JPS6328449B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing film-forming polyester. Polyester film, especially polyethylene terephthalate film, has excellent mechanical properties, electrical properties, chemical resistance, dimensional stability, etc., so it is used for magnetic tapes, capacitors, packaging, plate making, electrical disconnection, etc. It is used as a base material for many purposes such as photographic film. In particular, the growth in magnetic tape applications is remarkable, and among these, the demand for video tape applications is rapidly increasing. The required characteristics are wide-ranging, but in home video there is a particularly strong demand for long-time recording, and high-density recording is desired. The characteristics required of the base film when performing high-density recording are that the film be smooth and have excellent handling properties, be free of coarse foreign matter that can cause drop-outs, and be free from long-term waviness of the film. In other words, there is little thickness unevenness. First, regarding the smoothness of the film, high-density recording generally requires shorter recording wavelengths and narrower tracks, which inevitably reduces the reproduction output and increases the ratio of noise to signal. I come to do it. Therefore, in this case, it is necessary to make the contact between the video head and the tape sufficiently close to reduce so-called spacing loss, but to do this, the surface of the magnetic layer must be made smooth, and it is necessary to make the base film as smooth as possible. Needed. On the other hand, in order to maintain the running properties of the tape, it is necessary to roughen the surface of the film to some extent to reduce the coefficient of friction of the film. Particularly in the case of long-term recording, the tape feed speed becomes slow, so stable running is required even at low speeds. Other properties required for a base film for magnetic tape include the absence of dropouts and little unevenness in film thickness. If coarse foreign matter is present near the film surface, the reproduced signal will be lost, or so-called dropout will occur, so it is necessary to prevent the presence of coarse foreign matter in the raw polyester. In addition, in recent years, the requirements for film quality have become increasingly strict, and particularly in magnetic tape applications, improving the film thickness accuracy has become an indispensable condition. For this purpose, when a sheet material melted and extruded from an extrusion die is rapidly cooled in a rotating cooling drum as described in Japanese Patent Publication No. 37-6142, an electrostatic charge is applied to the surface of the sheet material. A so-called electrostatic cooling method is known in which an object is brought into close contact with a cooling surface. However, in this electrostatic application cooling method, when the speed of the rotating cooling drum is increased for the purpose of increasing productivity, the adhesion between the sheet material and the cooling drum decreases, resulting in the formation of so-called bound bubbles. The quality characteristics required for the product are unacceptable. Therefore, the raw material polyester must be one to which the electrostatic application cooling method can be effectively applied. It is extremely difficult to simultaneously satisfy all of the characteristics required of a base film for magnetic tape, but in particular it is extremely difficult to satisfy the contradictory characteristics of being smooth and easily slippery. Attempts have been made to practically satisfy these characteristics by developing a uniform and fine structure. It is well known that inorganic or organic fine particles may be present in the polyester for this purpose, and there are broadly two methods for this. One of them is called the addition method, in which silica, kaolin, talc, calcium carbonate, etc. are crushed and classified and then added to the polyester reaction system, molding, etc. However, this method often results in an unacceptably large incorporation of coarse particles due to mechanical limitations in the ability to classify and remove coarse particles. Also, unlike general applications, when the particle size of additive particles is reduced for magnetic tape applications that require a particularly uniform and fine surface condition, the dispersibility is often insufficient and agglomerated secondary particles are produced. begins to appear. Another method is called the precipitation method,
This is a method in which fine particles are precipitated within the system using the metal compound residue used as a transesterification reaction catalyst. This method does not require special equipment or complicated operations and is therefore easy to implement, but it still has the major problem of the presence of coarse particles. That is, conventional methods for obtaining fine precipitated particles include adding a phosphorus compound having an acid value, such as phosphoric acid, phosphorous acid, ethyl acid phosphate, butyl, to a reaction system containing a metal compound, such as a calcium compound or a lithium compound. A method of adding acid phosphate or the like is known. This method utilizes the rapid reaction rate between a phosphorus compound having an acid value and a metal compound to make the precipitated particles finer, but the inventors have found that this method has a major drawback. In other words, in this method, the reaction rate is fast, so the average particle size is small, but when a phosphorus compound is added, a reaction occurs immediately, resulting in a locally high concentration, and secondary particles are generated due to partial aggregation. . The coarse particles thus produced are hardly loosened and refined during the polymerization reaction, and therefore, when formed into a film, they are observed as fish eyes and cause dropouts. The inventor of the present invention focused on this point, and as a result of intensive studies on a method for obtaining a large number of uniform and fine precipitated particles without adding a phosphorus compound having an acid value,
It has been discovered that it is sufficient to allow a calcium compound and a pentavalent phosphorus compound to exist in a specific state, and then add trialkyl phosphite. Moreover, by adjusting the amount of the trialkyl phosphite added, the specific resistance (measuring method will be described later) of the polyester produced can be reduced to 5×10 ⁸ Ω.
-cm or less, and it has been found that by applying an electrostatic cooling method to the polyester, a polyester film with extremely small thickness unevenness can be obtained. That is, the present invention provides a method for producing polyester by carrying out polycondensation after transesterification using a lower alkyl ester of terephthalic acid as the main acid component and ethylene glycol as the main glycol component. At this point, a calcium compound and a pentavalent phosphorus compound are made to exist in a dissolved state in the reaction system, and then a trialkyl phosphite is produced.The total number of atoms of phosphorus element remaining in the polyester and the total number of atoms of calcium element are The specific resistance at the time of melting measured by the method described below is 5×
A method for producing polyester for magnetic tape film, characterized in that the resistance is 10 ⁸ Ω-cm or less. (Measurement of specific resistance during melting of polyester: Brit. J. Appl. Phys.) Vol. 17, No. 1149~
Method described on page 1154 (1966). However, in this case, the temperature at the time of melting the polymer composition is 290°C, and the value immediately after applying 3000 V DC is taken as the specific resistance at the time of melting. ) The present invention will be explained in more detail below. In the present invention, the lower alkyl ester of terephthalic acid as the acid component of the polyester raw material mainly refers to the alkyl ester of terephthalic acid having 1 to 4 carbon atoms, particularly dimethyl terephthalate, but some of the lower alkyl esters of terephthalic acid are Components such as dicarboxylic or oxycarboxylic acids other than terephthalic acid, lower alkyl esters such as p-hydroxyethoxybenzoic acid, adipic acid, and sebacic acid may be substituted. In addition, the glycol component of polyester raw materials is
Although ethylene glycol is the main target, a part of it may be replaced with other glycol components such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, etc. In any case, the term "polyester" used in the present invention refers to a polyester in which 80 mol% or more is ethylene terephthalate units. Furthermore, the calcium compound referred to in the present invention must be one that can be dissolved in the reaction system in the presence of a pentavalent phosphorus compound, such as calcium salts of aliphatic carboxylic acids such as acetic acid, propionic acid, butyric acid, benzoic acid, Calcium salts of aromatic carboxylic acids such as p-methylbenzoic acid, as well as ethylene glycol,
It refers to calcium alcoholates such as calcium glycolate of propylene glycol, inorganic calcium compounds such as calcium hydride, etc. These calcium compounds are used when transesterification is carried out using one or more types of calcium compounds, or when the transesterification is completed in a system in which transesterification is carried out with or without these calcium compounds. In some cases, a calcium compound is added afterwards. When transesterification is carried out using the above calcium compounds, these calcium compounds turn into calcium salts of polyester oligomers at the end of the reaction, but in the present invention, the reaction system is There is no problem even if the form of the calcium compound changes as long as it is dissolved in the calcium compound. The amount of calcium compound used in the present invention is 0.1 to 0.5 based on the total acid component of the polyester raw material.
Mol%, especially 0.15 to 0.3 mol% is preferred. If the amount of the calcium compound added is too small, the amount of precipitated particles will be insufficient, resulting in insufficient slipperiness when formed into a film, and if the amount added is too large, undesirable coarse particles will often be produced. One of the features of the present invention is that before adding the trialkyl phosphite, the calcium compound is
The purpose is to make a phosphorus compound of high valence act. The phosphorus compound used in this case is preferably one that reacts with a calcium compound in the reaction system to form precipitated particles, such as trialkyl phosphate or triaryl phosphate rather than phosphoric acid or acidic phosphoric acid ester. Specific examples include trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, etc., but trace amounts of phosphoric acid or Acidic phosphoric acid ester may be included. Does not have a hydroxyl group directly connected to these phosphorus atoms,
In other words, the phosphorus compound, which does not have an acid value, gradually changes in the reaction system and exhibits a complex reaction with the calcium compound, and the form of each compound differs from that at the time of addition. However, in the present invention, this reaction product is It must be substantially soluble in the system. In the present invention, some preferred methods for making the calcium compound and the pentavalent phosphorus compound exist in a dissolved state in the reaction system before adding the trivalent phosphorus compound are shown in more detail as follows. Approximately 0.05 to total acid component of polyester raw material
After performing a transesterification reaction using 0.1 mol % of a calcium compound, trialkyl phosphate is added in an amount of about 0.5 to 1.0 times the mole of the calcium compound. After the above-mentioned transesterification reaction is completed, 0.05 to 0.4 mol% of a calcium compound based on the total acid component of the polyester raw material and trialkyl phosphate in an amount of about 0.5 to 1.0 times the mole of the total calcium compound present in the reaction system are added. Among these methods, these methods are particularly preferably used. This is because, according to the present inventor's findings, normally calcium compounds dissolve only about 0.1 mol% in the transesterification product;
This is because if such an amount of pentavalent phosphorus compound is allowed to coexist, a large amount of calcium compound can be dissolved in the system, and ultimately a large amount of precipitated particles can be obtained. In the present invention, a specific amount of a specific pentavalent phosphorus compound is reacted with a calcium compound before adding a trialkyl phosphite in this way, but in this case, the longer the reaction time between the two, the more the final precipitation will be. The particle size of the particles becomes smaller. Examples of the trialkyl phosphite that plays a role in precipitating uniform, fine particles include trimethyl phosphite, triethyl phosphite, and tributyl phosphite. In the present invention, the size of the precipitated particles depends on the addition interval between the pentavalent phosphorus compound and the trialkyl phosphite, and the longer the addition interval, the smaller the precipitated particles become. This phenomenon is utilized to adjust the precipitated particle size to the desired size. control the size. However, if the addition interval exceeds 30 minutes, the initial precipitated particle size will no longer decrease, and on the contrary, the amount of by-product diethylene glycol will increase, so the addition interval should be set to 30 minutes.
It is best to keep it within minutes. In addition, in the present invention, the trialkyl phosphite has a specific resistance of 5× when the polyester produced is melted.
The amount must be selected and added so that the resistance is 10 ⁸ Ω-cm or less. The specific resistance of polyester when melted is 5×10 ⁸ Ω−
When the thickness exceeds cm, the electrostatic application cooling method cannot be applied effectively, and only a film with a large thickness unevenness that is unacceptable as a base film for a magnetic tape can be obtained. To this end, the ratio of the total number of atoms of phosphorus elements remaining in the normally produced polyester to the total number of atoms of calcium elements should be 0.84 or less, and in order to satisfy this condition, pentavalent phosphorus The amount of trialkyl phosphite to be added to the compound must be selected. In addition, in the present invention, the molar ratio of trialkyl phosphite to the pentavalent phosphorus compound is 0.01 to
1, preferably in the range of 0.02 to 0.5. In this case, when a plurality of phosphorus compounds are used as the pentavalent phosphorus compound or the trialkyl phosphite, the above molar ratio is based on the total amount of each phosphorus compound. If this value is less than 0.01, the amount of precipitated particles will be small and the slipperiness will be insufficient when formed into a film.If this value is greater than 1, the diameter of the precipitated particles will be uneven and the resulting polymer will have a black color. The taste becomes extremely strong. As explained above, according to the present invention, a large amount of uniform and fine precipitated particles can be obtained without adding a phosphorus compound having an acid value, and most of the precipitated particles do not contain coarse particles. By controlling the ratio of the phosphorus element and the calcium element remaining in the produced polyester, it is possible to produce a polyester to which the electrostatic cooling method can be effectively applied. The film obtained is extremely suitable as a base film for magnetic tape. In addition, when making a polyester film, known film forming methods are used, for example, usually melt extrusion at 270 to 295°C into a film, cooling and solidifying at 50 to 70°C to form an amorphous sheet, followed by sequential biaxial stretching vertically and horizontally, or simultaneous biaxial stretching. A method such as biaxial stretching and heat treatment at 160 to 240° C. (for example, the method described in Japanese Patent Publication No. 30-5639) can be used. The present invention will be explained in more detail below based on Examples. In the examples, "parts" indicate "parts by weight." The measurement method used is shown below. (1) Running properties The film is run using the running system shown in Figure 1.
The dynamic friction coefficient μD of the 5 mmφ hard chrome fixing pin shown in Figure 1 was measured. (Temperature 20±2
℃, humidity 60±10% RH) The traveling speed of the film was 1.0 to 2.1 m/min, and θ was 107°.
The film was also made into a tape using method (3), and its runnability was evaluated when it was repeatedly used on a deck at various temperatures and humidity. (2) Electromagnetic conversion characteristics, dropout The electromagnetic conversion characteristics (frequency characteristics and dropout) of the magnetic tape manufactured by the method (3) were measured at normal speed using a commercially available video deck, Victor-HR-3300. Dropouts with a signal output of 50% or less and caused by the base film were counted using a dropout counter manufactured by Japan Automatic Control Co., Ltd. (3) Manufacture of magnetic tape Composition (weight) Ferromagnetic material mainly composed of γ-Fe ₂ O ₃ 250 Polyurethane 50 Nitrocellulose 15 Vinyl chloride/vinyl acetate copolymer 20 Conductive carbon black 5 Lecithin 10 Methyl ethyl ketone 300 Butyl acetate 200 The above composition was kneaded in a ball mill for 24 hours to form a dispersion, 20 parts of a polyisocyanate compound was added, and dispersion treatment was further carried out for 1 hour to obtain a magnetic paint. This can be done using known methods (for example, Japanese Patent Application Laid-Open No.
The film was coated to a dry thickness of 6 μm using the method described in Japanese Patent Publication No. 145302, and while the paint was still wet, it was magnetically oriented using a conventional method and then placed in an oven for drying and curing. The magnetic tape thus obtained is subjected to supercalender treatment,
It was slit into 1/2 inch width and made into tape. (4) Thickness unevenness of polyester film Measure the film thickness at 10 points every 10 cm in the width direction at 10 points every 1000 m in the longitudinal direction of the film, for a total of 100 points. The film thickness is measured using a micrometer made by Anritsu Denshi, and 10 films around the relevant location are stacked and measured and converted into a value per film. When the maximum value of all measured values is Xmax., the minimum value is Xmin., and the arithmetic average value is

[Formula] is the film thickness unevenness, and the smaller the value, the better, and particularly preferably 0.13 or less. Example 1 (Manufacture of polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.09 part of calcium acetate monohydrate (0.10 mol% relative to dimethyl terephthalate) were placed in a reactor and heated to raise the temperature, and methanol was distilled off to form an ester. The exchange reaction was carried out, and it took about 4 hours after the start of the reaction to reach 230°C, and the transesterification reaction was substantially completed. At this point the reaction mixture was clear and the calcium compound was in solution. Next, 0.09 parts of calcium acetate monohydrate (0.10 mol% based on dimethyl terephthalate) and triethyl phosphate were added to the transesterification product.
0.15 part (0.8 times mole based on the total amount of calcium compounds)
An ethylene glycol solution containing was added. Then, 15 minutes later, 0.017 part of triethyl phosphite (0.12 times the mole relative to triethyl phosphate) was added. In this case, the total amount of phosphorus compounds is 0.91 times the total amount of calcium compounds by mole. Next, after adding 0.04 part of antimony trioxide as a polymerization catalyst, polymerization was carried out according to a conventional method. That is, 100 minutes after the addition of antimony trioxide, the temperature in the system was raised to 280° C. and the pressure reached 10 mmHg, and thereafter the pressure was gradually reduced until it was finally 1 mmHg or less. After 4 hours, the reaction was stopped and a polyester having an intrinsic viscosity of 0.66 was obtained. The ratio of the number of atoms of phosphorus element to calcium element remaining in this polyester (P/Ca) was determined to be 0.75 using a fluorescent X-ray method for which a calibration curve had been prepared in advance. In addition, the specific resistance of the polyester when melted is 9×
It was 10 ⁷ Ω-cm. (Manufacture of polyester film) The obtained polyester was extruded into a sheet form from an extruder at 290°C, and an amorphous sheet was formed using an electrostatic cooling method. The conditions for applying static electricity at this time are as follows. That is, a tungsten wire with a diameter of 0.1 mm was used as a positive electrode, and this wire was stretched on the upper surface of a rotating cooling drum in a direction perpendicular to the flow of the sheet, and a DC voltage of 9 KV was applied thereto. After obtaining the amorphous sheet, it was stretched 3.4 times in the longitudinal direction and 3.5 times in the transverse direction, and the extrusion rate and speed of the rotary cooling body were adjusted so that a biaxially stretched film with a thickness of 15μ was always obtained. The relationship between the cooling body speed and film thickness unevenness was observed. The speed of the rotary cooling body was gradually increased from 20 m/min, but even at 40 m/min, the adhesion between the rotary cooling body and the sheet was strong enough.
The thickness unevenness of the film obtained by heat setting was as small as 0.09, which was sufficiently satisfactory. On the surface of the film, many extremely uniform and minute protrusions of 0.5 μm or less were observed, and the coefficient of dynamic friction measured by method (1) was as low as 0.34, indicating excellent workability. (Evaluation as a magnetic tape) The thus obtained film was coated with a magnetic layer by the method (3), dried, and then slit into 1/2 inch width to form a tape. The running properties of the tape,
Table 1 shows the measurement results of frequency characteristics (VTR head output at 4 MHz) and dropout. Example 2 Triethyl phosphate 0.15 in Example 1
A polyester was obtained in the same manner as in Example 1, except that 0.13 parts of trimethyl phosphate (0.9 times the mole relative to the total amount of calcium compounds) was used instead of 0.13 parts of trimethyl phosphite, and 0.013 parts of trimethyl phosphite was used instead of 0.017 parts of triethyl phosphite. . The polyester had a P/Ca value of 0.84 and a specific resistance when melted of 2×10 ⁸ Ω-cm. Next, an amorphous sheet was obtained using the electrostatic cooling method in the same manner as in Example 1, and then biaxially stretched. It was possible. The evaluation results of the film and the magnetic tape obtained using the film are shown in Table 1, and all had excellent properties. Comparative Example 1 A polyester was obtained in the same manner as in Example 1 except that the amount of triethyl phosphate added was changed to the value shown in Table 1. Next, using the polyester, a polyester film having a thickness of 15 μm was obtained in the same manner as in Example 1. However, when applying the electrostatic cooling method, the adhesion between the rotary cooling body and the sheet becomes weak when the speed of the rotating cooling body is around 33 m/min, and the thickness unevenness of the final film obtained is extremely poor at 0.33 m/min. It was not worthy of being made into magnetic tape. Comparative Example 2 A polyester film was obtained in the same manner as in Example 1 except that triethyl phosphite was not added, and then a magnetic tape obtained using the film was evaluated. These results are shown in Table 1, and although the film has excellent electromagnetic conversion characteristics since almost no precipitated particles are observed, the handling workability of the film and the runnability of the product tape are extremely poor, making it impractical. It was hot. Comparative Example 3 Triethyl phosphate 0.15 in Example 1
A polyester was obtained in the same manner as in Example 1, except that 0.08 parts of phosphoric acid was used instead of 0.08 parts of phosphoric acid, and triethyl phosphite was not added. Next, using the polyester, a biaxially stretched polyester was obtained in the same manner as in Example 1, and further evaluated as a magnetic tape. These results are shown in Table 1.
Shown below. The particles precipitated in the polyester are extremely small, so the VTR head output is at a good level.
Driving performance is somewhat unstable. In addition to fine precipitated particles, agglomerated particles of 3μ or more were frequently observed.
This impairs the dropout characteristics. Comparative Example 4 A polyester was obtained in the same manner as in Example 1 except that triethyl phosphate and triethyl phosphite were added at the same time. Next, a polyester film was obtained using the polyester in the same manner as in Example 1, and further evaluated as a magnetic tape. These results are shown in Table 1.
Shown below. The particles precipitated in the polyester were large, about 1 to 3 microns, and although a film with excellent running properties was obtained, the VTR head output was poor.

[Table] * Molar ratio to total amount of calcium compounds ** Head output 1mV is 0dB

[Brief explanation of drawings]

Figure 1 shows the running system for evaluating running performance, where 5mmφ hard chrome fixing pin, entrance tension meter, exit tension meter, and θ are 107°.

Claims (1)

[Claims] 1. In a method for producing polyester by polycondensation after transesterification using a lower alkyl ester of terephthalic acid as the main acid component and ethylene glycol as the main glycol component, at any time before the start of the polycondensation reaction, calcium The compound and the pentavalent phosphorus compound are made to exist in a dissolved state in the reaction system, and then trialkyl phosphite is produced.The ratio of the total number of atoms of the phosphorus element remaining in the polyester to the total number of atoms of the calcium element is
0.84 or less, and the specific resistance at the time of melting measured by the method defined in the text is 5 × 10 ⁸ Ω.
A method for producing polyester for magnetic tape film, characterized in that the polyester film has a thickness of −cm or less.