JP6102422B2 - Polyester resin and polyester film for inner lamination of cans - Google Patents

Description

  The present invention relates to a polyester resin used for an adhesive layer of a film for laminating can inner surfaces. More specifically, the present invention relates to a polyethylene terephthalate resin obtained by copolymerizing a specific amount of isophthalic acid using a specific polymerization catalyst, and a technique for improving the adhesiveness of the polyester resin by adopting the above configuration.

  Food cans and beverage cans in which food products and liquid contents are sealed in cans are excellent in strength, heat resistance, and cold resistance, and therefore metal materials such as steel and aluminum are used. When these metal cans are used for food applications, it is necessary to prevent the so-called flavor poorness in which the metal odor shifts to the food or beverage as the contents, deterioration of the contents, and corrosion due to the contents of the metal itself. For this reason, for the purpose of process simplification, hygiene improvement, pollution prevention, etc., a method of making a can by heating and pressure bonding a polyester film to a metal plate without using an organic solvent and processing the laminated steel plate (For example, Patent Documents 1 to 3).

  However, in Patent Documents 1 to 3, there was a problem of local film breakage due to an impact during can manufacturing after laminating a film and a steel plate. In order to avoid this, a method using a two-layer composite polyester film composed of a base material layer and an adhesive layer is disclosed (for example, Patent Documents 4 to 5).

  However, in Patent Document 4, there is a serious problem that the film after lamination shrinks due to various thermal histories in the can making process, and when the shrinkage is remarkable, the film peels off from the steel sheet. Therefore, in Patent Document 5, out of two layers of polyester films composed of a base layer and an adhesive layer, a resin for base layer is a blend of polyethylene terephthalate and polybutylene terephthalate, while isophthalic acid is used as a raw material resin for the adhesive layer. By using an ethylene terephthalate / ethylene isophthalate copolymer copolymerized with each other and controlling the melting point to an appropriate value, good adhesion, impact resistance and shrinkage resistance are imparted. However, blending a polybutylene terephthalate component with the base material layer may cause a deterioration in the flavor properties of foods and beverages. Moreover, about patent document 5, the polymerization method of the polyester resin for contact bonding layers is not described, The trace was carried out by the general polymerization method, and the adhesiveness of the polyester film of 2 layers of a base material layer and a contact bonding layer was confirmed. In the conventional can manufacturing process, sufficient adhesiveness was not obtained. It was considered necessary to improve adhesion.

  Furthermore, in Patent Document 6, among two layers of polyester film consisting of a base material layer and an adhesive layer, as a resin for the adhesive layer, by blending polyethylene terephthalate / isophthalate copolymer and polybutylene terephthalate, a conventional can manufacturing process It is disclosed that sufficient adhesiveness can be exhibited. However, there is a concern that the use of polybutylene terephthalate leads to a deterioration in the flavor properties of the beverage, and the heat resistance of the adhesive layer resin is deteriorated, thereby reducing the strength of the polyester film.

  On the other hand, it is generally known to use an antimony compound, a titanium compound, a germanium compound, or an aluminum compound as a polymerization catalyst for polyester. Any of these catalysts is suitable as a polyester polymerization catalyst, but each has specific properties and can be used properly depending on the application, polymerization mode, and process type.

Japanese Patent Publication No.57-23584 Japanese Patent Publication No.59-34580 Japanese Examined Patent Publication No. 62-61427 Japanese Patent Laid-Open No. 2-81630 Japanese Patent No. 3304002 JP 2006-150606 A

  The object of the present invention is to simultaneously solve the problems of adhesiveness and heat resistance in a two-layer polyester film comprising a base layer / adhesive layer for metal plate lamination that can be used in food cans and beverage cans. It is to solve.

  In order to solve the above-mentioned problems of adhesion and heat resistance at the same time, polyester resins using several polymerization catalysts were used to confirm the properties as food cans and beverage cans. As a result, it has been found that only when an aluminum catalyst is used, a polyester film satisfying the effects that have not been seen so far, that is, adhesiveness and heat resistance, can be obtained at the same time. .

That is, the present invention has the following configuration.
[1] A polyester resin using an aluminum compound and a phosphorus compound as a polymerization catalyst, the polyester resin containing the polymerization catalyst, wherein the main dicarboxylic acid component of the polyester resin is terephthalic acid, and the main diol component of the polyester resin is ethylene glycol The inner surface laminate of the can, wherein the polyester resin has a melting point (Tm) of 222.0 to 233.5 ° C. and an intrinsic viscosity (IV) of 0.50 to 0.80 dl / g Polyester resin used for adhesive layers of films.
[2] The polyester resin according to [1], which contains isophthalic acid as a dicarboxylic acid component, and the content of isophthalic acid is 8.0 to 13.0 mol% of all dicarboxylic acid components.
[3] A polyester film for laminating a can inner surface, comprising a base material layer and an adhesive layer, wherein the polyester resin according to [1] or [2] is used for the adhesive layer.

  The polyester film for laminating the inner surface of the can using the polyester resin for the adhesive layer of the present invention has better adhesion than before, and in the can manufacturing process after lamination, deterioration due to thermal history, peeling, occurrence of film displacement Can be suppressed more than ever. Moreover, since the component which has a bad influence on the flavor property of foodstuffs and drinks is not used, it can be said that it is a suitable polyester film also in preventing modification | denaturation of the content.

(Polyester resin polymerization catalyst)
As the aluminum compound constituting the polyester polymerization catalyst used when synthesizing the polyester resin for the adhesive layer of the present invention, known aluminum compounds can be used without limitation.

  Specific examples of aluminum compounds include aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate, organoaluminum compounds such as aluminum oxalate, and partial hydrolysates thereof. Can be mentioned. Among these, carboxylate, inorganic acid salt and chelate compound are preferable, and among these, aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are more preferable, Aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum hydroxide and aluminum hydroxide chloride are more preferred, and aluminum acetate and basic aluminum acetate are most preferred.

The amount of the aluminum compound used in the polyester polymerization catalyst according to the present invention is preferably 1 to 80 ppm, more preferably 2 to 60 ppm, as aluminum atoms with respect to the total mass of the obtained polyester resin. Yes, more preferably 3 to 50 ppm, particularly preferably 5 to 40 ppm, and most preferably 10 to 30 ppm.
If it is less than the above, the catalyst activity may be poor, and if it exceeds the above, aluminum-based foreign matter may be generated.
Even if the aluminum compound is placed in a reduced pressure environment at the time of polyester polymerization, almost 100% of the addition amount remains, so it may be considered that the addition amount becomes a residual amount.

  The phosphorus compound used in the polyester polymerization catalyst is not particularly limited. However, the use of a phosphonic acid compound or a phosphinic acid compound has a large effect of improving the catalytic activity. Among these, the use of a phosphonic acid compound improves the catalytic activity. The effect is particularly large and preferable.

  Of these phosphorus compounds, phosphorus compounds having a phenol moiety in the same molecule are preferred. It is not particularly limited as long as it is a phosphorus compound having a phenol structure, but it is a catalyst if one or more compounds selected from the group consisting of phosphonic acid compounds and phosphinic acid compounds having a phenol moiety in the same molecule are used. The effect of improving activity is large and preferable. Among these, the use of a phosphonic acid compound having a phenol moiety in one or two or more of the same molecules is particularly preferable because the effect of improving the catalytic activity is particularly large.

  Examples of the phosphorus compound having a phenol moiety in the same molecule include compounds represented by the following general formulas (1) and (2).

(In the formulas (1) to (2), R ¹ is a hydrocarbon group having 1 to 50 carbon atoms including a phenol part, a substituent such as a hydroxyl group, a halogen group, an alkoxyl group or an amino group, and a carbon number 1 including a phenol part. R ⁴ represents a hydrocarbon group having a carbon number of 1 to 50, including a hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydroxyl group, a halogen group, an alkoxyl group, or an amino group. R ² and R ³ each independently represent hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, a hydrocarbon group having 1 to 50 carbon atoms including a substituent such as a hydroxyl group or an alkoxyl group, provided that they are hydrocarbons. The group may contain a branched structure, an alicyclic structure such as cyclohexyl, or an aromatic ring structure such as phenyl or naphthyl, and the ends of R ² and R ⁴ may be bonded to each other.)

  Examples of the phosphorus compound having a phenol moiety in the same molecule include p-hydroxyphenylphosphonic acid, dimethyl p-hydroxyphenylphosphonate, diethyl p-hydroxyphenylphosphonate, diphenyl p-hydroxyphenylphosphonate, bis ( p-hydroxyphenyl) phosphinic acid, methyl bis (p-hydroxyphenyl) phosphinate, phenyl bis (p-hydroxyphenyl) phosphinate, p-hydroxyphenylphenylphosphinic acid, methyl p-hydroxyphenylphenylphosphinate, p-hydroxy Examples include phenyl phenylphenylphosphinate, p-hydroxyphenylphosphinic acid, methyl p-hydroxyphenylphosphinate, phenyl p-hydroxyphenylphosphinate, and the like. Other examples include phosphorus compounds represented by the following general formula (3).

Wherein _{(3), X 1, X} 2 each represent hydrogen, an alkyl group having 1 to 4 carbon atoms or a monovalent or more metals.
Moreover, X ₁ is metal be two or more valences, X ₂ may be absent. Furthermore, an anion corresponding to the surplus valence of the metal may be arranged with respect to the phosphorus compound.
As the metal, Li, Na, K, Ca, Mg, and Al are preferable.

  By adding a phosphorus compound having a phenol moiety in the same molecule during the polymerization of the polyester, the catalytic activity of the aluminum compound is improved and the thermal stability of the polymerized polyester is also improved.

  Among the above, the phosphorus compound that is preferably used as the polycondensation catalyst is at least one phosphorus compound selected from the compounds represented by the chemical formulas (4) and (5).

  As the compound represented by the above chemical formula (4), Irganox 1222 (manufactured by BASF) is commercially available. As the compound represented by the chemical formula (5), Irganox 1425 (manufactured by BASF) is commercially available and can be used.

The phosphorus compound used in the polyester polymerization catalyst according to the present invention is preferably used in an amount of 10 to 100 ppm, more preferably 15 to 90 ppm as a phosphorus atom with respect to the total mass of the obtained polyester resin. Yes, more preferably 20 to 80 ppm, particularly preferably 25 to 70 ppm, and most preferably 30 to 60 ppm.
If the amount of phosphorus atoms exceeding the upper and lower limits remains, the polymerization activity may be reduced.
When the phosphorus compound is placed in a reduced pressure environment during polyester polymerization, about 10 to 30% of the addition amount is removed from the system depending on the conditions. Therefore, in practice, it is necessary to determine the amount of addition after conducting trial experiments several times and determining the residual ratio of the phosphorus compound in the polyester.

  Moreover, the heat resistance of resin can be improved by using a phosphorus compound. Although the cause is not clear, it is considered that the phosphorus compound improves the heat resistance of the polyester resin. In the case of this invention, the adhesiveness of the polyester resin for contact bonding layers can be improved by suppressing the thermal deterioration of the polyester resin for contact bonding layers by addition of a phosphorus compound. This is thought to be due to the suppression of the production of a medium molecular weight polyester resin due to thermal degradation. It is considered that the polyester resin in the medium molecular weight region enters the irregularities on the surface of the metal plate, thereby inhibiting the adhesion of the polyester resin for the adhesive layer, and as a result, lowering the adhesiveness of the polyester resin for the adhesive layer. The effect of this phosphorus compound is further increased by having a hindered phenol moiety in the phosphorus compound.

  When the residual amount of the phosphorus compound is less than 10 ppm, the effect of improving the heat resistance is reduced, and as a result, the effect of improving the adhesion of the polyester resin for the adhesive layer is not seen.

  In order not to impair the effects of the present invention, a metal-containing polyester polycondensation catalyst such as an antimony compound, a titanium compound, a tin compound, or a germanium compound may be used in combination in order to further improve the catalytic activity. In that case, the antimony compound is preferably 30 ppm or less as the antimony atom with respect to the mass of the obtained polyester, the germanium compound is preferably 10 ppm or less as the germanium atom with respect to the mass of the obtained polyester, and the titanium compound is obtained. It is preferable that it is 3 ppm or less as a titanium atom with respect to the mass of the polyester obtained, and 3 ppm or less is preferable as a tin atom with respect to the mass of the polyester obtained. For the purposes of the present invention, it is preferable to avoid using these metal-containing polyester polycondensation catalysts such as antimony compounds, titanium compounds, tin compounds, and germanium compounds as much as possible.

In the present invention, in addition to the aluminum compound, a small amount of alkali metal, alkaline earth metal and at least one selected from the compound may coexist as the second metal-containing component. The coexistence of such a second metal-containing component in the catalyst system is effective in improving productivity by obtaining a catalyst component having an increased reaction rate in addition to an effect of suppressing the formation of diethylene glycol, and thus a higher reaction rate. . When an alkali metal, an alkaline earth metal, or a compound thereof is added in combination, the addition amount (mol%) is preferably 1 × 10 ^{−5 with} respect to the number of moles of the dicarboxylic acid component constituting the polyester resin. -0.01 mol%.

(Polyester resin)
In the present invention, “polyester resin” refers to a resin containing a residue of the polymerization catalyst.
The polyester resin of the present invention is a polyester resin in which the main dicarboxylic acid component is terephthalic acid and the main diol component is ethylene glycol. Of 100 mol% of the dicarboxylic acid component, terephthalic acid is preferably contained in an amount of 70 mol% or more, more preferably 80 mol% or more. As the dicarboxylic acid component other than terephthalic acid, any dicarboxylic acid can be used, but isophthalic acid is preferred.
Of the glycol component of 100 mol%, ethylene glycol is preferably contained in an amount of 80 mol% or more, and more preferably 90 mol% or more. Arbitrary glycol can be used as diglycol components other than ethylene glycol, but it is also a preferable aspect that it is 100 mol% of ethylene glycol (except diethylene glycol by-product described below).

The amount of the isophthalic acid component copolymerized with the polyester resin is preferably 8.0 to 13.0 mol% out of 100 mol% of the dicarboxylic acid component. If the content of isophthalic acid is less than 8.0 mol%, the melting point of the polyester resin of the adhesive layer resin becomes high, and more heat treatment is required than the normal lamination conditions of the polyester film on the steel plate in the actual can manufacturing process. This is not preferable for practical use. Moreover, when the content of isophthalic acid is more than 13.0 mol%, the melting point of the polyester resin for the adhesive layer becomes too low, so that the polyester film laminated to the steel plate during the heat treatment in the can manufacturing process is removed from the laminated position. The phenomenon of moving up (film slippage) occurs, causing problems in the finish of the can. On the other hand, if the content of isophthalic acid is more than 13.0 mol%, the heat resistance of the polyester is adversely affected.
It is preferable that the dicarboxylic acid component occupies 100 mol% with terephthalic acid and isophthalic acid, and isophthalic acid is preferably 8.0 to 13.0 mol% with respect to 92.0 to 87.0 mol of terephthalic acid.

  In addition, when polycondensing a polyester resin as described below, diethylene glycol of about 0.0 mol% to 3.0 mol% may be generated by condensation of ethylene glycol as a raw material in the course of polymerization. Even if this polyester resin is used as it is, the performance as a polyester resin for the adhesive layer is not impaired.

  The intrinsic viscosity (IV) of the polyester resin of the present invention needs to be 0.50 to 0.80 dl / g. When the IV is lower than 0.50 dl / g, the film is liable to be broken during film formation, and the operability is deteriorated. When IV is higher than 0.80 dl / g, the adhesiveness (initial sealing temperature) becomes poor, and the laminate processability with the metal plate becomes poor. The upper limit of IV of the polyester of the present invention is preferably 0.75 dl / g or less, more preferably 0.70 dl / g or less. Further, the lower limit of IV is preferably 0.55 dl / g or more, and more preferably 0.58 dl / g or more.

  The melting point (Tm) of the polyester resin of the present invention needs to be 222.0 to 233.5 ° C. When Tm is higher than 233.5 ° C., more heat treatment is required than normal lamination conditions for a polyester film on a steel plate in an actual can manufacturing process, which is not preferable in practice. On the other hand, when Tm is lower than 222.0 ° C., the film displacement of the polyester film laminated on the steel plate occurs during the heat treatment in the can making process, which causes a problem in the finish of the can.

(Polymerization method of polyester resin for adhesive layer)
The polymerization catalyst according to the present invention has catalytic activity not only in the polycondensation reaction but also in the esterification reaction and transesterification reaction. The transesterification reaction between an alkyl ester of a dicarboxylic acid such as dimethyl terephthalate and a glycol such as ethylene glycol is usually carried out in the presence of a transesterification catalyst such as zinc. The catalyst of the present invention is used in place of these catalysts. You can also The catalyst of the present invention has catalytic activity not only in melt polymerization but also in solid phase polymerization or solution polymerization.

  The polyester polymerization catalyst used in the present invention can be added to the reaction system at any stage of the polymerization reaction. For example, it can be added to the reaction system at any stage before and during the esterification reaction or transesterification reaction, immediately before the start of the polycondensation reaction, or at any stage during the polycondensation reaction. In particular, the aluminum compound and the phosphorus compound of the present invention are preferably added immediately before the start of the polycondensation reaction.

  The method of polymerizing the polyester for the adhesive layer is not particularly limited, and terephthalic acid can be obtained by direct esterification of terephthalic acid and isophthalic acid with ethylene glycol, or by transesterification of alkyl ester of terephthalic acid and isophthalic acid with ethylene glycol. In addition, an oligomer of isophthalic acid and ethylene glycol is obtained, and thereafter, a polyester can be obtained by melt polymerization under normal pressure or reduced pressure.

The polyester according to the present invention can be produced by a method having a conventionally known process. For example, terephthalic acid and isophthalic acid as acid components are directly reacted with ethylene glycol as a glycol component, water is distilled off for esterification, and then polyesterification is performed under reduced pressure, or as acid component It is produced by a transesterification method in which dimethyl terephthalate, dimethyl isophthalate, and ethylene glycol as a glycol component are reacted to distill off methyl alcohol and transesterify, followed by polycondensation under reduced pressure. This melt polycondensation reaction is preferably carried out in a continuous reaction apparatus. Continuous reaction equipment means that the reaction vessel for esterification or transesterification and the melt polycondensation reaction vessel are connected by piping, and the raw materials are continuously charged without melting each reaction vessel, and the melt polycondensation reaction in the piping This is a method of transferring to a container and extracting the resin from the melt polycondensation reaction container. In this case, continuous does not need to be completely withdrawn from the raw material input, but is intermittent, such as withdrawing from the raw material input in small amounts, for example, about 1/10 of the reaction vessel amount. It may be anything.
In any of these methods, the esterification reaction or transesterification reaction may be performed in one stage or may be performed in multiple stages. The melt polycondensation reaction may be performed in one stage or may be performed in multiple stages.

(Film forming method)
The polyester film for laminating can inner surfaces of the present invention is a film comprising two layers of a base material layer and an adhesive layer.

The polyester resin for the substrate layer is not particularly limited, but is preferably a polyethylene terephthalate resin from the viewpoint of heat resistance of the polyester film and availability. The intrinsic viscosity (IV) of this resin is preferably about the same as that of the polyester resin for the adhesive layer described above.
The polymerization catalyst for the polyester resin for the base material layer is not particularly limited, and a known polymerization catalyst such as antimony oxide, germanium oxide, aluminum compound, titanium compound and the like can be used.

  In addition to the polymerization catalyst, the polyester resin used for the base material layer and the adhesive layer has magnesium acetate, magnesium chloride, etc. in order to impart electrostatic adhesion when forming a melt-extruded film in addition to the polymerization catalyst. Mg salt, Ca salt such as calcium acetate and calcium chloride, Mn salt such as manganese acetate and manganese chloride, Zn salt such as zinc chloride and zinc acetate, Co salt such as cobalt acetate and cobalt chloride, phosphoric acid or trimethyl phosphate It is also possible to add phosphate ester derivatives such as ester and phosphate triethyl ester.

  Using such a base material layer and an adhesive layer resin, a two-layer polyester film is obtained according to the following method.

The method for producing the polyester film of the present invention is not particularly limited, but after forming the base material layer and the adhesive layer by using an inflation film production apparatus or a T-die film production apparatus, respectively, they can be bonded together by an extrusion laminating method. A multilayer film may be formed by coextrusion from the beginning.
Here, in order to obtain the required range of the present invention, it is preferable to perform uniaxial stretching or biaxial stretching after forming an unstretched film by an extrusion method. By using a stretched film, crystal orientation occurs, and strength and excellent processability can be obtained.

  Taking the case of the longitudinal stretching temperature at the time of sequential biaxial stretching as an example, a preferable temperature range can be exemplified by 70 to 120 ° C. as the preheating temperature at the longitudinal stretching and 100 to 130 ° C. as the stretching temperature. Examples of the preheating temperature at the time of transverse stretching include 80 to 120 ° C., and the degree of heat fixation includes 225 to 235 ° C.

  In addition, it is preferable to take an appropriate range for the draw ratio. If the ratio is low, the film strength and the flavor of the contents may be impaired, and if the ratio is high, the production may be difficult. Preferable stretching ratios for sequential biaxial stretching include 3 to 6 times in the longitudinal direction and 3 to 6 times in the transverse direction.

  In addition, when forming a polyester film as described above, a master batch containing silica particles and calcium carbonate particles, if necessary, together with a base layer and / or a polyester resin for an adhesive layer, a predetermined amount in a fixed screw feeder. By supplying, the slipperiness | lubricity and concealment property of a polyester film can also be provided.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. In addition, the evaluation method used in each Example and the comparative example is demonstrated below.

(Evaluation method of intrinsic viscosity (IV))
A polyester resin sample (0.1 g) was precisely weighed, dissolved in 25 mL of a mixed solvent of phenol / tetrachloroethane = 3/2 (mass ratio), and measured at 30 ° C. using an Ostwald viscometer.

(Measuring method of melting point (Tm))
Measurement was performed using DSCQ100 manufactured by TA Instruments. 10.0 mg of the polyester resin was placed in an aluminum pan, heated to 300 ° C. at a temperature rising temperature of 20 ° C./min, held for 3 minutes after reaching 300 ° C., and immediately quenched in liquid nitrogen. Then, it heated up to 300 degreeC with the temperature increase rate from 20 degreeC / min from room temperature, and calculated | required melting | fusing point (Tm). Tm was the temperature at the maximum part of the peak.

(Evaluation method of initial seal temperature)
The initial sealing temperature, which is a method for evaluating the adhesion of the polyester film of the present invention to a metal plate, is defined as follows. That is, the adhesive layers of two polyester films obtained by the film forming method described later are combined, using a seal bar heated to a predetermined temperature, a pressure of 0.2 MPa is applied for 2 seconds, and the polyester films are bonded together. Heat sealed. At this time, in the peel strength measurement described later, about 10 mm of an unbonded portion was left in order to make a grip portion with a tensile tester. The heat-sealed film sample was cut into a strip having a width of 15 mm, and the peel strength was measured using a tensile tester. The unbonded portion was placed on a gripping tool of a tensile tester and measured by a T-type peeling method at a tensile speed of 300 mm / min. The peel strength is weak when the temperature of the seal bar during heat sealing is low, but the peel strength is increased by increasing the seal bar temperature. The set temperature of the seal bar at the time of heat sealing when the peel strength was 0.5 N or more was defined as the initial sealing temperature of the polyester film.

  When the initial seal temperature (heating temperature of the seal bar) is set to A ° C., it can be determined that the adhesion performance of the polyester film is appropriate in the actual can manufacturing process if 70 ° C. ≦ A ≦ 100 ° C.

(Evaluation method of film slippage)
The film deviation evaluation method of the polyester film of the present invention will be described. As a laminating method, a thermal laminating method was used. Lamination was performed by heating the metal plate to 180 ° C., bringing the film into contact with the surface of the metal plate, passing between the nip rolls in this state, and then quenching and curing at 10 to 40 ° C. A notch marked with a cross (X) was made in the middle of the laminated film. The laminated metal plate was heat-treated in an oven heated to 240 ° C. for 1 minute, and the distance at which the cross portion of the X-mark cut was opened was measured. As the determination methods of “◯” and “X” described in Examples and Comparative Examples, the case where there is substantially no film displacement (distance of the cut cross portion after heat treatment is 0 mm) was evaluated as “◯”, and the case where there was film displacement was evaluated as “X”.

(Method for evaluating heat resistance)
The polyester resin ([IV] _i ) was frozen and ground to a powder of 20 mesh or less. This powder was vacuum-dried at 130 ° C. for 12 hours, and 300 mg of the powder was placed in a glass test tube having an inner diameter of about 8 mm and a length of about 140 mm and vacuum-dried at 70 ° C. for 12 hours. [IV] _f1 was then measured after a drying tube containing silica gel was attached to the top of the test tube and immersed in a salt bath at 210 ° C. and heated for 15 minutes under dry air. Using this result, TOS was calculated according to the following formula as an index of heat resistance. However, [IV] _i and [IV] _f1 indicate IV (dL / g) before and after the heating test, respectively. The freeze pulverization was performed using a freezer mill (Specks Corp., Model 6750). After putting about 2 g of polyester resin and a dedicated impactor in the dedicated cell, set the cell in the device, fill the device with liquid nitrogen and hold it for about 10 minutes, then RATE10 (the impactor is about 20 times per second) Pulverized for 5 minutes.
TOS = 0.245 {[IV] _f1 ^-1.47- [IV] _i ^-1.47 }
It can be determined that the smaller the TOS value, the higher the heat resistance.

Example 1
(A) Polymerization method of polyester resin for substrate layer (preparation of aqueous solution of aluminum compound)
After adding 5.0 liters of pure water to a flask equipped with a cooling tube at room temperature and normal pressure, 200 g of basic aluminum acetate was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added so as to be 10.0 liters as a whole, and the mixture was stirred at room temperature and normal pressure for 12 hours. Thereafter, the jacket temperature was changed to 100.5 ° C., the temperature was raised, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was allowed to cool to room temperature to obtain an aqueous solution. (Preparation of ethylene glycol mixed solution of aluminum compound)
After adding an equal volume of ethylene glycol to the aqueous aluminum compound solution obtained by the above method and stirring at room temperature for 30 minutes, the internal temperature is controlled to 80 to 90 ° C., the pressure is gradually reduced to reach 2.7 kPa, and stirring is continued for several hours. While removing water from the system, an ethylene glycol solution of 20 g / l aluminum compound was obtained.

(Preparation of ethylene glycol solution of phosphorus compound)
After adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen introduction tube and a cooling tube at room temperature and normal pressure, 200 g of Irganox 1222 (manufactured by BASF) was added as a phosphorus compound while stirring at 200 rpm in a nitrogen atmosphere. . Further, 2.0 liters of ethylene glycol was added, the temperature was raised by changing the jacket temperature setting to 196 ° C., and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. Thereafter, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or less within 30 minutes while maintaining the nitrogen atmosphere.

(Production method of polyester resin)
Addition of terephthalic acid and ethylene glycol to a stainless steel autoclave equipped with a stirrer, distillation tower, and pressure regulator, and at 240 ° C and a gauge pressure of 3.5 MPa, the esterification reaction is carried out for 2 hours while sequentially removing water produced by esterification. Went. Subsequently, the ethylene glycol solution of the aluminum compound and the ethylene glycol solution of the phosphorus compound prepared by the above method were added to the polyester resin so that 28 ppm and 50 ppm remained as aluminum atoms and phosphorus atoms, respectively. The temperature was raised to 280 ° C., and the pressure of the system was gradually reduced to 150 Pa during this time, and a polycondensation reaction was carried out for 1 hour under these conditions to obtain a polyester resin with IV = 0.61 dl / g. This polyester resin was subjected to solid phase polymerization at 230 ° C. under reduced pressure for 7 hours using a batch type solid phase polymerization apparatus, to obtain a polyester resin for a base material layer having IV = 0.68 dl / g.

(B) Polymerization Method for Polyester Resin for Adhesive Layer Addition of terephthalic acid, isophthalic acid, and ethylene glycol to a stainless steel autoclave equipped with a stirrer, distillation tower, and pressure regulator, and esterification at 240 ° C. and gauge pressure of 3.5 MPa The esterification reaction was carried out for 2 hours while sequentially removing the water produced in step 1. Subsequently, the ethylene glycol solution of the aluminum compound and the ethylene glycol solution of the phosphorus compound prepared by the above method were added to the polyester resin so that 28 ppm and 50 ppm remained as aluminum atoms and phosphorus atoms, respectively. The temperature is raised to 280 ° C., and the pressure of the system is gradually reduced to 150 Pa during this time, and a polycondensation reaction is performed for 1 hour under these conditions. The amount of isophthalic acid copolymerized in the acid component is 11.0 mol%, A polyester resin composition for an adhesive layer having an IV = 0.63 dl / g was obtained. The Tm of this polyester resin was 225.0 ° C.

(Formation of a two-layer polyester film comprising a base material layer and an adhesive layer)
The polyester resin A for the base material layer and the polyester resin B for the adhesive layer are respectively supplied to separate hoppers, melted in an extruder heated to a resin temperature of 280 ° C. and 270 ° C., respectively, and two layers are formed in the die. And then extruded onto a cooling drum to form an amorphous sheet. Thereafter, the amorphous sheet was stretched 3.3 times in the longitudinal direction and 4.0 times in the transverse direction at 110 ° C., and heat-set at 230 ° C. to form a base material layer thickness of 11 μm, an adhesive layer thickness of 1 μm, A two-layer polyester film having a thickness of 12 μm was obtained.

  Table 1 shows the results of physical properties evaluation of this adhesive layer polyester resin and a two-layer polyester film using the same. The results of the following examples and comparative examples are also shown in Table 1.

(Example 2)
The polyester resin for the adhesive layer was polymerized in the same manner as in Example 1 except that the isophthalic acid component of the acid component was 8.0 mol%, and the polyester resin for the adhesive layer with IV = 0.63 dl / g. Got. The polyester resin had a Tm of 233.5 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Example 3)
The polyester resin for the adhesive layer was polymerized in the same manner as in Example 1 except that the isophthalic acid component of the acid component was 13.0 mol%, and the polyester resin for the adhesive layer had an IV = 0.64 dl / g. Got. The polyester resin had a Tm of 222.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

Example 4
Polymerization was performed in the same manner as in Example 1 except that IV = 0.56 dl / g in the polyester resin for the adhesive layer, to obtain a polyester resin for the adhesive layer having an isophthalic acid component of 10.8 mol%. The polyester resin had a Tm of 226.1 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Example 5)
Polymerization was performed in the same manner as in Example 1 except that IV = 0.73 dl / g in the polyester resin for the adhesive layer, to obtain a polyester resin for the adhesive layer having an isophthalic acid component of 11.0 mol%. The Tm of this polyester resin was 225.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 1)
The polyester resin for the adhesive layer was polymerized in the same manner as in Example 1 except that the isophthalic acid component of the acid component was 7.0 mol%, and the polyester resin for the adhesive layer with IV = 0.64 dl / g. Got. The polyester resin had a Tm of 234.5.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 2)
The polyester resin for the adhesive layer was polymerized in the same manner as in Example 1 except that the isophthalic acid component of the acid component was changed to 13.5 mol%, and the polyester resin for the adhesive layer with IV = 0.62 dl / g. Got. The polyester resin had a Tm of 221.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 3)
Polymerization was performed in the same manner as in Example 1 except that IV = 0.85 dl / g in the polyester resin for the adhesive layer, to obtain a polyester resin for the adhesive layer having an isophthalic acid component of 11.0 mol%. The Tm of this polyester resin was 225.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 4)
Adds terephthalic acid, isophthalic acid, ethylene glycol, and germanium catalyst to a stainless steel autoclave equipped with a stirrer, distillation column, and pressure regulator, and sequentially removes water generated by esterification at 240 ° C and gauge pressure of 3.5 MPa. The esterification reaction was carried out for 2 hours. Subsequently, the temperature of the system is raised to 280 ° C. over 1 hour, and during this time, the pressure of the system is gradually reduced to 150 Pa. Under these conditions, a polycondensation reaction is performed for 1 hour, and the isophthalic acid co-polymer is included in the acid components. A polyester resin composition for an adhesive layer having a polymerization amount of 11.2 mol% and IV = 0.63 dl / g was obtained. The polyester resin had a Tm of 224.7 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 5)
The polyester resin for the adhesive layer was polymerized in the same manner as in Comparative Example 4 except that the isophthalic acid component of the acid component was changed to 8.1 mol%, and the polyester resin for the adhesive layer having an IV = 0.62 dl / g. Got. The Tm of this polyester resin was 233.4 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 6)
Adds terephthalic acid, isophthalic acid, ethylene glycol, and antimony catalyst to a stainless steel autoclave equipped with a stirrer, distillation column, and pressure regulator, and sequentially removes water generated by esterification at 240 ° C and gauge pressure of 3.5 MPa. The esterification reaction was carried out for 2 hours. Subsequently, the temperature of the system is raised to 280 ° C. over 1 hour, and during this time, the pressure of the system is gradually reduced to 150 Pa. Under these conditions, a polycondensation reaction is performed for 1 hour, and the isophthalic acid co-polymer is included in the acid components. A polyester resin composition for an adhesive layer having a polymerization amount of 11.0 mol% and IV = 0.63 dl / g was obtained. The Tm of this polyester resin was 225.0 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 7)
The polyester resin for the adhesive layer was polymerized in the same manner as in Comparative Example 6 except that the isophthalic acid component of the acid component was changed to 8.2 mol%, and IV = 0.65 dl / g polyester resin for the adhesive layer. Got. The polyester resin had a Tm of 233.2 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 8)
Adds terephthalic acid, isophthalic acid, ethylene glycol, and titanium catalyst to a stainless steel autoclave equipped with a stirrer, distillation column, and pressure regulator, and sequentially removes water generated by esterification at 240 ° C and gauge pressure of 3.5 MPa. The esterification reaction was carried out for 2 hours. Subsequently, the temperature of the system is raised to 280 ° C. over 1 hour, and during this time, the pressure of the system is gradually reduced to 150 Pa. Under these conditions, a polycondensation reaction is performed for 1 hour, and the isophthalic acid co-polymer is included in the acid components. A polyester resin composition for an adhesive layer having a polymerization amount of 11.0 mol% and IV = 0.62 dl / g was obtained. The polyester resin had a Tm of 225.2 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

(Comparative Example 9)
The polyester resin for the adhesive layer was polymerized in the same manner as in Comparative Example 8 except that the isophthalic acid component of the acid component was changed to 8.0 mol%, and the polyester resin for the adhesive layer with IV = 0.63 dl / g. Got. The polyester resin had a Tm of 233.5 ° C. A two-layer polyester film was obtained by the same film forming method as in Example 1.

  By using an aluminum compound and a phosphorus compound as a polymerization catalyst for the polyester resin for the adhesive layer, it can be confirmed that the heat resistance of the film is improved as compared with the case of using another catalyst. This is considered that the hindered phenol part in the phosphorus compound suppresses thermal decomposition of the polyester resin. Further, by using the aluminum compound and the phosphorus compound, it can be confirmed that the initial sealing temperature is lower even when the polyester resin for the adhesive layer having the same Tm is used as the two polyester film adhesive layers. This is because, as mentioned above, the thermal decomposition of the polyester is suppressed by the effect of the phosphorus compound, so that the frequency of entering the metal plate surface of the polyester resin having a medium molecular weight can be reduced, and the adhesive effect of the polyester resin for the adhesive layer Is estimated to have improved.

  By using the polyester resin containing a specified amount of isophthalic acid using an aluminum compound and a phosphorus compound as a polymerization catalyst of the present invention as an adhesive layer of a polyester film for can inner surface lamination, It is possible to provide a polyester film having both adhesiveness and heat resistance.

Claims (2)

A polyester resin using an aluminum compound and a phosphorus compound as a polymerization catalyst, the polyester resin containing the polymerization catalyst, wherein the main dicarboxylic acid component of the polyester resin is terephthalic acid, isophthalic acid is included as the dicarboxylic acid component, and isophthalic acid is contained The amount is 8.0 to 13.0 mol% of the total dicarboxylic acid component, the main diol component of the polyester resin is ethylene glycol, and the melting point (Tm) of the polyester resin is 222.0 to 233.5 ° C. And the intrinsic viscosity (IV) satisfy | fills 0.50-0.80 dl / g, The polyester resin used for the adhesive layer of the film for can inner surface lamination. A polyester film for laminating can inner surface comprising two layers of a base material layer and an adhesive layer, the polyester film for laminating can inner surface using the polyester resin according to claim 1 as an adhesive layer.