JPH01110554A - Polyester film - Google Patents

Abstract

PURPOSE:To obtain the subject film having excellent balanced mechanical properties in the longitudinal and transverse directions, heat dimensional stability to heat and heat resistance, by drawing a film consisting of a composition obtained by blending a liquid crystal polyester with a nonliquid crystal polyester at a specific amount. CONSTITUTION:A composition containing (A) a polyester modified by 29.4-43mol., preferably 30.7-38mol. p-hydroxybenzoic acid and capable of forming anisotropic melt, preferably a polyester obtained by modifying a copolymer of polyethylene terephthalate, etc., and a nonlinear dicarboxylic acid component (e.g. isophthalic acid) or a nonlinear diol component (e.g., bisphenol A) with p-hydroxy benzoic acid and (B) a polyester (preferably polyethylene terephthalate or polybutylene terephthalate) capable of forming isotropic melt at a weight ratio of 7:3-1:9, preferably 50:50-15:85 is melt-extruded to provide a film and the resultant film is drawn in at least monoaxial direction at a draw ratio of >=1.5 times.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a polyester capable of forming an anisotropic melt (hereinafter referred to as liquid crystalline polyester) and a polyester capable of forming a substantially isotropic melt. It relates to a polyester film made of a composition of liquid crystalline polyester (hereinafter referred to as non-liquid crystalline polyester), and more specifically, it is made of liquid crystalline polyester and non-liquid crystalline polyester and is stretched in at least one axis. It relates to polyester film.

(Prior art) Two-wheel stretched polyethylene terephthalate films are currently used as base films for magnetic recording media, but the tensile modulus in the longitudinal direction is approximately 4 for balance stretched films.
00 kg/d, approximately 70 kg/d even for tensilized stretched film
0 kg/m+/L, recording unevenness due to distortion under tension is a problem. In particular, recently, films have been made thinner in order to increase the amount of recording, and even under low tension, they tend to deform easily, often resulting in recording spots. Furthermore, deformation due to frictional heat with the magnetic head cannot be ignored.

On the other hand, biaxially oriented polyethylene terephthalate film is also used as a base film for thermal transfer media.
There were problems such as deformation due to tension at high temperatures and holes caused by heating of the thermal head.

(Problems to be Solved by the Invention) In order to suppress distortion under tension, it was further stretched in the vertical direction. It has also been proposed to use a so-called supertensilized film, but this has the disadvantage that the stretching ratio is too high, which increases shrinkage due to heating.

To improve this, Japanese Patent Publication No. 48-29541 proposes the use of a two-wheel stretched film made of polyethylene naphthalate, but this film is much more expensive than the two-wheel stretched polyethylene terephthalate film. It is expensive and has practical problems.

Further, Japanese Patent Application Laid-Open No. 102234/1983 proposes a method for producing a biaxially oriented film from liquid crystalline polyester by an inflation method. However, according to this method, the film of liquid crystalline polyester in a molten state is oriented by drafting it during film formation, and the balance between the vertical and horizontal directions of the film is difficult to maintain due to the orientation.
This results in a film with insufficient strength in the horizontal direction, which poses a practical problem.

An object of the present invention is to provide a polyester film that has excellent mechanical properties in both the longitudinal and longitudinal directions, without causing extreme imbalance in the mechanical properties, especially Young's modulus.

Another object of the present invention is to provide a polyester film that has excellent heat resistance and does not suffer from a decrease in rigidity due to frictional heat with a magnetic head, or partial melting due to heating of a thermal head.

Another object of the present invention is to provide a polyester film that does not easily tear in the horizontal direction.

(Means for Solving the Problems) As a result of intensive research in order to provide a polyester film that does not have the above problems, the inventors of the present invention have blended liquid crystalline polyester and non-liquid crystalline polyester in a specific ratio. The inventors have discovered that a stretched film can achieve the above objectives and have arrived at the present invention.

That is, 1 the present invention consists of a polyester composition in which the weight ratio of liquid crystalline polyester modified with p-hydroxybenzoic acid and non-liquid crystalline polyester is 7:3 to 1:9,
The gist of the invention is a polyester film characterized by being stretched in at least one direction.

The film of the present invention comprises liquid crystalline polyester and (p-
It consists of a polyester composition in which the weight ratio of a liquid crystalline polyester made of a copolymerized polyester modified with hydroxybenzoic acid and a non-liquid crystalline polyester is 7:3 to 1:9.

If the proportion of the p-hydroxybenzoic acid component in the liquid crystalline polyester is too small, it will be difficult to obtain the effect of improving slipperiness, while if it is too large, it will be difficult to obtain a uniform film, so 29.4 to 43 .0 mol%, especially 30.
It is preferably 7 to 38.0 mol%.

Examples of liquid crystalline polyesters include liquid crystalline polyesters consisting of a p-hydroxybenzoic acid component, a terephthalic acid component, and an ethylene glycol component; in this case, the ratio of the p-hydroxybenzoic acid component is 29.4 to 32.0.
It is preferable that the mol% and the proportions of the terephthalic acid component and the ethylene glycol component are each 35.3 to 34.0 mol%, but a more preferable liquid crystalline polyester is p
- A nonlinear dicarboxylic acid component as a dicarboxylic acid component and/or diol component in place of a part of the terephthalic acid component and/or ethylene glycol of the liquid crystalline polyester sent from the hydroxybenzoic acid component, terephthalic acid component, and ethylene glycol component. Alternatively, it is a liquid crystalline polyester containing a diol component (excluding ethylene glycol) as a copolymer component.

In this case, if the proportion of p-hydroxybenzoic acid component in the liquid crystalline polyester is too small, it will be difficult to obtain a film with high elastic modulus and heat resistance, and if the proportion of nonlinear dicarboxylic acid component or diol component is too small. If the proportion of the non-linear dicarboxylic acid component or diol component is too high, it will be difficult to obtain a heat-resistant film with a high elastic modulus. As the diol component, the following formula (1),
Particularly preferred is a liquid crystalline polyester containing as a copolymer component a nonlinear dicarboxylic acid component or diol component (excluding ethylene glycol) in an amount that simultaneously satisfies (IT) and (Ill).

y>0 (1) 0.7(x -30,7) +2≧y≧0.7(x
-30,7) -2(II)43.0≧x>29.
4 (III) [In the formula, y is the ratio (mol%) of the total amount of the nonlinear dicarboxylic acid component and the nonlinear diol component in the liquid crystalline polyester, and X is the p-hydroxybenzoic acid component in the liquid crystalline polyester. Represents the proportion of acid components (mol%). ] Here, the nonlinear dicarboxylic acid component or the nonlinear diol component means a dicarboxylic acid component or diol component that gives bending to the main chain of the polyester and alleviates liquid crystallinity. Examples of such components include those where the SF3 bond gives a bend to the main chain, the position of an aromatic ring bond gives a bend to the main chain, and the position of a benzene ring or polycyclic aromatic bond gives a bend to the main chain. A non-linear bond between two or more aromatic rings, such as a carbon atom or an oxygen atom, gives a bend to the main chain.

Examples include those in which an ether bond between an aromatic ring and an alkyl chain gives bending to the main chain. Specific examples of such dicarboxylic acid components and diol components include the following.

Dicarboxylic acid components include malonic acid and succinic acid.

Speric acid, adipic acid, azelaic acid, sebacic acid,
Aliphatic dicarboxylic acids having 20 or less carbon atoms, such as dodecanoic acid, tetradecanoic acid, and eicosanniic acid, and long-chain aliphatic dicarboxylic acids, such as dimer acid.

SP3 bonds in alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid give bending to the main chain and alleviate liquid crystallinity, phthalic acid, and isophthalic acid.

Aromatic dicarboxylic acids such as 2.6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, and 1.5-naphthalene dicarboxylic acid, where the bond position of the aromatic ring gives bending to the main chain and alleviates liquid crystallinity. Examples include group dicarboxylic acids and derivatives thereof.

Among these, aliphatic dicarboxylic acids having 4 to 20 carbon atoms and isophthalic acid are preferred because they have excellent film smoothness and are economical.

The diol component is propylene glycol.

Aliphatic glycols with 3 or more carbon atoms such as butanediol and hexanediol, diethylene glycol 1 Polyols such as triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol, alicyclics such as cyclohexanediol and cyclohexane dimetatool Group diols and their Kg 8 bodies are mentioned. In these materials, the SP3 bond gives bending to the main chain and alleviates liquid crystallinity. Examples of other diols include resorcinol, catechol, and 2,6-hydroxynaphthalene, which have benzene rings or polycyclic aromatic bonds that give bending to the main chain and alleviate liquid crystallinity, and bisphenol A.
, 4.4-dihydroxydiphenylmethane, 4.4-dihydroxydiphenyl ether, etc. Non-linear bonds such as carbon atoms and oxygen atoms between two or more aromatic rings give bending to the main chain.

Aromatic diols that alleviate liquid crystallinity, as well as ether bonds between aromatic rings and alkyl chains such as ethylene glycol monohydroquinone ether and diethylene glycol hydroquinone ether, which give bending to the main chain and alleviate liquid crystallinity, and derivatives of these are listed. It will be done. Among these, bisphenol A and resorcinol are used because they have excellent film smoothness and uniformity, and are economical.

Diethylene glycol and ethylene glycol monohydroquinone ether are preferred, and bisphenol A is particularly preferred since it improves the heat resistance of the film.

The method for preparing such a liquid crystalline polyester is not particularly limited.2For example, polyethylene terephthalate or polyethylene terephthalate copolymerized with a nonlinear dicarboxylic acid component or a nonlinear diol component is mixed with acetoxybenzoic acid. Various conventionally known methods can be appropriately employed, such as the method described in Japanese Patent Publication No. 5G-18016, which involves mixing, then heating and melting to perform acidolysis, and further reducing the pressure to increase the viscosity.

Further, the non-liquid crystalline polyester is a polymer of one or more dicarboxylic acid components and one or more diol components, and its type is not particularly limited as long as it is non-liquid crystalline.

Dicarboxylic acid components include malonic acid and succinic acid.

Speric acid, adipic acid, azelaic acid, sebacic acid,
Aliphatic dicarboxylic acids having 20 or less carbon atoms, such as dodecanoic acid, tetradecanoic acid, and eicosanniic acid, and long-chain aliphatic dicarboxylic acids, such as dimer acid.

Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, terephthalic acid, phthalic acid, and isophthalic acid.

Examples include aromatic dicarboxylic acids such as 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, and 1,5-naphthalene dicarboxylic acid.

The diol component is ethylene glycol.

Aliphatic glycols such as propylene glycol, butanediol, hexanediol, diethylene glycol,
Examples include polyols such as triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol, alicyclic diols such as cyclohexanediol and cyclohexane dimetatool, and derivatives thereof.

In the present invention, the non-liquid crystalline polyester is selected from consideration of economical efficiency, film formability, and stretchability.

Particularly preferred are polyethylene terephthalate and polybutylene terephthalate.

The mixing ratio of liquid crystalline polyester and non-liquid crystalline polyester is 7:3 to 1:9 by weight. Preferably 50:50-15
:85. If the proportion of liquid crystalline polyester exceeds this mixing ratio, the dispersion of the polyester becomes poor, and the strength of the resulting film decreases, causing a practical problem.

On the other hand, if the proportion of liquid crystalline polyester is less than this mixing ratio, the effect of improving the elastic modulus and heat resistance will not be exhibited.

The film of the present invention can be produced by melt-extruding a composition consisting of a liquid crystalline polyester and a non-liquid crystalline polyester as described above to form a film, and then stretching the film in at least one direction. As the film forming apparatus, a conventionally known melt extrusion film forming apparatus for polyester can be used.

The film of the present invention may be a single layer, but in order to reduce costs, it may be a multilayer film.

Such a film includes, for example, a polyester resin film provided with a layer made of the composition of the present invention on one or both sides, and in at least one direction.
Examples include films that have been stretched five times or more.

The method of stretching the film is not particularly limited, but may include -axial stretching,
Sequential two-stage stretching, simultaneous two-wheel stretching, etc. can be applied. Also,
Applicable devices for this purpose include a two-roll type axial stretching machine, a tenter type lateral stretching machine, and a tenter type or tubular type simultaneous biaxial stretching machine.

The stretching temperature of the film is preferably higher than or equal to the glass transition temperature of the non-liquid crystalline polyester (glass transition temperature +120°C) or lower. Further, the heat setting temperature is preferably higher than (the melting point of the non-liquid crystalline polyester -60°C) and lower than the melting point of the non-liquid crystalline polyester.

(Example) The present invention will be explained in more detail below by giving examples.

In addition, the intrinsic viscosity of the polyester in one example is 3 in a mixed solvent of phenol/tetrachloroethane-1/1 (weight ratio).
Measured at 0°C. The liquid crystallinity of the polyester was determined by observing it under crossed nicol conditions at 280° C. using a polarizing microscope. The tensile modulus of the film was measured using a tensile tester (Autograph manufactured by Shimadzu Corporation).

Examples 1-4. Comparative Example 1 According to the polymerization method described in Japanese Patent Publication No. 56-18016, p-acetoxybenzoic acid was added to polyethylene terephthalate, acidolysis reaction was carried out under a stream of dry nitrogen, and then the pressure was gradually reduced until finally 0. 2mm11
Polymerized for 4 hours under reduced pressure of g, molar specific strength of residues of p-hydroxybenzoic acid with intrinsic viscosity 0.73/residues of terephthalic acid/residues of ethylene glycol 43.0/28.5/28
．． 5 (however, the molar ratio of terephthalic acid residues and ethylene glycol residues was 1:1) was produced.

The obtained liquid crystalline polyester and polyethylene terephthalate were heated and melted at 280°C while changing the mixing ratio so that the content of liquid crystalline polyester was as shown in Table 1, and the mixture was attached to the tip of a 40mm axle extruder. The material was extruded into air at room temperature through a slit with a thickness of 0.8 fins and a width of 300 mm at an extrusion rate of 90 an/min (discharge amount: 280 g/min), and wound up onto a roll at a take-up rate of 216 cm/min.

The obtained unstretched film was stretched 3.2 times in the vertical direction at 90°C using a stretcher manufactured by Toyo Seiki Seisakusho, and then
A stretched film was obtained by stretching 3.5 times in the horizontal direction at 00°C.

The results of measuring the tensile modulus and tear strength at 20° C. of the obtained stretched film are shown in Table 1.2.

As is clear from Tables 1 and 2, the tensile modulus of the film of the present invention is significantly improved compared to the conventional two-wheel stretched polyethylene terephthalate film (Comparative Example 1).
Moreover, the balance between vertical and horizontal directions was maintained.

Furthermore, the difference in tear strength in the vertical and horizontal directions was also small.

Next, in order to examine deformation at high temperatures, the tensile modulus at 70° C. was measured and the results are shown in Table 3.

As is clear from Table 3, even at 70°C, there was little decrease in the tensile modulus.

Furthermore, when the film was brought into contact with the thermal gutter of a thermal transfer printer and the temperature was increased by applying electricity, no pinholes were observed in the film of the example.

Table 1 (blank below) Table 2 Table 3 (Effects of the invention) The polyester film of the present invention has good mechanical performance with a good vertical and horizontal balance, excellent thermal dimensional stability, and It also has good heat resistance. By taking advantage of these properties, the polyester film of the present invention can be used for magnetic recording materials such as audio tapes, video tapes, and floppy disks, base films for thermal transfer recording media, and films for heavy packaging.

Claims (1)

[Claims] (1) The weight ratio of the polyester modified with p-hydroxybenzoic acid capable of forming an anisotropic melt to the polyester capable of forming a substantially isotropic melt is 7:3 to 1:9.
A polyester film, characterized in that it is made of a polyester composition and is stretched in at least one axis.