JPH07211149A - Insulating film for flat cable - Google Patents

Abstract

PURPOSE:To provide an insulative film for use in flat cable which is not likely to tend to wind even when exposed to a high temp. and which is excellent in the heat resistance, by using a biaxially oriented polyethylene-2,6-naphthalate film having specific physical properties. CONSTITUTION:An insulative film for a flat cable is composed of a biaxially oriented polyethylene-2,6-naphthalate film, where tandelta in longitudinal direction due to the tensile visco-elasticity at 0.05Hz is below 0.08 at 80 deg.C and the rate of thermal contraction when left at 150 deg.C for 30min ranges from 0.2 to 2.5% in the longitudinal and/or transverse direction. One of the most favorable heat treatment methods for reducing tandelta is to put a web film in a heating oven in the condition taken up in a roll, followed by an annealing process. To effiectively reduce the rate of thermal contraction, usually the magnification of film elongation is lowered or the heat fix temp. is heightened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat cable insulating film, and more particularly to a biaxially oriented polyethylene-2,6-naphthalate film, which is useful for a flexible flat cable used for a circuit wire of electric / electronic equipment. Insulation film

[0002]

2. Description of the Related Art In a flat cable, thin conductors are arranged on upper and lower insulating films via an adhesive as shown in FIG. 1, and a large number of wirings are built in one cable. It is widely used because wiring between printed circuit boards and many wirings between devices can be collectively formed, so that the number of wiring steps can be greatly reduced and the reliability thereof can be improved.

Hitherto, as these insulating films, a biaxially stretched polyethylene terephthalate (PET) film has been used because of its mechanical strength, heat resistance and reliability of insulating properties.

However, in recent years, more advanced characteristics have been required for these cables, and for example, a cable that can withstand a higher temperature environment is desired. Conventionally used PET films can withstand mechanical strength and insulating properties even at relatively high temperatures, but have the following problems. For example, if you wrap a flat cable on a thin shaft and store it in a high-temperature environment for a long time, the curl will remain, and when you try to unwind this flat cable into a flat plate, the curl will remain as a distorted shape. As a result, the circuit may come into contact with the surrounding circuit, and the circuit may be damaged, or the insulation film on the flat cable side may be punctured due to wear, damage, or in the worst case, the conductor may be exposed, causing a short circuit in the circuit. I will end up. Therefore, when the conventional PET film is used, it is necessary to take measures such as limiting the operating temperature and providing a new mechanism for preventing contact. These are not desirable because they not only increase the cost of the device but also increase the total space.

As a method for reducing such curl, it is possible to use, for example, a film of polyimide or polyetheretherketone having a high glass transition temperature as an insulator, but the film is expensive and widely used. Cannot be used for. In addition, JP-A-51-16358
Although a method of heating a film at a temperature 5 to 30 ° C. lower than the glass transition temperature is proposed as described in Japanese Patent Publication No.
It has not been possible to sufficiently reduce the curl. On the other hand, polyethylene-2,6-naphthalate film seems to be suitable for this application because it has a relatively high glass transition temperature and is superior in heat resistance to PET film. It is still strong and has not yet been put to practical use.

[0006]

DISCLOSURE OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, to prevent the formation of curl even when exposed to a high temperature condition, and to provide biaxially oriented polyethylene-2 having excellent heat resistance.
An object of the present invention is to provide an insulating film for a flat cable made of 6-naphthalate film.

[0007]

The present inventors have completed the present invention as a result of further studies to achieve the above object.

That is, the present invention relates to a biaxially oriented polyethylene-2,6-naphthalate film having a thickness of 0.05
The tan δ in the longitudinal direction by tensile viscoelasticity at Hz is 0.08 or less at 80 ° C., and the heat shrinkage rate when held at 150 ° C. for 30 minutes is 0.2 to 2 in the longitudinal direction and / or the transverse direction. The insulating film for a flat cable is characterized by having a content of 0.5%.

The polyethylene-2,6-naphthalate in the present invention is not only a polyethylene-2,6-naphthalate homopolymer but also a small proportion (eg 10 mol% or less, further 5 mol% or less) of the third component. It also includes a modified polyethylene-2,6-naphthalate copolymer and a blend polymer in which a small proportion (for example, 20% by weight or less, further 10% by weight or less) of a third component is mixed.

Such polyethylene-2,6-naphthalate is basically known and can be produced by a known method. For example, polyethylene-2,6-naphthalate is generally produced by polycondensation reaction of 2,6-naphthalenedicarboxylic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative in the presence of a catalyst. It In the case of producing a copolymer, the third component may be added and reacted at a stage until the polycondensation reaction is completed, and in the case of producing a blended polymer, the polymer of the third component may be added before the film formation. Should be mixed.

Suitable third component is a compound having a divalent ester-forming functional group, for example, oxalic acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, 2,7.
-Dicarboxylic acids such as naphthalenedicarboxylic acid and diphenyl ether dicarboxylic acid or lower alkyl esters thereof; oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid or lower alkyl esters thereof; or propylene glycol, trimethylene glycol And dihydric alcohols such as tetramethylene glycol, hexamethylene glycol, neopentyl glycol and the like.

Polyethylene-2,6-naphthalate may be obtained by blocking some or all of the terminal hydroxyl groups and / or carboxyl groups with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Alternatively, it may be modified with a trifunctional or higher functional ester-forming compound such as glycerin or pentaerythritol in a very small amount within a range where a substantially linear polymer is obtained.

The polyethylene-2,6-naphthalate may contain a lubricant such as silica in the form of fine particles, talc, clay, a heat-resistant polymer, etc. for imparting a slip property to the film, and other additives such as, for example, Stabilizers, UV absorbers, colorants, flame retardants and the like can also be added.

Biaxially oriented polyethylene in the present invention
The 2,6-naphthalate film has a longitudinal tan δ of 0.8 at 80 ° C. due to tensile viscoelasticity at 0.05 Hz.
It must be 08 or less. This tan δ is 0.
If it exceeds 08, the curl cannot be reduced to a sufficiently satisfactory level.

The biaxially oriented polyethylene-2,6-naphthalate film formed by a conventional method has a tan δ of about 0.10, and it is necessary to reduce the tan δ to 0.08 or less.

As a heat treatment method for lowering this tan δ, biaxially stretched heat-fixed polyethylene-2 is used.
6-Method of heating naphthalate film (original film) without contacting with heating roller while heating while contacting with heating roll, method of non-contact heating while running in heated air, winding of material film with roll An example of such a method is to put it in a heating oven in such a state and subject it to an annealing treatment. However, as long as tan δ can be 0.08 or less, the method is arbitrary and is not limited to a specific method.

Among these methods, as a particularly preferable method, the original film is wound into a roll and gradually heated from room temperature in the oven (for example, over 24 hours).
After raising the temperature to a predetermined temperature and holding at that temperature for a long time (for example, 24 hours or more), gradually (for example, over 24 hours)
A method of lowering the temperature to room temperature is used. At that time, the annealing temperature is 70 to 150 ° C., and further 80 to 1
30 ° C. is preferred. If the annealing temperature is too low, the curl cannot be sufficiently removed. Conversely, if the annealing temperature is too high, the oligomer deposition on the film surface decreases the adhesive strength between the conductor and the insulating film, and easily peels off. Occurs, which is not preferable.

Biaxially oriented polyethylene in the present invention
Further, the 2,6-naphthalate film needs to have a heat shrinkage ratio of 0.2 to 2.5% in at least one of the longitudinal direction and the lateral direction when kept at 150 ° C. for 30 minutes. Is.

In order to reduce the heat shrinkage rate, it is usually effective to lower the draw ratio of the film or raise the heat setting temperature. However, if this is done, the thickness unevenness of the film becomes large and the film surface wrinkles. Occurs and the flatness is remarkably reduced, so that the heat shrinkage ratio needs to be 0.2% or more. It is preferably 0.4% or more. On the other hand, if the heat shrinkage rate is too high, it is exposed to a high temperature for a long time during the above-mentioned annealing treatment, so that heat shrinkage occurs, and particularly when annealing in a roll state, the core portion is blocked due to winding tightness (blocking ( Sticking phenomenon) occurs, and deformation due to contraction occurs. Further, generally, the insulating film and the conductor are bonded to each other while heating in many cases. Therefore, if the shrinkage ratio is large, wrinkles are generated and the value of the product is significantly reduced. Therefore, the heat shrinkage rate when kept at 150 ° C. for 30 minutes needs to be 2.5% or less, preferably 2% or less, and more preferably 1.5% or less.

The method of adjusting the heat shrinkage ratio is as described above, and the conditions satisfying these conditions may be selected from the necessary heat shrinkage ratio and other characteristics.

Biaxially oriented polyethylene-2,6-of the present invention
Biaxial stretching in producing the naphthalate film may be sequential stretching in the machine direction and transverse direction, or simultaneous biaxial stretching.
At that time, the stretching ratio is 3.5 to 4.3 times in the longitudinal direction, 3.7 to 4.1 times in the longitudinal direction, and 3.7 to 4.5 times in the transverse direction.
Further, it is preferable to set it to 3.9 to 4.3 times.

In the present invention, the biaxially oriented polyethylene-2,6-naphthalate film usually has a thickness of 10
It is often set to 75 μm.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

In the examples and comparative examples, tan δ,
The curl value, the deformation of the film before and after annealing, and the heat shrinkage ratio were measured as follows.

(1) tan δ Seiko Denshi Kogyo Co., Ltd. thermal stress strain measurement system TMA / S
The measurement is performed under the following conditions using S120C. Load mode: sin wave (load change frequency 0.05Hz) Median load per cross-sectional area: 120g / mm ² Load amplitude per cross-sectional area: 90g / mm ² Temperature rising rate: 5 ° C / min Sample width: 4mm Sample length (Between chucks): 10 mm Measuring direction: vertical direction

(2) Curling habit value A film sample having a width of 10 mm and a length of 120 mm (longitudinal direction) is wound around a core having a diameter of 10 mm, and the temperature is set to 80 ° C. and 10
After heating at 5 ° C for 24 hours each, cooling it to room temperature,
The diameter (mm) of the circular film with a curl is released from the core to determine the curl value. That is, the smaller the curl value, the stronger the curl.

(3) Planarity of Film A film having a width of 500 mm and a length of 500 m is wound into a roll, the film on the surface of the roll immediately after winding, and the roll after annealing at 120 ° C. for 24 hours With respect to the film at a total of three places, that is, the surface portion and the winding core portion cut out by about 400 m from the surface portion, the flatness of the film, the presence or absence of blocking, and the presence or absence of deformation of the film due to annealing are visually observed. The judgment is based on the following criteria.

◯: No blocking occurs, and the flatness of the film is good. Δ: There are 1 to 5 granular blocking points, but the flatness of the film is good. ×: 6 or more granular blocking points or 10 mm ²
The above blocking is at one or more places or the flatness of the film is poor.

(4) Heat shrinkage rate: Hold in hot air at 150 ° C. for 30 minutes, and obtain the dimensional change before and after this by the following formula.

[0030]

[Equation 1]

[0031]

Example 1 and Comparative Examples 1 to 4 Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.60 was melt extruded from a die slit by a conventional method and cooled and solidified on a casting drum to prepare an unstretched film.

The unstretched film was biaxially stretched under the conditions shown in Table 1, heat-fixed under tension, and annealed under the conditions shown in Table 1 to obtain a biaxially oriented film having a thickness of 25 μm.

In the annealing treatment, the film after biaxial stretching and heat setting is brought into contact with a cooling roll in a tensioned state to be rapidly cooled, and a width of 500 m from a wound film parent roll.
A film with a length of 500 m and a length of 95 m
It was carried out by winding in a roll shape on a m core and heating in a heating oven.

The characteristics of the obtained film are shown in Table 1.

[0035]

[Table 1]

The annealing conditions in Table 1 are as shown below.

Condition A: The temperature is raised to 120 ° C. over 2 hours, kept at this temperature for 24 hours, and then lowered to room temperature over 2 hours.

Condition B: The temperature was raised to 60 ° C. over 2 hours,
After holding at this temperature for 24 hours, the temperature is lowered to room temperature over 2 hours.

As is clear from the above results, the biaxially oriented polyethylene-2,6-naphthalate film of the present invention has a low tan δ and is unlikely to have a curling tendency when exposed to high temperatures. Moreover, there is no blocking and the flatness is excellent.

On the other hand, in Comparative Example 1 in which annealing is not performed and Comparative Example 2 in which the conditions are not appropriate, tan δ is higher than 0.08,
It tends to have a curl. Further, Comparative Example 3 in which the thermal shrinkage rate is less than 0.2% has already poor planarity before annealing, and Comparative Example 4 in which the thermal shrinkage rate exceeds 2.5% has good planarity before annealing, but Later blocking and deterioration of flatness are observed.

[0041]

According to the present invention, it is possible to provide an insulating film for a flat cable which is less likely to have a curling tendency at high temperatures and has excellent flatness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a general flat cable in a thickness direction.

[Explanation of symbols]

 1: Insulating film 2: Conductor

Claims (1)

[Claims] 1. A biaxially oriented polyethylene-2,6-naphthalate film having a longitudinal tan δ of 0.08 or less at 80 ° C. and 30 at 150 ° C. due to tensile viscoelasticity at 0.05 Hz. An insulating film for a flat cable, which has a heat shrinkage ratio of 0.2 to 2.5% in the longitudinal direction and / or the lateral direction when held for a minute.