JP2001026083A - Film for package having excellent heat sealing strength in low temperature atmosphere and packaging body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polypropylene-based film, in which heat sealing strength is excellent in the low temperature atmosphere. SOLUTION: The film for package contains a layer constitution, in which both a base material layer having crystalline polypropylene as a main component and the following heat sealing layer having 2-25 μm thickness are directly laminated and haze value is <=10 and the conditions of the undermentioned formula are satisfied and heat sealing strength in the low temperature atmosphere is excellent. The heat sealing layer contains the mixture of a propylene-α olefin random copolymer and straight chainlike low density polyethylene polymerized in a metallocene catalyst as a main component. S0.c>=S23.c>=200 g/15 mm (wherein, after heat seal is performed, heat sealing layer is allowed to stand for 24 hours in the atmosphere at 0 deg.C and SO.c shows value of heat sealing strength measured in the atmosphere at 0 deg.C. After heat seal is performed, heat sealing layer is allowed to stand for 24 hours in the atmosphere at 23 deg.C and S23.c shows value of heat sealing strength measured in the atmosphere at 23 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-sided or double-sided heat-sealable biaxially oriented polypropylene (hereinafter abbreviated as OPP) film mainly used for food packaging, and more particularly to a food packaging filled and stored in a low-temperature atmosphere. In the case of films, packaging films with excellent heat seal strength even at low temperatures, as well as high heat seal strength at room temperature, are easily manufactured by laminating heat seal layers without using adhesives. A packaging film.

[0002]

2. Description of the Related Art For example, in order to assemble sprouts, leeks, fruits, various cut vegetables, as well as to pack fish paste products such as chikuwa and kamaboko, a film is formed into a bag and the object to be packaged is packed and sealed. A form is used. As these packaging films, unstretched films such as polyethylene and polypropylene have been used, but in recent years, OPP films provided with heat sealing properties have been used. This is because OP
This is because both the seller and the consumer have accepted the p-film's waist, crispness, gloss, transparency, and workability to make the packaged product look fresh and enhance its commercial value.

[0003] In general, a simple heat-sealing property given to an OPP film includes a melting point of 120 to 145 °.
C-order propylene-ethylene random copolymer, propylene-ethylene-butene ternary random copolymer, or a mixture thereof with a low-crystalline propylene-α-olefin copolymer, or a low-density polyethylene (hereinafter LDPE) ), A film formed by laminating a linear low-density polyethylene (hereinafter abbreviated as LLDPE), an ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA), and the like. These can be easily manufactured by a co-extrusion / extrusion lamination method or the like and are widely used.

[0004]

What is important in packaging the above-mentioned vegetables and seafood paste products is that these objects to be packaged are not so light, so that a certain degree of high heat sealing strength, Filling / transporting / low-temperature atmosphere
In order to be displayed, it is required that the high heat seal strength is maintained or higher even in a low-temperature atmosphere.
In addition, as a method for packaging these vegetables and fishery products, for example, in a bag manufacturing converter, a bag made of a film is formed in advance under a normal temperature atmosphere, and a vegetable manufacturer purchases the bag product, There is also a packaging form in which packing is performed under a low-temperature atmosphere. Since the heat seal strength of the bag is checked at the stage of making the bag under the normal temperature atmosphere, even if there is no problem at that time, the heat seal strength decreases when the vegetable manufacturer actually packs in the low temperature atmosphere If it has been done, troubles such as bag breakage occur, which is a problem. Of course, transparency, gloss, lubricity, blocking resistance, stiffness and cost performance of the film are also required.

However, the above-mentioned propylene-ethylene random copolymer, propylene-ethylene-butene tertiary random copolymer, or a mixture thereof with a low-crystalline propylene-α-olefin copolymer is used as the heat seal layer. In the OPP film used, the transparency of the film
Despite excellent gloss, lubricity, and heat seal strength at room temperature, propylene resin tends to be brittle in a low-temperature atmosphere, and heat seal strength tends to decrease in a low-temperature atmosphere, causing problems such as bag breakage. Is rare and unsatisfactory. In addition, the absolute value of the heat seal strength is not large and is not satisfactory.

[0006] In the case where the heat sealing layer is made of LDPE or LLDPE polymerized in the presence of a Ziegler catalyst, the heat sealing strength at low temperatures is small, but the adhesiveness with propylene resin is originally poor. In rare cases, delamination may occur, which is not satisfactory. Furthermore, when attempting to use defective products and slit ears generated in the manufacturing stage as recycled materials, LPEPE polymerized under LDPE or Ziegler-based catalyst is poorly compatible with propylene-based resin and deteriorates transparency. It is difficult to use it suitably.

When EVA is used for the heat seal layer,
Although the heat seal strength at low temperatures is excellent, the lubricity and blocking resistance of the film tend to deteriorate, and if a large amount of an anti-blocking agent such as silica is mixed as a measure for solving the problem, the transparency deteriorates. Further, when the defective product or the ear loss is used as a recycled material as described above, not only the transparency is deteriorated, but also burns and spots are generated.

[0008]

Means for Solving the Problems The present invention provides the following items 1 to
Consists of six.

(Claim 1) A base layer (A) containing crystalline polypropylene as a main component and a lower melting point than the base layer (A) containing an olefin resin as a main component and having a thickness of 2 to 25 μm.
A heat-sealing layer (B), a haze value of 10 or less, and excellent heat-sealing strength in a low-temperature atmosphere satisfying the following conditions. S _{0 ° C} ≧ S _{23 ° C} ≧ 200 g / 15 mm S _{0 ° C .} : After heat sealing, 24 under an atmosphere of 0 ° C.
Heat seal strength value measured at 0 ° C atmosphere after standing for 23 hours S23 _{° C} : After heat sealing, left at 23 ° C atmosphere for 24 hours and heat seal measured at 23 ° C atmosphere Strength value

(Item 2) The item (1), wherein the olefin resin is a mixture of a propylene-α-olefin random copolymer and a linear low-density polyethylene polymerized under a metallocene catalyst. Packaging film with excellent heat seal strength in low temperature atmosphere.

(Claim 3) The olefin resin is a mixture of a propylene-α-olefin random copolymer, a linear low-density polyethylene polymerized under a metallocene catalyst, and an olefin thermoplastic elastomer. Item 4. A packaging film having excellent heat seal strength in a low-temperature atmosphere according to item 1.

(Item 4) The linear low-density polyethylene polymerized under a metallocene catalyst has an olefin having 8 or more carbon atoms as a comonomer and has a density of 0.89 or less. The packaging film having excellent heat seal strength under a low temperature atmosphere according to any one of the above.

(Item 5) 140 ° C. 2 kg / cm ² (2
(3 ° C.), heat-sealed under 0 ° C. atmosphere for 24 hours, and heat seal strength measured at 0 ° C. atmosphere is 600 g / 15 mm or more. Item 5. A packaging film having excellent heat seal strength in a low-temperature atmosphere according to any one of Items 1 to 4.

(Item 6) A package using the film for packaging according to any one of Items 1 to 5, which has excellent heat seal strength in a low-temperature atmosphere.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a polymer forming a base material layer (A) is mainly composed of crystalline polypropylene. As the crystalline polypropylene, a propylene homopolymer having a high isotacticity and having a boiling n-heptane insoluble content of 95% by weight or more, which is used in ordinary extrusion molding or the like,
Alternatively, it may be a copolymer of propylene and α-olefin showing a crystal melting peak on a differential scanning calorimeter. Examples of the α-olefin include α-olefins having 2 to 8 carbon atoms, for example, ethylene, butene-1, pentene-1, hexene-
1,4-methyl-1-pentene and the like are preferred. Here, the copolymer includes a random or block copolymer. In the case of a random copolymer, the content of the α-olefin to be copolymerized is preferably 4% by weight or less, and in the case of the block copolymer, the content of the α-olefin to be copolymerized is preferably 6% by weight or less.

Depending on the purpose, other olefin resins,
For example, hydrogenated petroleum resin, hydrogenated terpene resin, hydrogenated styrene elastomers, propylene-ethylene rubber, and the like may be blended. Melt flow rate (MFR)
Is 0.1 to 100 g / 10 min, preferably 0.5
-20 g / 10 min, more preferably 1.0-5.0
g / 10 min. Further, the crystalline polypropylene of the base material layer (A) is, depending on the purpose,
Two or more layers such as (A) / (A ′) / (A ″) / heat seal layer (B) may be used. In this case, the layer (A '),
Layer (A ″) may be transparent, translucent or opaque. The thickness of the base material layer (A) is 10 to 100.
μm, and more preferably 20 to 80 μm.

Next, the polymer forming the heat seal layer (B) will be described. The polymer forming the heat seal layer (B) is not particularly limited,
It is necessary to satisfy the following points. First, the melting point of the polymer used for the heat seal layer (B) is determined based on the base layer (A).
It is necessary that the melting point be lower than the melting point. Particularly, a melting point lower by 20 to 70 ° C. than the melting point of the base material layer (A) is preferable.
After heat sealing under the conditions of 140 ° C. and 2 kg / cm ² (23 ° C.), the seal strength measured in an atmosphere of 0 ° C. is higher than the seal strength measured in an atmosphere of 23 ° C. It is necessary that the resin does not decrease.

The thickness of the heat seal layer (B) is 2 to 25.
μm. The thickness of the heat seal layer can be freely set, and the higher the thickness, the easier it is to obtain a high heat seal strength. Since the main purpose is "resource saving" that heat seal strength can be obtained, 25μ
Those exceeding m are out of the scope of the present invention. Further, when the thickness is 25 μm or more, blocking is liable to occur, and it becomes an obstacle to opening during bag making. If it is less than 2 μm, high heat sealing strength cannot be obtained. Preferably it is 3 to 15 μm, more preferably 4 to 10 μm.

The polymer forming the heat seal layer (B) is not particularly limited, but has a certain degree of interlayer adhesion to the base material layer (A) because it is laminated without using an adhesive. In addition, since it is inevitably desired to use a defective product, a slit ear, or the like as a regenerating material, it is desirable that the material be compatible with the crystalline polypropylene of the base material layer (A).

According to the present invention, by appropriately selecting the thickness of the base material layer (A), the heat seal layer (B) and the resin composition of the heat seal layer (B), 140 ° C. · 2 kg / c
After heat sealing under the condition of m ² (23 ° C.), 0
It was left for 24 hours in an atmosphere of 0 ° C, and the heat sealing strength measured in an atmosphere of 0 ° C was 140 ° C · 2 kg / cm.
After heat sealing under the condition of ² (23 ° C), 23
It is allowed to stand for 24 hours in an atmosphere at 23 ° C., and the heat sealing strength measured in an atmosphere at 23 ° C. can be increased.

Also, at 140 ° C. 2 kg / cm ² (23
After heat-sealing under the conditions of (° C), it was left in an atmosphere of 0 ° C for 24 hours, and the heat-sealing strength measured in an atmosphere of 0 ° C was 200 g / 15 mm or more, more preferably 400 g / 15 mm or more. , More preferably 600 g
/ 15 mm or more. 140 ° C
・ After heat sealing under the condition of ² kg / cm ² (23 ° C), it was left in an atmosphere of 23 ° C for 24 hours,
Heat seal strength measured under C atmosphere is 200g
/ 15 mm or more, more preferably 400 g / 15 mm or more, and still more preferably 600 g / 15 mm or more.

Specific examples of the olefin polymer satisfying the above conditions include the following.

LLDP polymerized under metallocene catalyst
E, butene resins, propylene-ethylene-propylene copolymer rubber, and the like (these are referred to as sealable UP groups). When these polymers are used alone, their lubricity and blocking resistance tend to be inferior. Therefore, propylene-α-olefin random copolymers such as propylene-ethylene random copolymer and propylene-ethylene-butene ternary random copolymer are used. It is preferably used as a mixture with a polymer (which is referred to as a random PP group). The mixtures are compatible with each other and the transparency is hardly degraded. The mixing ratio was such that the heat-sealable layer (B) contained 7
It is preferable that the content of the resin in the random PP group be 93 to 50% by weight. If the resin in the sealability UP group is less than 7% by weight, the effect is small.
The blocking resistance tends to be inferior. More preferably, it is 10 to 35% by weight.

Among the above polymers, particularly preferred as the heat seal layer (B) is a mixture of LLDPE polymerized under a metallocene catalyst and a random PP group (hereinafter referred to as a heat seal layer mixture). Conventionally, LLDPE polymerized with a Ziegler-based catalyst and propylene-based resin have poor compatibility and poor adhesion, but LLDPE polymerized under a metallocene catalyst has good compatibility with propylene-based resin. Have been found by the present inventor. As a result of further intensive studies, LLDPE polymerized under the metallocene catalyst has good adhesion to the propylene-based resin layer. When this mixture is used for the heat seal layer (B), the random PP group is used alone. It has been found that the absolute heat seal strength is remarkably increased as compared with the above, and the heat seal strength in a low-temperature atmosphere is also improved.

LL polymerized under the metallocene catalyst
Among the DPEs, the most preferred examples are:
A comonomer having 8 or more carbon atoms is used as a side chain and has a density of 0.89.
These are: The side chain has 8 or more carbon atoms and a density of 0.
If it is 89 or less, it becomes difficult for the LLDPE resin itself to form a lamella, and almost no crystals are formed. Therefore, it is easily dispersed in the random PP group in an elastomeric manner, and not only works advantageously in transparency, but also imparts flexibility, so that the heat seal layer mixture is apt to be sticky. In addition, since the melting point and the glass transition temperature are necessarily lowered by lowering the density, the temperature at which the viscosity of the heat seal layer mixture becomes maximum can be shifted to a lower temperature in terms of viscoelasticity. For these reasons, the heat seal strength characteristics in a low-temperature atmosphere can be further improved.

Here, the random PP group may be a modified product modified with maleic anhydride or the like.

The heat-sealable layer mixture may be appropriately blended with a resin other than those described above as long as the inherent properties of the mixture are not impaired. For example, butene resin, propylene-ethylene-propylene copolymer rubber, waxes, low-crystalline propylene-α-olefin copolymer,
And low-crystalline ethylene-α-olefin copolymers.
Particularly preferred is propylene-ethylene-propylene copolymer rubber, the amount of which is added in the heat seal layer (B).
In the resin composition constituting the above, about 5 to 40% by weight can be mentioned as a preferable example. More preferably 15 to
25% by weight.

The heat seal layer (B) may be composed of two or more base layers (A) / (B) / (B ′) / (B ″) according to the purpose.

In order to impart double-sided heat sealing properties to the film of the present invention, the heat sealing layer (B) is made of a base material layer (A).
And a layer structure of (B) / (A) / (B).

Next, the manufacturing method of the present invention will be described.
The film of the present invention is a film formed by a T-die method or a tubular method. The substrate layer (A) may be unstretched or stretched, but is preferably a biaxially stretched film. The stretching method may be a known method, and examples thereof include a sequential biaxial stretching method and a simultaneous biaxial stretching method. Regarding the heat seal layer (B), there is no particular limitation on the presence or absence and conditions of stretching. In the case of stretching, the conditions may be different from those of the base material layer (A). For example, a method may be used in which the base material layer (A) is stretched in the longitudinal direction, the heat seal layer (B) is laminated, and stretched in the transverse direction by a tenter.

As means for lamination, a coextrusion method, an extrusion lamination method, and a thermocompression bonding method can be mentioned.

There are no particular restrictions on the addition of additives to the polymer of each layer during lamination. For example, antioxidants, heat stabilizers, antifogging agents, antistatic agents, antiblocking agents, lubricants, mold release agents, etc., which are generally used in connection with polyolefin films for packaging, may be mentioned. These additives may be added to only the base material layer (A), only the heat seal layer (B), or both of them, if necessary. desirable.

Further, as long as the properties of the film of the present invention are not impaired, the surface may be subjected to, for example, a corona treatment, a flame treatment, a plasma treatment or the like.

The packaging film of the present invention basically comprises a base layer (A) and a heat seal layer (B). However, a film or resin layer having a completely different function is laminated. It does not matter at all, and it may be used as a package. There is no particular limitation on the lamination method.

[0035]

The effects of the present invention will be described in detail with reference to the following examples. The properties and performance of the film are determined by the following methods.
Measured and evaluated.

[Haze]: Measured in accordance with JIS-K-7105.

[Heat seal strength S at 0 ° C. atmosphere]
_{0 ° C} ] After heat sealing under the conditions of 140 ° C and 2 kg / cm ² (23 ° C), it was left in an atmosphere of 0 ° C for 24 hours, and then JIS-Z- 1707
It was measured according to the standard method.

[Heat seal strength at 23 ° C. atmosphere S _{23 ° C.} ] 140 ° C. 2 kg / cm ² (23 ° C.)
After heat-sealing under the conditions described above, it was left under an atmosphere of 23 ° C for 24 hours, and then, under an atmosphere of 23 ° C, JIS-Z-
It was measured by a method based on 1707.

[Opening property (blocking resistance)] Three sides of the obtained film were heat-sealed to form a bag.
After stacking 0 sheets, a load of 1 kg / 500 cm ² was applied from above and left in a constant temperature bath of 40 ° C. and 65% RH for 24 hours, and then the openability of the bag was examined. The rating was sensory-assessed as four steps of ◎ (open easily)-○-△-× (open without using cellophane tape).

Example 1 A base layer (A) made of a crystalline polypropylene resin (melting point: 160 ° C., MFR: 2.2 g / 10 min) and a heat seal layer (B) made of the following resin composition After laminating in a T-die at 240 ° C. and co-extrusion, it is quadrupled in the MD direction (stretching temperature 110 ° C.) and TD direction (stretching temperature 159 °) by a roll-tenter method.
C) was stretched 10 times to obtain a biaxially stretched two-layer film. The thickness of the obtained film is (A) / (B) = 25/5 μm
Met. The physical properties of the obtained film were measured and evaluated, and the results are shown in Table 1. Various additives were mixed in each layer as needed, but the amount and type of addition were common to Examples 1 and Comparative Example 2. <Heat seal layer (B)> Propylene-ethylene random copolymer having an ethylene content of 7% by weight (melting point: 132 ° C, MFR: 7.0 g / 1)
0 min): 70% by weight LLDPE polymerized under a metallocene catalyst (Dow
Chemical Company, affinity KC8852 (density 0.
875, MFR: 3.0 g / 10 min)): 30% by weight

Example 2 The same procedure as in Example 1 was carried out except that the heat seal layer (B) was changed to the following resin composition. The properties of the obtained film were measured and evaluated, and the results are shown in Table 1. <Heat seal layer (B)> Propylene-ethylene random copolymer having an ethylene content of 7% by weight (melting point: 132 ° C, MFR: 7.0 g / 1)
0 min): 60% by weight LLDPE polymerized under a metallocene catalyst (Dow
Chemical Company, affinity KC8852 (density 0.
875, MFR: 3.0 g / 10 min)): 20% by weight propylene-ethylene-propylene copolymer rubber (Mo
natter-JPO, Cataloy: C200F (M
FR: 6.0 g / 10 min)): 20% by weight

Example 3 The same procedures as in Example 1 were carried out except that the heat seal layer (B) was changed to the following resin composition. The properties of the obtained film were measured and evaluated, and the results are shown in Table 1. <Heat seal layer (B)> Propylene-ethylene random copolymer having an ethylene content of 7% by weight (melting point: 132 ° C, MFR: 7.0 g / 1)
0 min): 60% by weight LLDPE polymerized under a metallocene catalyst (Dow
Chemical Company, affinity KC8852 (density 0.
875, MFR: 3.0 g / 10 min): 20% by weight Propylene-butene copolymer rubber (manufactured by Mitsui Chemicals, Inc., Tuffmer XR106L (MFR: 8.0 g / 10 m)
in)): 20% by weight

Comparative Example 1 The same procedure as in Example 1 was carried out except that the heat seal layer (B) was made of the following resin composition. The physical properties of the obtained film were measured and evaluated, and the results are shown in Table 1. <Heat seal layer (B)> Propylene-ethylene random copolymer having an ethylene content of 7% by weight (melting point: 132 ° C, MFR: 7.0 g / 1)
0 min): 70% by weight LLDPE polymerized under Ziegler catalyst (Ultzex 2022L, manufactured by Mitsui Chemicals, Inc. (density 0.9)
20, MFR: 2.1 g / 10 min)): 30% by weight

Comparative Example 2 The same procedures as in Example 1 were carried out except that the heat seal layer (B) was made of the following resin. The properties of the obtained film were measured and evaluated, and the results are shown in Table 1. <Heat seal layer (B)> Propylene-ethylene random copolymer having an ethylene content of 7% by weight (melting point: 132 ° C, MFR: 7.0 g / 1)
0 min): 100% by weight

[0045]

[Table 1]

[0046]

Industrial Applicability The packaging film of the present invention having excellent heat seal strength in a low temperature atmosphere is excellent in heat seal strength, haze and opening property at a low temperature, and is particularly suitable for packaging vegetables stored in a refrigerator. It can be suitably used as a material.

Claims (6)

[Claims] 1. A heat seal having a base layer (A) containing crystalline polypropylene as a main component and a melting point lower than that of the base layer (A) containing an olefin resin as a main component and having a thickness of 2 to 25 μm. A packaging film comprising a layer (B), a haze value of 10 or less, and excellent heat seal strength in a low-temperature atmosphere satisfying the following conditions. S _{0 ° C} ≧ S _{23 ° C} ≧ 200 g / 15 mm S _{0 ° C .} : After heat sealing, 24 under an atmosphere of 0 ° C.
Heat seal strength value measured at 0 ° C atmosphere after standing for 23 hours S23 _{° C} : After heat sealing, left at 24 ° C atmosphere for 24 hours and heat seal measured at 23 ° C atmosphere Strength value 2. The low-temperature low-temperature resin according to claim 1, wherein the olefin-based resin is a mixture of a propylene-α-olefin random copolymer and a linear low-density polyethylene polymerized under a metallocene catalyst. Packaging film with excellent heat seal strength in atmosphere. 3. The olefin-based resin is a mixture of a propylene-α-olefin random copolymer, a linear low-density polyethylene polymerized under a metallocene catalyst, and an olefin-based thermoplastic elastomer. 2. The packaging film having excellent heat seal strength in a low temperature atmosphere according to 1. 4. The linear low-density polyethylene polymerized under the metallocene catalyst has an olefin having 8 or more carbon atoms as a comonomer and has a density of 0.89 or less. The packaging film according to any one of the above, which has excellent heat seal strength in a low-temperature atmosphere. 5. 140 ° C. · 2 kg / cm ² (23 °
After heat-sealing under the condition of (C), it is left in an atmosphere of 0 ° C for 24 hours, and the heat-sealing strength measured in the atmosphere of 0 ° C is 600 g / 15 mm or more. 5. The packaging film according to any one of 1 to 4, which has excellent heat seal strength in a low-temperature atmosphere. 6. A package using the packaging film according to claim 1, which has excellent heat seal strength in a low-temperature atmosphere.