JPH0641170B2 - Polyethylene-2,6-naphthalene dicarboxylate film for electrical insulation - Google Patents

Description

The present invention relates to a polyethylene-2,6-naphthalenedicarboxylate film for electrical insulating material, and more specifically, a substantially polyethylene-free amorphous polyethylene. −2,6−
Naphthalene dicarboxylate (hereinafter, polyethylene-
Abbreviated as 2,6-naphthalate) The surface of the film is treated with a crystallization accelerator, and then stretched and oriented biaxially to form a flat, smooth electrical insulation with excellent delamination resistance. The present invention relates to a polyethylene-2,6-naphthalate film for wood.

<Prior art and its problems> Polyethylene-2,6-naphthalate film has excellent physical and chemical characteristics, so that it is used as a dielectric film for capacitors, a film for speaker diaphragms, magnetic tape, and photographic film. It is attracting attention as a film such as a support.

In these films, the slidability is good or bad in the workability of the film manufacturing process and the processing process in each application,
Furthermore, it is a major factor in determining the quality of the product.

Generally, in order to improve the slipperiness of the film, a method of reducing the contact area between the film surfaces, guide rolls, etc. by giving extremely fine unevenness to the film surface is adopted, and it is roughly classified. There are used a method of precipitating inactive fine particles from a polymer catalyst residue used for a film raw material, a method of adding inactive inorganic or organic fine particles to a film raw material, and a combination method thereof.

Further, the fine particles in these film raw materials have a greater effect of improving the slipperiness as the size thereof becomes larger to some extent. However, when the fine particles are present in the film and stretch-oriented, another problem occurs that voids are formed around the particles. The larger the particle size, the larger the void.

Also, if voids are formed near the surface of the film,
Part of the void is broken and the particles are exposed, and the minute fragments adhere to the surface of the film.

By the way, when a polyethylene-2,6-naphthalate film is used as a film for electrical insulation, this film is a very useful material because it is excellent in heat deterioration resistance and contains few oligomers. However, compared to polyethylene terephthalate film, there is a problem that delamination is likely to occur. That is, delamination is likely to occur when the film is bent at a sharp angle or when an impact force is applied when the cut has a minute notch. If there is such a delaminated portion, the dielectric breakdown voltage is lowered, causing a problem.

When the delamination portion of the film is observed in detail, the added inorganic particles and the like can be seen at the portion where the delamination starts. And
It is considered that these inorganic particles contribute to the occurrence of delamination and growth.

<Purpose of the Invention> As a result of intensive studies to solve the above-mentioned drawbacks of the prior art, the present inventors have found that a polyethylene-2,6-naphthalate film that is substantially free of lubricant and is amorphous. The biaxially oriented polyethylene-2,6-naphthalate film, which has been biaxially stretched and oriented after being surface-treated with a crystallization accelerator, solves the above-mentioned drawbacks and is flat and has excellent slipperiness and delamination resistance. However, the present invention has been found to be extremely useful as a film for an electric insulating material, and has arrived at the present invention.

<Structure of Invention> That is, according to the present invention, an amorphous polyethylene-2,6-naphthalate film containing substantially no lubricant is surface-treated with a crystallization accelerator, and then stretched biaxially. Is a polyethylene-2,6-naphthalate film for electrical insulation.

In the present invention, polyethylene-2,6-naphthalate is
The constitutional unit is substantially composed of ethylene-2,6-naphthalate, and not only polyethylene-2,6-naphthalate but also a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of Also included are ethylene-2,6-naphthalate modified polymers modified with three components.

Polyethylene-2,6-naphthalate is generally prepared by reacting and polymerizing naphthalene-2,6-dicarboxylic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative, preferably in the presence of a catalyst. Can be manufactured. As the modified polymer, one or more appropriate third component (modifying agent) is added before the completion of the polymerization of the polyethylene-2,6-naphthalate,
It can be produced by copolymerization or mixing.

Suitable third components include compounds having divalent ester-forming functional groups such as oxalic acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,7-
Dicarboxylic acids such as dicarboxylic acids and diphenyl ether dicarboxylic acids or lower alkyl esters thereof; oxycarboxylic acids such as p-benzoic acid and p-oxyethoxybenzoic acid or lower alkyl esters thereof; or propylene glycol, trimethylene glycol, tetramethylene glycol, Examples thereof include compounds such as divalent alcohols such as hexamethylene glycol and neopentyl glycol. Further, polyethylene-2,6-naphthalate or a modified polymer thereof is, for example, a monofunctional compound such as benzoic acid or trimethoxypolyalkylene glycol,
It may be one in which terminal hydroxyl groups and / or carboxyl groups are blocked, or, for example, a substantially linear copolymer with a tri- or tetra-functional ester-forming compound such as a very small amount of glycerin or pentaerythritol. It may be modified within the range in which

In the present invention, polyethylene-2,6-naphthalate is
It contains substantially no lubricant (fine particles). The polyethylene-2,6-naphthalate has an intrinsic viscosity of 0.40 or more measured at 35 ° C. in an orthochlorophenol solution. Particularly, those having an intrinsic viscosity of 0.50 to 0.70 are preferable because they are excellent in film physical properties and stretching operation.

The present invention is practiced with an unstretched film formed from polyethylene-2,6-naphthalate as described above.
To form the unstretched film, for example, a melt extrusion method may be adopted.

The unstretched film formed by the melt extrusion method is rapidly cooled to be substantially amorphous. The surface of the polyethylene-2,6-naphthalate unstretched film thus obtained is surface-treated with a crystallization accelerator.

Although various organic solvents can be used as the crystallization accelerator in the present invention, since chlorine-containing organic compounds such as dichloromethane, methylene chloride, chloroform, trichloroethylene, tetrachloroethane and monochlorobenzene produce remarkable effects. preferable. Particularly, methylene chloride, chloroform and the like are preferable. Further, in order to control the effect of promoting crystallization, the above substances can be mixed with a solvent of alcohols or ketones and used. The degree of surface treatment with these crystallization accelerators is
It can be changed by selecting treatment conditions by conducting preliminary experiments under conditions such as the mixing ratio of the treatment agent, the contact time with the film surface, and the temperature.

The biaxially oriented polyethylene-2,6-naphthalate film of the present invention has fine projections on its surface. The large number of projections are derived from a large number of microcrystalline particles formed on the surface of the film. The microcrystalline particles are formed by the crystallization accelerator treatment and the subsequent biaxial stretching treatment.

The biaxial stretching treatment can be carried out by a conventionally known method, for example, a simultaneous biaxial stretching method, a sequential biaxial stretching method or the like, but a sequential biaxial stretching method is particularly preferable. At that time, the stretching temperature is Tg to (Tg + 30) ° C. (here, Tg
Is the second-order transition point of polyethylene-2,6-naphthalate), and is preferably selected from 110 to 140 ° C. The draw ratio is preferably 3 times or more.

<Effects of the Invention> According to the present invention, the following new effects can be obtained.

(1) Since the surface characteristics of the oriented film can be efficiently controlled only by coating the surface of the film with an organic compound having a crystallization promoting action, the industrial advantage is extremely large.

(2) Since it does not contain a lubricant such as fine particles of inorganic compounds, it has no voids. Therefore, an extremely clean film can be obtained without any void breakage found in a film containing a lubricant. Furthermore, delamination that occurs when the film is bent at a steep angle is less likely to occur.

(3) When the crystallization accelerator is allowed to act on only one side of the film, it is possible to produce oriented films having different surface roughnesses on the front and back sides.

<Example> Hereinafter, the present invention will be further described with reference to Examples. Various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Surface roughness of film (Ra) Measured according to JIS B 0601. Using a stylus type surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd., the radius of the needle is 2μ.
A chart (film surface roughness curve) was drawn under the conditions of m and a load of 0.07 g. From the film surface roughness curve, a portion of the measurement length L is extracted in the direction of the center line, the center line of this extracted portion is the X axis, the direction of longitudinal magnification is the Y axis, and the roughness curve is Y = When expressed as f (x), the value (Ra: μm) given by the following equation is defined as the surface roughness of the film.

In the present invention, Ra was expressed as an average value of 5 pieces of which 8 pieces were measured with a reference length of 0.2 mm and 3 pieces were removed from the one with the largest value.

(2) Frequency of void breakage Aluminum was vacuum-deposited uniformly on the film surface to a thickness of 40 to 50 nm or less, magnified 600 times with a microscope and the position was changed to take 20 surface photographs. . From this photograph, the number of protrusions where polyethylene-2,6-naphthalate was completely or partially peeled off at the tips of the protrusions was counted and expressed as a value per unit area.

(3) Delamination characteristics Using a sewing machine manufactured by NEW LONG Co., Ltd., 100 was punched in a direction perpendicular to the film surface with a sewing machine needle (diameter 2 mm).
Individual holes were formed. The delamination was evaluated by determining the area of the punched portion (including the through hole and the portion where the crack was formed and expanded due to delamination) with Luzex 500 (manufactured by Nippon Regulator Co., Ltd.).

In the non-delaminated film, the punched hole is as small as the diameter of the needle, while in the bad film, the punched hole is enlarged to the periphery and the delamination increases the area of the punched part.

Example 1 and Comparative Examples 1 and 2 Intrinsic viscosity numbers of 0.
Polyethylene-2,6-naphthalate, which is 60, was melt extruded and cooled on a casting drum to obtain an unstretched film. This unstretched film was treated with chloroform on both sides for 3 seconds. The unstretched film was heated to 130 ° C. and stretched 3.6 times in the machine direction. Then, it was stretched 3.7 times in the transverse direction at 125 ° C. Further, heat setting was carried out at 230 ° C. to obtain a film having a thickness of 75 μm (Example 1).

On the other hand, the above polyethylene added with 0.25% by weight of kaolin (average particle size 0.6 μm) which is an inert fine particle as a lubricant
2,6-Naphthalate was melt-extruded, biaxially stretched under the same conditions as above, and heat-set to obtain a film (Comparative Example 1).

Further, a film was produced under the same conditions as in Example 1 and did not include only the chloroform treatment step in the unstretched state (Comparative Example 2).

The characteristics of these films are shown in Table 1. The film of Example 1 had no void breakage. In Comparative Example 2 as well, there was no void breakage, but the surface roughness was too small, and when the film was wound into a roll, a bump-like defect was formed in some places.

Example 2 and Comparative Example 3 Polyethylene-2,6-containing no lubricant such as inorganic particles
Naphthalate (intrinsic viscosity 0.62) was melt extruded at 300 ° C. and rapidly cooled to obtain an unstretched film having a thickness of about 1000 μm.
Chloroform was brought into contact with both sides of this unstretched film for processing. Then, this was stretched in the machine direction at 125 ° C by 3.6 times and in the transverse direction at 135 ° C by 3.7 times, and heat set at 230 ° C for 20 seconds. Thus, a film having a thickness of 75 μm was obtained (Example 2).

On the other hand, a film was obtained in exactly the same manner as in Example 2 except that polyethylene-2,6-naphthalate (intrinsic viscosity 0.62) obtained by adding 0.25% of calcium carbonate having an average particle diameter of 0.60 μm was used and the surface treatment was performed. (Comparative example 3).

The obtained film was evaluated for delamination.

The punched area of the film of Example 2 was 4.5 mm ² per needle hole, and that of Comparative Example 3 was 7.0 mm ² . It was found that the film of the present invention of Example 2 was excellent in that it was resistant to delamination.

Claims (1)

[Claims] 1. An electrical insulation obtained by subjecting an amorphous polyethylene-2,6-naphthalene dicarboxylate film containing substantially no lubricant to a surface treatment with a crystallization accelerator and then stretching and orienting it biaxially. Polyethylene for wood-2,6-
Naphthalene dicarboxylate film.