with a thickness of 1.9 μm was obtained in the same manner as in Example 1.

Comparative Example 3 Same as Example 1 except that the raw material was a mixture of 94 parts of polyethylene terephthalate produced in Example 1 and 6 parts of polyethylene-2,6-naphthalate, and the heat treatment temperature after stretching was 220°C. A biaxially oriented film with a thickness of 1.8 μm was obtained.

Comparative Example 4 Using the same raw materials as in Example 1, the heat treatment temperature after stretching was 11
The thickness was 1.8 μm in the same manner as in Example 1 except that the temperature was 0°C.
A biaxially oriented film was obtained.

Comparative Example 5 A biaxially oriented film with a thickness of 8 μm was obtained in the same manner as in Example 1 except that the amount of polymer discharged from the extruder was increased to adjust the film thickness.

Comparative Example 6 Polyethylene terephthalate I. having an intrinsic viscosity of 0.67 was produced in the same manner as in Example 1 except that the silica particles added in Example 1 were not added. 90 parts of the obtained polymer and 10 parts of polyethylene-2,6-naphthalate used in Example 1 were mixed as a raw material, and a biaxially oriented film with a thickness of 2.0 μm was produced in the same manner as in Example 1. .

The film obtained above was laminated to porous thin paper according to a conventional method to prepare a heat-sensitive stencil printing base paper, and mimeograph printing was performed.

The physical properties and mimeograph properties of the film are summarized in Table 1.

The heat-sensitive stencil printing base papers using the films of Examples 1 to 3 had good mimeograph printing properties and did not cause the problem of curling of the base paper. Furthermore, the film handling properties during film production and base paper processing were also extremely good.

On the other hand, since Comparative Example 1 had a melting point higher than the range of the present invention, Printing 1 also had poor properties. Comparative Example 2 is an example in which the glass transition temperature is low, but a problem arose in curling properties.

Comparative Examples 3 to 5 are examples in which the heat shrinkage rate or film thickness is outside the range of the present invention, but all of them had poor printing characteristics.

Furthermore, in Comparative Example 6, the Ra of the film surface was too small, resulting in poor slipperiness and poor handling during film production or base paper production, resulting in a significant drop in productivity.

〔Effect of the invention〕

The polyester film of the present invention has excellent printing properties, good workability when handling the film, and does not cause the problem of curling of the base paper, and is suitable as an excellent film for heat-sensitive stencil printing base paper.

Claims (1)

[Claims] (1) Melting point is 200℃~250℃, glass transition temperature is 7
A biaxially oriented film made of a polyester composition having a temperature of 0° C. or higher, the film having a thickness of 0.5 to 6 μm,
A polyester film for heat-sensitive stencil printing base paper, characterized in that the surface has an Ra of 0.03 to 0.5 μm and a heat shrinkage rate of 3 to 35% in at least one direction within the film surface after being treated at 150° C. for 3 minutes. .