JPH08245771A - Polyester film for packaging - Google Patents

Abstract

PURPOSE: To prepare a film for packaging having excellent heat-bonding property and moldability and processability. CONSTITUTION: This polyester film for packaging is a biaxially oriented film of copolymerpolyester containing 95-99mol% terephthalic acid and 1-5mol% isophthalic acid as acid components and 95-99mol% ethylene glycol and 1-5mol% diethylene glycol as glycol components and simultaneously satisfies the formulas (1) to (4). (1) 235<=Tm<=250, (2) [COOH]<=45, (3) 0.150<=ΔP<=0.165, (4) 0.01<=Ra<=0.07. [Tm is a melting point ( deg.C) of the film; [COOH] is a terminal carboxyl group amount (equivalent amount/10<6> g) in the film; ΔP is a planar orientation degree; Ra represents a centerline average roughness (μm) on the film surface].

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially stretched film obtained from a specific copolyester,
The present invention relates to a packaging film having excellent heat adhesiveness and moldability.

[0002]

BACKGROUND OF THE INVENTION Since polyester films are hygienic and have excellent mechanical properties, they can sufficiently protect contents such as foods when used as packaging materials. Further, since the polyester film has an excellent gas barrier property, it is possible to maintain the scent of the contents when packaging a product having an aromatic component such as food.

However, since the polyester film is usually stretched and heat-fixed, it has a drawback of poor thermal adhesion when used as a packaging material for retort foods or general foods, and improvement is required. There is.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventor has found that a biaxially stretched film which is a specific copolyester and has specific properties is suitable for packaging. The present invention has been completed.

That is, the gist of the present invention is to use 95 to 99 mol% of terephthalic acid and 1 to 1 of isophthalic acid as acid components.
A copolymerized polyester biaxially stretched film containing 5 mol% and ethylene glycol 95 to 99 mol% and diethylene glycol 1 to 5 mol% as glycol components, and simultaneously satisfies the following formulas (1) to (4). It exists in the polyester film for packaging characterized by being.

[0006]

## EQU2 ## 235 ≦ Tm ≦ 250 (1) [COOH] ≦ 45 (2) 0.150 ≦ ΔP ≦ 0.165 (3) 0.01 ≦ Ra ≦ 0.07 (4) [where Tm is the melting point (° C.) of the film, [COO
H] is the amount of terminal carboxyl groups in the film (equivalent / 10
⁶ g), ΔP represents the degree of plane orientation of the film, and Ra represents the center line average roughness (μm) of the film surface].

Hereinafter, the present invention will be described in detail. The copolyester in the present invention means that 95 to 99 mol% of the acid component is terephthalic acid, 1 to 5 mol% is isophthalic acid, 95 to 99 mol% of the glycol component is ethylene glycol, and 1 to 5 mol% is diethylene glycol. Is. If the amount of isophthalic acid or diethylene glycol is less than 1 mol%, the thermal adhesiveness of a film becomes poor, which is not preferable. On the other hand, if the amount of isophthalic acid or diethylene glycol exceeds 5 mol%, the mechanical strength of a film becomes poor, which is not preferable.

The thickness of the film made of the copolyester of the present invention is usually 5 to 50 μm, generally 12 μm. The melting point (Tm) of the film of the present invention is 235 to 2
The temperature is 50 ° C, preferably 240 to 250 ° C. Tm is 2
If it is lower than 35 ° C., the heat resistance and mechanical strength of the formed film become poor, which is not preferable. Tm is 25
If the temperature exceeds 0 ° C, the thermal adhesiveness becomes poor, which is not preferable.

The amount of terminal carboxyl groups of the copolymer film in the present invention is less than 45 equivalents / 10 ⁶ g, preferably 4
It is less than 0 equivalent / 10 ⁶ g. When the amount of terminal carboxyl groups in the film exceeds 45 equivalents / 10 ⁶ g, heat deterioration products are generated due to heat history when melt-extruded by a known melt-extrusion device such as an extruder during film production. Streaky substances caused by the above are present in the film, and the flatness of the film becomes poor, which is not preferable.

The degree of plane orientation of the copolymer film of the present invention (Δ
P) is 0.150 to 0.165. ΔP is 0.15
If it is less than 0, the mechanical strength, especially the tensile rupture strength becomes poor, which is not preferable. Further, when ΔP exceeds 0.165, thermal characteristics such as heat shrinkage deteriorate, which is not preferable.

The copolymer film of the present invention has a roughened surface to improve the workability in the winding process during film production and the coating and laminating process during film production for packaging. It is preferable to impart the property, and for that purpose, fine inert particles may be added.

The average particle size of the fine inert particles used for such purpose is usually 0.5 to 3.0 μm, preferably 1.0.
.About.2.5 .mu.m, and the amount of particles added is usually 0.05 to 1.
It is 0% by weight, preferably 0.1 to 0.5% by weight. If the average particle size of the particles is less than 0.5 μm or the amount of the particles added is less than 0.05% by weight, the winding property and workability during film production may be deteriorated. When the average particle size exceeds 3.0 μm or the addition amount exceeds 1.0% by weight, the degree of roughening of the film surface is too large and the film becomes so-called shimofuri, and the transparency of the film is high. May be damaged.

Examples of the inert particles that can be used in the present invention include silicon oxide, titanium oxide, zeolite, silicon nitride, boron nitride, celite, alumina, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate. Examples thereof include, but are not limited to, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, kaolin, talc, carbon black and crosslinked polymer fine powder as described in JP-B-59-5216. It is not something that will be done. At this time, the inert particles to be blended may be a single component, or two or more components may be used simultaneously. Further, the method of blending the polyester with the inert particles is not particularly limited, but for example, a method of adding the inert particles to the polyester polymerization step, or a method of melt kneading before forming into a film is preferably used. .

In the present invention, a film having an appropriately roughened surface can be obtained by the above-mentioned method, but the winding property during film production and the workability during processing into a packaging film are further enhanced. In order to satisfy, the center line average roughness (Ra) of the film surface is 0.01 to 0.07.
μm, preferably 0.02 to 0.05 μm. When Ra is less than 0.01 μm, the winding property and workability during film production are deteriorated, which is not preferable. Further, when Ra exceeds 0.07 μm, the degree of roughening of the film surface is too large, the film becomes uneven, the transparency of the film is impaired, and the film is slipped too much and the winding property is deteriorated. Is not preferable.

Further, in the copolymer film of the present invention, by using a raw material having a specific resistance in a specific range at the time of melting,
Further, a film having excellent flatness can be obtained. That is, when a film is obtained from the copolyester of the present invention, the raw material polyester is usually extruded from the extruder through the lip portion into a sheet form in the temperature range of 275 to 300 ° C to obtain an amorphous sheet. In so doing, while adopting the so-called electrostatic application contact method,
It was found that a film having more excellent flatness can be obtained by using a raw material having a specific resistance at the time of melting of 5 × 10 ^{6 to} 5 × 10 ⁸ Ω-cm.

The electrostatic application contact method is, for example, Japanese Patent Publication No. 37-
As described in Japanese Patent No. 6142, when an amorphous sheet is obtained from a molten polymer, the sheet is electrostatically imparted and electrostatically strongly pressed against a rotating cooling drum to rapidly cool it. When the melt resistivity is in the above range, it can be applied particularly effectively, and the flatness of the obtained film can be further improved. The more preferable range of the specific resistance is 1 × 10 ⁷ to 1 × 10 ⁸ Ω−
cm.

In order to adjust the specific resistance within a desired range, for example, the following method may be adopted. That is, it suffices to solubilize the metal component in the polymerized polyester. For this purpose, for example, a metal component used as a transesterification reaction catalyst or a metal component added after the transesterification reaction or the esterification reaction may be compared with the metal component used after the transesterification reaction. A means for adding a very small amount, for example, an equimolar amount or less of a phosphorus compound is preferably adopted. On the other hand, in order to increase the specific resistance, a method of reducing the amount of the metal component dissolved in the raw material polyester or adding the amount of the phosphorus compound with respect to the metal component in the equimolar amount or more is preferably adopted.

The thermal adhesiveness (HS) of the film of the present invention
Is 400 g / 10 mm or more, and further 450 g / mm
The above is preferable. When HS is less than 400 g / 10 mm,
When the films are overlapped and the surroundings are heat-bonded and the contents such as foods are packed in a bag, the bonded portion tends to be easily peeled off. Next, the method for producing the film of the present invention will be specifically described, but the invention is not particularly limited to the following examples as long as the constituent requirements of the present invention are satisfied.

Copolymerized polyester containing a predetermined amount of inert inorganic particles such as titanium dioxide and silica particles is supplied to a well-known melt-extruding apparatus typified by an extruder, and heated to a temperature higher than the melting point of the polyester to be melted. . Next, the melted polyester is extruded from a slit die and rapidly cooled and solidified on a rotating cooling drum to a temperature not higher than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum, and therefore, the electrostatic application adhesion method or the liquid application adhesion method is preferably adopted.

The electrostatic application contact method is as described above. Specifically, a linear electrode is provided on the upper surface side of the sheet in a direction orthogonal to the flow of the sheet, and about 5 to 10 kV is applied to the electrode.
Is applied to the sheet to apply an electrostatic charge to the sheet to improve the adhesion to the drum. Also,
The liquid application contact method is a method of improving the adhesion between the drum and the sheet by uniformly applying the liquid to the entire surface or a part of the surface of the rotary cooling drum (for example, only the portions contacting both ends of the sheet). . In the present invention, both may be used together if necessary.

In the present invention, the sheet thus obtained is usually biaxially stretched to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times in the machine direction at 70 to 145 ° C.,
After forming a longitudinally uniaxially stretched film, the coating solution is sequentially applied to both surfaces of the film as necessary, and is appropriately dried, or is undried and stretched 2 to 6 times in the transverse direction at 90 to 160 ° C., It is preferable to perform heat treatment at 150 to 250 ° C. for 1 to 600 seconds. Further, in this case, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the exit of the heat treatment is preferable. Further, it is also possible to add re-longitudinal stretching and re-transverse stretching if necessary.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. The physical property measuring methods used in the present invention are shown below.

(1) Melting point (Tm) Differential calorimeter SSC580DS manufactured by Seiko Instruments Inc.
It measured using C20 type. The DSC measurement conditions are as follows. That is, 10 mg of the sample film is used for DSC
Set it in the device and raise the temperature at a rate of 10 ° C / min.
It was measured in the range of 00 ° C., and the peak of the melting endothermic peak was defined as Tm.

(2) Terminal carboxyl group ([COO
H]) A. Conix's method (Makromol. Chem. 26,226 (1958))
Was determined in accordance with

(3) Specific resistance upon melting (ρv) Brit. J. Appl. Phya. Volume 17, 114
It was measured by the method described on pages 9 to 1154 (1966). However, in this case, the melting temperature of the polymer is 2
The value immediately after the temperature was set to 95 ° C. and a direct current of 1000 V was applied was taken as the specific resistance during melting.

(4) Measurement of degree of plane orientation (ΔP) Using an Abbe refractometer manufactured by Atago Optical Co., Ltd., the maximum refractive index nγ in the film plane, the refractive index nβ in the direction perpendicular thereto, and the refractive index in the thickness direction of the film The rate nα was measured, and the plane orientation degree was calculated from the following equation. The refractive index was measured at 23 ° C. using sodium D line.

[0027]

## EQU3 ## Degree of plane orientation (ΔP) = (nγ-nβ) / 2-nα

(5) Center line average roughness (Ra) According to the method described in Japanese Industrial Standard JIS B0601, a surface roughness measuring device (SE-3 manufactured by Kosaka Laboratory Ltd.)
The center line average roughness (Ra) was determined using F). The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

(6) Tensile breaking strength (FB) Intesco Model 20 tensile tester manufactured by Intesco Co., Ltd.
Using the 01 type, a sample film having a length of 50 mm and a width of 15 mm was pulled at a speed of 200 mm / min in a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH, and the value was calculated by the following formula.

[0030]

[Formula 4] FB (kg / mm²) = F / A (In the above formula, F is the load (kg) at break, A is the test
Original cross-section area (mm) ²Represents)

(7) Thermal Shrinkage (S) The sample was heat-treated in an oven kept at 180 ° C. in a tensionless state for 3 minutes, and the lengths of the sample before and after the heat treatment were measured. Was calculated.

[0032]

## EQU5 ## S (%) = {(L0-L1) / L0} × 100 (In the above formula, S is the heat shrinkage ratio, L0 is the sample length before heat treatment, and L1 is the sample length after heat treatment.) The film was measured at 5 points each in the machine direction and the transverse direction, and the average value was obtained.

(8) Heat Adhesion (HS) A sample film having a film thickness of 12 μm is 200 m long.
m, width 50 mm. The obtained two sample films are overlapped, and the central portion in the longitudinal direction is 10 mm in width and 5 in length.
Heat-adhered over 0 mm. Thermal contact pressure is 2kg / c
m ² and 150 ° C. for 5 seconds. The T-type peel adhesion of the obtained sample film was measured at 25 ° C. using a tensile tester Intesco Model 2001 manufactured by Intesco Corporation.
The pulling speed at this time was 200 mm / min.

(9) Thermal Stability About 10 g of polymer was placed in a glass test tube having an internal volume of 50 ml, dried under high vacuum at 160 ° C. for 2 hours, and then recompressed to 100 mmHg with nitrogen gas to melt the glass test tube. After sealing, 2
Heat treatment was performed at 90 ° C. for 2 hours, the intrinsic viscosity before and after the heat treatment was measured to obtain the intrinsic viscosity retention rate, and the thermal stability was evaluated according to the following criteria.

[0035]

[Equation 6] Intrinsic viscosity retention (%) = (Intrinsic viscosity after heat treatment / Intrinsic viscosity before heat treatment) × 100 Evaluation criteria A: Intrinsic viscosity retention ≧ 90% B: Intrinsic viscosity retention ≧ 80% C: Ultimate Viscosity retention rate <80% In addition, the intrinsic viscosity is 100 g of a mixed solvent of 1 g of polymer and phenol / tetrachloroethane = 50/50 (weight ratio).
It was dissolved in 1 and measured at 30.0 ° C.

(10) Winding Characteristics A film produced at a line speed of about 170 m / min was wound on a paper tube having a diameter of 15 cm, and the state of the winding end face of 6000 m was observed and classified into the following three ranks. A: All the end faces are aligned B: The end faces are almost aligned and can be used C: Part of the end face is uneven D: The lower part of the end face is uneven

(11) Thickness unevenness At each of 10 locations in the longitudinal direction of the film at 1000 mm, the film thickness was measured at 10 points every 10 cm in the lateral direction, for a total of 100 points. The film thickness was measured using an Anritsu electronic micrometer, and 10 films around the relevant portion were piled up and measured, and converted into 1 film. Among all the measured values, the maximum value is Xmax, the minimum value is Xmin, and the arithmetic mean value is X. (Xmax-Xmin) / X is the thickness unevenness. The smaller this value is, the more preferable.

(12) Copolymer Composition The copolymer composition ratio in the polyester resin was measured by JSX GSX-400 type NMR.

(13) Average particle size of fine particles Centrifugal sedimentation type particle size distribution measuring device SA- manufactured by Shimadzu Corporation
The particle size was measured by a sedimentation method based on Stokes's resistance law using CP3 type. The value of 50% integrated (volume basis) in the equivalent spherical distribution of the particles obtained by the measurement was used as the average particle diameter.

Example 1 98 parts by weight of terephthalic acid, 2 parts by weight of isophthalic acid, 70 parts by weight of ethylene glycol and 1.
Using 5 parts by weight as a starting material and 0.09 parts by weight of magnesium acetate / tetrahydrate as a catalyst in a reactor, esterification was carried out for 5 hours under the conditions of a reaction starting temperature of 250 ° C. and a pressure of 2.5 kg / cm. After 5 hours, 5 parts by weight of an ethylene glycol slurry containing 0.07 part by weight of silica particles having an average particle size of 2.15 μm was added to the reaction mixture which had been substantially subjected to the esterification reaction, and ethyl acid phosphate was added. Add 0.04 parts, antimony trioxide 0.04 parts,
The polycondensation reaction was performed for 4 hours. That is, the temperature is 230 ℃
Then, the temperature was gradually raised to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure to finally set it to 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure to produce a copolyester.

The obtained polyester was extruded into a sheet form from an extruder set at 285 ° C. and rapidly cooled and solidified by using an electrostatic cooling method in a rotary cooling drum set at a surface temperature of 30 ° C. to obtain a substance having a thickness of 187 μm. An amorphous sheet was obtained. The obtained sheet was stretched in the machine direction at a temperature of 83 ° C. to 3.8 times, and in the transverse direction at a temperature of 90 ° C. to 4.1 times, and further stretched at 235 ° C.
Heat treatment was performed for 2 seconds to produce a biaxially stretched film having a thickness of 12 μm.

Example 2 The same as Example 1 except that terephthalic acid was changed to 96 parts by weight, isophthalic acid was changed to 4 parts by weight, ethylene glycol was changed to 67.5 parts by weight, and diethylene glycol was changed to 2.5 parts by weight. A biaxially stretched film having a thickness of 12 μm was manufactured by the method described above.

Comparative Example 1 A biaxially stretched film having a thickness of 12 μm was produced in the same manner as in Example 1 except that 100 parts by weight of terephthalic acid and 70 parts by weight of ethylene glycol were used as starting materials for polyester.

Comparative Example 2 A thickness of 12 μm was obtained in the same manner as in Example 1 except that 94 parts by weight of terephthalic acid, 6 parts by weight of isophthalic acid, 64 parts by weight of ethylene glycol and 6 parts by weight of diethylene glycol were used. Was produced.

Comparative Example 3 A biaxially stretched film having a thickness of 12 μm was produced in the same manner as in Example 1 except that the heat setting temperature was changed to 225 ° C.

Comparative Example 4 In Example 1, magnesium acetate / tetrahydrate was added to 0.1%.
8 parts by weight and ethyl acid phosphate 0.08
The thickness is 12 μm in the same manner as in Example 1 except that the parts are changed.
Was produced.

Comparative Example 5 In Example 1, 5 parts by weight of an ethylene glycol slurry containing 0.01 parts by weight of silica particles having an average particle size of 2.15 μm was added to the reaction mixture which had been substantially esterified. A biaxially stretched film having a thickness of 12 μm was manufactured in the same manner as in Example 1 except that the above was carried out.

Comparative Example 6 In Example 1, an ethylene glycol slurry 5 containing 0.3 parts by weight of silica particles having an average particle size of 2.15 μm was added to the reaction mixture which had been substantially esterified.
A thickness of 1 was obtained by the same method as in Example 1 except that parts by weight were added.
A 2 μm biaxially stretched film was produced. The results obtained above are summarized in Tables 1 and 2 below.

[0049]

[Table 1] *: DEG diethylene glycol; IPA isophthalic acid

[0050]

[Table 2]

[0051]

Industrial Applicability The film of the present invention has excellent heat adhesion and molding processability, and its industrial value is high.

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Claims (1)

[Claims] 1. A copolyester comprising 95 to 99 mol% of terephthalic acid and 1 to 5 mol% of isophthalic acid as an acid component, and 95 to 99 mol% of ethylene glycol and 1 to 5 mol% of diethylene glycol as a glycol component. A biaxially stretched film having the following formula (1)
A polyester film for packaging which is characterized by simultaneously satisfying (4) to (4). ## EQU1 ## 235 ≦ Tm ≦ 250 (1) [COOH] ≦ 45 (2) 0.150 ≦ ΔP ≦ 0.165 (3) 0.01 ≦ Ra ≦ 0.07 (4) [where Tm is the melting point (° C.) of the film, [COO
H] is the amount of terminal carboxyl groups in the film (equivalent / 10
⁶ g), ΔP represents the degree of plane orientation of the film, and Ra represents the center line average roughness (μm) of the film surface].