JPH0331346B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a multilayer film, and more particularly to a multilayer film that can be effectively used for packaging articles such as home appliances, office equipment, and furniture. [Prior art and problems to be solved by the invention] Conventionally, packaging of items such as home appliances such as televisions and audio equipment, office equipment, precision equipment, and furniture has been done to prevent scratches and damage to these items. In order to do this, the article is usually wrapped in advance with a film such as polyethylene, then fixed with a cushioning material such as resin foam or cardboard, and then placed in an outer case. However, in this case, there is a problem that the protection of the article is insufficient due to friction between the film and the article, resulting in scratches, peeling of the paint, etc. For this reason, it has been proposed to use a laminated film made by laminating a foamed low-density polyethylene film and an unfoamed polyethylene film, or a low-density polyethylene coextruded multilayer film consisting of a foamed layer and a non-foamed layer, as these packaging films. ing. However, the former laminate film requires high processing costs, and it is substantially difficult to produce a thin foamed film, so the film must be thick. Moreover, it has the disadvantage that its strength is low compared to the film thickness, and packaging costs are high. In addition, in the case of the latter multilayer film, since the resin used is the same, the middle layer is a foam layer, which provides cushioning properties, and when compared with films of the same weight, it has characteristics such as stiffness, but it is difficult to wrap. In terms of friction with articles and cushioning materials, it is no different from a single layer film, and there is a problem in that it does not provide sufficient protection for articles. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and to provide a multilayer film that can sufficiently protect packaged articles, is easy to manufacture, and has high strength. [Means for Solving the Problems] That is, the present invention provides a cylindrical coextruded multilayer film in which the intermediate layer is made of a foamed polyolefin resin layer, and both outer layers are made of non-foamed polyolefin resin layers. One of the outer layers has a static friction coefficient of 0.4
The object of the present invention is to provide a multilayer film which has the above-mentioned non-slip properties, the other layer has easy slip properties with a static friction coefficient of less than 0.4, and the difference in the static friction coefficients between the two outer layers is 0.1 or more. A polyolefin resin is used as a raw material for the multilayer film of the present invention. Here, polyolefin resins include polyethylene resins,
Mention may be made of polypropylene, polybutene, and mixtures thereof. Any known polyethylene resin can be used as the above polyethylene resin, such as high density polyethylene (HDPE),
Examples include medium density polyethylene (MDPE) and low density polyethylene (LDPE), and in addition to ethylene homopolymers, ethylene-ethyl acrylate copolymers, ethylene-vinyl acetate copolymers (vinyl acetate content 10% by weight or less), Low crystallinity ethylene
Random or block copolymers such as α-olefin copolymers, ethylene-unsaturated carboxylic acid copolymers, etc., or mixtures thereof may be used. Here, high density polyethylene has a density of 0.940 to 0.970.
g/ ^cm3 , melt index (MI) 0.01~10
g/10 minutes, preferably 0.02 to 5 g/10 minutes.
In addition, medium- and low-density polyethylenes include high-pressure polyethylene, ethylene and propylene obtained by medium- and low-pressure methods, butene-1,4-methylpentene-1,
There is a so-called linear low-density polyethylene (LLDPE), which is a copolymer with an α-olefin having 3 to 12 carbon atoms such as octene-1. Here, medium/low density polyethylene has a density of 0.900 to 0.940 g/cm ³ ,
The MI is 0.1 to 50 g/10 minutes, preferably 0.2 to 20 g/10 minutes. In addition, low-crystalline ethylene-α-olefin copolymers include ethylene-propylene copolymers (EPR) with a density of 0.900 g/cm ³ or less, ethylene-
Examples include propylene-diene copolymer (EPDM) and ethylene-butene-1 copolymer. The multilayer film of the present invention is obtained by coextrusion inflation molding the above-mentioned raw material resin, in which the middle layer is made of a foamed polyolefin resin layer, and both outer layers are made of non-foamed polyolefin resin layers. . Although the raw material resin constituting the intermediate layer is not particularly limited, it is preferable to use a polyethylene resin, particularly a low-density polyethylene resin as a main component. Furthermore, the foaming agents that can be used to form the intermediate foamed resin layer can be broadly classified into chemical foaming agents and physical foaming agents based on their foaming mechanism. Among these, chemical blowing agents include azodicarbonamide, dinitropentamethylenetetramine, azodiisobutyronitrile, etc., and physical blowing agents include butane, heptane, hexane, dichlorodifluoromethane, nitrogen, carbon dioxide, etc. can give. In this foamed resin layer, the blending ratio of the raw resin and the foaming agent is not particularly limited and varies depending on the type of foaming agent, etc., but in short, the foaming ratio is 1.2 to 5.0, preferably
It may be set between 1.2 and 4.0. In addition, this foamed resin layer may contain a nucleating agent such as inorganic fine powder if necessary.
In addition to colorants, rubbers, carboxylic acid metal salts, etc. can also be added as appropriate. Next, both outer layers of the multilayer film of the present invention are made of non-foamed polyolefin resin layers, and one is made to be non-slip and the other is easy to slip. Here, slip resistance refers to the coefficient of static friction on the surface.
0.4 or more, preferably 0.45 or more. In this case, the static friction coefficient refers to the static friction coefficient between two layers of the same type. On the other hand, slipperiness means that the coefficient of static friction of the surface is less than 0.4, preferably 0.35 or less. In the present invention, it is necessary that the difference in the coefficient of static friction between the surfaces of both outer layers is 0.1 or more. However, the static friction coefficients of the surfaces of both outer layers should be determined in consideration of moldability and the like. The raw material resin constituting the non-foamed resin layer may be appropriately selected from the polyolefin resins mentioned above, but in particular, the non-slip layer may be made mainly of low density polyethylene, ethylene-vinyl acetate copolymer, etc. Preferably, the slippery layer is preferably made mainly of high-density polyethylene, polypropylene, or the like. In the present invention, a difference in the coefficient of static friction may be created by selecting the raw resin as described above, or a difference in the coefficient of static friction may be created by adding a lubricant. There are various types of lubricants, including fatty acid lubricants such as higher fatty acids and oxyfatty acids; fatty acid amide lubricants such as fatty acid amide; fatty acid esters; hydrocarbons; and alcohol-based lubricants. can. Note that it is preferable to add antistatic agents such as various surfactants to this non-foamed resin layer. The multilayer film of the present invention has the above-mentioned structure, and usually consists of a three-layer film including an intermediate layer and both outer layers. Here, one of both outer layers is outer layer A.
and the other layer is outer layer B, and the layer ratio is expressed as outer layer A: intermediate layer: outer layer B: 5~60:10~80:5~
It is preferable to set it to 60. Further, the thickness of the multilayer film is usually 20 to 200μ. Although the multilayer film of the present invention is a cylindrical coextruded multilayer film, it can also be opened to form a flat film. In the present invention, the inner side of the cylindrical film is usually a slippery layer. Such a multilayer film of the present invention can be produced by coextrusion inflation molding the raw material resin using usually three extrusion molding machines. Specifically, the above-mentioned raw material resins were sufficiently melted and kneaded using each extruder, and then co-extruded with a foamed resin layer as an intermediate layer and a non-foamed resin layer as both outer layers with adhesion in a die, and further at a blowing ratio of 1.5 to 5. Inflation molding can be performed. Note that the die temperature at this time is usually 130 to 180°C, and the die lip gap is usually 0.5 to 2 mm. [Effects of the Invention] Since the multilayer film of the present invention has different coefficients of static friction on the surfaces of both outer layers, when used as a packaging film, there is little slippage against the packaged article, and moreover, it easily slips against external cushioning materials, etc. It's summery. Therefore, the packaged articles can be effectively protected without damaging the packaged articles or peeling off the coating due to friction between the film and the packaged articles. Furthermore, since the multilayer film of the present invention has a foamed resin layer as an intermediate layer, the foaming efficiency is high and there is no occurrence of so-called eye stain. Therefore, manufacturing is also easy. Further, the multilayer film of the present invention can be made thin, and has sufficient strength even as a thin film. Therefore, packaging costs can be reduced and resources can be saved. Furthermore, the multilayer film of the present invention has good surface printability and has a luxurious appearance with a pearl-like luster and a Japanese paper feel. Therefore, the multilayer film of the present invention can be effectively used for packaging various articles including home appliances, office equipment, furniture, and the like. Examples Next, examples of the present invention will be shown. Examples 1 to 4 The resins shown in Table 1 were melt-kneaded using three extrusion molding machines, introduced into an in-die adhesive type circular die, extruded, and inflation molded at a blow ratio of 3 to form a mixture having a predetermined layer ratio. A three-layer film with a pearl-like luster and having a foamed resin layer in the middle was obtained. Table 1 shows the results of measuring the physical properties of this film. Note that the film thickness when the intermediate layer was not foamed was 60 μm. Further, 4% by weight of azodicarbonamide was added as a foaming agent to the intermediate layer. Reference Example Table 1 shows the results of measuring the physical properties of a commercially available laminate film (a laminate film of a 500μ thick low density polyethylene foam film and a 13μ thick high density polyethylene film).

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Claims (1)

[Claims] 1. A cylindrical coextruded multilayer film in which the middle layer is made of a foamed polyolefin resin layer and both outer layers are made of non-foamed polyolefin resin layers, and one of the outer layers is non-slip with a coefficient of static friction of 0.4 or more. ,
A multilayer film characterized in that the other layer is slippery with a coefficient of static friction of less than 0.4, and the difference in the coefficient of static friction between the two outer layers is 0.1 or more.