JPH09277466A - Cloudproof polyolefin film with good cold resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which has enough low temperature adhesion and impact resistance to be applicable to automatic packaging and transportation especially in a cold district and is excellent in cloudproof, rigidity, and appearance. SOLUTION: A cloudproof polyolefin film having a Young's modulus of at least 20kg/mm<2> a low temperature impact breaking ratio measured by a method defined in the text of at most 40%, and cold resistance of at least grade 2 cloudproof is preferably a multilayered film in which a surface layer of cloudproof copolypropylene of 120-145 deg.C melting point is laminated on both sides of a base layer film of linear low density copolyethylene which contains 0.1-2.0wt.% of a cloudproofing agent and has density of 0.905-0.930.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin-based unstretched composite resin film which has low-temperature impact resistance, and is excellent in all of antifogging properties, low-temperature thermal adhesion properties, appearance properties, and rigidity. The film is useful as various packaging materials including automatic packaging of fresh vegetables and fruits.

[0002]

2. Description of the Related Art Packaging of articles by an automatic packaging machine has been widely put into practical use because of its advantages such as simplicity and high-speed packaging. Further, recent automatic packaging machines are increasingly directed to higher efficiency and higher speed, and under such circumstances, further low-temperature heat adhesiveness is required for the packaging film applied to the automatic packaging machines. In addition, with the modernization of distribution of agricultural products, automatic packaging is being applied to packaging of fresh vegetables and fruits, but in packaging of fresh vegetables and the like, the appearance of the packaging and water rot caused by dew condensation, etc. In order to prevent this, the anti-fogging property is also a great required property required for the packaging film.

By the way, a polyolefin resin film that has been widely used as a film for automatic packaging of fresh vegetables has been improved in its antifogging property by containing an appropriate amount of an antifogging agent in the film material. The method of doing so has been adopted, and at present, this method is tentatively satisfactory. However, the development of logistics in recent years has been remarkable, and along with that, there is a tendency that the number of direct shipments from the cold districts to the production areas directly increases. It is also important to secure cold resistance, that is, impact resistance property at low temperature, while maintaining. Therefore, in order to satisfy such required characteristics, at present, a linear low-density polyethylene-based resin film excellent in thermal adhesiveness and impact resistance at low temperature is widely used. Is inferior,
In addition to the problem that the film becomes less stiff and the handling property is significantly deteriorated, making it difficult to apply to an automatic packaging machine, the transparency and gloss are inferior and the commercial value may be reduced.

As a means for improving such a problem of insufficient rigidity that is pointed out in linear low-density polyethylene-based unstretched film, polypropylene resin having high rigidity is used as a base layer constituting film to improve thermal adhesiveness at low temperature. Therefore, it is possible to use a composite film in which polyethylene resin is laminated as the surface layer, but in such a composite film, the low temperature impact resistance of the polypropylene resin as the base layer is revealed, and the low temperature impact characteristics of the composite film are revealed. Becomes insufficient, and the object of the present invention, which focuses on the improvement of physical properties in a low temperature environment, cannot be achieved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and its purpose is to provide automatic packaging and transportation, especially in cold regions, in the present time when distribution has been remarkably developed. The present invention intends to provide a film having excellent low-temperature heat-adhesiveness and impact resistance which can be sufficiently applied to, and also excellent in antifogging property, rigidity, and appearance characteristics.

[0006]

The anti-fog polyolefin film having excellent cold resistance according to the present invention, which has been able to solve the above problems, has a Young's modulus of 20 kg / mm ² or more, and is prepared by the method described below. Its characteristic is that the measured low temperature impact fracture rate is 40% or less and the antifogging property is second grade or higher.

The composition of the film satisfying all of the above Young's modulus, cold resistance and antifogging property defined in the present invention is 0.
Containing 1 to 2.0% by weight of antifogging agent, density 0.905
The melting point of 120 ° C. to 145 on both surfaces of the base layer film composed of the linear low density polyethylene copolymer of 0.930.
The surface layer made of a polypropylene-based copolymer having a temperature of 0 ° C. is laminated, and a substantially unstretched composite film having a multilayer structure is preferable, and as the linear low-density polyethylene-based copolymer constituting the base layer, a melt is used. Index is 0.5 ~
A polymer having a melt index of 4 g / 10 min (at 190 ° C.) and a polypropylene-based copolymer constituting the surface layer has a melt index of 2 to 5.5 g / 10 min (at 190 ° C.).
C.) are preferred. Further, the thickness of the base layer in the total thickness of the composite film is preferably in the range of 30 to 90%, and by adding such preferable requirements, a composite film having further excellent performance in packaging and transportation under low temperature conditions is obtained. Become.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the present invention, the Young's modulus is 20 kg // m as a requirement for simultaneously satisfying the rigidity and the impact resistance at low temperature which are usually contradictory to each other.
The low-temperature impact fracture rate is 40% or less, and the antifogging property is specified to be second grade or less, which are mm ² or more, and which are obtained by the method described later. That is, in the present invention, by controlling the Young's modulus and the low temperature impact rupture rate in this manner, the impact resistance at low temperature is satisfied, the rigidity is good, and the applicability to an automatic packaging machine is also excellent. A hydrophilic polyolefin film is provided.

The film having the above-mentioned characteristics has a multi-layer structure in which surface layers are laminated on both sides of a base layer constituting film, and a linear low density polyethylene copolymer having a specified density is selected as the base layer constituting film. With the surface layer, a polypropylene copolymer having a specified melting point is selected, and the base layer film contains an appropriate amount of an antifogging agent, or the melt index of each film constituting the base layer and the surface layer. By specifying (MI) and further defining the thickness ratio of the base layer occupying the entire laminated film, the target characteristics are satisfied.

Hereinafter, the reasons for setting the respective constituents defined in the present invention will be clarified one after another. The first requirement of the film of the present invention is that the Young's modulus is 20 kg / mm ² or more. The rigidity of the film is an extremely important characteristic for smoother automatic packaging. If the Young's modulus is less than 20 kg / mm ² , the rigidity is insufficient and it is difficult to apply it to an automatic bag making machine. The second requirement is the low-temperature impact rupture rate, and if this value exceeds 40%, the impact resistance at low temperatures is poor, and the film is likely to break during the packaging and transportation processes in cold regions. The third requirement is antifogging property, and if it is less than the second grade, when fresh vegetables and the like are packaged, the appearance will be deteriorated due to clouding and water rot due to dew will easily occur. The Young's modulus is 25 kg / m
A film having a m ² or more and a low temperature impact rupture rate of 30% or less is more excellent in automatic packaging suitability and low temperature impact resistance.

As a preferable film forming the base layer, a linear low density polyethylene copolymer having a density in the range of 0.905 to 0.930 can be mentioned. Therefore, the density of the base layer film is an important property for giving the film an appropriate rigidity for enabling automatic packaging and enhancing the impact resistance property at a low temperature. If it is less than 1.0, the rigidity of the film becomes low, making it difficult to apply it to an automatic packaging machine, while the density is less than 0.
If it exceeds 930, the impact resistance at low temperature becomes poor, and the film easily breaks easily during packaging or transportation in cold regions. A more preferable density is 0.91 in order to more effectively exhibit the above properties as the base layer constituting film.
It is in the range of 0 to 0.925.

The method for producing the linear low-density polyethylene-based copolymer constituting the base layer is not particularly limited, but a particularly preferable method for ensuring the above-mentioned characteristics is to use a metallocene catalyst in the step of polymerizing a monomer component containing ethylene. Examples of the method include a method of sharpening the molecular weight distribution by using it.

There are no particular restrictions on the type of this linear low-density polyethylene-based copolymer as long as it satisfies the above-mentioned density, and various linear copolymers containing ethylene as a main monomer component can be mentioned. As the copolymerizable monomer used with ethylene, any monomer may be used as long as it is a monomer that gives a linear copolymer without substantially causing a branched structure, Particularly preferred is an α-olefin having 3 to 12 carbon atoms such as propylene, butene-1, pentene-1, hexene-1, octene-1,
4-Methylpentene-1, decene-1, dodecene-1, etc., which can be copolymerized with ethylene alone, or can be copolymerized by combining two or more kinds in an arbitrary ratio if necessary. The copolymerization ratio of these copolymerizable monomers, considering the type of the copolymerizable monomer component selected,
The ethylene-based copolymer may be appropriately determined so as to satisfy the above-mentioned density.

As the polyethylene-based copolymer constituting the base layer film, it is preferable to select one having an appropriate melt index (hereinafter abbreviated as MI) in addition to the above density, and the preferable range of the MI is 0. 0.5 to 4 g / 10 minutes (at 190 ° C.). If the MI is less than 0.5 g / 10 min, the rigidity of the base layer film tends to be insufficient, and it tends to be difficult to obtain a composite film having good appearance and handleability. MI
This is because the impact resistance of the base layer film tends to be inadequate when it becomes one. Considering both rigidity, handleability and impact resistance, the more preferable MI range is 0.7 to 3 g /
The range is 10 minutes.

It is necessary to add an appropriate amount of an antifogging agent for imparting antifogging property to the composite film in the above-mentioned base layer-constituting film. In order to impart sufficient antifogging property to the composite film by leaching into the composite film, about 0.1% by weight or more of an antifogging agent should be contained. However, if the amount of antifogging agent added is too large, there is a risk that the base layer film will be bleached or bleeding out will be noticeable and the package will be contaminated. Should be suppressed. The content of the antifogging agent is more preferably 0.2 to 1.0% by weight in order to provide an excellent antifogging effect without causing problems such as excessive bleed-out.

The antifogging agent used here may be any one having an antifogging effect, including those generally marketed as "antifogging agent" or "antistatic agent". Typical examples thereof include fatty acid esters of polyhydric alcohols, ethylene oxide adducts of higher aliphatic amines, higher aliphatic alkanolamides, and the like. These may be added alone or, if necessary, two or more kinds. It is also possible to add in combination. These antifogging agents may be mixed at any stage (for example, a melt-kneading step using a screw or the like) before forming the linear low-density polyethylene-based copolymer constituting the base layer film into a film.

Next, as a preferable film material constituting the surface layers laminated on both sides of the base layer film, a polypropylene-based copolymer having a melting point in the range of 120 to 145 ° C. can be mentioned. That is, in the present invention, the surface layer is laminated in order to obtain low-temperature thermal adhesiveness that cannot be secured by the above-mentioned base layer film, and if the melting point is higher than 145 ° C, the sealing start temperature will be high. Therefore, satisfactory low temperature thermal adhesiveness cannot be obtained. On the other hand, when the melting point is less than 120 ° C., the surface layer becomes difficult and the composite film as a whole has a problem in applicability to an automatic packaging machine and handleability. come. From this viewpoint, the more preferable melting point range of the polypropylene-based copolymer constituting the surface layer is 1
It is 25-140 degreeC.

The polypropylene-based copolymer constituting the surface layer is not particularly limited in kind as long as it satisfies the above melting point, and various copolymers containing propylene as a main monomer component can be mentioned. Various olefins can be used as the copolymerizable monomer used together with ethylene, and the most common one is ethylene and a carbon number of 4 to 12
Α-olefins, specifically butene-1, pentene-
1, hexene-1, octene-1, 4-methylpentene-1, decene-1, dodecene-1, etc., which can be copolymerized alone with propylene, and if necessary, two or more kinds can be used in any ratio. They can be combined and copolymerized. Block copolymers and random copolymers are included in the copolymers, but random copolymers are particularly preferable in view of transparency.

Of the above-mentioned copolymers, propylene is particularly preferable in consideration of the performance as the surface layer, the cost and the like.
Ethylene copolymer, propylene-butene-1 copolymer,
Propylene-ethylene-butene-1 copolymers and the like, especially random copolymers thereof.

The copolymerization ratio of these copolymerizable monomers is appropriately determined in consideration of the type of the copolymerizable monomer component selected and the like so that the above-mentioned melting point can be satisfied as a propylene-based copolymer. Good.

As the propylene-based copolymer constituting the surface layer, it is preferable to select an appropriate MI in addition to the above melting point, and the preferable range of the MI is 2 to 5.5 g /
10 minutes (at 190 ° C.). Because MI is 2
If it is less than g / 10 minutes, the rigidity of the surface layer tends to be insufficient, and it tends to be difficult to obtain a composite film having good appearance and handleability. On the other hand, a high MI of more than 5.5 g / 10 minutes is required. This is because the low temperature thermal adhesiveness becomes poor and the impact resistance as a composite film tends to be insufficient. Considering all the characteristics of rigidity, handleability, impact resistance, and low temperature heat adhesion, a more preferable MI as the surface layer is in the range of 2.5 to 5.0 g / 10 minutes.

In the present invention, in order to secure the antifogging property as a composite film, it is essential to include a predetermined amount of antifogging agent in the base layer constituting film as described above. The structure is such that the action of the antifogging agent that is leached out sequentially from the base layer to the surface layer is effectively exerted, and the antifogging action is exerted for a long period of time. If you include a clouding agent,
Due to the action of the antifogging agent leaching to the surface side of the surface layer, an excellent antifogging action can be exhibited from the initial stage of packaging.
By the way, in the case where the base layer-constituting film contains the antifogging agent only, it takes some time for the antifogging agent to pass through the surface layer and to be leached to the surface thereof. Although depending on the case, when the composite film after production is immediately used for packaging, leaching of the antifogging agent may be slightly insufficient,
It is preferable to add a small amount of anti-fogging agent to the surface layer as well, since the excellent anti-fogging effect is surely exhibited from the initial stage of packaging.

The constituent materials of the base layer constituting film and surface layer according to the present invention are as described above.
Additives such as appropriate amounts of heat stabilizers, antioxidants, antiblocking agents, neutralizing agents, lubricants, nucleating agents, colorants, pigments, plasticizers and the like as necessary within the range that does not impair the above properties of the present invention. It is also possible to contain an inorganic filler or the like.

The method for forming a laminate for obtaining a laminated structure consisting of a base layer and a surface layer is not particularly limited, but as a general method, a known laminate forming method such as a coextrusion method can be mentioned. An inflation molding method using a circular die, a T-die molding method, or the like can be adopted. As a preferable condition when the T-die molding method is adopted, it is preferable to select a draft ratio of 1 to 10 and a resin temperature of 190 to 300 ° C. The thus obtained composite film of the present invention is preferably used without being substantially stretched, whereby the above-mentioned various properties can be exhibited more effectively.

The preferred thickness of the resulting composite film is
Although it cannot be uniformly specified because it varies depending on the application, the general thickness is 5 to 100 μm, and more generally 10 to 50 μm. Also, the thickness of the base layer is 30-90%, more generally 35-85%, of the total thickness.
Is preferable, and if it is less than 30%, the low temperature impact mainly provided by the base layer tends to be insufficient.
On the other hand, if it exceeds 90%, the rigidity of the composite film tends to be insufficient, and the applicability to an automatic wrapping machine and the handleability tend to deteriorate.

[0026]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, but may be appropriately adjusted within a range that can conform to the purpose of the preceding and following examples. Modifications can be made and all are included in the technical scope of the present invention. The measurement and evaluation methods employed in the following examples are as follows.

(Haze Value) According to JIS K 6714,
Measured using "Haze Tester J" manufactured by Toyo Seiki Seisakusho. (Narrow-angle diffuse transmission value) Measured using a visual transparency tester manufactured by Toyo Seiki Seisakusho. The smaller the measured value, the higher the transparency. (Melting point) Measured using a differential scanning calorimeter.

(Sealing start temperature) Using a heat gradient heat sealer manufactured by Toyo Seiki Seisakusho, pressure 1 kg / cm ² ×
After heat sealing under the condition of 1.0 second, its strength is measured, and the temperature at which the strength reaches 500 g / 15 mm is taken as the sealing start temperature. (Young's modulus) Measured in accordance with ASTM D882.

(Low temperature impact fracture rate) Seal temperature: 150 ° C., seal pressure: 2 kg / cm ² ,
Sealing time: The sealed portion of the bag prepared by heat sealing under the condition of 1 second is cut into a width of 15 mm and a length of 50 mm to prepare a test piece. The impact strength of the seal portion of this test piece was measured in the environment of −10 ° C. using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., and 50 samples were measured.

(Anti-fog property) 55 ° C. in a 500 cc beaker
Put 300 cc of warm water in (3), cover with a beaker with the anti-fog surface of the sample inside, and allow to cool in a room at 5 ° C for 30 minutes. After the lapse of 30 minutes, the state of water droplets adhering to the film surface was visually observed, and evaluated according to the following criteria in Table 1 in 6 levels.

[0031]

[Table 1]

Example 1 As a base layer constituent material, erucic acid amide: 0.1% by weight,
Higher fatty acid monoglyceride: 0.1% by weight, ethylene oxide adduct of higher aliphatic amine: 0.4% by weight, octene copolymerized linear low density polyethylene copolymer [Density: 0.916, MI: 2. 0g / 10 minutes (at
190 ° C.)], as the surface layer constituent material, higher fatty acid monoglyceride: 0.1% by weight, ethylene oxide adduct of higher aliphatic amine: 0.4% by weight, and an average particle size of 2.
5 μm crosslinked polymethylmethacrylate particles: 5000
Polypropylene-based copolymer containing ppm [melting point: 132
C., MI: 4.0 g / 10 min (at 190 ° C.), propylene / ethylene / butene-1 random copolymer], and melt-extruding each material by using a separate extruder, and multi-manifold By supplying to a multi-layer T-die and coextruding at a temperature of 260 ° C. and cooling with a chill roll at 40 ° C., surface layer / base layer / surface layer = 5/20/5 (μm)
A non-stretched composite film of was obtained.

After performing corona treatment on both sides of the film, the performance of the composite film was measured and the results shown in Table 2 below were obtained. As is clear from Table 2, the film obtained in this example is excellent in transparency, low temperature heat adhesiveness, impact resistance at low temperature and antifogging property, and rigidity. It is also high, and it can be seen that it is an extremely excellent anti-fog film for automatic packaging.

Comparative Example 1 An unstretched composite film was produced in the same manner as in Example 1 except that the same linear low-density polyethylene-based copolymer as the base layer constituent material was used as the surface layer constituent material. After performing corona treatment on both sides, check the performance of the film,
The results shown in Table 2 below were obtained. As is clear from Table 2, in this comparative example, the antifogging property, the low temperature heat-adhesive property and the impact resistance at a low temperature are good, but the surface layer constituent material is a polyethylene-based copolymer so that the rigidity is high. It was inferior, and the composite film had a weak rigidity, it was difficult to apply to an automatic packaging machine, and the appearance was poor.

Comparative Example 2 An unstretched composite film was produced in the same manner as in Example 1 except that the same polypropylene-based copolymer as the surface layer forming material was used as the base layer forming material, and corona treatment was performed on both sides thereof. After performing the above, the performance of the film was examined, and Table 2 below is given.
Were obtained. As is clear from Table 2, this comparative example is excellent in terms of anti-fogging property, low-temperature heat-adhesiveness and rigidity, but it is very poor in impact resistance at low temperature as a composite film and practically used. I can't stand it.

Comparative Examples 3 to 6 Preparation of a composite film and corona treatment were carried out in the same manner as in Example 1 except that the constituent materials of the base layer or surface layer were changed as shown in Table 2 below. ,
A performance test was conducted in the same manner.

The results are shown in Table 2 below. In Comparative Example 3, the density of the base layer film material was too low, and in Comparative Example 5, the surface layer film material had a too low melting point.
In either case, the composite film was too soft due to insufficient rigidity and was difficult to apply to an automatic packaging machine. In Comparative Example 4, the impact resistance property at low temperature was poor because the density of the base layer film material was too high, and in Comparative Example 6, Since the melting point of the surface layer is too high, the low temperature thermal adhesiveness is poor, and none of them meets the purpose of the present invention.

Examples 2, 3 and 4 Production of a composite film was carried out in the same manner as in Example 1 except that the type of base layer constituting film material, the type of surface layer and the thickness of those films were changed as shown in Table 2. Corona treatment was performed on the surface, and the performance of the obtained composite film was examined in the same manner as above. The results are shown in Table 2, and it can be seen that the three kinds of composite films are excellent in any performance.

Comparative Example 7 An unstretched composite film was prepared in the same manner as in Example 1 except that the addition of an antifogging agent (higher fatty acid monoglyceride, etc.) to the materials constituting the base layer and the surface layer was omitted. After performing corona treatment in the same manner, the film characteristics were examined. The results are shown in Table 2, and the composite film of this example does not contain an antifogging agent, and therefore cannot satisfy the antifogging property.

[0040]

[Table 2]

[0041]

The present invention is constituted as described above, and in addition to specifying the Young's modulus and the low temperature impact rupture rate,
It has excellent antifogging properties, and in particular, a surface layer made of a polypropylene copolymer having a specified melting point range is laminated on both sides of a base layer film made of a linear low density polyethylene copolymer having a specified density range. By having a multi-layer structure and further defining the MI of the linear low-density polyethylene-based copolymer forming the base layer and the polypropylene-based copolymer forming the surface layer, the rigidity and impact resistance at low temperature are excellent. In addition, it has become possible to provide a polyolefin-based film which is excellent in low-temperature heat adhesiveness and appearance characteristics and is useful as various packaging materials including automatic packaging of fresh vegetables and fruits.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // C08L 23:00

Claims (5)

[Claims] 1. The Young's modulus is 20 kg / mm ² or more, the low temperature impact fracture rate measured by the method defined in the detailed description of the invention is 40% or less, and the antifogging property is second grade or more. An anti-fog polyolefin film with good cold resistance. 2. Both sides of a base layer film comprising a linear low density polyethylene copolymer having a density of 0.905 to 0.930, containing 0.1 to 2.0% by weight of an antifogging agent,
The antifogging polyolefin film according to claim 1, which is provided with a surface layer made of a polypropylene copolymer having a melting point of 120 to 145 ° C. 3. The linear low-density polyethylene-based copolymer constituting the base layer has a melt index at 190 ° C. of 0.5 to 4 g / 10 minutes and is not stretched. The anti-fog polyolefin film according to. 4. The polypropylene-based copolymer constituting the surface layer has a melt index at 190 ° C. of 2-5.
The antifogging polyolefin film according to claim 3, which has an amount of 5 g / 10 minutes. 5. The antifogging polyolefin film according to claim 1, wherein the base layer has a thickness of 30 to 90% of the total thickness.