JPH0764131B2 - Film for heat-sensitive stencil printing base paper - Google Patents

Description

The present invention relates to a polyester film for heat-sensitive stencil printing base paper. More specifically, the present invention relates to a film for heat-sensitive stencil printing base paper, which has excellent perforation properties, resolution during printing, and printing durability.

[Problems to be Solved by Conventional Techniques and Inventions]

Conventionally, as a heat-sensitive stencil printing base paper, a laminate of porous thin paper on a thermoplastic resin film is known.

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

The film used for such an application is required to have the following characteristics.

(1) Good thermal piercing property. That is, it has a sufficient heat absorption rate so that it can be melted with a small amount of heat and a perforation of an appropriate size can be obtained so that an image at the time of printing becomes clear.

(2) It has a strength and elastic modulus that can withstand the work of laminating with porous thin paper and printing. Conventionally, as the film used for the base paper, a very thin film (usually 1.5 to 10 μm) has been used to obtain good thermal perforation characteristics, and in order to have workability and durability at the time of making the base paper and printing. ,
The film must have sufficient strength and elastic modulus.

(3) It can withstand organic solvents such as toluene and xylene used for printing ink for a long time.

In addition to these requirements, it is also necessary to have excellent productivity during film production. That is, the stretchability of the film is good, troubles such as breakage do not occur, and the winding property and slitting property are good, and wrinkles may occur during winding,
It is necessary not to cause winding deviation.

Furthermore, handling workability at the time of producing a base paper using such a film must be excellent.

Conventionally, as a film used for such an application, a biaxially stretched film intended for a thermoplastic resin, the film having improved printing characteristics by prescribing its thermal characteristics (Tokikai Sho 62-149596) Was proposed, but it did not meet all the above requirements.

[Means for Solving the Problems]

The present inventor, in view of the above problems, as a result of diligent study, a biaxially oriented polyester film containing specific inorganic particles and having a surface state satisfying specific conditions is suitable as a film for heat-sensitive stencil printing base paper. The present invention has been completed and the present invention has been completed.

That is, the gist of the present invention is that spherical silica having an average particle size of 0.1 to 2.0 μm and d ₂₅ / d ₇₅ of 1.0 to 1.5 is 0.01 to
A biaxially oriented polyester film containing 3% by weight, the film having a thickness of 0.5 to 6 μm and a surface Ra of 0.03.
.About.0.2 .mu.m, Rt 0.2.about.2.0 .mu.m, and a polyester film for heat-sensitive stencil printing base paper.

The present invention will be described in detail below.

The polyester referred to in the present invention refers to a polyester having 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, and 2,6-naphthalenedicarboxylic acid. Examples of the alkylene glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like.

Such polyester comprises one aromatic dicarboxylic acid,
A polyester obtained by using one kind of alkylene glycol as a starting material may be used, but a copolymer containing two or more kinds of components is more preferable. In addition to the above, examples of the component to be copolymerized include diethylene glycol, polyalkylene glycol, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and oxycarboxylic acids such as p-hydroxybenzoic acid.

The thickness of the film of the present invention needs to be in the range of 0.5 to 6 μm, preferably 0.5 to 3 μm. The thinner the film, the shorter the heat transfer distance, and the less heat energy required for perforation, which improves perforation and improves resolution and print quality during printing.However, if the thickness is less than 0.5 μm, printing is unclear. Therefore, unevenness in light and shade is likely to occur, and productivity and winding workability are deteriorated even in film production. A film having a thickness of more than 6 μm is not preferable because the perforation property is deteriorated and unevenness occurs during printing.

The film of the present invention contains specific inorganic particles, and the surface shape needs to satisfy specific conditions. It is necessary to impart appropriate slipperiness to the film in order to improve workability in winding, coating, laminating processes and printing of the film. Therefore, a method of forming fine protrusions on the surface is adopted, but if the size and number of such protrusions are inappropriate, heat transfer becomes uneven, perforations become uneven, resolution is poor, and print quality is poor. You will lose your sex.

Therefore, the film of the present invention has an average particle size of 0.1 to 2.0 μm.
0.01 to 3% by weight of spherical silica with m, d ₂₅ / d ₇₅ of 1.0 to 1.5
It is necessary to contain. Spherical silica has a silanol group on the surface, has excellent affinity with polyester, has good dispersibility, and has a suitable hardness, and therefore contributes greatly to slipperiness and is compounded in the film of the present invention. Particularly suitable as particles. Even with such spherical silica, if the average particle size is less than 0.1 μm, it is not possible to impart sufficient slip properties to the film, and if the average particle size exceeds 2.0 μm, slip properties are improved, but film production Occasionally, breakage frequently occurs, resulting in a marked decrease in productivity, and when used as a heat-sensitive stencil printing base paper, problems such as a decrease in printing resolution occur, which is not preferable.

Further, d ₂₅ / d ₇₅ is a numerical value representing the particle size distribution of particles,
If it exceeds 1.5, the particle size distribution becomes broad, and the number of coarse particles increases, which causes coarse projections on the film surface to lower the resolution during printing, which is not preferable. This value is more preferably 1.0 to 1.3.

The content of such particles is 0.01 to 3% by weight, preferably 0.03
~ 2% by weight. The optimum range of content varies depending on the average grain type of the particles, but in any grain type, if the content exceeds 3% by weight, the productivity of the film deteriorates,
It is not preferable because it lowers the resolution during printing. Also,
If it is less than 0.01% by weight, the film cannot be provided with sufficient slip properties, which is not preferable.

The spherical silica to be contained may be of one type, or may be of two or more types having different average particle diameters and the like at the same time. Even when two or more kinds are contained, the average particle diameter and the value of d ₂₅ / d ₇₅ in each particle must satisfy the conditions of the present invention, and the total content must satisfy the conditions. Is.

In the present invention, in addition to such spherical silica, one or more kinds of inorganic or organic fine particles may be contained. Examples of such fine particles include kaolin, talc, magnesium carbonate, calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, titanium oxide, carbon black, and the like. it can. The average particle size of such fine particles is usually 0.005 to 1.0 μm, preferably 0.01 to 0.7 μm, and d ₂₅ / d ₇₅ is preferably 2.0 or less. If the average particle size exceeds 1.0 μm or d ₂₅ / d ₇₅ exceeds 2.0, coarse projections increase, and the heat-sensitive stencil sheet becomes deteriorated in quality such as resolution. Is not achieved.

In the film of the present invention produced by the above method, it is further necessary that the surface shape of the film satisfies specific conditions. That is, the film of the present invention has a center line average roughness (Ra) of 0.03 to 0.2 μm, preferably 0.05 to 0.15 μm, and a maximum protrusion height (Rt) of 0.2 with respect to the surface shape.
.About.2.0 .mu.m, preferably 0.3 to 1.5 .mu.m.

If Ra is less than 0.03 μm, the slipperiness of the film will be insufficient, resulting in poor handling during film production and during the production of stencil printing base paper, as well as slippage with the thermal head during perforation when used as a base paper. It is not preferable because it deteriorates sex. Further, when Ra exceeds 0.2 μm, the resolution during printing is deteriorated, which is not preferable.

On the other hand, when Rt exceeds 2.0 μm, it is not preferable because it causes deterioration of resolution during printing, and when Rt is less than 0.2, wrinkles caused by air entrainment occur in the film winding step, which is preferable. Absent.

Regarding the surface shape of the film of the present invention, in addition to the above requirements, it was measured using a three-dimensional surface roughness meter described later,
The number of protrusions with a protrusion height of 0.1 μm or more is in the range of 1000 to 15000 / mm ² , preferably 2000 to 12000 / mm ² , and the protrusion height is 0.4.
The number of protrusions of μm or more is usually 20 to 2000 / mm ² , preferably 50
The range is up to 1000 pieces / mm ² . When such requirements are satisfied at the same time in addition to Ra and Rt, workability and printing resolution,
The print quality is more highly satisfied.

In the present invention, the film has a high degree of thermal perforation when used as a stencil printing base paper, and in order to improve the resolution at the time of printing, the sum of the shrinkage ratio of the film at 150 ° C. for 3 minutes in the longitudinal direction and the transverse direction is usually It is in the range of 5 to 45%, preferably 10 to 40%. If the sum of the heat shrinkage ratios is less than 5%, sufficient heat piercing properties cannot be obtained, and the resolution during printing becomes poor. Also,
If the sum exceeds 45%, curling due to the shrinkage of the film may occur after forming the base paper, or the printability may deteriorate, which is not preferable.

Since the film of the present invention is manufactured as an extremely thin film, unless the strength is low, the handling workability deteriorates, which is not preferable. In the present invention, it is preferable that the tensile modulus of elasticity in both the longitudinal direction and the width direction of the film is 200 kg / mm ² or more, preferably 300 kg / mm ² or more, since handling workability and printing durability are better.

The polyester used in the present invention has an intrinsic viscosity of 0.40 or more, preferably 0.45 to 0.90, because mechanical properties deteriorate if the degree of polymerization is too low.

Next, a method for producing the polyester film of the present invention will be described. In the present invention, the polymer is supplied to a well-known melt extrusion apparatus typified by an extruder, and heated to a temperature equal to or higher than the melting point of the polymer to melt it. Then, the melted polymer is extruded from a slit-shaped die and rapidly cooled and solidified on a rotating cooling drum to a temperature not higher than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is necessary to enhance the adhesion between the sheet and the rotating cooling drum, and the electrostatic application adhesion method and / or the liquid coating adhesion method are preferably used in the present invention.

The electrostatic application adhesion method is usually a method in which a linear electrode is attached on the upper surface side of the sheet in a direction orthogonal to the flow of the sheet, and the electrode is attached for about 5 to 10
This is a method of applying a DC voltage of kV to give an electrostatic charge to the sheet to improve the adhesion to the drum. Also,
The liquid application contact method is a method of improving the adhesion between the drum and the sheet by uniformly applying the liquid to the entire surface or a part of the surface of the rotary cooling drum (for example, only the portions contacting both ends of the sheet). In the present invention, both may be used together if necessary.

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

Specifically, the unstretched sheet is stretched in one direction in a temperature range of preferably 50 to 120 ° C., more preferably 60 to 110 ° C. by a roll or tenter type stretching machine by 2.5 to 7 times. To do. Next, in the direction orthogonal to the first stage, preferably 55 to 125 ° C, more preferably 65 to 115 ° C.
The film is stretched 2.5 to 7 times in the above temperature range to obtain a biaxially oriented film. A method in which unidirectional stretching is performed in two or more steps can be used, but in that case as well, it is desirable that the final stretching ratio falls within the above range. Also,
It is also possible to simultaneously biaxially stretch the unstretched sheet so that the area ratio becomes 6 to 30 times.

The film thus obtained is preferably subjected to heat treatment, but if necessary, it may be stretched in the machine direction and / or the transverse direction again before or after the heat treatment.

In the present invention, it is preferable that the sum of the heat shrinkage in the longitudinal direction and the heat shrinkage in the horizontal direction at 150 ° C. for 3 minutes is 5 to 45%. However, in order to obtain such heat shrinkage, the heat treatment temperature is 100 ° C. to 200 ° C. ,
It is preferably in the range of 120 ° C to 180 ° C, and the heat treatment time is usually 1 second to 10 minutes. Such heat treatment is a film 20
Restriction shrinkage or elongation within%, or under constant length, or may be carried out in two or more steps.

In the present invention, other polymers (for example, polyethylene, polystyrene, polycarbonate, polysulfone, polyphenylene sulfide, polyamide, polyimide, etc.) can be contained in an amount of about 10% by weight or less based on the total amount of polyester used for film formation. Further, if necessary, additives such as an antioxidant, a heat stabilizer, a lubricant, a dye and a pigment may be added.

Thus, the polyethylene film of the present invention is laminated with a known porous thin paper using a known adhesive according to a conventional method to provide thermal piercing properties, workability during base paper production and printing, durability, and resolution of printing. Also, the heat-sensitive stencil printing base paper having excellent printing quality can be obtained.

〔Example〕

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The methods for measuring the physical properties of the film of the present invention are shown below.

(1) The average particle diameter (d ₅₀ ) of the particles and the spherical diameter were measured by a photography method using an d ₂₅ / d ₇₅ electron microscope. That is, the particle size of about 1000 particles was measured, the volume was integrated from the large particle side, and the particle size at 50% of the total volume was taken as the average particle size (d ₅₀ ). Further, similarly, the value of the ratio (d ₂₅ / d ₇₅ ) was calculated with the particle diameter at 25% relative to the total volume as d ₂₅ and the particle diameter at 75% as d ₇₅ . d
The value of ₂₅ / d ₇₅ indicates the sharpness of the particle size distribution, and the closer to 1.0, the sharper the distribution.

(2) Centerline average roughness (Ra) and maximum height (Rt) Ra, R
The value of t is the surface roughness measuring device (SE-3
It calculated | required as follows using F). That is, the reference length L (2.5 mm) in the direction of the center line from the film section curve
The part of is drawn out, and the center line of this extracted part is the x-axis,
When the roughness curve y = f (x) is represented with the direction of the longitudinal magnification as the y-axis, the value given by the following equation is represented by [μm].

Further, when the extracted portion is sandwiched by two straight lines parallel to the average line of the extracted portion of the sectional curve obtained at this time,
The distance between the straight lines was measured in the direction of the longitudinal magnification of the cross-section curve, and the value was taken as the maximum height (Rt) and expressed in [μm].

Ra and Rt are 10 cross-section curves from the sample film surface,
It is represented by the average value of Ra and Rt obtained from these sectional curves. The tip radius of the stylus is 2 μm and the load is 30 mg.
The cutoff value was 0.08 mm.

(3) Number of protrusions having a protrusion height of 0.1 μm or more and 0.4 μm or more Using a three-dimensional surface roughness meter (SE-3AK) manufactured by Kosaka Laboratory Ltd., the tip radius of the stylus is 5 μm, the needle pressure is 30 mg, Measuring length 0.5m
The protrusion height and the number of protrusions were measured under the conditions of m, sampling pitch 1.0 μm, cutoff 0.25 mm, vertical magnification 50000 times or 20000 times, horizontal magnification 200 times, and 500 scanning lines. The projection height (X, μm) here means the height of the point where the number of projections is maximum as 0 level, and the height from this level is defined as the projection height, and the number of projections at each projection height (Y, The relationship with the number of particles / mm ² ) was graphically represented as a distribution curve.

The number of protrusions having a protrusion height of 0.1 μm or more and 0.4 μm or more is represented by the total number of protrusions corresponding to the protrusions having the protrusion heights exceeding 0.1 μm and 0.4 μm, respectively.

The measurement is 3 points in the longitudinal direction of the film, and 3 points in the direction perpendicular to it.
A total of 6 points were performed, and the average value was used as the measured value.

(4) Heat shrinkage rate In an oven in which the sample was kept at a temperature of 150 ° C without tension,
It heat-processed for 3 minutes, the length of the sample before and behind that was measured, and it calculated by the following formula.

Five points were measured in the machine direction and the transverse direction of the film, and the average value of each was used as the measured value.

(5) Transfer printing characteristics Polyester thin paper made of polyester was attached to the obtained film to prepare a base paper. Using the obtained base paper, the characters and images printed by using Lithograph FX7200 manufactured by Ideal Chemical Industry Co., Ltd. as a plate making machine and AP7200 as a printing machine were visually judged, and the following characteristics were evaluated.

i) Print quality ◯: Good print quality with no uneven density or blurring.

Δ: Slight unevenness in shades and bleeding were observed, and the image was slightly lacking in sharpness.

×: Uneven shading or bleeding is clearly visible.

ii) Printing durability ○ ... Continuous printing of 2000 sheets or more is possible.

×: Only several hundred sheets can be continuously printed.

(6) Handling workability The handling workability of the film in the winding work and the base paper making work during the film production was divided into the following three ranks.

◯: Good handleability and smooth work.

Δ: Handling property is generally good, but slightly smooth.

X: The films are easily blocked and wrinkled, and the handleability is poor.

Example 1 100 parts dimethyl terephthalate, ethylene glycol 64
Parts, and 0.11 parts of calcium acetate-hydrate in a reactor,
A transesterification reaction was performed. At this time, the reaction start temperature
The temperature was raised to 180 ° C., the reaction temperature was gradually raised as the methanol was distilled off, and after 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction.

Next, after adding 0.07 part of triethyl phosphate, 0.5 part of spherical silica particles having an average particle size of 0.75 μm and ad ₂₅ / d ₇₅ value of 1.2 and 0.04 part of antimony trioxide were added, and a polycondensation reaction was carried out by a conventional method. In this reaction, the temperature was gradually raised and the pressure was gradually reduced from normal pressure, and after 2 hours, the temperature was raised to 285
The test was performed at a temperature of ℃ and pressure of 0.3 mmHg. After 5 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyethylene terephthalate was 0.66.

In the same manner, the starting material was 86 parts of dimethyl terephthalate, 14 parts of dimethyl isophthalate, and 64 parts of ethylene glycol, and 0.5 parts of spherical silica particles having an average particle diameter of 0.3 μm and d ₂₅ / d ₇₅ 1.2 were added. A polymerized polyester was produced. The intrinsic viscosity was 0.70.

Next, 50 parts of the obtained polyethylene terephthalate was mixed with 50 parts of copolyester. This was extruded in a sheet form from an extruder at 285 ° C, and rapidly cooled and solidified by using an electrostatic cooling method with a rotary cooling drum whose surface temperature was set to 40 ° C to obtain a substantially amorphous sheet having a thickness of 26 μm. Obtained.

Next, the obtained sheet was stretched 3.7 times in the longitudinal direction at 80 ° C. and 4.0 times in the transverse direction at 95 ° C., and further heat-treated at 140 ° C. for 7 seconds to obtain a biaxially oriented film having a thickness of 1.8 μm.

Example 2 In the same manner as in Example 1, the isophthalic acid content was 10 mol%.
A copolyester containing 0.3% by weight of spherical silica having an average particle size of 0.95 μm and d ₂₅ / d ₇₅ 1.1 and 0.3% by weight of titanium dioxide having an average particle size of 0.30 μm and d ₂₅ / d ₇₅ 1.5. A viscosity of 0.68) was produced.

Using the obtained copolyester, the heat treatment temperature was set to 15
The film was formed under the same conditions as in Example 1 except that the temperature was 0 ° C, and the thickness was
A 1.7 μm biaxially oriented film was obtained.

Example 3 An average particle size of 0.95 μm, d, produced in the same manner as in Example 1.
95 parts of polyethylene terephthalate (intrinsic viscosity 0.67) containing 0.7% by weight of spherical silica of ₂₅ / d ₇₅ 1.1 and 5 parts of polybutylene terephthalate produced by a conventional method were mixed, and film forming conditions were the same as in Example 1. To produce a biaxially oriented film having a thickness of 1.9 μm.

Comparative Example 1 In the same manner as in Example 1, the average particle size was 1.6 μm, and d ₂₅ / d ₇₅ 2.5
A polyethylene terephthalate containing 1.0% by weight of the silica particles was produced. The intrinsic viscosity was 0.66. 50 parts of the obtained polymer and 50 parts of the isophthalic acid copolymerized polyester used in Example 1 were mixed and formed into a film under the same conditions as in Example 1 to obtain a biaxially oriented film having a thickness of 1.8 μm.

Comparative Example 2 The content of isophthalic acid was 5 mol% and the average particle size was 0.
A biaxially oriented film having a thickness of 1.8 μm was obtained in the same manner as in Example 1 by using a copolymerized polyester (intrinsic viscosity 0.68) containing 0.1% by weight of spherical silica particles of 3 μm and d ₂₅ / d ₇₅ 1.2.

Comparative Example 3 Calcium carbonate particles having an average particle size of 1.3 μm and d ₂₅ / d ₇₅ 1.9 were used.
Polyethylene terephthalate containing 2.6% by weight (intrinsic viscosity 0.65) was produced. 50 parts of the obtained polymer and 50 parts of the isophthalic acid copolyester used in Example 1 were mixed, and a film was formed under the same conditions as in Example 1 to obtain a film having a thickness of 2.1 μm.
An axially oriented film was obtained. However, when the film is produced, the film may be broken during the steps of transverse stretching or heat setting, and the productivity is slightly inferior.

Comparative Example 4 A biaxially oriented polyester film having a thickness of 8 μm was produced by using the raw material of Example 1 under the same film forming conditions and changing only the polymer extrusion rate of the extruder.

The above-obtained film was adhered to a porous thin paper according to a conventional method to prepare a heat-sensitive stencil printing base paper, which was imprinted.

Table 1 shows the physical properties and the imprinting characteristics of the film.

The films of Examples 1 to 3 were excellent in handleability at the time of producing the film and at the time of producing the base paper, and were also excellent in the transcription printing property.

On the other hand, Comparative Example 1 is an example in which particles having a large d ₂₅ / d ₇₅ , that is, particles having a large content of large particles are used because the particle size distribution is not sharp. Since the Rt increases and Rt increases, the printing resolution decreases and the printing quality deteriorates. Comparative Example 2 is an example in which Ra is too low, and the handleability of the film is significantly deteriorated. Comparative Example 3 is an example in which other inorganic particles are added together with spherical silica, but since the particle size of the inorganic particles is large, R
Both a and Rt became large, and the print quality deteriorated. Comparative Example 4
Is an example in which the thickness is too thick, but the print quality was remarkably deteriorated due to the deterioration of the perforation property.

[Effect of the Invention] The polyester film of the present invention is suitable as a film for heat-sensitive stencil printing base paper, which is excellent in handleability in film production and base paper production, and is excellent in printing quality and printing durability.

Claims (1)

[Claims] 1. An average particle diameter of 0.1 to 2.0 μm, and d ₂₅ /
A biaxially oriented polyester film containing 0.01 to 3% by weight of spherical silica having a d ₇₅ of 1.0 to 1.5, the film having a thickness of 0.5 to 6 μm, a surface Ra of 0.03 to 0.2 μm, and Rt.
Is 0.2 to 2.0 μm. A polyester film for heat-sensitive stencil printing base paper.