JPH07246687A - Composite biaxially stretched polypropylene based film having excellent adhesiveness - Google Patents

Abstract

PURPOSE:To obtain a composite biaxially stretched polypropylene based film improved in adhesiveness based and generating no edge cutting by laminating a propylene based copolymer containing olefin other than propylene to the single surface of a polypropylene resin and coating the formed coating layer with a coating agent containing chlorinated polyolefin. CONSTITUTION:A coating layer composed of a heat-sealable resin based on a propylene based copolymer containing 1mol% or more of alpha-olefin other than propylene or ethylene is laminated to the single surface of a base layer composed of a biaxially stretched film based on a polypropylene resin and at least the single surface of the coating layer is entirely or partially coated with a coating agent containing chlorinated polyolefin. The coating agent to be used is dissolved or suspended in an org. solvent and, as chlorinated polyolefin, chlorinated polyethylene, chlorinated polypropylene or a chlorinated ethylene/vinyl acetate copolymer with a chlorination degree of 3-70% is designated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packaging bag for products, and more particularly to a composite biaxially oriented polypropylene film which is excellent in adhesiveness and has no edge breakage, and a packaging bag using this film.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene film has excellent mechanical strength, transparency, water vapor barrier property, glossiness, chemical resistance and the like as a packaging material. Normal heat sealing is difficult because it shrinks due to heating for sealing. Therefore, in order to impart heat-sealing property, there has been a technique in which an easily heat-sealing resin is laminated on a biaxially oriented polypropylene film, or at least a part of the polypropylene film is coated with an adhesive resin composition. For applications requiring heat-sealing strength, or for use in winter at low temperatures, use a packaging material in which biaxially oriented polypropylene (OPP) and unoriented polypropylene (CPP) are laminated with an adhesive, and these materials. There was a technology of making bags and making them into packaging bags.

[0003]

Among the conventional techniques, a packaging material obtained by laminating biaxially stretched polypropylene and unstretched polypropylene has a high manufacturing cost, and an easily heat-sealing resin is laminated to improve the drawback. There was a way. However, when a bag is made using a heat-sealable resin-laminated biaxially stretched film by this laminating method, the bag has sealing strength, but when the bag is opened, edge breakage occurs in the sealed portion of the bag, and the bag is easily broken. There was a drawback.
Incidentally, the edge breakage, when peeling the heat-sealed portion for opening, the whole area that is heat-sealed is not smoothly peeled in the direction in which force is applied, and in the middle of peeling, the heat-sealed portion of the film , The phenomenon of tearing at the end on the stressed side. Even if the thickness of the coating layer of the heat-sealable resin is increased in order to improve the heat-sealing strength, the edge breakage at the time of unsealing still occurs.

Such edge breakage occurs because the interlayer adhesion strength between the heat-sealing layer and the base layer is strong, and the biaxially oriented polypropylene film serving as the base layer has a plane orientation and is rigid. The reason is that the heat-sealing layer is destroyed at the time of performing to the base layer portion, and the base layer film is broken while being cleaved.

On the other hand, when heat-sealing property is imparted by coating a part of the biaxially oriented polypropylene film with a coating agent (hereinafter referred to as "part coat method").
The adhesive strength between the polypropylene film as the base layer and the coating agent was not sufficient, so that the heat seal strength was as low as 300 to 400 g / 15 mm width. In order to improve the adhesion between the biaxially stretched polypropylene film and the coating agent, there may be a means for increasing the surface activity of the biaxially stretched polypropylene film by corona discharge treatment. The result was that the heat-sealing strength was decreased on the contrary. As described above, in the case of using the part coat method, edge breakage does not occur at the time of opening like in the case of bag making using the heat-sealable resin laminated biaxially stretched film, but the heat seal strength is low,
In addition to the need to limit the size of the packaging bag and the weight of the contents, at low temperatures in winter, the resin in the adhesive layer of the coating agent hardens and the interlaminar strength deteriorates, which has the drawback of poor cold resistance. It was

Therefore, there has been a demand for a biaxially oriented polypropylene film which has higher heat seal strength than the conventional part coat method and does not cause edge breakage, and a packaging bag made of the biaxially oriented polypropylene film.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and an α-olefin other than propylene or ethylene other than propylene is provided on at least one surface of a base layer composed of a biaxially stretched film mainly containing polypropylene resin. 1
A composite 2 comprising a coating layer mainly composed of a propylene-based copolymer containing at least mol% and a coating agent containing a chlorinated polyolefin applied to all or part of at least one side of the coating layer. A packaging bag comprising an axially stretched film and such a composite biaxially stretched film.

[0008]

[Operation] The conventional part coat method is inferior in heat seal strength to the method of laminating heat sealable resin.
Since it is a simple method of coating a coating agent on a biaxially stretched polypropylene film as an adherend, the adhesiveness between the coating agent and the polypropylene film does not have sufficient strength. Therefore, when this is heat-sealed. The heat seal strength of the heat seal part of
Caused by not being enough. The present invention is
By providing a coating layer mainly composed of a heat-sealable resin between a base layer mainly composed of a biaxially oriented polypropylene film and the coating agent, and using this as a means for strengthening the adhesion between the base layer and the coating agent, a coating agent The adhesion of the base layer is enhanced. As a result, the adhesiveness of the heat-sealed portion when heat-sealed becomes higher than that when simply coated with a coating agent.

On the other hand, the adhesive effect of the heat-sealing portion of the present invention is caused by the coated coating agent. However, in order to increase the interlaminar strength between the polypropylene film and the coating agent, the coating effect is higher than that of polypropylene alone. The adhesive layer has a strong adhesive strength to the agent and is difficult to cleave, and is provided as a coating layer mainly containing propylene-based copolymerizability containing α-olefin other than propylene or ethylene in an amount of 1 mol% or more, and having a cohesive force higher than that of the composite film. By coating the weakest coating agent on the innermost layer of the heat-sealing layer, the destruction site when peeling off the heat-sealing section causes cohesive failure inside the coating layer and the coating agent, so-called edge breakage occurs. And a packaging bag with improved heat seal strength.

That is, by providing the coating layer, the interlaminar strength between the base layer film and the coating agent is strengthened, and the destruction at the time of opening the heat-sealed portion is
The coating agent and the coating layer do not reach the base layer portion, and in particular, the coating layer has no orientation in the constituent molecules, is flexible, and disperses the force, so that so-called edge cutting does not occur in the base layer portion.

[0011]

EXAMPLES The composition of the biaxially stretched film which is the base layer mainly composed of polypropylene in the present invention includes polypropylene homopolymer, a copolymer mainly composed of propylene and α-olefin, or a mixture thereof. However, the total amount of propylene in these polypropylene resins is 9
It is preferably 8 mol% or more from the viewpoint of dimensional stability and heat resistance of the film.

The coating layer in the present invention contains a polypropylene-based copolymer as a main component, and the polypropylene-based copolymer means a propylene / ethylene copolymer, a propylene / butene-1 copolymer, a propylene / propylene copolymer. ethylene·
Examples thereof include butene-1 copolymer and propylene / hexene-1 copolymer. However, these are preferably random copolymers from the viewpoint of transparency and stability of adhesive strength. It is essential that the content of the α-olefin component other than propylene in these copolymers is 1 mol% or more. This is because if it is less than 1 mol%, sufficient adhesive strength cannot be obtained. The upper limit of the α-olefin content is not particularly limited, but is preferably 15 mol% or less from the viewpoint of hardness of the film surface and solvent resistance.

The base layer used in the present invention and the coating layer to be laminated are heat stabilizers such as calcium stearate, phenolic antioxidants, antistatic agents such as monoglycerides and alkyl jetanol amines, antifogging agents, Additives such as organic lubricants, inorganic lubricants, anti-UV agents, weathering stabilizers, nucleating agents, and resin components other than propylene such as petroleum resin, rosin, polyethylene, ethylene propylene rubber, ethylene butene rubber, etc. It can be added within a range that does not impair the properties of the biaxially stretched film.

Such a propylene homopolymer, a silica-based inorganic lubricant, monoglyceride as an antistatic agent,
A raw material containing calcium stearate as a phenolic antioxidant and a heat stabilizer is introduced into the extruder for the base layer, and an ethylene / propylene copolymer having an ethylene content of 3.5 mol% is added to the silica-based inorganic lubricant and organic lubricant. Lead the raw material with erucic acid amide, heat stabilizer calcium stearate, and phenolic antioxidant to the extruder for coating layer,
Simultaneously extruding and stretching in the vertical and horizontal directions, a composite biaxially oriented polypropylene film having a base layer thickness of 49 μm and a coating layer thickness of 1 μm is obtained.

The thickness of the coating layer is required to be 2 μm or more in order to obtain the minimum heat sealing strength in the conventional method of laminating the heat sealable resin. Since the layer is used to improve the adhesive strength between the biaxially stretched polypropylene film which is the base layer, the coating agent and the layer, even if it is 2 μm or less, a minimum of 0.3 μm or more is sufficient. If the thickness is less than 0.3 μm, a uniform layer cannot be formed and the desired effect is not sufficiently produced. As described above, the thickness of the base layer and the coating layer of the present invention is not particularly limited, but the thickness of the base layer is 5 to 100.
μm is preferred. The thickness of the coating layer is 0.3 μm to 2
A thickness of μm is preferred.

The method of laminating the coating layer in the present invention is as follows.
It is not particularly limited. For example, a method of laminating the raw material for the base layer and the raw material for the coating layer in an extrusion die, a melt laminating method on a sheet before stretching the base layer, a melt laminating method during stretching of the base layer, and the like can be mentioned. A binder layer may exist between the base layer and the coating layer.

The coating agent used in the present invention is prepared by dissolving or suspending a commonly used chlorinated polyolefin in an organic solvent. As the chlorinated polyolefin, chlorinated polyethylene or chlorinated polypropylene having a chlorination degree of 3 to 70% is used. Examples thereof include, but are not limited to, chlorinated ethylene / vinyl acetate copolymers. In addition, a mixture of these chlorinated polyolefins with a resin such as ethylene or various additives can be used as a coating agent.

As an example, among those commercially available as chlorinated polypropylene, the chlorine content is 20.5 ± 1.
%, Viscosity 200-500 cps (20% toluene solution), and solid content 20 ± 1% are directly coated on the innermost layer of the coating layer, or an appropriate amount of an organic solvent such as toluene is used depending on the conditions of the coating device and temperature. Diluted to 1
The innermost layer of the coating layer is coated as a 0% toluene solution. In this example, chlorinated polypropylene having a chlorination degree of 21% was used.

The coating amount of this coating agent is not particularly limited, but is preferably ² to 6 g / m ² . In this example, the above-mentioned composite biaxially stretched film had a chlorination degree of 2
1% chlorinated polypropylene was coated with a gravure coater so that the coating amount was 4 g / m ² .

The composite 2 of the present invention obtained as described above
A packaging bag heat-bonded with a heat sealer using an axially stretched polypropylene film to make a bag, and a composite biaxially stretched polypropylene film that does not apply a coating agent, which has been used in the past, was heat bonded with a heat sealer to make a bag. A packaging bag (comparative example-1) and a monolayer biaxially oriented polypropylene film coated with the same amount of the coating agent as in the example were heat-bonded with a heat sealer to form a bag (comparative example- The results of the peeling test and vibration resistance test of each heat-sealed part in 2) are as follows.

[0021]

[Table 1]

Heat seal strength: 140 ° C., 1 second, 2 kg / using a heat sealer manufactured by Tester Sangyo Co., Ltd.
Heat-sealed under the condition of cm ^{2, and} the width of the sealing portion is 16 cm,
Cut a 15 mm wide test piece from a sample with a seal length of 15 mm and use a TENSILON type tensile tester to make 20
It was measured at a tensile speed of 0 mm / min and an inter-chaak distance of 60 mm. Peeling length: When the length of the heat-sealing portion is 15 mm, the longest peeling length is obtained when the distance between the sample holders when peeling the heat-sealing portion is increased by 30 mm from the initial length. Edge break: When measuring the heat-sealing strength, before the peeling of the entire surface of the sealed part was completed, it was cut from the peeling side of the seal part and it became impossible to continue the measurement. . Peeling energy: The peeling energy is defined as the area of the peeling test chart when the vertical axis is the heat seal strength (g) and the horizontal axis is the length (mm) of the sample holder spacing (however, when the sample is set). .. Impact strength: Similar to the heat seal strength measurement sample,
A sample having a seal portion width of 16 cm and a seal portion length of 10 mm was prepared, and the impact strength of the heat seal portion of this sample was measured at a temperature of 23 ° C. and 5 ° C. using a dirt impact tester manufactured by Toyo Seiki Seisakusho.

[0023]

[Table 2]

Vibration resistance and bag breaking resistance: ambient temperature (ambient temperature) 1
At 5 ° C, one bag weighs 5.5g and has a diameter of 1c
A total of 82.5 g of 15 metal balls of m were filled, the bag was set in an automatic vibrometer, and the metal balls were repeatedly collided with the heat-sealed portion, and the number of times until they burst was measured.

According to the result of the experiment (A) in Table 1 above, the maximum heat seal strength (g / 15 mm) of the example of the present invention was obtained.
Is 625, while the one coated with the coating agent is 370, the mere laminated film is 55.
7, the heat-sealing strength is superior to that of the conventional one in terms of step-expanding, and the laminated film having a simple peeling length has edge breakage at 12 mm.
In the example of the present invention, the longest peeling distance of 30 mm was achieved without cutting edges, and the energy required for breaking was greatly improved. It is also clear that the impact strength is higher than that of the conventional one even at low temperature.

Next, according to the results of the experiment (B) in Table 2 above, the examples of the present invention show significantly better vibration resistance than the comparative examples 1 and 2.

[0027]

Since the present invention is constructed as described above, it has the following effects. Heat seal strength is better than conventional single-layer polypropylene film coated with coating agent,
The peeling energy is greatly improved, and the heat sealing strength at low temperature is also improved. As a result, the packaging bag using these is greatly relaxed in the weight limitation of the contents. That is,
Even if the size of the packaging bag is the same as before, the heat sealing strength has been remarkably improved, making it possible to increase the filling amount of the contents, and as a result, it is possible to pack the same amount of articles. It is possible to save the number of required bags. This also reduces the amount of plastic film that becomes waste when used. Further, by eliminating the edge breakage seen in the packaging bag by the simple lamination method, it is possible to prevent the contents from jumping out at the time of opening. Further, since the vibration-breaking resistance is greatly improved, soybeans can be filled, which is a remarkable effect.

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Claims (2)

[Claims] 1. A coating layer mainly composed of a propylene-based copolymer containing 1 mol% or more of α-olefin other than propylene or ethylene on at least one surface of a base layer composed of a biaxially stretched film mainly composed of polypropylene resin. And a coating agent containing a chlorinated polyolefin is applied to all or a part of at least one surface of the coating layer, the composite biaxially stretched film. 2. A coating layer mainly composed of a propylene-based copolymer containing 1 mol% or more of α-olefin other than propylene or ethylene on at least one surface of a base layer composed of a biaxially stretched film mainly composed of polypropylene resin. A packaging bag made of a composite biaxially stretched film obtained by coating a coating agent containing a chlorinated polyolefin on all or a part of at least one surface of the coating layer.