JPH10138421A - Polypropylene based composite film and fusion cut plastic bag employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase fusing cut seal strength and improve appearance property by a method wherein a heat fusion bonding layer, consisting of propylene based resin having a melting point lower than that of a substrate layer, and a protective layer, consisting of propylene based resin having a melting point higher than that of the heat fusion bonding layer, are laminated sequentially on the substrate layer, consisting of biaxially oriented polypropylene film. SOLUTION: Polypropylene based composite films 10, 10a are formed by laminating heat fusion welding layers 22, 22a and protective layers 23, 23a sequentially on at least one side of the substrate layers 21, 21a. The substrate layers 21, 21a provide the composite film with desired strength and sealing property while are constituted of a biaxially oriented film consisting of a resin, whose principal constituent is polypropylene. The heat fusion welding layers 22, 22a provide the composite film with excellent fusing seal property and are constituted of the propylene based resin of propylene-ethylene copolymer and the like, having a melting point lower than that of the substrate layer. The protective layers 23, 23a are constituted of propylene based resin, having a melting point higher than that of the heat fusion welding layers 22, 22a and the resin, constituting the same, is preferably the same as the resin, constituting the substrate layers 21, 21a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene-based composite film and a plastic bag (sealed by fusing) using the same.

[0002]

2. Description of the Related Art Conventionally, a single-layer biaxially oriented polypropylene film or a heat-fusible composite biaxially oriented polypropylene having a propylene-ethylene-based copolymer resin laminated on its surface has been conventionally used for packaging foods, daily necessities, pharmaceuticals and the like. A bag formed by sealing by fusing using a film is widely used. In addition, the sealing by fusing is performed by sandwiching the stacked plastic films with a heat sealing device, cutting by melting, and melting the plastic film at the cut end surface to solidify into a lump, thereby fusing the plastic films to each other at the end surfaces. (Adhesion), which is different from heat sealing in which plastic films are fused to each other with a certain width.

[0003] However, these films have the following problems. That is, generally, a plastic film for packaging is subjected to a corona treatment in order to enhance the film surface characteristics such as antistatic properties, antifogging properties, slipperiness, and printability. However, when the corona-treated single-layer biaxially-stretched polypropylene film was formed into a bag by fusing, the fusing seal strength at the open end of the bag was blown using the single-layer biaxially-stretched polypropylene film before the corona treatment. There is a problem that it cannot be used for packaging heavy goods because it is significantly lower than bags.

Further, in the heat-fusible composite biaxially oriented polypropylene film, fusing sealability is sufficient by melting the heat-fusible layer, but the surface is made of a copolymer softer than polypropylene, so that scratches are not generated. Since it is easy to stick and wrinkles easily when the film is wound, there is a problem that the appearance is poor and the commercial value is reduced. Furthermore, when fusing, the heat-sealed layer on the surface of the film comes into direct contact with the heated heater, so that the molten and sticky resin adheres to the heater, There is a problem that workability cannot be said to be good, for example, the film cannot be removed from the heater cleanly.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a polypropylene-based composite film having high fusing seal strength and excellent appearance, and a fusing plastic bag. Things.

[0006]

Means for Solving the Problems A first aspect of the present invention is a heat-sealing layer made of a propylene-based resin having a lower melting point than the base layer, on at least one surface of a base layer made of a biaxially stretched film mainly composed of polypropylene. The present invention relates to a polypropylene-based composite film in which a protective layer made of a propylene-based resin having a higher melting point than the heat-sealing layer is laminated in this order.

A second invention provides a blown plastic bag in which an open end of a bag made of a plastic film is sealed by fusing, wherein the plastic film is provided on at least one surface of a base layer made of a biaxially stretched film mainly composed of polypropylene. Fusing characterized by comprising a polypropylene-based composite film in which a heat-fusion layer made of a propylene-based resin having a lower melting point than the base layer and a protective layer made of a propylene-based resin having a higher melting point than the heat-fusion layer are laminated in this order. Pertains to plastic bags.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a cross section of an example of a polypropylene-based composite film of the present invention, FIG. 2 is a partial perspective view showing an example of a blown plastic bag of the present invention, and FIG.

As shown in FIGS. 1A and 1B, the polypropylene composite films 10 and 10a of the present invention are:
At least one surface of the base layers 21 and 21 a
2a and a protective layer 23, 23a are sequentially laminated.

The base layers 21 and 21a are provided mainly for imparting desired strength and sealing properties to the polypropylene-based composite film, and are formed of a biaxially stretched film formed of a resin mainly composed of polypropylene. The resin mainly composed of polypropylene means a resin containing 50% by weight or more of polypropylene as a whole. As the resin material for the base layer, other resins, such as polypropylene, may be used as long as the characteristics required for the base layers 21 and 21a are not impaired, such as a higher melting point than the heat-fused layers 22 and 22a, strength and sealing properties. For example, a mixture of a resin such as a propylene-butene copolymer may be used, and further, an antistatic agent, an antifogging agent, an ultraviolet inhibitor, an antioxidant, a lubricant, an antibacterial agent for enhancing the functional effect of the film may be used. And other well-known additives.

The heat-sealing layers 22 and 22a are for imparting good fusing sealing properties to the polypropylene-based composite film, and are made of a propylene-based resin having a lower melting point than the base layers 21 and 21a. As the resin constituting the heat-sealing layers 22, 22a, a propylene-ethylene copolymer, a polypropylene-butene copolymer, or polyethylene, polybutene, and a mixture of these with polypropylene are preferable. This is because the base layers 21 and 21a and the heat fusion layer 2
This is because, by using the same type of resin having compatibility with 2,2a, when the heat-sealing layers 22,22a are extruded onto the base layers 21,21a, the two layers can be integrated well. The heat-sealing layers 22 and 22a correspond to the base layer 2
It is sufficient that the melting point is lower than that of the base layers 21 and 21a. Various additives may be blended into the heat-sealing layers 22 and 22a as in the case of the base layers 21 and 21a.

The protective layers 23 and 23a are used to increase the surface strength and gloss and transparency of the polypropylene-based composite film.
It is made of a propylene resin having a higher melting point than 22a. As the resin forming the protective layers 23 and 23a, a resin mainly composed of polypropylene having a higher melting point than the heat-sealing layers 22 and 22a is preferable. Also, the protective layers 23, 23a
Is particularly preferably a mixture of the same resin or the same composition as the resin constituting the base layers 21 and 21a, and may further contain various additives. Especially,
When all the layers are made of the same resin, the compatibility of the layers in contact with each other can be enhanced, and the integration of all the layers can be performed well when the respective layers are laminated by extrusion.

The protective layers 23 and 23a are made of a heat-sealing layer 2
The melting point is preferably higher than that of the base layers 21 and 21a by 10 ° C. or more. Since the plastic film has a property of increasing in strength as its melting point is higher, the protective layers 23, 23a having a higher melting point than the heat-fusible layers 22, 22a are combined with the heat-fusible layers 22, 22a.
By providing the film on the film, the strength of the film surface is increased, and scratches and wrinkles can be prevented.

Further, at the time of fusing and sealing performed by stacking the polypropylene composite films, the protective layers 23, 2 having a high melting point are used.
Since 3a comes into contact with the heater (the base layer 21 may come into contact with the heater in the case of the three-layered polypropylene composite film 10), the resin does not easily adhere to the heater, and the fusing operation is impaired. There is no. In addition, at the time of the fusing sealing, the heat fusion layers 22, 22a are melted and solidified at the fusion end face of the polypropylene-based composite film to strengthen the fusion (adhesion) of the film, so that the fusion (adhesion) is protected. There is no risk of being hindered by the layers 23 and 23a, and good fusing seal strength can be obtained.
Further, even if corona treatment is performed on the surface of the polypropylene-based composite film of the present invention, that is, the surfaces of the protective layers 23 and 23a and the base layer 21, the heat-sealing layers 22 and 22a covered by the protective layers 23 and 23a and the base layer 21. Is hardly affected by the corona treatment, and there is almost no possibility that the fusing property is impaired.

The thickness of each layer is not particularly limited, but is not less than 8 μm for the base layers 21 and 21 a, 0.3 μm to 20 μm for the heat sealing layers 22 and 22 a, and 0.3 μm for the protection layers 23 and 23 a. It is preferable that the thickness of the heat sealing layers 22 and 22a and the thickness of the protective layers 23 and 23a do not exceed the thickness of the base layers 21 and 21a. If necessary, the surface functions of the film can be enhanced by subjecting the protective layers 23 and 23a to the above-mentioned corona treatment, flame treatment, plasma treatment and the like.

The polypropylene-based composite film of the present invention having the above-described structure is manufactured as follows. The resin material for each layer is guided to an extruder, kneaded, and extruded to form a three-layer composite sheet. This is stretched in the vertical and horizontal directions to form a base layer 21, a heat-sealing layer 22, a protective layer 23
To obtain a three-layer biaxially stretched polypropylene-based composite film of 10 to 100 μm. Then, a corona treatment, a flame treatment, a plasma treatment, or the like is performed on the protective layer 23 on the film surface as necessary.

In addition, depending on the film application and thickness, etc.,
First, the base layer 21 is extruded and stretched in a uniaxial direction. Then, the heat-sealing layer 22 and the protective layer 23 are extruded and laminated on the base layer, and the three layers are stretched in a direction orthogonal to the stretching. Biaxially stretched film, other layers 22, 2
3 may be a uniaxially stretched film. Further, the heat-sealing layers 22a, 22a and the protective layers 23a, 23a may be laminated on both sides of the base layer 21a by an extruder and stretched to form a five-layer polypropylene-based composite film.
Of course, the polypropylene-based composite film of the present invention may be formed by other known methods.

FIG. 2 shows a part of a blown plastic bag 11 using the polypropylene composite film of the present invention, and FIG. 3 shows an enlarged cross section of the part. This blown plastic bag 11 is shown in FIG.
(A) Three-layer polypropylene composite film 1 shown in (A)
No. 0 is formed in an envelope shape such that the protective layer 23 is on the inside, and the overlapping open end portions 12a, 12a are fused and sealed. This blown plastic bag 11
Are heat-sealed layers 22 at the blown open end 12.
Is melted, and the overlapping end portions 12a, 12a are fused and solidified to securely seal. In this example using the three-layered polypropylene-based composite film 10, the heat-sealing layers 22, 22 may be in direct contact with each other, or may be damaged by contact with a product in a bag.
Alternatively, the protective layers 23, 23 are placed on the inner side of the bag,
1, 21 are outside the bag. In addition, depending on the application and the like, the blown plastic bag is composed of the five-layered polypropylene-based composite film 10a shown in FIG. 1B, and is blown and sealed at the heat-sealing layers 22a at the opening ends. Further, in this case, the inner and outer surfaces of the blown plastic bag are constituted by the protective layer 23a.

Since the outer surface of the blown plastic bag 11 is composed of the base layer 21 (the protective layer 23a in the case of using a five-layered polypropylene composite film), the plastic bag 11 is hardly damaged, and is excellent in gloss and transparency. . Further, even when a corona-treated polypropylene composite film is used as the film constituting the blown plastic bag, the heat is located inside the base layer 21 and the protective layer 23 and is not directly affected by the corona treatment. Since the fusion is strengthened by the fusion layer 22, the sealing strength of the open end 12 is sufficient. Therefore, it is suitable for packaging various foods, daily necessities, medical products, and the like, and also suitable for packaging heavy objects because the opening end 12 has a sufficient sealing property. Furthermore, it can be used for packaging of fruits and vegetables, and if necessary, 0.3 mm
By providing a small hole of about 20 mm in the range of about 0.03 to 3% of the total area of the bag, a freshness maintaining effect can be obtained in addition to the display effect of the product.

[0020]

EXAMPLES Hereinafter, specific examples of the present invention and comparative examples for confirming the effects thereof will be described. The physical properties of the examples and comparative examples were measured by the following methods, and the results are shown in Tables 1 to 3.

(1) Melting point (unit: ° C.) Using a differential scanning calorimeter DSC8230 manufactured by Rigaku Denki, 5 mg of a sample was once melted at 200 ° C. under a nitrogen stream, and then melted.
After cooling to 40 ° C at 40 ° C / min and solidifying, 10 ° C
In the DSC curve (melting endothermic curve) obtained by raising the temperature at / min, the peak temperature was defined as the melting point.

(2) Heat sealability (unit: ° C.) Films are superimposed on each other, and H-manufactured by Toyo Seiki Seisaku-sho, Ltd.
4 kg for 1 second using a G-2001 type heat sealer
/ Cm ² , and a peeling speed of 200 m using UTM-4-100 manufactured by Toyo Baldwin Co., Ltd.
The sample was pulled under the condition of / min, and the temperature at which the peel resistance was 300 g at a sample width of 15 mm was measured.

(3) Fusing (seal) strength (unit: kg /
15 mm) Using a PP400 type fusing bag making machine manufactured by Kyoei Printing Machinery Co., Ltd., making a bag at 350 ° C. and 80 shots / min, cutting off the fusing seal portion with a width of 15 mm, and measuring the adhesive strength by using the Toyo Baldwin Co., Ltd. 200m with UTM-4-100
/ Min.

(4) Transparency (unit:%) The haze was measured with an NDH-20D haze meter manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS-K-7105.

(5) Gloss (unit:%) JI was measured using a UGV-4D type gloss meter manufactured by Suga Test Instruments Co., Ltd.
The gloss of the film surface was measured according to SK-7105.

(6) Scratch resistance (unit:%) A haze difference before and after a 30 cm friction was measured under a load of 3 kg / cm ² using a dynamic friction tester manufactured by Toyo Tester Industry Co., Ltd.

(7) Anti-fog property 150 cc of 70 ° C. hot water is poured into a 200 cc beaker,
Immediately, the beaker was covered with a film, and the degree of haze of the film was visually observed.

(8) Appearance The see-through feeling of one film was visually observed. (9) Hot Slip Using Strograph P, the slipperiness with a stainless steel plate heated to 70 ° C. was measured in accordance with JIS-K-7125.

(10) Blocking resistance 20 films of 30 cm × 21 cm in size are stacked,
Applying a load of 60 kg to 20 cm x 20 cm, 50
After 24 hours, the degree of adhesion of the film was evaluated.

First, an example will be described in which five layers are formed and all the layers are stretched biaxially in the vertical and horizontal directions. [Example 1] A blend of polypropylene having a melting point of 160 ° C and 1% of an amine-based antistatic agent added thereto as a base layer raw material,
Ethylene-propylene copolymer having a melting point of 130 ° C. as a raw material for a heat-sealing layer, and 160 ° C. as a raw material for a protective layer
Particle size of 1.8 as a anti-blocking agent on polypropylene
A formulation containing 0.2% of silica was used. Then, these are extruded from a five-layer T-die consisting of three types, a protective layer, a heat-sealing layer, and a base layer. Thereafter, the film is stretched in the vertical and horizontal directions, and the thickness configuration is 0.6 μ / 1.3 μ / 21.2 μ / 1.3 μ in the order of the protective layer / heat-fused layer / base layer / heat-fused layer / protective layer.
/0.6μ polypropylene composite film was obtained. Further, the protective layers on both surfaces of the film were subjected to corona treatment, and then the film was wound up. The winding state at this time was good without wrinkles. Tables 1 and 2 show the measurement results of the physical properties of the obtained film.

[Comparative Example 1] As a base layer raw material, the melting point was 16
1% amine antistatic agent in polypropylene at 0 ° C,
A formulation to which 0.2% silica having a particle size of 1.8 μm was added was used. After the base layer material was extruded from a T-die and biaxially stretched, both surfaces were subjected to corona treatment to obtain a single-layer biaxially stretched polypropylene film of 25 μm. Tables 1 and 2 show the measurement results of the physical properties of the obtained film.

Comparative Example 2 The composition described in Example 1 was used as a raw material for a base layer, and 0.2% silica having a particle size of 1.8 μm was added to the raw material described in Example 1 as a raw material for a heat sealing layer. % Added formulation was used. This was extruded from a three-layer T-die consisting of three types of base layer and heat fusion layer, and then stretched in the vertical and horizontal directions. The thickness was 2 μ / 21 μ in the order of heat fusion layer / base layer / heat fusion layer. / 2μ of a heat-fusible composite biaxially oriented polypropylene film was obtained. Further, after the corona treatment was applied to both surfaces of the heat-sealing layer of the film, the film was wound up. Tables 1 and 2 show the measurement results of the physical properties of the obtained film.

Example 2 The procedure of Example 1 was repeated, except that the corona treatment was not performed.
A polypropylene-based composite film stacked in the order of the heat sealing layer / protective layer was obtained. Table 2 shows the measurement results of the physical properties of the obtained film.

Comparative Example 3 A single-layer polypropylene film consisting of only a base layer was obtained in the same manner as in Comparative Example 1 except that the corona treatment was not performed. Table 2 shows the measurement results of the physical properties of the obtained film.

Comparative Example 4 A heat-fusible composite biaxially oriented polypropylene film loaded in the order of heat-fusible layer / base layer / heat-fusible layer in the same manner as in Comparative Example 2 except that no corona treatment was performed. I got Table 2 shows the measurement results of the physical properties of the obtained film.

[0036]

[Table 1]

[0037]

[Table 2]

As apparent from the above measurement results, the polypropylene composite film having a five-layer structure shown in Example 1 had heat sealability, slipperiness (hot slip), scratch resistance (scratch resistance), and adhesion. Various physical properties required for a film for a plastic bag, such as difficulty (blocking resistance), transparency, gloss, appearance, and resistance to wrinkling during winding, were good. Further, the corona-treated embodiment 1 has significantly higher fusing seal strength than that of the corona-treated comparative example. Can be

Next, there will be described an embodiment in which only the base layer is formed of five layers and the other layer is biaxially stretched, and the other layers are uniaxially stretched. [Example 3] A blend of polypropylene having a melting point of 160 ° C and 1% of an amine-based antistatic agent added as a raw material for a base layer,
Ethylene-propylene copolymer having a melting point of 130 ° C. as a raw material for a heat-sealing layer, and 160 ° C. as a raw material for a protective layer
What blended 0.2% of silica having a particle size of 1.8 μm to polypropylene was used. Then, the raw material for the base layer was guided to an extruder and extruded from a T-die to form a 650 μ sheet, which was stretched 5 times in the machine direction. On the other hand, the raw material for the heat-sealing layer and the raw material for the protective layer are guided to a two-type and two-layer extruder, and are extruded above and below the base layer so that the heat-fused layer / protective layer becomes 10 μ / 5 μm, respectively. After integrating the five layers of the fusion layer / base layer / heat fusion layer / protective layer, it was laterally stretched eight times. The resulting polypropylene-based composite film has a protective layer / heat-sealing layer /
0.6μ / 1.3μ / 1 in the order of base layer / heat fusion layer / protective layer
6.3μ / 1.3μ / 0.6μ. Further, both sides of the film were subjected to corona treatment, and the film was wound up. Table 3 shows the measurement results of the physical properties of the obtained film.

Example 4 When laminating the heat-sealing layer and the protective layer on the stretched base layer, the heat-sealing layer / protective layer was 10 μ /
Except for extruding to 8 μm, the procedure was the same as in Example 3. The thickness composition of the obtained polypropylene-based composite film was 1.0 μ / 1.3 μ / 16.3 μ / 1.3 μ / 1.3 μm in the order of protective layer / heat-fused layer / base layer / heat-fused layer / protective layer.
It was 0μ. Table 3 shows the measurement results of the physical properties of the obtained film.

Example 5 When laminating a heat-sealing layer and a protective layer on a vertically stretched base layer, the heat-sealing layer / protective layer was 15 μm.
The same procedure as in Example 3 was carried out except that the resin was extruded so as to be / 5 μ. The resulting polypropylene composite film is
The thickness configuration is 0.6 μ / 1.9 μ / 16.3 μ / 1.9 μ / in the order of protective layer / heat-fused layer / base layer / heat-fused layer / protective layer.
0.6μ. Table 3 shows the measurement results of the physical properties of the obtained film.

Example 6 The raw material mixture described in Example 3 was extruded from a three-type three-layer T-die and stretched, so that the protective layer / heat-fused layer / base layer had a thickness of 1.0 μm.
/1.3μ/17.7μ to obtain a three-layer biaxially stretched polypropylene composite film. Then, the protective layer on the film surface was subjected to corona treatment and wound up. Table 3 shows the measurement results of the physical properties of the obtained film.

[0043]

[Table 3]

As is clear from the measurement results in Table 3, in Examples 3 to 5 in which only the base layer was biaxially stretched and the other layers were uniaxially stretched, not only wrinkles did not occur at the time of winding, but also
It can be seen that it exhibits excellent fusing sealability. Also in Example 6, the fusing seal strength is higher than the fusing seal strength of Comparative Examples 1 and 2 which have been subjected to corona treatment, and is suitable for fusing and bag making.

[0045]

As shown and described above, the polypropylene-based composite film of the present invention comprises a propylene-based resin having a melting point lower than that of the base layer on at least one surface of a base layer composed of a biaxially stretched film mainly composed of polypropylene. Since the heat-fused layer and the protective layer made of a propylene-based resin having a higher melting point than the heat-fused layer are laminated in this order, not only is the surface hardly damaged by the presence of the protective layer, and the appearance is good, Wrinkles are less likely to occur during winding, and even if corona treatment is applied, the heat-sealing layer inside the protective layer is hardly affected, and exhibits excellent fusing seal strength. Therefore, the polypropylene-based composite film of the present invention is suitable for blown plastic bags, and also suitable for packaging heavy objects.

Further, the plastic bag made by fusing of the present invention uses the polypropylene composite film having excellent fusing seal strength as described above, so that the sealing strength at the open end is high and is suitable for packaging heavy objects. Moreover, in this blown plastic bag, the polypropylene-based composite film constituting the bag is hardly damaged on the surface as described above,
Since wrinkles are less likely to occur and the appearance such as transparency is also excellent, a high display effect can be obtained without impairing the commercial value of the contents.

[Brief description of the drawings]

FIG. 1 is a sectional view of a polypropylene-based composite film according to the present invention.

FIG. 2 is a partial perspective view of one example of a blown plastic bag using the polypropylene-based composite film of the present invention.

FIG. 3 is an enlarged sectional view of a portion A in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Polypropylene-based composite film 11 Fused plastic bag 12 Open end 21 Base layer 22 Thermal fusion layer 23 Protective layer

Claims (2)

[Claims] 1. A heat-sealing layer made of a propylene-based resin having a lower melting point than the base layer, and a propylene-based resin having a higher melting point than the heat-sealing layer on at least one surface of a base layer made of a biaxially stretched film mainly composed of polypropylene. A polypropylene composite film obtained by laminating a protective layer made of a resin in this order. 2. A blown plastic bag in which an open end of a bag made of a plastic film is sealed by fusing, wherein the plastic film is lower than at least one surface of a base layer made of a biaxially stretched film mainly composed of polypropylene. A blown plastic bag comprising a polypropylene composite film in which a heat fusion layer made of a propylene resin having a melting point and a protective layer made of a propylene resin having a higher melting point than the heat fusion layer are laminated in this order.