JPH0656979A - Water-soluble copolyester for film and coating agent for magnetic recording material - Google Patents

Abstract

PURPOSE:To obtain a coating agent excellent in water solubility, adhesion, blocking resistance and solvent resistance by mixing aromatic and aliphatic dicarboxylic acids with an alkali metal salt of an esterifiable sulfonic acid, an aliphatic or alicyclic glycol and diethylene glycol. CONSTITUTION:The copolyester comprises an acid component comprising at least 70mol% at least two aromatic dicarboxylic acids, 0.01-8mol% aliphatic dicarboxylic acid and 8-25mol% alkali metal salt of an esterifiable sulfonic acid and a glycol component comprising 80-99mol% 2-8 C aliphatic glycol and/or 6-16 C alicyclic glycol. This copolyester is useful as a coating agent for base films used in magnetic recording materials, photographic materials, packaging materials electrical insulation materials, general industrial materials, etc.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a water-soluble copolyester for a film. Specifically, it has excellent water solubility, adhesiveness, blocking resistance, solvent resistance, etc. and is suitable as a coating agent for base film used in magnetic recording materials, various photographic materials, packaging materials, electrical insulating materials, general industrial materials, etc. The present invention relates to a water-soluble copolyester for a film. More specifically, the present invention relates to a water-soluble copolyester for a film, which is suitable as a coating agent for a base film used in a magnetic recording material.

[0002]

2. Description of the Related Art Polyesters, particularly polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate or poly-1,4-cyclohexanedimethylene terephthalate, and polyesters mainly containing these have excellent physical and chemical properties. It is widely used as a fiber, a film or a sheet, and a molded product thereof. In particular, polyester films have excellent heat resistance, chemical resistance, and mechanical properties, and are therefore used in many applications such as magnetic recording materials, various photographic materials, packaging materials, electrical insulating materials, and general industrial materials. There is.

In these applications, the polyester film is not used alone, and various coatings such as a magnetic paint, a chemical mat paint, a diazo photosensitive paint, a gelatin composition, a heat seal imparting composition are used on the film surface. Used by applying or printing ink.

In particular, films used for magnetic recording materials such as magnetic tapes and floppy disks are required to have flatness and smoothness for high reliability and high density of magnetic recording, and magnetic coating materials. There is a strong demand for improvement in the adhesive strength between the base film and the base film. However, when the film is provided with an adhesive force to the magnetic coating material, conversely, blocking occurs between the films, which deteriorates various workability and deteriorates magnetic recording performance. For this reason, the method of imparting adhesiveness to the film does not cause a blocking phenomenon between the films and is resistant to various solvents contained in various coatings applied or printed on the film surface. An easily adhesive substance is desired.

In general, polyester itself is inactive and poor in adhesiveness, and therefore various coating materials such as magnetic paints, chemical mat paints, diazo photosensitive paints, gelatin compositions, heat seal imparting compositions and inks are formed on the film surface. When applying or printing, physical treatment such as corona discharge or plasma or chemical treatment using chemicals such as alkali or amines is performed on the film surface in order to improve the adhesion with the coating. There is known a method of coating, and a method of coating an easily adhesive substance. However, the physical or chemical surface treatment method complicates the steps, not only increases the cost, but also fails to obtain sufficient adhesiveness.

On the other hand, the method of coating an easily adhesive substance can be carried out in the production process of the polyester film, is advantageous in terms of cost, and can select an adhesive substance which can be applied to various coatings. is there. Further, various water-dispersed or water-soluble copolyesters and films have been proposed from the viewpoints of handleability of polyester films and workability during film production. For example, JP-B-47-40873 and JP-A-50-121336 disclose that polyester is copolymerized with polyethylene glycol and an ester-forming sulfonic acid metal salt compound, JP-A-50-83497, and JP-A-50-83497. 53-25
No. 36, JP-A-54-3848 and JP-A-59-215318 include copolymers of ester-forming sulfonic acid metal salt compounds and aliphatic dicarboxylic acid components.

[0007]

However, the above-mentioned prior art has the following problems. That is, a conventional water-dispersed or water-soluble copolyester is one in which an ester-forming sulfonic acid metal salt compound and a polyethylene glycol or an aliphatic dicarboxylic acid component are used in combination for the purpose of improving water dispersion or water solubility. Insufficient water dispersion or water solubility, or copolymerization of polyethylene glycol and aliphatic dicarboxylic acid components in a large amount causes the glass transition temperature of the polyester to drop significantly and the adhesiveness to develop, but the blocking resistance of the film However, there are drawbacks such as poor solvent resistance.

An object of the present invention is to solve these drawbacks and to provide a water-soluble copolyester for a film which is excellent in water solubility, adhesiveness, blocking resistance and solvent resistance and which is suitable as a coating agent for a base film. It is in.

[0009]

The above-mentioned object of the present invention is to use two or more aromatic dicarboxylic acids 70 as the acid component.
Mol% or more, 0.01 to 8 mol% of aliphatic dicarboxylic acid and ester-forming sulfonic acid alkali metal salt compound 8
Water-soluble copolymer for a film, comprising 25 to 25 mol%, an aliphatic glycol having 2 to 8 carbon atoms and / or 80 to 99 mol% alicyclic glycol having 6 to 16 carbon atoms, and 1 to 20 mol% diethylene glycol as a glycol component. Can be achieved with polyester.

The water-soluble copolyester of the present invention contains 70 mol% of two or more aromatic dicarboxylic acids as an acid component.
It is necessary to set the content above, and preferably 80% by mole or more is preferable from the viewpoint of excellent adhesiveness, water solubility and solvent resistance. If the content of the two or more aromatic dicarboxylic acids is less than 70 mol%, the blocking resistance and solvent resistance are poor. The aromatic dicarboxylic acid is not particularly limited, and examples thereof include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, and other aromatic dicarboxylic acids. Two or more kinds of aromatic dicarboxylic acids can be appropriately selected from the above. Preferred aromatic dicarboxylic acids are terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid. It is preferable to select two or more kinds of aromatic dicarboxylic acids from these, and particularly preferable two or more kinds of aromatic dicarboxylic acids include terephthalic acid and
Isophthalic acid.

The ratio of the two or more aromatic dicarboxylic acids in the present invention is not particularly limited, but the total amount of the one or more aromatic dicarboxylic acids relative to one aromatic dicarboxylic acid is molar. The ratio is preferably 0.001 to 0.1, and more preferably 0.005 to 0.05.
It is preferable that it is excellent in adhesiveness, water solubility and solvent resistance.

The aliphatic dicarboxylic acid in the present invention is required to be 0.01 to 8 mol%, preferably 0.05 to 5 mol%, from the viewpoint of adhesiveness. If the amount of the aliphatic dicarboxylic acid is less than 0.01 mol%, the adhesiveness will be poor,
If it exceeds 8 mol%, the adhesion is good, but the blocking resistance and the solvent resistance are poor. The aliphatic dicarboxylic acid is not particularly limited, and examples thereof include adipic acid, sebacic acid, azelaic acid, dodecadioic acid, and dimer acid. Among them, preferable aliphatic dicarboxylic acid is adipic acid, Sebacic acid and azelaic acid. Two or more kinds of these aliphatic dicarboxylic acids may be used in combination.

In the water-soluble copolyester of the present invention, the ester-forming sulfonic acid alkali metal salt compound needs to be 8 to 25 mol%, preferably 10 to 20 mol%, based on all the acid components. More preferably 11 to 1
It is 5 mol%. If the amount of the ester-forming sulfonic acid alkali metal salt compound is less than 8 mol%, sufficient water solubility and adhesiveness cannot be obtained. On the other hand, when it exceeds 25 mol%, the adhesiveness reaches saturation and, conversely, the blocking resistance and solvent resistance deteriorate. The ester-forming sulfonic acid alkali metal salt compound is not particularly limited, and examples thereof include sulfoterephthalic acid, 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2, Mention may be made of alkali metal salts such as 6-dicarboxylic acid and their alkyl esters,
Among these, lithium, sodium and potassium salts of 5-sulfoisophthalic acid and sulfoterephthalic acid are more preferably used.

The glycol component of the water-soluble copolyester of the present invention comprises an aliphatic glycol having 2 to 8 carbon atoms and / or an alicyclic glycol having 6 to 16 carbon atoms 80 to 99.
It is necessary to use mol% and 1 to 20 mol% of diethylene glycol. Preferably an aliphatic glycol having 2 to 8 carbon atoms and / or an alicyclic glycol 8 having 6 to 16 carbon atoms
2.5-95 mol%, diethylene glycol 5-17.
It is 5 mol%, and more preferably 85 to 92.5 mol% of aliphatic glycol having 2 to 8 carbon atoms and / or alicyclic glycol having 6 to 16 carbon atoms and 7.5 to 15 mol% of diethylene glycol. Less than 80 mol% of C2-C8 aliphatic glycol and / or C6-C16 alicyclic glycol or diethylene glycol of 2
If it exceeds 0 mol%, blocking resistance and solvent resistance are poor. On the other hand, an aliphatic glycol having 2 to 8 carbon atoms and /
Or 99 mol% of alicyclic glycol having 6 to 16 carbon atoms
Or more than 1 mol% diethylene glycol
If it is less than 1, the blocking resistance is good but the adhesiveness is poor.

The C2-C8 aliphatic glycol and / or C6-C16 alicyclic glycol of the present invention include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol and neo. Pentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3
There may be mentioned glycols such as -cyclohexanedimethanol and 1,4-cyclohexanedimethanol.
Preferred aliphatic glycols having 2 to 8 carbon atoms and / or alicyclic glycols having 6 to 16 carbon atoms are ethylene glycol, neopentyl glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol, and Preferred are ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. These glycols may be used alone or in combination of two or more.

The water-soluble copolyester of the present invention may be partially copolymerized with an oxyacid or polyoxyalkylene glycol within a range not impairing the effects of the present invention. You may copolymerize other compounds, such as a functional compound.

The water-soluble copolyester of the present invention contains 1 to 500 ppm of an alkaline earth metal and at least one metal element selected from Mn, Zn and Co in order to improve blocking resistance and solvent resistance. , 1-10 at least one metal element selected from alkali metals
It is preferable to contain 00 ppm. The method for incorporating the alkaline earth metal and at least one metal element selected from Mn, Zn and Co, and at least one metal element selected from alkali metal into the water-soluble copolyester is not particularly limited. However, it can be contained by adding a metal compound during the production of the water-soluble copolyester. As the metal compound to be added, alkaline earth metals and Mn, Zn, C
o and a glycol-soluble salt of an alkali metal alcoholate, chloride or monocarboxylic acid, and preferable alkaline earth metal and Mn, Zn and Co compounds are calcium acetate, magnesium acetate, manganese acetate, zinc acetate and cobalt acetate. The amount of addition is 0.001 to the water-soluble copolyester.
0.5% by weight is preferable, and further 0.005-0.3
Weight percent is preferred. Moreover, as a preferable alkali metal compound, lithium acetate, sodium acetate, potassium acetate can be mentioned, and among them, lithium acetate is preferable. The addition amount is preferably 0.001 to 1.5% by weight with respect to the water-soluble copolyester, and further 0.0
1 to 1.0% by weight is preferable.

The method for producing the water-soluble copolyester of the present invention is, for example, a water-soluble composition comprising terephthalic acid, isophthalic acid, adipic acid, 5-sodiumsulfoisophthalic acid component as an acid component and ethylene glycol or diethylene glycol as a glycol component. Explaining the copolyester, terephthalic acid, isophthalic acid, adipic acid, 5-sodium sulfoisophthalic acid and ethylene glycol, diethylene glycol by direct esterification reaction, or dimethyl terephthalate,
Produced by a first step of transesterifying dimethyl isophthalate, dimethyl adipate, dimethyl 5-sodium sulfoisophthalate and ethylene glycol, diethylene glycol, and a second step of polycondensing the reaction product of the first step. And the like.

At this time, conventionally known alkali metals, alkaline earth metals, manganese, cobalt, zinc, antimony, germanium, titanium compounds and the like are used as the reaction catalyst, and phosphorus compounds and the like are further used as the coloring preventing agent. Good.

The intrinsic viscosity of the water-soluble copolyester of the present invention is not particularly limited, but is 0.3 in terms of adhesiveness.
The above is preferable, further 0.35 or more is preferable, and 0.4 or more is particularly preferable.

The water-soluble copolyester of the present invention may optionally contain a flame retardant, a heat stabilizer, an ultraviolet absorber, a pigment,
Organic lubricants such as dyes, fatty acid esters and waxes, or defoaming agents such as polysiloxanes may be added, and clay, mica, titanium oxide, calcium carbonate, kaolin, wet and dry type may be added for the purpose of imparting lubricity. Inorganic particles such as method silica, colloidal silica, calcium phosphate, barium sulfate, and alumina, as well as organic particles containing acrylic acid, styrene, and the like as constituent components may be blended.

The water-soluble copolyester of the present invention is preferably used as a coating agent for various films for the purpose of imparting adhesiveness. In this case, the copolyester is dissolved in water and used as an aqueous solution. This aqueous solution does not have rigor in terms of physical and chemical senses, but also includes an aqueous solution that is mostly dissolved in water and partially dispersed. Further, the above-mentioned organic lubricant, antifoaming agent, various particles and the like may be added to the water-soluble copolyester when water-solubilized or in an aqueous solution, if necessary.

As a specific method for producing a film using the water-soluble copolyester of the present invention, the case of applying the water-soluble copolyester of the present invention to a film made of polyethylene terephthalate will be described. After drying the terephthalate,
Melt extruded into an unstretched sheet, followed by heat treatment into a film. Biaxial stretching may be either longitudinal or transverse sequential stretching or biaxial simultaneous stretching, and the stretching ratio is not particularly limited, but usually 2.0 to 2.0 in both longitudinal and transverse directions.
5.0 times is appropriate. Also, after biaxial stretching, further longitudinal,
It may be re-stretched in any of the transverse directions.

The application of the aqueous solution of the water-soluble copolyester of the present invention onto the surface of the polyester film is preferably carried out during the production process of the polyester film, more preferably the unstretched sheet is stretched in either the longitudinal or transverse direction. After uniaxially stretching, a method of producing a film by applying an aqueous solution of a water-soluble copolyester, then biaxially stretching in a direction different from uniaxial stretching, and heat-treating is preferable. As a coating method, a known coating method such as a reverse coating method, a gravure coating method, a die coating method, or a wire bar method can be used.

The water-soluble copolyester of the present invention can be used not only as a film coating agent but also as a coating agent for fibers, other molded products, and a sizing agent in the weaving process.

[0026]

EXAMPLES The present invention will now be described in more detail by way of examples. The properties in the examples were measured as follows.

A. Intrinsic viscosity of copolyester:
[Η] It was measured at 25 ° C. using an o-chlorophenol solvent.

B. Water solubility of copolyester 2 g of copolyester is put in 100 g of water,
After stirring and dissolving at 2 ° C. for 2 hours and cooling, the mixture is filtered through a 2 μ filter. The water solubility of the copolyester was determined by the dissolved state and the amount of the filtered substance. ◯: The aqueous solution was transparent or slightly clouded, but almost nothing was detected on the filter. Δ: The aqueous solution was slightly cloudy, and a substance filtered off was observed. X: It was difficult to dissolve, or the aqueous solution was strongly clouded, and a large amount of filtered substances was recognized.

C. Adhesive Copolymerized polyester aqueous solution is applied to the surface of the film on which the adhesive layer is provided. After being dried, the coating composition consisting of 1 part was applied by a bar coater so as to have a thickness of 5 μm and dried at 100 ° C. for 5 minutes to form a coating layer. A cellophane adhesive tape is attached to the surface of the coating layer, passed through a nip roll having a linear pressure of 50 kg / cm, and then rapidly peeled in the direction of 180 degrees. The area of the coating layer adhering to the cellophane adhesive tape at that time was determined to determine the adhesiveness. ⊚: Area of coating layer attached to cellophane adhesive tape is 5%
And the adhesiveness is excellent. ◯: Area of coating layer attached to cellophane adhesive tape is 5%
It is less than 10%, and the adhesiveness is slightly excellent. Δ: The area of the coating layer attached to the cellophane adhesive tape was 10
% To less than 30%, and the adhesiveness is slightly inferior. X: The area of the coating layer attached to the cellophane adhesive tape is 30
% Or more, and the adhesiveness is poor.

D. Blocking resistance A film obtained by applying an aqueous solution of a copolyester and superposing the adhesive layer surfaces of the film provided with an adhesive layer (a) and the film surface having no adhesive layer on the adhesive layer surface of the film provided with an adhesive layer Tensileon tensile test of shearing stress of superposed part (b) (overlapping area: 3cm x 4cm) with a load of 500g / 12cm ² left at 50 ° C and 85% RH for 24 hours. Using a machine, the tensile rate was 20 cm / min.

E. Solvent resistance An aqueous solution of copolyester was applied, and methyl ethyl ketone, toluene, and acetone were dropped as organic solvents on the adhesive layer surface of the film provided with the adhesive layer, and the cloudiness of the adhesive layer was evaluated. ○: Almost no cloudiness. Δ: Slightly clouded. X: Cloudy.

Example 1 78.7 parts by weight of dimethyl terephthalate, 2.8 parts by weight of dimethyl isophthalate, 2.5 parts by weight of dimethyl adipate, dimethyl 5-sodium sulfoisophthalate 17.
0 parts by weight, ethylene glycol 59.9 parts by weight, diethylene glycol 4.0 parts by weight and calcium acetate 0.
1 part by weight, 0.3 part by weight of lithium acetate and 0.03 part by weight of antimony trioxide were added, and the transesterification reaction was carried out by a conventional method, and then 0.05 part by weight of trimethyl phosphate was added. Then gradually raise the temperature and reduce the pressure, and finally 280
A polycondensation reaction was performed at a temperature of 1 mmHg or less to obtain a water-soluble copolyester. The composition of the obtained water-soluble copolyester was measured by NMR ( ¹³ C-NMR spectrum). As a result, the acid components were 82 mol% terephthalic acid, 3.0 mol% isophthalic acid, 3.0 mol% adipic acid, and 5 mol%. -Sodium sulfoisophthalic acid 12 mol%, the glycol component was ethylene glycol 87 mol%, diethylene glycol 13 mol%. Also, the intrinsic viscosity is 0.57,
Metal content determined by atomic absorption method is Ca205pp
m, Li was 190 ppm.

2 g of the obtained water-soluble copolyester was put in 100 g of water, dissolved by stirring at 80 ° C. for 2 hours, cooled, and filtered with a 2 μ filter to obtain a water-soluble copolyester aqueous solution. The aqueous solution of the water-soluble copolyester was almost transparent, and no filter residue was observed.

On the other hand, polyethylene terephthalate containing 0.2% by weight of silicon dioxide having an average particle diameter of 0.2 μ and an intrinsic viscosity of 0.60 was sufficiently dried and then fed to an extruder to melt at 290 ° C. It was extruded into a sheet form from the die and cooled and solidified in a cooling drum at 30 ° C. to obtain an unstretched film. Then, the unstretched film was heated to 95 ° C. and stretched 3.4 times in the machine direction to obtain a uniaxially stretched film. Further, the aqueous solution of the water-soluble copolyester obtained above was applied to one surface of this uniaxially stretched film by a gravure coating method so that the coating thickness after biaxial stretching was 0.1 μm. Subsequently, it was heated to 100 ° C., stretched 3.5 times in the transverse direction, and heat-treated at 200 ° C. to obtain a 15 μm-thick polyester film having an adhesive layer. The characteristics of the obtained film are shown in Table 2. The film had good adhesiveness, blocking resistance, and solvent resistance.

Example 2 78.3 parts by weight of dimethyl terephthalate, 1.0 part by weight of dimethyl isophthalate, 4.3 parts by weight of dimethyl adipate, dimethyl 5-sodium sulfoisophthalate 17.
5 parts by weight, 61.0 parts by weight of ethylene glycol, 0.07 part by weight of calcium acetate, 0.07 part by weight of lithium acetate, and 0.03 part by weight of antimony trioxide were added, and the transesterification reaction was carried out according to a conventional method. 0.05 parts by weight of trimethyl acid were added. Then, the temperature was gradually raised and the pressure was reduced, and finally a polycondensation reaction was performed at 280 ° C. and 1 mmHg or less to obtain a water-soluble copolyester. The composition of the obtained water-soluble copolyester was measured by NMR ( ¹³ C-NMR spectrum). As a result, the acid components were 82 mol% terephthalic acid, 1.0 mol% isophthalic acid, 5.0 mol% adipic acid, and 5 mol%. -Sodium sulfoisophthalic acid 12
Mol% was 90 mol% for ethylene glycol and 10 mol% for diethylene glycol. Also,
The intrinsic viscosity was 0.56, and the metal content determined by the atomic absorption method was Ca 150 ppm and Li 45 ppm.

2 g of the obtained water-soluble copolyester was put in 100 g of water, dissolved by stirring at 80 ° C. for 2 hours, cooled, and filtered with a 2 μ filter to obtain a water-soluble copolyester aqueous solution. The aqueous solution of the water-soluble copolyester was almost transparent, and no filter residue was observed.

On the other hand, in the same manner as in Example 1, a polyester film having an adhesive layer and having a thickness of 15 μm was obtained. The characteristics of the obtained film are shown in Table 2. Film adhesion,
Both blocking resistance and solvent resistance were good.

Comparative Example 1 83.6 parts by weight of dimethyl terephthalate, 17.4 parts by weight of dimethyl 5-sodium sulfoisophthalate, 61.0 parts by weight of ethylene glycol and 0.1 of calcium acetate.
1 part by weight and 0.03 part by weight of antimony trioxide were added, and an ester exchange reaction was carried out according to a conventional method, and then 0.05 part by weight of trimethyl phosphate was added. Then, the temperature was gradually raised and the pressure was reduced, and finally a polycondensation reaction was performed at 280 ° C. and 1 mmHg or less to obtain a water-soluble copolyester. The composition of the obtained water-soluble copolyester is analyzed by NMR ( ¹³ C-NMR
As a result of measurement by a spectrum), the acid component was 88 mol% terephthalic acid, 12-sodium sulfoisophthalic acid 12
The mol% and the glycol component were 83 mol% of ethylene glycol and 17 mol% of diethylene glycol. Also,
The intrinsic viscosity was 0.55, and the metal content determined by the atomic absorption method was Ca 210 ppm.

2 g of the obtained water-soluble copolyester was put in 100 g of water, dissolved by stirring at 80 ° C. for 2 hours, cooled, and filtered with a 2 μ filter to obtain a water-soluble copolyester aqueous solution. The aqueous solution of the water-soluble copolyester was slightly cloudy, and the substance filtered off was observed.

On the other hand, in the same manner as in Example 1, a 15 μm-thick polyester film having an adhesive layer was obtained. The characteristics of the obtained film are shown in Table 2. The film had poor adhesion.

Examples 3-5, Comparative Examples 2-4 In the same manner as in Example 1, the types and amounts of the acid component, glycol component and metal compound were changed as shown in Table 1 to obtain polyesters and films. . The results are shown in Table 2.
Examples 3 to 5 were within the scope of the present invention, and the film had good adhesiveness, blocking resistance, and solvent resistance.

On the other hand, in Comparative Example 2, the amount of the aliphatic dicarboxylic acid was out of the range of the present invention, and although the film had good adhesiveness, it had poor blocking resistance and solvent resistance. In Comparative Example 3, the amount of diethylene glycol was outside the range of the present invention, and the blocking resistance and solvent resistance were poor.

Furthermore, in Comparative Example 4, the ester-forming alkali metal sulfonate compound was out of the scope of the present invention, and the obtained copolyester was poor in water solubility.

[0044]

[Table 1]

[Table 2]

[0045]

As described above, the present invention provides a specific amount of two or more aromatic dicarboxylic acids, aliphatic dicarboxylic acids and ester-forming sulfonic acid metal salt compounds as acid components,
A water-soluble copolyester for a film, which comprises a specific amount of an aliphatic glycol having 2 to 8 carbon atoms and / or an alicyclic glycol having 6 to 16 carbon atoms as a glycol component, and diethylene glycol, and is water-soluble, adhesive, and blocking-resistant. , Excellent solvent resistance, coating agent for base film used in magnetic recording materials, various photographic materials, packaging materials, electrical insulating materials, general industrial materials, etc., especially for base film used in magnetic recording materials. It is preferably used as a coating agent.

Claims (4)

[Claims] 1. As an acid component, 70 mol% or more of two or more aromatic dicarboxylic acids and 0.01 to 8 aliphatic dicarboxylic acids.
Mol% and ester forming sulfonic acid alkali metal salt compound 8 to 25 mol%, as a glycol component, an aliphatic glycol having 2 to 8 carbon atoms and / or 6 to 1 carbon atoms
A water-soluble copolyester for a film, which comprises 80 to 99 mol% of an alicyclic glycol of 6 and 1 to 20 mol% of diethylene glycol. 2. In two or more kinds of aromatic dicarboxylic acids,
The total amount of one or more aromatic dicarboxylic acids with respect to one aromatic dicarboxylic acid is 0.001 to 0.
The water-soluble copolyester for a film according to claim 1, which is 1. 3. The water-soluble copolyester for a film according to claim 1, wherein the two or more kinds of aromatic dicarboxylic acids are selected from the group consisting of terephthalic acid, isophthalic acid and naphthalene dicarboxylic acid. 4. A coating agent for a magnetic recording material comprising the water-soluble copolyester according to claim 1.