JPS5912453B2 - Roughened polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a stretched film of saturated polyester (hereinafter simply referred to as polyester) having a fifurlated rough surface and a method for producing the same.

10 Roughened polyester films are widely used for applications such as tracing, release paper, and labels.

These are made by sandblasting or chemical etching the film surface. Others are made by blending inorganic fine particles to make them matte, embossing, coating with a matting agent, or laminating fibers or powder with a film to roughen the surface. However, the rough surface of these conventional products, except when laminating fibers, is due to the unevenness of the surface.
This is not due to fifurlation.
Conventional products have the following drawbacks. (1) A film roughened by blending a large amount of inorganic fine particles or by embossing has a low dielectric breakdown voltage and is unsuitable for electrical insulation25.

(2) If a large amount of inorganic fine particles are added, the film is likely to break during stretching, and the mechanical properties of the resulting stretched film will deteriorate.

(3) Sandblasting and chemical etching process 30
Since these treatments cannot be carried out continuously during the film forming process, these treatments are performed on the finished ordinary stretched film, resulting in very high costs. In terms of quality, since the film is washed with water after processing, it shrinks and wrinkles when it dries. (4) In the method of laminating fibers or resin powder to a film, it is difficult to obtain fibers with small diameter and viscosity, so the thickness of the roughened layer usually exceeds 25 μm.

Therefore, 100μ is the most commonly used roughening film.
When making the following roughened film, the roughened layer will be too thick. In addition, there is fuzzing of fibers and detachment of fine powder. If an attempt is made to make the roughened layer thinner, the density of the fibers and powder will decrease, making it impossible to obtain a satisfactory roughened surface. The present inventors conducted research to overcome the above-mentioned drawbacks, and as a result, they arrived at the present invention. That is, at least one side has a gloss level of 100 to 20%, the thickness of the roughened layer is 25% or less of the thickness of the film, and the roughened surface is fibrillated. This is an excellent polyester stretched and heat treated film. In the present invention, "fifril" means a fine fiber, and its shape is a complex entanglement of fibers with an amorphous cross section with many irregular protrusions or branches, which is suitable for liquid impregnation. Particularly preferred.

Further, fibers having a smooth surface and a circular, oval, or flat cross section like ordinary melt-spun fibers may be used. The diameter of the fifrill (the maximum length of the cross section is referred to as the diameter) is approximately 10 microns or less, preferably 5 microns or less, and for electrical insulation purposes, it is 2 microns from the viewpoint of impregnation with insulating oil and withstand voltage. The following ultra-fine ones are particularly preferred. The product of this invention has a roughened surface without adding a large amount of inorganic fine particles or embossing, and is stretched and heat treated, so the decrease in electrical properties, especially dielectric breakdown voltage, is very small and can be ignored. be.

In other words, in the present invention, "excellent in insulation breakdown properties" means that when the dielectric breakdown voltage is compared with that of a film of the same thickness that is not roughened, the value decreases by less than 20% (
It is very small (preferably less than 15%) and does not pose any practical problem. On the other hand, conventional films whose surface has been roughened by other methods have a significant drop in breakdown voltage. In addition, since the rough surface is fibrillated, it has good impregnability with liquids such as insulating oil, making it very suitable as an insulating film for oil-immersed type foil-wound transformers. It is also effective for wrapping.
Regarding impregnability, conventional embossed products, chemically etched, etc. roughened films have low impregnability because the air contained inside the roll is difficult to escape. On the other hand, the product of the present invention has the characteristic that it easily penetrates into the inside of the roll due to capillary action.
Very good impregnation properties. The fifryl of the present invention is
Rather than attaching preformed fibers to a film, the fibrils are first formed by mechanically roughening the surface and then stretching it.
This is a technology that could never have been imagined.

During surface roughening, there is no problem as long as some fifriles are formed to the extent that they do not adversely affect the drawing process, but it is preferably limited to about 10% or less of the total fifriles. Furthermore, the film differs greatly from conventional roughened films in that the fibrils are not formed only by stretching without mechanically roughening the surface. Further, in the present invention, since fifrills are developed by stretching, there is no need to worry about fuzzing, and the roughened layer can be made very thin (for example, 1 to 2 microns). The saturated polyester referred to in the present invention is a polyester consisting of a glycol component and a dicarboxylic acid component, and typical glycol components include ethylene glycol, diethylene glycol, propylene glycol, butanediol, and the like.

Dicarboxylic acid components include terephthalic acid, phthalic acid,
Examples include isophthalic acid, sebacic acid, adipic acid, naphthalene dicarboxylic acid, and those obtained by introducing a sulfonic acid group (or a metal salt thereof) into the above dicarboxylic acids. Typical polyesters are polyethylene terephthalate and its copolymers. In addition, if necessary, a known polymer such as polyolefin, polyamide, polycarbonate, etc. may be added to the polyester, preferably within a range that does not substantially reduce the performance of the polyester.
It can be blended at 0 wt% or less. Further, various stabilizers such as heat stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, inorganic fine particles, pigments, and viscosity modifiers can be added depending on the purpose. The product of the present invention is manufactured by the following method.

The surface temperature of the unstretched or uniaxially stretched polyester film is (T9-20°C) to TE [preferably (T9-10
C) - TE], and then stretched in at least one direction at a temperature of TE, and then heat treated at 200C or higher. Here, "mechanically roughening" refers to rolls with countless needles or protrusions planted on the surface, rolls with countless protrusions carved on the surface (or in some cases, sandblasting rolls, etc.), wire brushes, etc. , sandpaper, a file grinder, etc. alone or in combination to scrape the surface of the film to create fine scratches and roughen the surface. These roughening rolls, brushes, etc. The moving speed (or peripheral speed) of the surface of the film is generally faster than the moving speed of the film (preferably 10
(more than double) is advantageous for surface roughening. When only one side is roughened, the circumferential speed of the roughening roll and the opposing roll of the brush is preferably the same as the moving speed of the film.
The depth of surface roughening cannot be determined unambiguously because it depends on the thickness of the film and the stretching conditions after roughening, mainly the stretching ratio and stretching temperature, but it is usually 25% or less of the film thickness. (average value) is preferred.

The film to be subjected to surface roughening may be a single film, or may be a multi-layer composite film in order to provide special properties such as heat sealing properties, gas barrier properties, and ease of cutting. The surface temperature of the film during roughening is within the range of (T9-2'C) to TE. Here, T9 means the glass transition temperature, and TE represents the stretching temperature at which the film is stretched after surface roughening. T
9 was carefully measured using a differential calorimeter (DSC) using the following method.

Pack vacuum-dried polyester 10~ into a sample holder and heat at 10°C/- to a temperature approximately 20°C higher than the expected melting end temperature (for example, 285°C for polyethylene terephthalate) in a dry nitrogen stream. The temperature rises,
Hold in that state for 5 minutes to completely dissolve. After that, the holder is removed and quenched in liquid nitrogen to erase the thermal history of the sample. The sample is then heated again at 10° C./7 nm. T9 is determined from the thermogram at this time. In the present invention, the range from (T9-2'C) to TE is at first glance considered to be a wide temperature range, but this is because there is a difference in surface roughening temperature between an unstretched film and a uniaxially stretched film. It's for a reason.

Generally, when the surface roughening temperature of a uniaxially stretched film is higher than that of an unstretched film, the film is less likely to tear during the subsequent stretching process. Specifically, in the case of polyethylene terephthalate and its copolymer, the unstretched film has a temperature of 50 to 1000C (preferably 60 to 9'C),
For uniaxially stretched film, 60 to 1100C (preferably 7
The surface is roughened within the range of 0 to 100'C). In this temperature range, the polymer will not be scraped off during surface roughening, and problems such as uneven stretching or film tearing will not occur during the stretching process, and fifrels are formed that are favorable for impregnation and cohesiveness. . If it is less than (T9-2 "C"), the film surface will be partially scratched off during roughening, which will accumulate on the stretching roll and cause damage to the film surface.
This cannot be used because it may cause the film to tear. Furthermore, if the surface is roughened at a temperature higher than TF, the film tends to stick to wire brushes and the like, resulting in uneven thickness, and the film tends to tear easily during stretching, and it also tends to make it difficult to form fibrils. Surface roughening is performed at a temperature of (T9-200C) to TE at the preheating stage when vertically stretching an unstretched film, at the preheating stage when horizontally stretching a vertically stretched film, and when casting melt-extruded polyester. However, the heating is not limited to these steps, and heating may be performed only for roughening. In order to eliminate the anisotropy in the distribution state of the fibrils formed,
In order to maintain a high withstand voltage, it is particularly preferable to roughen the surface of the unstretched film. In particular, when it is desired to have anisotropy in the distribution state of fibrils, it is preferable to roughen the surface of a longitudinally stretched film and then stretch it laterally. stretching,
The thickness of the final roughened layer after heat treatment is 25% or less of the film thickness, preferably 20-1? It is. Here, since the thickness of the fifrills is usually not uniform, the thickness of the roughened layer varies partially depending on the thickness of the fifrills, but in the present invention, the average value is adopted. Therefore, even if there are a few places that are significantly thicker or thinner than the average value, it is acceptable as long as there is no practical problem. The roughening layer thickness is 2 of the film thickness.
If it exceeds 5%, performance such as impregnation and cohesiveness is very good, but mechanical properties and withstand voltage deteriorate, which is not preferable. The gloss of the rough surface of the product of the present invention is 100
-20%, preferably 90-40% is preferable from the viewpoint of impregnating properties, cohesiveness, and electrical properties.

When the glossiness exceeds 100%, the degree of surface roughening is small, so the density of the fibrils is low, and characteristics of impregnation and cohesion are difficult to develop. On the other hand, if it is less than 20%, the surface is roughened more than necessary, so that the withstand voltage is extremely low, and it tends to become extremely slippery, resulting in a decrease in cohesiveness. The gloss level referred to in the present invention is 60 according to JIS Z-8741.
This is a value measured using the specular gloss method. The glossiness, roughened layer thickness, fibril structure, etc. of the product of the present invention have been described above, but the product of the present invention exhibits its excellent performance only when these conditions are met, and one of those conditions is If even one of them is missing, its characteristics are lost.

Note that the rough surface of the product of the present invention has the same properties as conventional roughened films.
Various treatments such as corona discharge treatment and coating can be performed. Example 1 1VO. 63 polyethylene terephthalate T972℃
was fed into a 40 mm extruder, extruded through a T-die at 280°C to a thickness of 270 microns, and cast on a cast drum at 60°C.

On the cast drum at a point where the surface temperature of the film is 80°C during the solidification process, a wire brush with a diameter of 100 fins and numerous wires with a diameter of 0.2511 is rotated at high speed (2
200 rpm1), and the film surface (moving speed 3.3 m).
/〒) to roughen the surface by making scratches with an average depth of 25 microns. Then, it was stretched 3.3 times in the vertical direction at 85°C,
The film was fed into a tenter and stretched 3.3 times in the transverse direction at 95°C, followed by heat treatment at 220°C to obtain a biaxially stretched film (Taki 1) with a thickness of 25 microns and roughened on one side.
In addition, the surface was not roughened on the cast drum, but was roughened with the wire brush mentioned above at a surface temperature of 75°C during the preheating stage of vertical stretching, and stretched and heat-set in the same manner as 7f61 (.7162 ). For comparison, the film (./F63
) was also made. When the rough surface of the unstretched film, which was not stretched after surface roughening, was examined using a scanning electron microscope (hereinafter abbreviated as SEM), it was found to consist of fine scratches and no fibrils were formed. When the finished stretched film was observed using a SEM, it was found that the rough surface was composed of intricately branched fifriles, and fifriles were formed by stretching. Table 1 shows the characteristic values of the biaxially stretched film.

Impregnation (oil flowability) was evaluated by the following method. 20? Roughened film? Cut out the corners and stack 10 of these to make 10k9/C! Pressurize with l and set 5mm in the center.
Dodecylbenzene was inserted through the φ hole under pressure at 11<9/CTit, and the amount of oil flowing out from between each film layer was measured every hour. The larger the flow rate, the better the impregnating property. The cohesiveness was determined by cutting the film into 201 tm1 pieces and using the simple method described below.

Approximately 6m1 in diameter! Approximately 11c for two L vinyl coated electric wires!
N. Using electric wires twisted at a period of , the above-mentioned film slit into a tape shape was wrapped around the wires to a width of 4 mu using a taping machine. The tape-wound wire thus produced was bent to form an arc with a radius of 5CTfL, the tape was observed for deviation at the bent portion, and the number of bends was counted until the tape shifted and the wire was exposed. The greater the number of times, the better the cohesiveness is, and it has been found that there is usually no problem in practical use if the number of times is 10 or more. As is clear from Table 1, the products of the present invention have good impregnating properties and binding properties. Waterfall 1,
2 was slit to a width of 20 nm and wound 30 times as an insulating layer on a twisted copper wire of approximately 500 m1Lφ to produce an oil-flow power cable. When wound, the film had good slippage, and even if it was bent after winding, the films did not stick together or shift, exposing the wire underneath. When the cable was energized, it was found to have good withstand voltage characteristics and no temperature rise on the surface of the outer protective coating, indicating that it had good properties as a cable. Comparative Example 1 SiO was added to the polyethylene terephthalate used in Example 1.
A roughened film (4) 4) having a thickness of 25 microns was produced by uniformly dispersing 1 wt % of the fine particles of No. 2 (average particle size 2 microns) under the same stretching conditions as in Example 1.

The rough surface was not fifurled. Also, in Example 1.
X). 3 was heated to 120°C and embossing was performed using an embossing roll with a hexagonal pattern of 1 mm side length to form a roughened film (thickness: 50 microns) (A6.
5) was created. The characteristic values are shown in Table 2. ．． /164 has a roughened surface, but has poor impregnation and bundling properties and cannot be used for electric wires and cables.

．． Although No. 46.5 had very good impregnating properties, it was found that the film was slippery and had poor bundling properties, causing poor covering during the manufacturing process of electric wires and cables. Example 2 Polyethylene terephthalate (T979
℃) was extruded from a T-die at 285°C and cast to a thickness of 415 microns to produce an unstretched film.

During the process of vertically stretching an unstretched film, the surface temperature of the film was changed and a wire brush (brush with a diameter of 1001L and 11L with a wire of 0.15 mmφ planted, 2200 rpm
? Roughen the surface by rotating (rotating at 90°C, 3.3 times)
The film was then fed into a tenter, stretched 3.3 times in the transverse direction at 95°C, and heat treated at 220°C to produce a film with a thickness of about 50 microns and roughened on one side. On the other hand, a vertically stretched film was roughened with a wire brush without being roughened in the unstretched state, and a laterally stretched film was also produced in the same way. These 2
When the surface of the roughened film after axial stretching was observed by SEM, it was found that the surface was fibrillated. rot 6 in table 3
Because the temperature during surface roughening was low, the polymer was scraped off and deposited on the vertical stretching rolls, causing stretching problems.

Moreover, the rough surface of the finished film had these polymer powders adhered to it in places, and the powder was of poor quality and could be removed by rubbing. S). In No. 9, the temperature during surface roughening was too high, so the film tended to stick to the wire, and the film frequently broke during vertical stretching, making it impossible to form a film stably.

Furthermore, the finished film had large thickness unevenness due to uneven stretching. When the oil flow rates of A6.7, 8, and 1O according to the present invention were measured, they were 15, 12, and 9cc/M, respectively.
uL, and the impregnating property was very good.

When we made an element winding for an oil-immersed transformer by laminating these roughened films and aluminum foil and conducted oil flow and current tests, we found that the withstand voltage was higher than that of the element winding using conventional insulating paper. It was found that because of its good flowability, the temperature increase during element winding was small, and that it had favorable properties for use in oil-immersed transformers. Comparative Example 2 A roughened film was made using the method of making the roughened film of Example 1, but without heat treatment at 220°C, and the dielectric breakdown voltage (JISC23
18-66) was measured.

Claims (1)

[Claims] 1. At least one side is roughened to a gloss level of 100 to 20%, a roughened layer thickness of 25% or less of the film thickness, and the roughened surface is fibrillated. A heat-treated, roughened saturated polyester stretched film with excellent electrical breakdown properties. 2 An unstretched or uniaxially stretched film of saturated polyester is roughened by mechanically rubbing at least one side at a surface temperature within the range of (Tg - 200°C) to TE, and then stretched in at least one direction at a temperature of TE. , then 20
Heat treated at 0°C or higher, at least one side has a gloss level of 100 to 20%, the thickness of the roughened layer is 25% or less of the film thickness, and the roughened surface is fibrillated and has excellent electrical insulation breakdown properties. A method for producing a roughened saturated polyester stretched film.