KR960011758B1 - Method for manufacturing polyester film - Google Patents

Abstract

The invention relates the preparation of polyester film having excellent heat resistance and general physical properties such as electrical insulating property, voltage-defect resistance, and abrasion resistance. The film owes its perfect usage for compression and injection molding to the decrease of oligomer content in the polyester film.

Description

Manufacturing method of polyester film

The present invention relates to a method for producing a polyester film, and more particularly, to a method for producing a biaxially stretched polyester film having a low content of oligomers in the film and having excellent physical properties such as heat resistance, electrical conductivity, voltage resistance, and wear resistance. will be.

Polyester film, especially polyethylene terephthalate film, has excellent mechanical properties, chemical and physical stability when manufactured by biaxial stretching, and has excellent heat resistance, durability, chemical resistance, and electrical insulation. It is widely used for molding, packaging, photographic film, labeling and other various molded products.

Polyethylene terephthalate film which is usefully applied as described above is a process of forming a sheet by melt extrusion of a chip produced by reacting dimethyl terephthalate and ethylene glycol, and then stretching and cooling in the longitudinal and transverse biaxial directions. It is manufactured through. That is, the amorphous and non-oriented polyester sheet is preheated and longitudinally produced, and then manufactured in a transverse stretching machine through preheating, stretching and heat setting.

However, the polyester film prepared as described above usually contains 2.0 to 2.5% by weight of an oligomer of which the cyclic trimer is a main component, and when it is used for electrical insulation, there is a problem that heat resistance in the motor is insufficient. When used as an insulating material, there is a problem that the oligomer inside the polyester film is extracted by the refrigerant to block the nozzle of the motor or to contaminate the refrigerant to cause product defects.

When used as a film for magnetic recording media, the oligomer inside the film easily precipitates to the surface and becomes a white powder or foreign matter through the application of a high temperature magnetic layer coating or a calendering process, and has a fatal effect on running and abrasion resistance. It may also cause the performance of the final product to fall out.

In addition, oligomers precipitate and accumulate in the electrostatic application wire during film production, which may cause electrostatic application defects, and during the heat treatment, the oligomer may accumulate in the tenta and contaminate the film. In addition, in the injection molding process for producing a container, the oligomer may provide a cause of process abnormality such as contamination of the mold.

As a result, the polyester used for extrusion or injection molding has a lower oligomer content, and the oligomer amount is preferably 1.0% by weight or less. However, it is very difficult to control the content of oligomers in the polyester at a low concentration because a certain amount is always present in equilibrium concentration with the polymer depending on the characteristics of the polymer during the polymerization process.

The oligomer refers to a low molecular weight polymer having a degree of polymerization of about 3 to 10. The oligomer mainly consists of a cyclic oligomer produced by a cyclization reaction between both ends of the molecule, and an example of the structure is shown below, which is a cyclic trimer of ethylene terephthalate. .

A method for solving the above problems caused by oligomers in polyester films is disclosed in Japanese Patent Application Nos. 43-23348 and 44-2120, which is intended to extract the oligomer using a specific solvent.

Selecting and using an appropriate solvent by the above method enables efficient extraction of oligomers, but it takes a long time to extract and requires a separate process for using a solvent, thereby reducing workability and increasing cost and lowering productivity. In addition, there is a drawback that the physical properties of the film are caused by the solvent.

Accordingly, an object of the present invention is to lower the oligomer content in the polyester film and at the same time control the structure of the film appropriately, thereby imparting heat resistance to the film to solve the defects of conventional polyester and excellent polyester properties. It is to provide a method for producing a film.

In order to achieve the above object, in the present invention, the main repeating unit is ethylene terephthalate, and contains 0.01 to 1.0 wt% of inert particles having an average particle size of 0.01 to 2.0 μm based on the total amount of polymer, and has an intrinsic viscosity of 0.5 to 1.0 dl / g. The polyester polymer is molded into an unstretched sheet under the conditions satisfying the following formula (1), and then stretched and heat treated to satisfy the following formula (2), thereby providing a method for producing a polyester film.

t≤15 [IV]-(T-Tm) / 5... … … … … … … … … … … … … … … … … … (One)

0.8 S / D 1.4... … … … … … … … … … … … … … … … … … … … … … (2)

Where t is the extrusion time in minutes, T is the extrusion temperature of the polyester polymer (° C.), Tm is the melting temperature of the polyester polymer (° C.), [IV] is the ultimate viscosity of the polyester, and S is the X-ray Crystal size of the polyester film by measurement, D is the crystallinity (%) of the polyester film.

The polyester used in the present invention shall have an intrinsic viscosity ranging from 0.5 to 1.0 dl / g, measured at a concentration of 0.3 grams per 25 milliliters of ortho chlorophenol at 35 ° C. This is because if the film is made of polyester with an extreme viscosity of less than 0.5 dl / g, breakage occurs frequently during stretching, which greatly reduces productivity and increases the content of oligomers, making it difficult to apply, and also having an extreme viscosity of 1.0 dl. If / g exceeds the oligomer content is not significantly lower than the increase in the ultimate viscosity, the melt viscosity of the polymer is very high, it is because the productivity in the post-process is greatly reduced due to difficulties in the manufacturing process, such as extrusion instability. Preferably, the intrinsic viscosity is used in the range of 0.6 to 0.8 dl / g.

The polyester used by the method of this invention polycondenses the acid component which mainly contains aromatic dicarboxylic acid, and the glycol component which has alkylene glycol as a main component.

Specific examples of the aromatic dicarboxylic acid include dimethyl terephthalate, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid and diphenyl ether. Dicarboxylic acid, anthracene dicarboxyl, α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylic acid, and the like, of which dimethyl terephthalate and terephthalic acid are particularly preferably used. do.

Specific examples of the alkylene glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol and the like, and among these, ethylene glycol is particularly preferably used.

In addition to the basic unit components of the polymer, known additives such as antistatic agents, ultraviolet absorbers, thermal stabilizers, crystallization accelerators, colorants, nucleating agents, antiblocking agents and the like can be added within a range not impairing the effects of the present invention. have.

As inert particles added to the polyester of the present invention, at least one or more selected from inert inorganic particles and organic particles insoluble in polyester are used.

Inert inorganic particles use chemically inert compounds selected from oxides and inorganic salts of Group 2, 3 and 4 elements on the periodic table of the elements. Specific examples include synthetic or natural calcium carbonate, wet or dry silica, calcium phosphate, magnesium carbonate, talc, alumina, sodium fluoride, titanium dioxide, mica, aluminum hydroxide and calcium terephthalate, among which silica, calcium carbonate and dioxide Titanium, sodium fluoride, calcium phosphate and the like are particularly preferred.

As organic particles insoluble in polyester, crosslinked polymers, elastomers, fluorine-based polymer fine particles and the like can be used without particular limitation, and among these, crosslinked polystyrene and fluorine-based polymer fine particles are particularly preferably used.

The inert particles use those having an average particle diameter of 0.01 to 2.0 µm. If the film is manufactured using particles having an average particle diameter of less than 0.01 μm, the roughness of the film is low so that the winding property is greatly poor, and the productivity is lowered. When the average particle diameter exceeds 2.0 μm, the surface of the film is excessively roughened, and the film is insulated. This is because it causes a defect. Preferably, an average particle diameter in the range of 0.05 to 1.0 mu m is used.

The addition amount of the inert particles is in the range of 0.01 to 1.0% by weight based on the total amount of the polymer, when the addition amount is less than 0.01% by weight, the crystallization rate of the film is too delayed to control the structure of the film and the heat resistance is also lowered, This is because when the added amount exceeds 1.0% by weight, no further heat resistance improvement and structure control effect can be obtained.

In the present invention, the addition timing of the inert particles is not particularly limited and may be any time as long as the polycondensation reaction is completed. When adding especially during a polymerization reaction, it is preferable to add immediately after a transesterification reaction or at the beginning of a polycondensation reaction.

The above inert particles are added within the above range, and heat treatment is performed for a certain time while reducing the polyester at a temperature below the melting point. The heat-treated polyester is made to satisfy the condition of t≤15 [IV]-(T-Tm) / 5, passed through an extruder at a temperature above the melting point and cast on a cooling drum to obtain an unstretched sheet. The resultant unstretched sheet was biaxially stretched 3.5 times in the film traveling direction and its vertical direction in the temperature range of Tg + 10 ° C. to Tg + 50 ° C., and then heat-treated at a temperature not higher than the melting point to obtain a condition of 0.8 S / D 1.4. A polyester film is produced according to the satisfactory method of the invention.

In the method for producing a polyester film according to the present invention, one of the important features is t≤15 [IV]-(T-Tm) / 5, which is a melt-extruded polyester. Where t is the melt compression time (minutes), [IV] is the intrinsic viscosity of the polyester, T is the extrusion temperature (° C) of the polyester polymer, and Tm is the melting temperature (° C) of the polyester polymer. If the extrusion time t is outside the range of the above formula, the heat resistance of the polymer is lowered and the content of the oligomer is increased so that the physical properties of the film are lowered.

Another feature of the present invention is that the crystal size and crystallinity of the film must be prepared to satisfy 0.8 S / D 1.4. Where S is the crystal size of the film by X-ray measurement, and D is the crystallinity (%) of the film. If the S / D is more than 1.4, the mechanical properties of the film are extremely reduced, and it is not good because there is no effect of preventing oligomer extraction when used in the refrigerator. If the S / D is 0.8 or less, the effect of preventing oligomer extraction of the film is no longer improved. Since numerical stability and thermal stability are not deteriorated, it is adjusted to the above range.

Hereinafter, the method of the present invention will be described in detail with reference to preferred examples, but the present invention is not limited only to the following examples.

Example 1

The unstretched sheet was formed by forming a polyester obtained by heat-treating a polyester having an intrinsic viscosity of 0.65 at a vacuum degree of 0.1torr or less at a temperature of 210 ° C for 6 hours at a melt extrusion temperature of 280 ° C and an extrusion time of 6 minutes. Got. The obtained sheet was stretched 3.5 times in the longitudinal direction at 90 ° C to prepare a biaxially stretched film. Subsequently, heat treatment was performed at 240 ° C. with appropriate relaxation to obtain a film having a crystal size of 55 kPa and a crystallinity of 50%. The oligomer content and heat resistance of the film were evaluated, and the results are shown in Table 1.

Comparative Example 1

The same method as in Example 1 was carried out, but the extrusion time was 10 minutes at the time of sheet forming, a biaxially stretched polyester film having a crystal size of 60 mm and a crystallinity of 50% was prepared.

Comparative Example 2

A biaxially stretched polyester film was prepared in the same manner as in Example 1, but having a crystal size of 45 GPa and a crystallinity of 60%.

Example 2

The same method as in Example 1 was carried out, but the sheet was melt-extruded at 290 ° C. and the extrusion time was 4 minutes, and a biaxially stretched polyester film having a crystal size of 60 μs and a crystallinity of 60% was prepared.

Comparative Example 3

A biaxially stretched polyester film was prepared in the same manner as in Example 2 except that the sheet forming temperature was 300 ° C., the extrusion time was 8 minutes, the crystal size was 50 μs, and the crystallinity was 60%.

[Comparative Example 4]

The same method as in Example 2 was carried out, except that the extrusion temperature was 300 ° C. when forming the sheet, and a biaxially stretched polyester film having a crystal size of 65 Pa and a crystallinity of 45% was prepared.

Various performances of the films produced in the above Examples and Comparative Examples were evaluated as follows.

1) oligomer content

The polymer and the oligomer were separated using a mixed solvent of trifluoro acetic acid, chloroform, acetone, and ammonium hydroxide, and the separated oligomer was expressed as weight percent with respect to the initial sample amount.

2) crystal size

The size of the crystal was measured using the X-ray measuring method.

3) crystallinity

After the density of the film was determined using the density gradient tube, the degree of crystallinity was converted according to the following equation.

Crystallinity = [Cd × (Cd-Sd)] / [Sd × (Cd-Ad)] × 100

Cd: density of polyester crystal region (1.455)

Ad: density of polyester amorphous portion (1.355)

Sd: Density of measurement sample

4) heat resistance

The specimens were made into a 3.5 × 3.5 times biaxially stretched film at 90 ° C., and the heat resistance was measured according to JIS K-7217. The heat resistance is evaluated by the time taken for the film elongation to drop to 50% after the test, and is expressed as follows.

Required time ≥ 300 hours: ◎ (very good)

100 hours ≤ time required 300 hours: ○ (good)

Time required: 100 hours: × (bad)

5) polymer melting point

The measured value was measured using a Perkin-Elmer differential scanning calorimeter (° C), and the temperature increase rate was 20 ° C / min.

As can be seen from the performance evaluation results of the films produced in the above Examples and Comparative Examples, the polyester film produced according to the method of the present invention has excellent heat resistance. This is to control the melting temperature and extrusion time during polyester molding, and to produce the crystal size and crystallinity of the film within a certain range, thereby lowering the content of the oligomer and excellent heat resistance. After all, it can be seen that the polyester film according to the method of the present invention is very excellent in electrical insulation, withstand voltage defects, surface properties, wear resistance and the like.

The biaxially stretched polyester film produced according to the method of the present invention is suitable for packaging, magnetic, electrical insulation, and the like, and can be used in various industrial fields such as capacitors and graphics.

Claims (1)

A polyester polymer having an ethylene terephthalate and an inert particle having an average particle diameter of 0.01 to 2.0 µm based on the total amount of the polymer and having an intrinsic viscosity of 0.5 to 1.0 dl / g with a main repeating unit of the following formula (1 Method of producing a polyester film, characterized in that after forming into an unstretched sheet in a condition that satisfies), the stretching and heat treatment to satisfy the following formula (2). t≤15 [IV]-(T-Tm) / 5... … … … … … … … … … … … … … … … … … (One) 0.8 & lt S / D & lt 1.4. … … … … … … … … … … … … … … … … … … … … … (2) Where t is the extrusion time in minutes, T is the extrusion temperature of the polyester polymer, Tm is the melting temperature of the polyester polymer, [IV ₀ ] is the ultimate viscosity of the polyester, and S is the poly by X-ray measurement. The crystal size of the ester film and D are the degree of crystallinity (%) of the polyester film.