JP3167063B2 - Polyolefin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyolefin film.

[0002]

2. Description of the Related Art Polyolefin films are used for packaging foods and the like. In such a polyolefin film, usually, the films have good slipperiness so that the film can be easily removed at the time of opening the package, or the film is hardly scratched to prevent the appearance of the package from being deteriorated. Is required. The polyolefin film is also required to have a heat-sealing property so that each wrapping piece can be easily fixed at the time of packaging.

A polyolefin film having such heat resistance and excellent slipperiness and scratch resistance is, for example, an average particle diameter of 0.5 to 3 μm and a rubber hardness already proposed by the present applicant. A polyolefin film is known in which a surface layer of a polyolefin containing 0.05 to 1% by weight of silicone rubber particles having an A of 30 to 80 degrees and a base layer having a higher melting point than the polyolefin are laminated. JP-A-4-220436).
Here, as the polyolefin forming the base layer in the polyolefin film, specifically, a propylene homopolymer and a propylene-ethylene random copolymer having an ethylene content of 3 mol% or less are shown.

[0004]

In the case where the article to be packaged with such a polyolefin film is an article having a high water content such as a diaper, the wrapping pieces of the polyolefin film overlap with each other in a package of the article. In the portion, moisture penetrates into the gap, so that both wrapping pieces easily adhere to each other. As a result, in such a package, when opening the package, an unnecessarily strong feeling of resistance occurs in peeling off the two wrapping pieces attached to each other, and in some cases,
Excessive force is applied to a packaged item such as a rice ball to be packaged, causing the article to crack. From these facts, when the thing having a high water content such as the above-mentioned diaper is an article to be packaged, the packaging film is required to have a remarkably high slipperiness between the films. Even in polyolefin films containing rubber particles, it has been desired to further improve the slipperiness between the films.

[0005] Further, as described above, polyolefin films and the like containing specific silicone rubber particles in the film surface layer are excellent in transparency because the material of the base layer is an inherently transparent resin such as propylene homopolymer. It has transparency. However, when such a highly transparent film is used for wrapping the diaper, the resulting diaper package has a product value in which the contact portion between the diaper and the film is seen through as if wet, and the appearance is prioritized. Had been lowered.

[0006] From the above background, in addition to being excellent in the scratch resistance and heat sealing property of the film, as described above, the film is further excellent in the slipperiness between the films, and furthermore has an appropriate opacity such that the inside cannot be seen through when packaged. The development of was desired.

[0007]

Means for Solving the Problems Accordingly, the present inventors have:
We have been conducting intensive research to solve the above problems. As a result, in a polyolefin film in which a specific silicone rubber particle is contained in the film surface layer as described above, the above-mentioned problem is solved by setting the base layer of the film to a mixture of polypropylene and high-density polyethylene having a specific composition ratio. They have found what they can do and have completed the present invention.

[0008] That is, the present invention relates to 90% to 70% by weight of polypropylene and 10% to 30% by weight of high density polyethylene.
Weight% and a mean particle size of 0.5 to 3 μm.
m, 0.5 to 5.0 μm containing 0.05 to 1% by weight of silicone rubber particles having a rubber hardness A of 30 to 80 degrees .
Thick, and the surface of the low melting point of the polyolefin from the base layer are laminated, poliovirus <br/> les fins film for high article moisture content packaging.

In the polyolefin film of the present invention, the layer serving as the base layer is composed of 90 to 70% by weight of polypropylene.
It is preferably formed from a mixture of 90 to 75% by weight of polypropylene and 10 to 30% by weight, preferably 10 to 25% by weight of high density polyethylene. Polypropylene films are generally transparent and the slipperiness between the films is not sufficient, but when a mixture of such polypropylene and the above amount of high-density polyethylene is used as the base layer of the film, The surface of the film is roughened so that the slipperiness between the films is improved, and the film has an appropriate degree of opacity such that the inside cannot be seen through when it is made into a packaging film. Here, as the polypropylene which is a component of the mixture, a known polypropylene can be used without any particular limitation. Specifically, in addition to a propylene homopolymer, a copolymer of propylene with another copolymerizable monomer such as an ethylene-propylene copolymer, a propylene-butene copolymer, and an ethylene-propylene-butene copolymer. It may be united. In the present invention, the polypropylene has a melt flow index (hereinafter, abbreviated as MFI) = 1.0 to
It is preferably 5.0 g / 10 min (230 ° C.).

On the other hand, known high-density polyethylene can be used without any particular limitation. Specifically, the density is 0.945 g / cm ³ or more, preferably 0.945 g or more.
At 0.960 / cm ³ , MFI = 0.05-2.0 g /
A time of 10 min (190 ° C.) is preferable for imparting opacity to the film.

When the amount of the high-density polyethylene is less than 10% by weight in the above-mentioned mixture of polypropylene and high-density polyethylene, the surface of the film is not sufficiently roughened, the slipperiness between the films is reduced, and the opacity of the film is reduced. Run out. On the other hand, when the amount of the high-density polyethylene is more than 30% by weight, the film forming property of the film is reduced.

Next, in the polyolefin film of the present invention, the base layer has an average particle diameter of 0.5 to 3 μm,
A surface layer of a polyolefin having a lower melting point than the base layer containing 0.05 to 1% by weight of silicone rubber particles having a rubber hardness A of 30 to 80 degrees is laminated. Therefore, the polyolefin film of the present invention can be subjected to heat sealing only the surface layer by applying heat lower than the melting point of the mixture forming the base layer and higher than the melting point of the polyolefin forming the surface layer. . The low-melting-point polyolefin described in the present invention, even if it does not necessarily show a clearly-defined melting point peak in thermal analysis, has a lower temperature than a mixture of polypropylene and high-density polyethylene, which are base layer materials. Any polyolefin that melts may be used.

Further, the surface of the film forming the surface layer is roughened by forming the unevenness in accordance with the unevenness of the base layer film because the surface of the base layer film is roughened. Thus, in the polyolefin film of the present invention, such a surface layer contains silicone rubber particles having a specific particle size and a rubber hardness A for imparting good slip properties to the film as described above,
In the polyolefin film of the present invention, the silicone rubber particles and the roughening of the film surface act synergistically to significantly improve the slipperiness. In addition, such a surface layer may be formed on only one surface of the base layer, but is preferably formed on both surfaces of the base layer in consideration of operability when used as a packaging film.

In the present invention, the silicone rubber particles contained in the surface layer have an average particle diameter of 0.5 to 3 μm, preferably 1 to 2 μm, and a rubber hardness A of 30 to 80 degrees, preferably 35 to 75 degrees. When the average particle size of the silicone rubber particles is less than 0.5 μm, the effect of improving the slipperiness is poor. On the other hand, when the average particle size exceeds 3 μm, fish eyes mainly composed of spherical particles are generated, which is preferable in the appearance of the film. Absent. The rubber hardness A of the silicone rubber particles is 3
If it is less than 0, the effect of improving the slip property is poor, and
If it exceeds the degree, the film is liable to be scratched when contacting with each other. The rubber hardness A is JIS K 630.
This is a value measured according to 1.

The shape of the silicone rubber particles is not particularly limited, but is preferably spherical in consideration of the improvement in slipperiness. Since commercially available silicone rubber particles are generally spherical, commercially available products may be used as they are.

In the polyolefin film of the present invention, the content of the silicone rubber particles contained in the surface layer is 0.05 to 1% by weight, and 0.1% to 0.1% by weight.
Preferably it is 8% by weight. When the compounding amount of the silicone rubber particles is less than 0.05% by weight, the effect of improving the slipperiness is poor. Even if the compounding amount exceeds 1% by weight, the effect of improving the slipperiness cannot be expected. .

In the polyolefin film of the present invention, the polyolefin having a lower melting point than the base layer, which is a material resin of the surface layer, is not particularly limited, but preferably has a melting point of 10 to 10 degrees higher than that of the base layer. It is better to be 80 ° C lower. Specific examples of such polyolefins include homopolymers of α-olefins such as ethylene, propylene and 1-butene, copolymers of the above α-olefins, and α-olefins copolymerizable with the α-olefin. A copolymer of a monomer with an α-olefin, a mixture thereof, and the like are employed without any limitation. Examples of the monomer other than the α-olefin copolymerizable with the α-olefin include vinyl acetate and maleic acid. In the present invention, polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-1-butene copolymer, ethylene-propylene-1
Most preferred are butene copolymers, ethylene-propylene-butadiene copolymers, and blends containing these polyolefins as main components.

In the polyolefin film of the present invention, the thickness of the base layer is not particularly limited, but is generally in the range of 10 to 50 μm, preferably 15 to 30 μm. The thickness of the surface layer laminated on the surface of the base layer prevents the loss of silicone rubber particles by friction between films or impart sufficient heat sealing properties to full Irumu, also, the surface of the base layer film In order to sufficiently generate unevenness due to the unevenness and to improve the slipperiness of the film, 0.5 to 5.0 μm, preferably 0.5 to 5.0 μm.
The range is preferably 5 to 3.0 μm, more preferably 0.5 to 2.0 μm.

In the polyolefin film of the present invention, the base layer formed of a mixture of polypropylene and high-density polyethylene preferably extends in a uniaxial direction, or in a uniaxial direction and a direction substantially perpendicular to the uniaxial direction. In this case, the stretching ratio is generally preferably 1.1 to 8 times in the case of uniaxial stretching, and 3 to 12 times in the direction perpendicular to the direction of uniaxial stretching in the case of biaxial stretching. Similarly, the surface layer laminated on the base layer may be stretched in the uniaxial direction, or in the uniaxial direction and a direction substantially perpendicular to the uniaxial direction.

[0020] The polyolefin film of the present invention may be produced by any method. Generally, it can be manufactured by the following method. First, a mixture of polypropylene and high-density polyethylene to be a base layer is extruded into a sheet, which is stretched in a uniaxial direction 1.1 to 8 times to obtain a uniaxially stretched sheet. Next, a polyolefin is extruded into a sheet to form a surface layer, and the polyolefin is laminated on the uniaxially stretched sheet. Alternatively, the laminated sheet is further subjected to 3 to 1 in a direction substantially perpendicular to the direction of uniaxial stretching.
By stretching the film twice, the polyolefin film of the present invention can be obtained. The base layer and the surface layer can be simultaneously extruded and laminated, and this can be uniaxially or biaxially stretched by the same method as described above.

In the base layer and the surface layer of the polyolefin film of the present invention, various additives which are generally known to be added to a plastic film, such as a heat stabilizer, an antioxidant, a crystal nucleating agent and an antistatic agent , A lubricant, an antiblocking agent, an antibacterial agent, a freshness preserving agent and the like may be added. Of these, use of a lubricant in the surface layer is preferred for improving the slipperiness of the film. As the lubricant, higher fatty acid amides such as erucamide, oleic amide,
Stearic acid amide, ethylene bis stearamide, N
-Stearyl erucamide and the like can be preferably used.

The polyolefin film of the present invention is not particularly limited, but is preferably used as a packaging material for various articles. Considering that the films are extremely slippery and have an appropriate degree of opacity such that the inside cannot be seen through, it is preferable to use the film as a food film having a high water content, particularly, a packaging film for diaper.

FIG. 1 shows an example in which the polyolefin film of the present invention is used as an inner wrapping film for diapers which is eaten by winding with nori.

That is, FIG. 1 is a cross-sectional view of a case where a seaweed is rolled and edible diapers are packaged using the polyolefin film of the present invention as an inner wrapping film. In FIG. 1, the diaper 1 is composed of two inner wrapping films 2a and 2b composed of the polyolefin film of the present invention.
Its surface is covered and packaged. And the above 2
In the two inner wrapping films a and 2b, at least one (2a) edge portion on the diaper has a folded structure inside, and most of the diaper surface is in contact with the folded piece 3. . In FIG. 1, reference numeral 4 denotes an outer wrapping film having a rupture portion 5 at a predetermined position, and the outer wrapping film and the inner wrapping film are adhered and fixed at predetermined positions at respective edges by heat sealing. A laver 6 is stored between the outer film and the inner wrapping films 2a and 2b. In such a diaper package, the rupture portion 5 of the outer packaging film is torn when edible,
By pulling both the interior and exterior packaging films together in the opposite directions of A and B and removing them from the diaper, a nori-wrapped diaper is easily made. At this time, in the folded piece 3 of the inner wrapping film 2a, the film is not simply slipped on the diaper in the above-described pulling direction (A direction), but is peeled off from the diaper. Therefore, the folded piece 3 can be easily separated from the surface of the diaper 3 even though the diaper having a highly adhesive surface is packaged.

On the other hand, the folded piece 3 is in close contact with the surface of the inner wrapping film 2a facing the folded piece in a wet state with the water of the diaper 1. However, since the inner wrapping film 2a is made of the polyolefin film of the present invention having extremely good slipperiness between the films as described above, the folded piece 3 can be easily taken in at the time of taking the film. 2a slide on the opposing surface. As a result, in such a diaper package, the inner wrapping film can be easily pulled from the diaper with a small resistance.

Further, in such a diaper package, even when a highly transparent film is used as the outer wrapping film 4, the inner wrapping film 2a, 2b has an appropriate degree of opacity, so that the inner diaper is not formed. Not seen through,
The diaper looks wet and does not impair the appearance.

[0027]

The polyolefin film of the present invention has excellent opacity such that the film is not easily damaged or heat-sealed, has excellent slipperiness between films, and cannot be seen through when packaged. . Therefore, for example, when the diaper is packaged, at the time of opening the packaging, the diaper can be taken out very smoothly,
In addition, the diaper is not cracked by applying excessive force to the diaper at the time of opening. Moreover, since the inside has an appropriate degree of opacity such that the inside cannot be seen through, the diaper is not seen through the wet feeling when the diaper or the like is packaged, and the commercial value of the diaper is not reduced. Further, it can be used for packaging by an automatic packaging machine by utilizing its heat sealing property.

[0028]

EXAMPLES The present invention will be described below in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The film properties in the following Examples and Comparative Examples were measured by the following methods.

(1) Haze Measured according to JIS K 6714.

(2) Scratch resistance Two films cut into a size of 20 cm × 30 cm were overlapped, one was fixed below, and the other was set above. Place a 4.6kg weight on the upper film, and lower film and 10c
The contact was made in an area of mx 10 cm, and the upper film was moved horizontally to rub twice between 20 cm. The haze was measured before and after the operation, and the difference was 0% or more to less than 3%, ○: 3% or more to less than 10%, and X: 10% or more.

(3) Slip properties ASTM-D after film formation and curing at 40 ° C. for 3 days
It measured according to the dynamic friction coefficient measuring method of -1894.

(4) Heat Sealability A heat seal bar of 5 × 200 mm was used. At each set temperature, a heat seal pressure of 1 kg / cm ² and a heat seal time of 1.0 second were used to obtain a sample 15 mm from the sample.
A sample having a width was cut out and measured at a tensile speed of 100 mm / min using a tensile tester. The results were average values of five samples.

(5) Opening property of diaper The double-sided heat-sealable polypropylene biaxially stretched film having a thickness of 20 μm was used as the outer wrapping film. In addition,
This outer wrapping film is provided with a 3 mm wide opening tape portion coated with a hot melt agent as a break portion at the time of opening. Each test film was used as an inner wrapping film, and an impulse sealing machine and a simple iron were used to prepare a diaper wrapping film having a structure as shown in FIG. A commercially available diaper was wrapped with the diaper packaging film as shown in FIG. The diaper was actually opened and the openability of the diaper was evaluated. Each test film was evaluated with ten diapers, and a five-point evaluation was performed based on whether the diaper was broken at the time of opening.

5 points: 0 broken diapers 4 points: 〃 1 to 2 3 points: 〃 3 to 4 2 points: ５ 5 to 6 1 point: ７ 7 to 10 (6 ) Permeability of diaper Each test film was applied to a commercially available diaper surface, and it was observed whether the surface of the diaper could be seen through the film. When the film was opaque and the diaper could not be seen through, it was evaluated as ○.

Example 1 Melt flow index at 230 ° C. = 2.0 g
A mixture of 80% by weight of polypropylene / 10% and 20% by weight of a high-density polyethylene having a melt flow index at 190 ° C. of 1.0 g / 10 minutes and a density of 0.955 g / cm ³ was 240 wt. The resin was extruded into a sheet at a resin temperature of 0 ° C., and cooled and solidified by a chill roll maintained at 60 ° C. to form a 1.1 mm thick sheet.

Melt flow index at 230 ° C. = 8.0 g / 10 min, 79.4% by weight of ethylene-propylene copolymer, 20% by weight of propylene-butene copolymer, average particle size 1.2 μm, rubber hardness A = A mixture of 0.3% by weight of silicone rubber sphere particles of 40 ° C. and 0.3% by weight of erucamide was extruded at 230 ° C. by an extruder and pelletized to obtain a polyolefin resin composition.

Next, the above-mentioned sheet was stretched 4.8 times at 150 ° C. with a hot roll stretching machine to obtain a 230 μm uniaxially stretched sheet. The above polyolefin-based resin composition was extruded into a sheet at a resin temperature of 230 ° C. using a T-die extruder, and laminated on a uniaxially stretched sheet and a roll maintained at 70 ° C. to obtain a 240 μm two-layer sheet.

Further, a polyolefin resin composition was similarly laminated on the uniaxially stretched sheet surface side of the two-layer sheet to obtain a 250-μm three-layer sheet.

Subsequently, the three-layer sheet was stretched 10 times at 160 ° C. using a transverse stretching machine, and a base layer comprising a mixture of polypropylene and high-density polyethylene was 23.0.
The polyolefin film having a thickness of 1.0 μm and a surface layer of the polyolefin-based resin composition of 1.0 μm and an overall thickness of 25.0 μm was obtained. The resulting polyolefin film was measured for haze, scratch resistance, slipperiness, heat sealability, diaper opening, and diaper transparency.
The results are shown in Table 2.

Example 2 A polyolefin film was obtained in the same manner as in Example 1, except that the resin composition of the base layer was changed to that shown in Table 1. The resulting polyolefin film was measured for haze, scratch resistance, slipperiness, heat sealability, diaper opening, and diaper transparency.
The results are shown in Table 2.

Example 3 In Example 1, the silicone rubber sphere particles contained in the surface layer were changed to those shown in Table 1. The thickness of the base layer and the surface layer was changed by adjusting the extrusion amount of the T-die extruder, and a polyolefin film having a total thickness of 25.0 μm was obtained in the same manner as in Example 1. The resulting polyolefin film was measured for haze, scratch resistance, slip property, heat sealing property, diaper opening property, and diaper transparency, and the results are shown in Table 2.

Examples 4 to 6 Polyolefin films were obtained in the same manner as in Example 1, except that the silicone rubber spherical particles contained in the surface layer were changed to those shown in Table 1. About the obtained polyolefin film, haze, scratch resistance, sliding property, heat sealing property, openability of diaper,
The transparency of the diaper was measured, and the results are shown in Table 2.

Comparative Example 1 In Example 1, polypropylene was melt extruded at a melt flow index of 2.0 g / 10 minutes at a resin temperature of 240 ° C. using a T-die extruder to form a base layer by extruding polypropylene. In the same manner as in Example 1, a polyolefin film was obtained. The resulting polyolefin film was measured for haze, scratch resistance, slipperiness, heat sealability, diaper opening property, and diaper transparency, and the results are shown in Table 1.

Comparative Examples 2 to 4 In Example 1, the particles contained in the surface layer were pulverized silica particles having an average particle diameter of 1.2 μm,
A polyolefin film was obtained in the same manner as in Example 1, except that the particles were changed to non-melting type silicone resin spherical particles of μm or silicone rubber spherical particles having an average particle diameter of 1.2 μm and a rubber hardness A of 20 °. The resulting polyolefin film was measured for haze, scratch resistance, slip property, heat sealing property, diaper opening property, and diaper transparency, and the results are shown in Table 2.

[0045]

[Table 1]

[0046]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a case where edible rice wrapped around nori is wrapped using the polyolefin film of the present invention as an inner wrapping film.

[Explanation of symbols]

 1: rice ball 2a, 2b: inner wrapping film 3: folded piece 4: outer wrapping film 5: broken part 6: laver

Continuation of front page (56) References JP-A-4-220436 (JP, A) JP-A-58-1525 (JP, A) JP-A-1-182040 (JP, A) JP-A-63-28642 (JP, A) , A) JP-A-54-135875 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A base layer of a mixture of 90% to 70% by weight of polypropylene and 10% to 30% by weight of high-density polyethylene, having an average particle size of 0.5 to 3 μm and a rubber hardness A of 30 to 80 degrees. Some silicone rubber particles are 0.05 to 1
A polyolefin film for packaging goods having a high water content, wherein a polyolefin film having a moisture content of 0.5 to 5.0 μm and a thickness of 0.5 to 5.0 μm and having a lower melting point than the base layer is laminated.