JPH078922B2 - Easy-cleavage film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a film which is easily cleaved.

[Conventional technology]

In a bag or container made of a thermoplastic such as polypropylene or polyethylene terephthalate as a constituent material, heat-sealing is performed between the thermoplastic plastics to be heat-sealed or between the container body and the lid. The existing packaging has been widely used in fields such as foods.

These film layers are not only heat-sealed to form a structure with excellent sealing reliability, but also the film is easy to open,
That is, it must have a strength such that it can be easily peeled off by hand when opening, and at the same time, it must have a smooth peeling interface without surface roughness or fluffing (feathering). In order to satisfy this requirement, the resin layer is made of polypropylene or polyethylene (for example, JP-A-57-77465) or a polyester copolymer such as polyethylene terephthalate / isophthalate copolymer. Attempts have been made to use it. However, all of these conventional heat-sealing resin layers are insufficient in terms of smoothness of the peeled surface, and have a drawback that the opening force changes with time.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned drawbacks, to provide a cleavable film having a constant and smooth opening surface when opened, and a slight change in the opening force with time that does not pose a practical problem. It is intended to be provided.

[Means for solving problems]

The present invention is based on 100 parts by weight of polyolefin resin (a), styrene resin, methacrylic acid ester resin,
A film obtained by mixing 15 to 45 parts by weight of at least one resin (b) selected from methylpentene resin, saturated polyester resin and polyamide resin, and the average of the resin (b) in the TD cross section of the film. The dispersion diameter continuously increases from the surface layer of at least one surface toward the center, and the average dispersion diameter (A μm) at a depth of at least 4 μm from the surface layer of at least one surface and the average dispersion diameter at the film center ± 6 μm ( B μm) has a relationship of 0.1 ≦ A ≦ 3 0.5 ≦ B ≦ 12 0.05 ≦ A / B ≦ 0.5, which is a cleavable film.

The polyolefin resin in the present invention has a melt index (hereinafter abbreviated as MI) of 0.1 to 5 measured at 190 ° C.
0 g / 10 min polyethylene or ethylene and other α
-Copolymers with olefins, MI 0.1-50 measured at 230 ° C
Examples thereof include polypropylene having a content of g / 10 minutes, a copolymer of propylene and another α-olefin, a modified polyolefin or an ionomer, and a mixture of these polyolefin resins.

The modified olefin described here is a graft polymerization of at least one monomer selected from α, β-ethylenically unsaturated basic acids and their acid anhydrides, esters, amides, and imides with a graft ratio of 20 mol% or less. It was done. Examples include polyethylene grafted with maleic anhydride. Further, the ionomer referred to in the present invention is an α-olefin and 1 to
It is a copolymer with an ionic group of an α, β-unsaturated carboxylic acid containing a trivalent metal ion. Examples include partial metal salts of ethylene and methacrylic acid copolymers.

The styrene-based resin referred to in the present invention is 70 mol% of styrene.
It is a polymer or copolymer containing the above. Specifically, it refers to, for example, polystyrene, styrene and acrylonitrile, or copolymer of styrene and a rubber-based substance.

The methacrylic acid ester-based resin referred to in the present invention is a polymer or copolymer containing 70 mol% or more of methacrylic acid ester. Specifically, for example, polymethylmethacrylate,
It means polyethyl methacrylate, a copolymer of methyl methacrylate and ethylene or α-methylstyrene, and a copolymer of methyl methacrylate and acrylic acid, methyl acrylate, ethyl acrylate and the like.

The methylpentene resin referred to in the present invention means, for example, poly-4-
Methylpentene-1 resin.

The saturated polyester resin referred to in the present invention is a polyester or copolyester composed of a dicarboxylic acid and a diol, for example, polyethylene terephthalate (PET), polyethylene terephthalate / isophthalate (PET / I).
PET resin such as. Polybutylene terephthalate (PB
T), polybutylene terephthalate / isophthalate (P
PBT resins such as BT / I) and mixtures of these saturated polyester resins can be mentioned.

Note that these resins preferably have an intrinsic viscosity (IV) of at least 0.5 or more.

The polyamide resin referred to in the present invention is a polyamide or copolyamide obtained by polycondensation of a diamine and a dibasic acid, and examples thereof include polycapramide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polyundecane amide, and polydodecaamide. Resins and copolymers and mixtures thereof.

One or more selected from these styrene resins, methacrylic acid ester resins, methylpentene resins, saturated polyester resins and polyamide resins (sometimes referred to as resin (b)), 100 parts by weight of polyolefin resin 15 to 45 parts by weight, preferably 20 to 40 parts by weight. If the amount of the resin (b) added is less than 15% by weight, the easiness of cleavage is poor and the peeled surface is extremely rough, which is not preferable.

If the added amount is more than 45 parts by weight, the cleavage force is low,
It is not preferable because the contents may leak and a feathering defect is likely to occur.

The present invention relates to an easily cleavable film characterized by the resin composition as described above, and in the resin composition, an antioxidant, a heat stabilizer, an ultraviolet absorber, a viscosity modifier, a plasticizer, if necessary. Additives such as agents, organic lubricants and pigments can be dispersed / blended. Inorganic fine particles such as titanium oxide are used in an amount of 0 to 20 parts, preferably 3 to 1 parts, per 100 parts of the resin composition.
0 parts can be added.

The dispersion diameter of the resin (b) in the present invention means the film thickness aromatic diameter of the resin (b) existing as an island component in the polyolefin resin which should be called the sea component in the TD of the film formed. is there. Here, the TD cross section means a cross section when the film is cut in a direction (generally also referred to as a width direction) orthogonal to the mechanical fragrance when considering the film forming process.

In the present invention, a mixture of a polyolefin resin and a resin (b) is formed under special film forming conditions to control the dispersion diameter of the resin (b) which is an island component.

That is, by adjusting the difference between the resin temperature in the cylinder head portion of the polymer melted in the cylinder and the resin temperature immediately after the die discharge, the polymer discharge amount (polymer linear velocity) and the draft ratio to specific conditions, the film TD cross section The dispersion diameter of the resin (b) can be made minute at the surface layer and coarse at the center.

The fact that the particle diameter in the surface layer of the film is very small has a great influence on the cleavage site, the cleavage force, and the surface irregularities after cleavage,
The coarse particle diameter in the central part has a great influence on the stability of the cleavage site.

The average dispersion diameter (A) of the resin (b) at a depth of 4 μm from the surface layer is preferably 0.1 to 3 μm. More preferably, it is 0.5 to 2 μm.

If it is less than 0.1 μm, the peeling force becomes too small,
There is a risk of leakage of the contents, and if it exceeds 3 μm, the surface unevenness after peeling becomes large and a smooth peeled surface cannot be obtained.

When the average dispersion diameter of the resin (b) in the center of the film ± 6 μm is B, the ratio of A and B is preferably 0.05 ≧ A / B ≧ 0.5 when the value of B is 0.5 to 12 μm. More preferably, 0.08 ≦ A / B ≦ 0.4. When A / B shows a value larger than 0.5 and B is smaller than 0.5, the peeling position becomes unstable, the unevenness of the film surface after peeling becomes large, and a feathering defect is likely to occur, which is not preferable. A / B shows a value less than 0.05 and B is 12
If it is larger than μm, the peeling force becomes large and the cleavability is lost.

The film thus obtained is adhered to the base material using heat or an adhesive. If necessary, the substrate may be subjected to anchor coating treatment, or may be directly melt-extruded and laminated on the substrate. The laminated body provided with the adhesive resin layer thus obtained or the laminated body or the lid body is adhered to various containers such as a polyethylene container, a polypropylene container or a metal by a heat sealing method, a high frequency induction heating method or the like. The thickness of the film provided on the substrate is 20 to 350 µ, and more preferably 40 to 250 µ. 20
When it is less than or equal to μ, the absolute diameter of the resin (b) particles in the central portion becomes too small, so that the peeling interface becomes unstable and feathering easily occurs. On the other hand, if it is 350 μm or more, the particle diameter of the olefin resin in the surface layer becomes too large, so that the roughness of the peeling interface tends to increase.

Next, a method for producing the film of the present invention will be described, but the method is not limited thereto.

After mixing the polyolefin resin and the resin (b) by the dry blend method, the composition is supplied to an extruder and formed into a film by the T-die method. The film forming conditions are preferably within the following range. When the temperature of the polymer melted in the cylinder at the cylinder head is T ₁ and the polymer temperature immediately after the die discharge is T ₂ , T ₁ −T ₂ = 5
~ 45 ℃

The linear velocity of the polymer passing through the lip is 60 to 160 (c
The draft ratio is 3 to 15 in m / min).

Needless to say, chips obtained by previously kneading these blend resins with a pelletizer or the like may be used.

Next, the TD cross section of the film formed under the preferred conditions
FIG. 2 shows a cross section in the longitudinal direction (MD).

In the figure, 1 indicates a resin (b) and 2 indicates a polyolefin resin.

In the film of the present invention, as shown in FIG. 1, it can be seen that the particle size of the resin (b), which is the island component, changes almost continuously from the surface to the center. Thus, the feature of the film of the present invention is that it is fine near the surface and coarse near the center.

Observing this state on the MD of the film is as shown in FIG. Resin near the ellipse in the center of the film (b)
It can be seen that the particles in No. 2 become elongated and elongated as they approach the surface, and become even more elongated near the surface layer and are almost continuous.

However, the film formed under the general film forming conditions does not form the structure shown in the figure, and the extremely coarse resin (b) only exists randomly as the island component.

Of course, the easily cleavable film of the present invention can be used as a sealing material for containers and lids of various contents including foods, but since the cleavage surface after opening is extremely good, the peeling surface directly touches the mouth. It is also suitable for applications such as soft drinks such as juice and containers for alcoholic beverages.

[Effects of the Invention] The effects of the present invention are listed below.

(1) Since the cohesive breaking force of the film is used, the sealing performance is stable. The cleaving force is stable because the dispersion diameter is controlled.

(2) Since the cleavage plane is set on the surface layer portion, the cleavage is extremely stable even when the tension angle and the tension speed are changed, and the feathering defect does not occur.

(3) Since the roughness of the cleavage interface is fine and stable,
It shows a good peel appearance and mouth feel.

(4) Substantially no change in opening force over time.

[Characteristic Measuring Method / Evaluation Criteria] The characteristic measuring method and evaluation criteria in the present invention are as follows.

(1) Average dispersion diameter of resin (b) A microtome manufactured by Nippon Microtome Co., Ltd. is used to cut a cross section of the film TD to prepare a section of several μm. This section is photographed under bright field illumination of an optical microscope at 100 to 200 times, and then printed on photographic paper at a total magnification of 1000 to 5000 times. The length of the island component particles in the finished photograph in the thickness direction is measured and used as the particle diameter of the resin (b). Using this method, the value obtained by calculating the arithmetic mean of the particles existing from the surface layer to a depth of 4 μ is A, and is ± from the center of the film thickness.
The value obtained by calculating the arithmetic mean in the thickness direction of 6 μ is B.

(2) Cleavage force (opening force) A condition that the sealing pressure is constant and the sealing time is constant with a heat sealer that sandwiches an easily cleavable film between polypropylene or polyethylene unstretched films with a thickness of about 200μ and heats them to a specified temperature Glued in.

The sample obtained in this way is cut into a strip of 0.5 cm width, and using Tensilon manufactured by Toyo Baldwin at a peeling angle of 180 °, it is pulled at a pulling speed of 300 m / min, and the cleavage strength (kg / cm) at that time is obtained. The cleavage force (opening force) was used. When the cleavage force evaluated in this way is 1.6 to 2.8 kg / cm, the state in which both the sealing property and the easy cleavage property (easy opening property) are compatible is indicated by "○".
And other than that was marked as "x".

(3) Cleavage force after lapse of time Cleavage force after leaving for 3 months in an atmosphere of 50 ° C. is shown.

(4) Cleavage surface Use a surface roughness meter to measure the surface condition of the polyolefin film after cleaving at a natural angle by hand and at a natural speed (about 300 to 500 mm / min) without using a measuring machine. It was evaluated by obtaining the surface roughness (JIS
B0601 method, 0.8mm cutoff). Those with Ra = 3 μm or less were evaluated as smooth “◯”, those with Ra = 3 μm or more and less than 5 μm were evaluated as somewhat rough “Δ”, and those with Ra = 5 μm or more were evaluated as rough “x”.

(5) Resin temperature The resin temperature T ₁ was measured between the screw of the extruder and the perforated plate using a thermocouple / type IC type. For T _2, the polymer temperature immediately after being discharged from the mouthpiece (a location about 1 cm away from the mouthpiece) was measured using a radiation thermometer manufactured by Minolta Co., Ltd.

(6) Polymer Flow Rate Calculated from the discharge amount of polymer and the slit gap area of the T die.

[Examples] Examples 1 to 9 and Comparative Examples 1 to 7 As a polyolefin resin, a polypropylene resin (MI
= 2, 15, 20g / 10 minutes), a resin (MI = 2) obtained by graft-polymerizing 0.5 mol% maleic anhydride onto polypropylene, a polyethylene resin (MI = 4), and an ionomer of 60% ionization rate (MI = 0.7).

Polystyrene, polymethylmethacrylate, 4-methylpentene resin, polybutylene terephthalate and nylon 6 were selected as the resin (b) to be the island component, and these resins were dry blended in the ratios shown in Table 1 and Table 2, respectively. Afterwards, it has a T-die (slit gap: 0.5, 0.7, 1.0)
40mmφ extruder (L / D = 22, compression ratio = 40, with dull image)
And melt-extruded into a film having a thickness of 15 to 400 μm.

The thus obtained film of 15 to 400 µ was heat-sealed in a form sandwiched between the upper and lower sides of the 200 µ polypropylene or polyethylene NO film. Heat seal temperature 200
° C., sealing pressure 50 g / cm ^2, was sealed time 2-5 seconds. Cleavage force of the sample thus obtained before and after aging,
Also, the surface condition after peeling was determined, and the results are shown in Tables 1 and 2 together with the average dispersion diameter values A and B of the resin (b) and the film thickness.

As can be seen from Table 1, the film forming temperature T ₁ −T ₂ = 8 to 40 ° C., the linear velocity when passing through the lip was 61 to 154, and the film was formed in the draft ratio range of 3.3 to 12.5. Nos. 1 to 9 showed excellent cleavability with good opening after passage of time. Also pulling speed,
The cleaved surface of the cleaved surface after manually unsealing the tension angle was not constant, and the R value was 3.0 or less, and the smoothness was excellent. On the other hand, Comparative Examples 1 and 2 in which the island component resin was not mixed showed no cleavage. Comparative Example 3 with a small polystyrene blend amount, Comparative Example 6 with a large A value of 3.4 μ and Comparative Example 7 with no difference between A and B of 6 μ cannot be put to practical use because the cleavage force is too large. There was a lot of rough surface.

Comparative Example 4 with a large amount of polystyrene blend, A is 0.1μ
In Comparative Example 5 having an A / B value less than 0.05 (A / B value of 0.05 or less), the cleavage force was too low, so that the contents might leak, and further, the surface roughness after cleavage was extremely large due to a feathering defect.

[Brief description of drawings]

FIG. 1 is a TD sectional view of an easily cleavable film according to the present invention, and FIG. 2 is an MD sectional view of an easily cleavable film according to the present invention. In the figure, 1 is a resin (b) which is an island component, and 2 is a polyolefin resin which is a sea component.

Claims (1)

[Claims] 1. One or more kinds of resin (b) selected from styrene resin, methacrylic acid ester resin, methylpentene resin, saturated polyester resin and polyamide resin with respect to 100 parts by weight of polyolefin resin (a). 15 to 45
A film formed by mixing parts by weight, wherein the TD of the film
The average dispersion diameter of the resin (b) in the cross section continuously increases from the surface layer of at least one surface toward the center,
Also, the average dispersion diameter (Aμm) at a depth of at least 4 μm from the surface layer on one side and the average dispersion diameter (Bμm) at the film center ± 6 μm are 0.1 ≦ A ≦ 3 0.5 ≦ B ≦ 12 0.05 ≦ A / B ≦ 0.5. A cleavable film characterized by having a relationship.