JPH02252557A - Easy heat-sealing laminated polyester film - Google Patents

Abstract

PURPOSE:To obtain an easy heat-sealing polyester film having high heat-sealing strength by respectively incorporating a specific amount of a copolymer component in an easy heat-sealing layer and a polyester layer becoming a substrate. CONSTITUTION:An easy heat-sealing laminated polyester film is formed by laminating a layer of polyester B to the single surface of a layer of polyester A. The polyester B is composed of a copolymerized polyester based on an ethylene terephthalate unit and containing 6-40mol% of one or more kind of a copolymer component and the polyester A is composed of copolymerized polyester based on an ethylene terephthalate unit and containing 0.5-5mol% of the copolymer component constituting the polyester B. When the content of the copolymer component in the polyester B is below 6%, sufficient heat- sealing strength is not obtained and, when said content exceeds 40%, curling is generated in the film. When the content of the copolymer component constituting the polyester B in the polyester A is below 0.5mol%, a heat sealed part is low in the force generating cohesive failure and, when said content exceeds 5mol%, the whole mechanical characteristic and heat resistance of the film are lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an easily heat-sealable laminated polyester film. More specifically, the present invention relates to an easily heat-sealable laminated polyester film that has extremely high heat-seal strength and excellent workability.

[Prior art and problems to be solved by the invention] Although polyester films generally have excellent strength and heat resistance, they have poor heat-sealing properties. It is necessary to impart heat sealability to the film.

Conventionally, as the above-mentioned method, a method is known in which an easily heat-sealable layer is formed on one side of a polyester film by laminating or coating with another film.

However, when using the coating method, it is difficult to obtain sufficient heat-sealing strength, and even in films where other films are laminated to form a heat-sealing layer, with conventional films, the front and back sides of the film are difficult to obtain. Even when the heat-sealed parts were brought into close contact with each other by using the heat-sealed parts, cohesive failure occurred in the heat-sealed parts due to relatively low tensile strength, and the heat-sealed strength obtained was actually a low value.

The problem of low heat-sealing strength due to such cohesive failure has been one of the major obstacles to expanding the uses of polyester films with conventional heat-sealing layers.

Therefore, it has been desired to develop an easily heat-sealable polyester film that has heat-sealability and a large force required for cohesive failure of the heat-sealed portion, that is, has high substantial heat-seal strength.

[Means to solve the problem]

In view of the above-mentioned problems, the inventors of the present invention have conducted intensive studies and found that in a polyester film having an easily heat-sealable layer formed on one side, a specific amount of a copolymer component was added to each of the easily heat-sealable layer and the polyester layer serving as the base material. It was discovered that the above-mentioned problems could be solved by containing it, and the present invention was created based on this discovery.

That is, the gist of the present invention is to provide a film in which polyester B is laminated as an easily heat-sealable layer on one side of polyester A, in which polyester B is mainly composed of ethylene terephthalate units and contains one or more copolymer components.
From a copolymerized polyester containing 40 mol% of copolymerized polyester, and in which polyester A is mainly composed of ethylene terephthalate units and contains 0.5 to 5 mol% of at least one component of the copolymerized component constituting polyester B. The present invention relates to an easily heat-sealable polyester film characterized by the following characteristics.

The present invention will be explained in detail below.

The polyester used for polyester A and polyester B of the present invention is a copolymerized polyester mainly composed of ethylene terephthalate units and copolymerized with other components.

The above copolymerization components include oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, and dicarboxylic acid components. One or more types of known dicarboxylic acids such as acids can be used, while the diol component includes neopentyl glycol, propylene glycol, 1,4-butadiol, trimedylene glycol, propylene glycol, and tetramethylene glycol. , hexamethylene glycol, diethylene glycol,
Polyalkylene glycol, engineering.

One or more known diol components such as 4-cyclohexane dimetatool can be used.

The copolymerized polyester of the present invention is obtained by substituting a part of the dicarboxylic acid component and/or diol component with another dicarboxylic acid or diol component, but other components,
For example, oxycarboxylic acids such as p-oxybenzoic acid 2 p-oxyethoxybenzoic acid, benzoic acid, benzoylbenzoic acid, monofunctional compounds such as methoxypolyalkylene glycols, glycerin, pentaerythritol.

Polyfunctional compounds such as trimethylol and trimethylenepropane can also be used to the extent that the product retains a substantially linear polymer.

In the present invention, the polyester B forming the easily heat-sealable layer is mainly composed of ethylene terephthalate units, and contains 6-=-40 mol% of copolymer components, preferably 10 to 40 mol%.
It is necessary that the polyester contains mol%.

In a film containing less than 6% of copolymer components, the melting point is insufficiently lowered and sufficient heat sealing strength cannot be obtained.
Undesirable. Furthermore, if the content exceeds 40%, curling will occur in the film, which is not preferable.

As the most important component constituting the present invention, the polyester A of the present invention is mainly composed of ethylene terephthalate alone, and contains 0.5 to 5 mol%, preferably 0.5 to 5 mol%, of at least one copolymer component constituting the polyester B. It is necessary to contain .5 to 4 mol%, more preferably 1 to 3 mol%. A film containing a copolymer component content of less than 0.5 mol % is undesirable because the heat-sealed portion after heat-sealing the front and back surfaces of the film has a low strength to cause cohesive failure.

The present inventors speculate that such cohesive failure of the heat-sealed part occurs when stress concentration occurs locally on the joint surface of the heat-sealed part when the film is pulled, and as a result, the film itself It is thought that cohesive failure occurs at an extremely low tensile strength compared to the tensile strength of steel. The surprising fact that when polyester A contains 0.5 mol% or more of polyester B, that is, the same copolymer component as the heat seal layer, as in the present invention, the strength required for cohesive failure is improved. It is thought that this is because the heat-sealed portions of the seal layer and the base film layer are integrated, and the stress concentration on this portion is alleviated.

A film in which the amount of copolymerization exceeds 5 mol % in polyester A is undesirable because the overall mechanical properties, heat resistance, etc. of the film deteriorate.

In the polyester of the present invention, other polymers may be added or mixed as long as it is 30 mol% or less.

In order to improve the slipperiness of the film in the polyester of the present invention, it is also preferable to contain fine particles of an organic lubricant, an inorganic lubricant, or the like. Moreover, additives such as stabilizers, colorants, antioxidants, antifoaming agents, and antistatic agents may be contained as necessary. Fine particles that impart slipperiness include known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, and carbon black, and melted polyester resin. Insoluble high melting point organic compounds during film formation, metal compound catalysts used during crosslinked polymer and polyester synthesis,
Examples include internal particles formed inside the polymer during polyester production by alkali metal compounds, alkaline earth metal compounds, and the like. The fine particles contained in the film are 0.005 to 0.9% and have an average particle diameter of 0.001 to 3.5 μm.

The glass transition temperature (Tg) of polyester B of the present invention is:
The temperature is preferably 40°C or higher, more preferably 50°C or higher and i o o 'c or lower. When the Tg is less than 40°C, blocking occurs when the film is stored, which is not preferable. Moreover, when Tg exceeds 100°C, heat sealability at low temperatures deteriorates, which is not preferable.

In the film of the present invention, the degree of plane orientation of the polyester B layer is preferably 0.020 or less, more preferably o,
oio or less. A film with a degree of plane orientation exceeding 0.020 is undesirable because heat sealability deteriorates.

In the film of the present invention, the average refractive index π1 of polyester B after biaxial stretching and heat setting has a relationship with the average refractive index 10 of an unstretched film in a substantially amorphous state obtained by rapidly cooling polyester B after melting. In n, ≦π. 10, O
O5 is preferably o nl (no+o, o0
Films exceeding 5) are not preferred because sufficient heat-sealing properties cannot be obtained.

In the film of the present invention, the ratio of the maximum height (Rt) to the center line average roughness (Ra) on the surface of polyester B (
Rt/Ra) is preferably 20 or less, more preferably 5 or more and 15 or less. Rt/Ra is one of the characteristic values representing the shape of the film surface; the larger the value, the more steep protrusions there are on the film surface, and the smaller the value, the more broad protrusions there are on the film surface. Rt/R of the surface of polyester B in the film of the present invention
A film with a greater than 20 is undesirable because it tends to lead to insufficient adhesion during heat sealing and cohesive failure of the heat sealed portion at low strength. In addition, for films with Rt/Ra of less than 5, the slipperiness of the film.

This is undesirable as it reduces workability.

On the other hand, in the film of the present invention, it is the surface roughness of the polyester A that greatly influences the quality of the slip properties and workability, and the center line average roughness (Ra) of the polyester A in the film of the present invention is preferably 0.020 μm or more,
More preferably, it is 0.030 μm or more and 0.060 μm or less. A film with an Ra value of less than 0.020 μm is undesirable because of its reduced slipperiness and workability. Furthermore, a film with an Ra value exceeding 0.060 μm loses transparency and is not preferred when used for packaging purposes.

The thickness of the film obtained as described above is not particularly limited, but - the thickness used for boat fishing is 5 to 400 mm.
It is μm.

Next, the method for producing the film of the present invention will be specifically explained, but the present invention is not particularly limited to the following production method.

In the present invention, known methods such as coextrusion, extrusion lamination, and dry lamination may be used to obtain the laminated film.

In particular, the coextrusion method is advantageous in forming a thin heat-sealing layer and is preferred from the viewpoint of productivity.

The manufacturing method will be explained below using a coextrusion method.

Polyester A and polyester B having the composition of the present invention containing an appropriate amount of inorganic particles as a lubricant as necessary are each dried using a conventional hopper dryer, paddle dryer, vacuum dryer, etc., and then dried in separate extruders. 2 using
After melting at a temperature of 00 to 320'C, the two polyesters are combined in a vibrator or die, extruded, and rapidly cooled to obtain an unstretched film. When extruding,
Any existing method may be used, such as the 'r die method or the tubular method. When using a T-die to obtain an unstretched film, using the so-called electrostatic adhesion method during rapid cooling is
This is preferred in order to obtain a film with uniform thickness.

The obtained unstretched film is then subjected to a stretching process with T
The area magnification is 1.1 to 50 times, preferably 6 to 30 times in the temperature range of g-10°C or higher and T c -10'C or lower.
It is stretched in the longitudinal direction and/or the width direction within a double range. The above Tg and Tc indicate the glass transition temperature and crystallization temperature upon heating, respectively, of polyester A. The stretching method may be uniaxial or biaxial stretching depending on the purpose.

When biaxial stretching is performed, any one of sequential biaxial stretching, simultaneous two-wheel stretching, and a combination thereof may be used. In the case of sequential biaxial stretching, a method of stretching in the longitudinal direction and then in the transverse direction is preferably adopted for -a.

Further, after biaxial stretching, re-stretching may be performed in the longitudinal direction and/or width direction before subjecting to the next heat treatment step.

The film stretched uniaxially or biaxially in this way is heated in a heat-setting zone as necessary to a length of 100 to 260'.
C. for 1 second to 10 minutes. One of the preferred embodiments for obtaining the film of the present invention is to set the maximum temperature of the heat treatment to a range from the melting point of polyester B -10°C to 260°C, preferably from the melting point to 260°C.

The above heat treatment is usually carried out under tension fixation, but it is also possible to loosen or widen the film by 20% or less in the longitudinal and/or width directions during the heat treatment and/or during cooling after the heat treatment. .

It is also possible to perform a corona discharge treatment on one side or the front surface of the film during, before, or after the stretching process to improve the adhesion of the film to the printed layer or the like.

It is also possible to improve the adhesion, antistatic properties, slipperiness, light-shielding properties, etc. of the film by coating one or both sides of the film during, before, or after the stretching process.

The film thus obtained is wound up to form a product.

As described above, by satisfying the constituent requirements of the present invention, it is possible to obtain an easily heat-sealable polyester film with greatly improved heat-sealing strength.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

The method for evaluating the film is shown below.

(1) Glass transition temperature (Tg) After heating and melting the polymer at 300°C under N2 for 5 minutes, it was rapidly cooled to an amorphous state, and then heated using a differential heating meter 5SC580/DSC20 manufactured by Seiko Electronics. Speed 4 degrees/
Measured at min.

(2) Planar orientation of the film “C(ΔP), average refractive index (n
Using an Atsube refractometer manufactured by Koatabo Optical Co., Ltd., the maximum value of the refractive index nγ in the film plane and the refractive index nβ in the direction perpendicular to it are determined.
, and the refractive index nα in the thickness direction of the film were measured, and the average refractive index, birefringence, and degree of plane orientation were calculated from the following equations. still,
The refractive index was measured using sodium D line at 23°C.

Δp = i/2 (nγ + nβ) - nα n = 1/3 (nα + nβ 7 nγ) (3) Center line average roughness (Ra) ■Surface roughness measuring machine manufactured by Koita Research Institute (SE-3F) It was calculated as follows using That is, a part with a reference length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y=f is created with the center line of this extracted part as the y-axis and the direction of vertical magnification as the y-axis. When expressed as (x), the value given by the following formula is expressed in [μm]. The centerline average roughness was determined by determining 10 cross-sectional curves from the surface of the sample film, and was expressed as the average value of the centerline average roughness of the sampled portions determined from these cross-sectional curves. The tip radius of the stylus is 2μm, the load is 30■, and the cutoff value is 0.08+
+m.

(4) Maximum height (Rt) ■A portion of the standard length (2.5 mm) extracted from the cross-sectional curve obtained by the surface roughness measuring machine (SE-3F) manufactured by Koita Research Institute (hereinafter referred to as the extracted portion) When the sampled part is sandwiched between two straight lines parallel to the average line of 6), these two
The distance between the straight lines was measured in the direction of the longitudinal magnification of the cross-sectional curve, and the value expressed in micrometers (μm) was taken as the maximum height of the extracted portion. The maximum height was determined by determining 10 cross-sectional curves from the surface of the sample film, and was expressed as the average value of the maximum height of the sampled portion determined from these cross-sectional curves.

The radius of the stylus used at this time was 2.0 μm and the load was 30 m.
g and the cutoff value is 0.08 mm.

(5) Cut out two sheets of heat seal strength film, stack them so that the polyester side and the B side are in contact, and then heat seal tester (TP701) manufactured by Tester Sangyo ■ at a temperature of 145'C and a pressure of 2 kg.
f. Heat sealing was performed for 1 second. A heat seal bar measuring 15 mm x 300 mm was used. A heat-sealed portion was cut out to have a width of 15 mm+, and a 90° peel test was conducted at a tensile speed of 50Q+*m/win.

Regardless of whether the peeling of the heat-sealed portion was due to interfacial peeling or peeling due to cohesive failure, the value of the initial stress of the peel strength was defined as the heat-seal strength (g/15IIIi+width).

Example 1 As polyester A, the dicarboxylic acid component contains 97.5 mol% of terephthalic acid units and 2.5 mol% of isophthalic acid units.
70 ppm of amorphous silica particles with an average particle size of 1.4 μm and whose diol component is ethylene glycol.
A copolymerized polyester (1) having an intrinsic viscosity of 0.65 was used.

On the other hand, as polyester B, the dicarboxylic acid component is 80 mol% of terephthalic acid units and 20 mol% of isophthalic acid units.
500 pp of amorphous silica particles with an average particle size of 1.2 μm, consisting of 97 mol% ethylene glycol monomer and 3 mol% diethylene glycol unit as a diol component.
A copolymerized polyester with an intrinsic viscosity of 0.70 containing m (
2) was used.

After drying the above polyesters A and B by a conventional method,
They were melted at 290'C in separate extruders, merged in a pipe, extruded, and rapidly cooled to obtain an unstretched film. The obtained unstretched film was stretched 3.6 times in the longitudinal direction between an 85° heating roll and a cooling roll, and then introduced into a tenter and stretched 4.0 times in the width direction at 100°C. Thereafter, heat treatment was performed at 230°C for 10 seconds. After the heat treatment, relaxation was performed by 3% in the width direction in a cooling zone at 180°C.

The thickness of the obtained film was 23 mm for the polyester A layer.
The thickness of the B layer was 2 μm.

Example 2 Polyester A had an average particle size of 0, in which the dicarboxylic acid component consisted of terephthalic acid, the di-produced component consisted of 97 mol% of ethylene glycol units, 2 mol% of neopentyl glycol units, and 1 mol% of diethylene glycol units.
．． A copolymerized polyester (3) with an intrinsic viscosity of 0.60 and containing 1200 ppm of 9 μm synthetic calcium carbonate particles was used. On the other hand, as polyester B, the dicarboxylic acid component consists of terephthalic acid, and the diol component contains 600 ppm of kaolin particles with an average particle size of 1.3 μm, consisting of 85 mol% of ethylene glycol units and 15 mol% of neopentyl glycol units. A copolymerized polyester (4) with an intrinsic viscosity of 0°66 was used.

The above polyesters A and B were dried, extruded and stretched in the same manner as in Example 1, and then heat treated under tension at 240°C for 6 seconds. The thickness of the polyester A layer of the obtained film was 12 μm.

The layer B was 3 μm thick.

Comparative Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.65 and containing particles similar to the copolymerized polyester (1) of Example 1 was used as polyester A, and the copolymerized polyester (2) of Example 1 was used as polyester B. there was. The polyesters A and B were dried, extruded, and film-formed in exactly the same manner as in Example 1 to obtain a film having a polyester A layer of 23 μm and a polyester B layer of 2 μm.

The physical properties of the films obtained in the above Examples and Comparative Examples are summarized in Table 1.

In the film of Comparative Example 1, since the composition of polyester B did not satisfy the constituent requirements of the present invention, cohesive failure occurred in the heat seal portion at a relatively low tensile strength, and sufficient heat seal strength was not obtained.

In contrast, in the films of Examples, the strength at which cohesive failure occurred in the heat-sealed portion was high, and sufficient heat-seal strength was obtained.

〔Effect of the invention〕

As described above, the film of the present invention has excellent heat sealing strength and can be used in a wide range of applications such as packaging, electrical disconnection, and general industrial use. Therefore, the industrial value of the present invention is great. be.

Applicant: Diafoil Co., Ltd. Agent Patent Attorney Nagatanikawa (1 other person)

Claims (1)

[Claims] (1) A film in which polyester B is laminated as an easily heat-sealable layer on one side of polyester A, in which polyester B is a copolymer mainly composed of ethylene terephthalate units and containing 6 to 40 mol% of one or more copolymer components. made of polyester, and polyester A is
The main component is ethylene terephthalate units, and at least one component of the copolymer component constituting polyester B is 0.5 to
An easily heat-sealable laminated polyester film comprising a copolymerized polyester containing 5 mol%.