JP2002210899A - Multi-layer polyolefin film and package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer polyolefin film which is excellent in low temperature heat-seal properties during packaging and in easy openability of a heat seal part and suitable for packaging, and a multi-layer polyolefin film which is excellent in low temperature heat fusion properties and easy openability without causing the lowering of fusion strength of the melt cutting seal part and gazette seal part of a bag for twist packaging. SOLUTION: The multi-layer polyolefin film excellent in low temperature heat-fusion properties and easy openability is composed of a heat fusion layer which can be obtained from 20-80 wt.% of a propylene.α-olefin random copolymer (A) 120-150 deg.C in melting point and 80-20 wt.% of a composition comprising polybutene (B) containing 5-50 wt.% of linear low density polyethylene (D), and the linear low density polyethylene (D); and a polypropylene (C) layer. In a multi-layer polyolefin film package, the contents of the multi-layer film are enclosed, and the upper or lower part of the twist part of the package is heat-fused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene multilayer film excellent in low-temperature heat-sealing property and easy-opening property, particularly suitable for bread packaging, and a package using the same.

[0002]

2. Description of the Related Art A single-layer or multi-layer film of unstretched polypropylene provided with a heat-sealing layer such as polyethylene, ethylene / vinyl acetate copolymer or propylene / α-olefin random copolymer has transparency, gloss, It is excellent in rigidity and the like, and is widely used as a packaging material for foods such as confectionery, bread, vegetables and the like, or clothing in all fields such as shirts, pants and underwear, as well as daily necessities. In recent years, as the performance required for such packaging films, in particular, heat sealability at low temperatures accompanying the speeding-up of actual packaging lines, low-temperature heat sealability suitable for packaging chocolate products which are easy to melt at warm temperatures, or an aging society (barrier) Free) is required. On the other hand, twisted packaging, which is frequently used for bread packaging, has a risk that dust or insects may fall into the upper part of the twist when transported or displayed on shelves at convenience stores or supermarkets due to its structure. Therefore, a package in which the upper or lower portion of the twist is heat-sealed has been developed.

However, conventionally used single-layer or multi-layer films of unstretched polypropylene lack a balance between low-temperature heat sealability and easy-openability.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a polypropylene multilayer film which is excellent in low-temperature heat sealability at the time of packaging, and which is excellent in easy-openability of a heat-sealed portion, and which is suitable for packaging. It is an object of the present invention to obtain a polypropylene multilayer film for packaging excellent in low-temperature heat-sealing property and easy-opening property without lowering the fusion strength of a fusing seal part and a gusset seal part of a bag-made product.

[0005]

[Means for Solving the Problems]

SUMMARY OF THE INVENTION That is, the present invention has a melting point of 120 to 15.
Butene polymer (B) containing 20 to 80% by weight of propylene / α-olefin random copolymer (A) and 5 to 50% by weight of linear low density polyethylene (D) at 0 ° C. and linear low density polyethylene (D) and a propylene polymer (C) layer obtainable from a composition of 80 to 20% by weight with the composition (D), and has excellent low-temperature heat sealability and easy-openability. For packaging, in particular, a polypropylene multilayer film suitable for bread packaging, and further a polypropylene multilayer film in which a substrate layer is laminated, and an article to be packaged is enclosed in the polypropylene multilayer film, and the upper portion of the twisted portion of the polypropylene multilayer film package or The present invention relates to a package formed by heat-sealing the lower part.

[0006]

DETAILED DESCRIPTION OF THE INVENTION Propylene / α-olefin run
Dam copolymer (A) The propylene / α-olefin random copolymer (A) according to the present invention has a melting point in the range of 120 to 150 ° C, preferably 125 to 147 ° C. The propylene / α-olefin random copolymer (A) having such a range generally has a propylene content of 98 to 86% by weight, preferably 96 to 88% by weight. The α-olefin copolymerized with propylene is an α-olefin having 2 to 10 carbon atoms, such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. Among them, ethylene content is 0.5 to 8% by weight, preferably 1 to 6% by weight, 1-butene is 0.5 to 10% by weight, preferably 1 to 1%.
Up to 8% by weight of a random copolymer is preferred because it has a good balance of low-temperature heat-sealing properties, easy-openability, and blocking resistance.

The propylene / α-olefin random copolymer (A) has a melt flow rate (MFR).
(ASTM D 1238, temperature 230 ° C, load 216
0 g) is not particularly limited as long as it can be used as a film, but is usually in the range of 1 to 20 g / 10 min, preferably 3 to 10 g / 10 min.

Butene polymer (B) The butene polymer (B) according to the present invention is a homopolymer of 1-butene and 1-butene and usually not more than 10% by weight of other α-olefins such as ethylene and propylene. Is a copolymer of The butene polymer (B) has an MFR of ASTM D12.
38 The value measured at a temperature of 190 ° C. and a load of 2160 g is
Usually 0.2 to 20, preferably 1 to 20 (g / 10 minutes)
It is desirable for obtaining good extrudability and sufficient mechanical strength when used as a heat-sealing layer. The butene polymer (B) generally has a melting point in the range of 70 to 130 ° C, preferably 70 to 115 ° C, and more preferably 70 to 80 ° C. The butene polymer (B) has the effect of reducing the cohesive force of the heat-sealing layer as a heat-sealing layer and imparting easy peelability when the package is peeled off.

Linear low-density polyethylene (D) The linear low-density polyethylene (D) according to the present invention generally has a density of 0.905 to 0.940 g / cm ³ , preferably 0.910 to 0.90 g / cm ³ . 935 g / cm ³ , MFR (AS
TM D1238, load 2160 g, temperature 190 ° C.) for 0.5 to 20 g / 10 min, preferably 1 to 10 g / 10
Is a random copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms, for example, propylene, butene-1, heptene-1, hexene-1, octene-1, and 4-methyl-pentene-1. The linear low-density polyethylene (D) has a molecular weight distribution (weight average molecular weight: Mw,
And the number average molecular weight: Mn, expressed as Mw / Mn) is usually in the range of 1.5 to 4.0, preferably 1.8 to 3.5. This Mw / Mn can be measured by gel permeation chromatography (GPC).

[0010] The linear low-density polyethylene (D) is
There is one or more sharp peaks determined from an endothermic curve measured by a differential scanning calorimeter (DSC) at a heating rate of 10 ° C./min, and the maximum temperature of the peak, that is, the melting point is usually 70 to
It is in the range of 130C, preferably 80-120C. The linear low-density polyethylene (D) as described above can be prepared by a conventionally known production method using a Ziegler catalyst, a single-site catalyst or the like.

Propylene polymer (C) The propylene polymer (C) according to the present invention is a homopolymer of propylene or propylene and ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene,
It is a random or block copolymer composed mainly of propylene with an α-olefin having 2 to 10 carbon atoms such as octene and 1-decene. In the case of a copolymer, the propylene content is usually 50% by weight or more, preferably 60% by weight or more. Whether a homopolymer or a copolymer is used can be appropriately selected depending on the required appearance.For example, to obtain a transparent multilayer film, a homopolymer or a random copolymer is selected, and an opaque multilayer film is obtained. In this case, a block copolymer may be selected.

MFR of the propylene polymer (C)
(ASTM D 1238, temperature 230 ° C, load 216
0 g) is not particularly limited as long as it can be used as a film, but is usually in the range of 0.5 to 20 g / 10 min, preferably 1 to 10 g / 10 min.

[0013] As the random copolymer, propylene
Copolymers in the same category as the α-olefin random copolymer (A) can be used, but in order to maintain the rigidity (rigidity) of the multilayer film, the propylene content is relatively 98 to 95% by weight and the propylene content is relatively low. A large number of random copolymers may be selected.

The block copolymer is obtained by polymerizing propylene and ethylene in a plurality of polymerization reactors with propylene and α-olefin such as ethylene, usually ethylene, respectively, or separately polymerized polypropylene and polyethylene. Or a combination thereof, and is a copolymer containing, as main components, a propylene polymerized portion, an ethylene polymerized portion, and a low-crystalline or amorphous ethylene-propylene copolymer. The propylene content in such block copolymers is usually in the range from 60 to 90% by weight.

The propylene / α-olefin random copolymer (A), the butene polymer (B) or the composition thereof, and the propylene polymer (C) according to the present invention do not impair the object of the present invention. Then, additives such as antioxidants, weather stabilizers, antistatic agents, antifogging agents and the like, which are usually used, or other polymers can be blended as required. In particular, by blending an anti-blocking agent and a slip agent, workability and workability during film forming, laminating, packaging, and the like can be improved.

The polypropylene multilayer film of the present invention has a melting point of 1
20-80% by weight, preferably 25-7% by weight of propylene / α-olefin random copolymer (A) at 20-150 ° C.
0% by weight and linear low density polyethylene (D)
Composition 8 of a butene polymer (B) containing 5% by weight, preferably 5 to 45% by weight, and a linear low-density polyethylene (D)
It comprises a heat-fusible layer and a propylene polymer (C) layer which can be obtained from 0 to 20% by weight, preferably 75 to 30% by weight.

The propylene / α-olefin random copolymer (A), which is the polymer component forming the heat-sealing layer, contains 20
When the amount is less than 80% by weight, the moldability of the film, the rigidity and the lubricity of the obtained film may be inferior. On the other hand, when it exceeds 80% by weight, the low-temperature heat sealability may be inferior. When the amount of the linear low-density polyethylene (D) in the composition of the butene polymer (B) and the linear low-density polyethylene (D) in the heat-sealing layer exceeds 50% by weight, low-temperature heat-sealing is performed. There is a possibility that the performance is not improved.

The multilayer polypropylene film of the present invention comprises:
Propylene / α-olefin random copolymer (A),
The propylene polymer (C) layer is composed of a heat-sealing layer made of a butene polymer (B) and a linear low-density polyethylene (D), and a propylene polymer (C) layer. (Printed layer). In this case, the propylene polymer (C) for forming the intermediate layer and the propylene polymer (C) for forming the layer to be printed can be appropriately selected depending on the application, and may be the same polymer or different polymers. good.

The base material layer according to the present invention is made of various materials usually used as packaging materials, for example, polyolefin films such as polyethylene film, polypropylene film, polybutene film and polymethylpentene film, polyethylene terephthalate film and polycarbonate film. Heat of polyester film, nylon film, polystyrene film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene-vinyl alcohol copolymer film, polymethyl methacrylate film, ethylene-vinyl acetate copolymer film, etc. Examples include plastic resin films, aluminum foil, and paper. The substrate made of such a thermoplastic resin film may be unstretched or a uniaxially or biaxially stretched film.
Of course, the base material may be one layer or two or more layers.

The total thickness of the polypropylene multilayer film is usually 20 to 100 μm, preferably 20 to 40 μm.
Usually, the heat-fused layer: 2 to 20 μm, the print-receiving layer: 18 to 80 μm, preferably the heat-fused layer: 2 to 10 μm
m, print-receiving layer: in the range of 18 to 30 μm. When the intermediate layer is provided, usually, the heat-sealing layer: 2 to 20 μm, the intermediate layer: 60 to 96 μm, and the print-receiving layer: 2 to 20 μm, preferably the heat-sealing layer: 2 to 10 μm, and the intermediate layer: 10 to 26 μm
m and print-receiving layer: in the range of 2 to 10 μm. The thickness of the base material layer when the base material layer is laminated is usually 12 to 500.
μm, preferably in the range of 12-100 μm.

The polypropylene multilayer film of the present invention can be produced by various known methods. For example, a heat-sealing layer, a layer to be printed, and, if necessary, a film to be an intermediate layer are separately formed, then bonded together, and the polymer forming each layer is individually melted by a plurality of extruders to form a single layer. It can be manufactured by a so-called co-extrusion molding method in which a multilayer film is formed from two dies. Among them, the coextrusion molding method is preferable because the multilayer film can be easily formed and the obtained multilayer film has excellent interlayer adhesion. As a method for producing a polypropylene multilayer film by such co-extrusion molding, for example, a propylene / α-olefin random copolymer (A) and a butene polymer (B) to be a heat-sealing layer are mixed in a predetermined amount. After that, the extruder is charged into one extruder, and the propylene polymer (C) to be a printed layer and, if necessary, the propylene polymer (C) to be an intermediate layer are charged into another extruder to form a multilayer film. Method: A propylene / α-olefin random copolymer (A) and a butene polymer (B) are mixed in a predetermined amount in advance, melt-kneaded with an extruder or the like to obtain a composition, and then molded by the above method. And the like. When the base material layer is further laminated on the propylene polymer (C), in addition to the co-extrusion molding method, a polyolefin multilayer film composed of the heat-sealing layer and the propylene polymer (C) is obtained in advance, A method of dry laminating the material layer, a method of extruding and laminating a polypropylene multilayer film composed of the heat-fusible layer and the propylene polymer (C) on the base material layer, and the like can be used.

The surface of the propylene polymer (C) layer to be a printing layer of the polypropylene multilayer film of the present invention is usually printed with a general gravure ink for packaging, but is not necessarily printed. .

Package The package of the present invention is a package made of a polypropylene multilayer film for packaging having the above-described structure, and is baked bread or other confectionery bread, confectionery, snacks, toys, daily goods. And the like, and the upper or lower part of the twist portion of the polypropylene multilayer film package is heat-sealed. The shape of the package can take various shapes according to the shape of the article to be packaged.
For example, in the case of a cubic bread, the shape may be a bottom type, a gusset type, or the like. Further, the side portion of the package is usually melt-sealed during bag making.

[0024]

Next, the present invention will be described through examples.
The present invention is not limited by these examples.

The characteristic values were measured by the following methods. (1) Heat seal strength (N / 15 mm): The surfaces of the heat-sealing layers were overlapped, sealed with a seal bar having a temperature of 5 mm and a width of 5 mm at a pressure of 0.2 MPa for 1 second, and then allowed to cool. From this, a test piece having a width of 15 mm was cut out, and the heat seal portion was peeled off at a crosshead speed of 500 mm / min.
The strength was defined as heat seal strength. Also, the peeled surface was observed, and the one that was peeled at the interface was rated as ○, the one that was slightly stretched and peeled or the one that was cohesively peeled was rated as Δ, and the one that caused the edge cut was ×. (2) Fusing strength (N / 15 mm): heat-fused layer surfaces are superimposed, cellophane is superimposed on top and bottom, and a seal bar having a triangular shape with a tip angle of 60 degrees is used.
Set at 0 ° C. and 300 ° C., at a pressure of 0.2 MPa and at 0.1 mm.
After sealing for 5 seconds, it was left to cool. From this, a 15 mm wide test piece was cut out and the heat-sealed portion was peeled off at a crosshead speed of 500 mm / min, and the strength was defined as the fusing strength. (3) Melting point (° C.): The melting point of the polymer was measured using DSC, and after melting the sample at 200 ° C., the melting point was 20 ° C. at a rate of 10 ° C./min.
C., kept for 1 minute, heated to 200 ° C. at a rate of 10 ° C./min, and measured. The raw materials used in this example and comparative examples are as follows. (1) Propylene / α-olefin random copolymer (R-PP-2) Ethylene content: 2.7% by weight, butene-1 content:
1.5% by weight, melting point: 138 ° C., MFR: 7 g / 10 minutes (2) propylene / α-olefin random copolymer (R-PP-3) Ethylene content: 3.1% by weight, butene-1 content:
2.5% by weight, melting point 131 ° C., MFR 7 g / 10 minutes (3) propylene homopolymer (PP), melting point 163 ° C., MFR 7 g / 10 minutes (4) butene polymer (PB) butene-1 · propylene copolymer, MFR4g / 10
(5) Propylene polymer (B-PP-1) Ethylene content: 7.6% by weight, amorphous ethylene / propylene random copolymer amount: 7.6% by weight, MFR 6.
5 g / 10 min (6) Propylene polymer (B-PP-2) Ethylene content: 26.1% by weight, amorphous ethylene / propylene random copolymer amount: 8.4% by weight, MFR
4.5 g / 10 min (7) Linear low-density polyethylene (LL-1) Density: 0.915 g / cm ³ , melting point 115 ° C., MFR
2.3 g / 10 min (8) Linear low density polyethylene (L
L-2) Density: 0.935 g / cm ³ , melting point 123 ° C, MFR
2.1g / 10min

Example 1 R-PP-3: 50% by weight, PB: 30% by weight and LL
-1: a polyolefin composition that forms a heat-sealing layer by dry blending with 20% by weight, and an intermediate layer that is dry-blended with 75% by weight of B-PP-1 and 25% by weight of R-PP-2. Polyolefin composition and B-PP-
2: 48.5% by weight and B-PP-1: 51.5% by weight and a dry-blended polyolefin composition for forming a print-receiving layer were supplied to separate extruders, and were heat-sealed by a T-die method. A three-layer co-extruded film having a constitution of / intermediate layer / printing layer was obtained. The total thickness of the film is 30 μm, and the thickness of each layer is heat-fused layer: intermediate layer: printed layer = 4.5 μm: 21 μm
m: 4.5 μm.

Example 2 The polyolefin composition for forming the heat-sealing layer used in Example 1 was R-PP-3: 60% by weight and PB: 30% by weight.
And LL-1: 10% by weight, except that the polyolefin composition was dry-blended to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Example 3 The polyolefin composition for forming the heat-sealing layer used in Example 1 was R-PP-2: 50% by weight and PB: 30% by weight.
And LL-1: 20% by weight, except that the polyolefin composition was dry-blended to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Example 4 The polyolefin composition for forming the heat-sealing layer used in Example 1 was R-PP-2: 40% by weight and PB: 40% by weight.
And LL-2: 20% by weight, except that the polyolefin composition was dry-blended to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Example 5 The polyolefin composition for forming the heat sealing layer used in Example 1 was prepared by adding R-PP-2: 50% by weight and PB: 40% by weight.
And LL-2: 10% by weight, except that the polyolefin composition was dry-blended to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Comparative Example 1 The polyolefin composition for forming the heat-sealing layer used in Example 1 was R-PP-2: 50% by weight and PB: 20% by weight.
And LL-2: 30% by weight, except that the polyolefin composition was dry-blended in the same manner as in Example 1 to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Comparative Example 2 R-PP-2: 50% by weight, PB: 10% by weight
And LL-2: 40% by weight, except that a dry-blended polyolefin composition was used in the same manner as in Example 1 to obtain a three-layer co-extruded film. The total thickness of the film is 30
μm, and the thickness of each layer is as follows: heat-fused layer: intermediate layer: printed layer =
4.5 μm: 21 μm: 4.5 μm.

Comparative Example 3 A three-layer coextruded film was produced in the same manner as in Example 1 except that the polyolefin composition for forming the heat-sealing layer used in Example 1 was changed to 100% by weight of R-PP-2. I got The total thickness of the film was 30 μm, and the thickness of each layer was heat-fused layer: intermediate layer: printing layer = 4.5 μm: 21 μm: 4.5 μm.

Comparative Example 4 A three-layer coextruded film was obtained in the same manner as in Example 1, except that the polyolefin composition for forming the heat-sealing layer used in Example 1 was changed to 100% by weight of PP. The total thickness of the film was 30 μm, and the thickness of each layer was heat-fused layer: intermediate layer: printing layer = 4.5 μm: 21 μm: 4.5 μm.

Example 6 A urethane-based adhesive was applied to a base layer made of a biaxially stretched polypropylene film having a thickness of 20 μm, and the heat-fused layer / intermediate layer / printed layer obtained in Example 1 was obtained. The printed layers of the three-layer co-extruded film were dry-laminated to obtain a polypropylene multilayer film.

Example 7 Example 2 was repeated in place of the three-layer coextrusion film used in Example 6.
Except for using the three-layer co-extruded film obtained in the above, the same procedure as in Example 6 was carried out to obtain a polypropylene multilayer film.

[0037] Instead of the three-layer co-extruded film used in Comparative Example 3 Example 6 Comparative Example 3
Except for using the three-layer co-extruded film obtained in the above, the same procedure as in Example 6 was carried out to obtain a polypropylene multilayer film.

Comparative Example 4 Instead of the three-layer co-extruded film used in Example 6, R-PP-2 of the three-layer co-extruded film of Comparative Example 3 was replaced with R-PP-3.
Was performed in the same manner as in Example 6 except that a three-layer co-extruded film was used in place of the above, to obtain a polypropylene multilayer film.

Table 1 shows the results of measuring the heat sealing strength between the film obtained in each of the examples and comparative examples and the adherend.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

The heat-sealing layer of the present invention has a specific propylene
A polypropylene multilayer film formed from an α-olefin random copolymer (A), a butene polymer (B), and a linear low-density polyethylene (D) has a low-temperature heat fusion while sufficiently maintaining the fusing strength. Because of its excellent properties of easy opening and easy opening, it can be suitably used as a packaging film. Also, breads such as sweet buns such as white bread, confectionery, snacks, toys, daily necessities, etc. Even when filling various kinds of packages, especially breads and other slightly heavy packages, there is no risk that the fusing portion or the bottom of the side will be broken, and after packaging, the upper or lower portion of the twist is heat-fused at a low temperature. Excellent workability because it can be worn. Also, when the purchaser takes out the package at home or the like, the heat-sealed portion can be easily opened without breaking the film of the packaging bag.

Continued on the front page F term (reference) 3E067 AA11 AB01 BA12A BB14A BB15A BB16A BB25A CA24 EA02 EA06 FA01 FC01 GD07 GD08 3E086 AA01 AB01 AC07 AD01 BA04 BA15 BB51 BB90 CA01 3E096 AA01 BA28 CA12 EA02A03 BA03 KA02 BA03 BA07 GB15 JA04A JL12 YY00A

Claims (6)

[Claims] 1. A propylene α having a melting point of 120 to 150 ° C.
-Olefin random copolymer (A) 20 to 80% by weight
Fusion obtainable from a composition of 80 to 20% by weight of a butene polymer (B) containing 5 to 50% by weight of a linear low density polyethylene (D) and a linear low density polyethylene (D) A multilayer polypropylene film comprising a layer and a propylene polymer (C) layer. 2. A propylene / α having a melting point of 120 to 150 ° C.
-Olefin random copolymer (A) 20 to 80% by weight
Fusion obtainable from a composition of 80 to 20% by weight of a butene polymer (B) containing 5 to 50% by weight of a linear low density polyethylene (D) and a linear low density polyethylene (D) A multilayer polypropylene film comprising a layer, a propylene polymer (C) layer and a substrate layer. 3. The polypropylene multilayer film according to claim 1, wherein the polypropylene multilayer film is for packaging. 4. The polypropylene multilayer film according to claim 1, wherein the polypropylene multilayer film is for bread packaging. 5. A package obtained by enclosing an article to be packaged in the polypropylene multilayer film according to claim 1 or 2, and heat-sealing the upper or lower portion of the twist portion of the polypropylene multilayer film package. 6. The package according to claim 5, wherein the article to be packaged is bread.