KR20100101332A - A multilayer film having excellent interfacial bonding strength - Google Patents

Abstract

PURPOSE: A multilayer film with the excellent interfacial bonding strength is provided to prevent the inter-layer delamination property of the film by using the properties of a polypropylene resin and a polyethylene resin. CONSTITUTION: A multilayer film with the excellent interfacial bonding strength includes a polypropylene layer blended with polyethylene, or a polyethylene layer blended with polypropylene. The content of polyethylene blended with the polypropylene layer is 40~50wt%. The polypropylene blended with the polyethylene layer is 20~50wt%.

Description

Multilayer film with excellent interfacial adhesion {A MULTILAYER FILM HAVING EXCELLENT INTERFACIAL BONDING STRENGTH}

The present invention relates to a multilayer film having excellent interfacial adhesion, and more particularly, to a multilayer film in which polyethylene is blended in a polypropylene layer or polypropylene is blended in a polyethylene layer.

Polypropylene film is widely used in general applications such as food packaging and textile packaging because of its excellent appearance, mechanical rigidity and heat resistance.However, polypropylene film has low impact strength at low temperature, low tearing strength and high thermal bonding temperature. Have Polyethylene film is widely used in general packaging applications due to its high tear strength, low thermal bonding temperature, and high impact strength at low temperatures.However, unlike polypropylene, polyethylene film requires high temperature pretreatment due to its low rigidity and low heat resistance. There are restrictions on use.

In order to complement the strengths and weaknesses of polypropylene and polyethylene, polypropylene and polyethylene have been attempted to form a multilayered film, but attempts have been made to co-extrude the resin to form a film, but due to the low interfacial adhesion between polypropylene and polyethylene, When the one side of the coextruded film was heat-bonded or adhered to another substrate with an adhesive, and then peeled off, the adhered portion did not fall and a problem occurred in which the peeling occurred at the interface between the polypropylene layer and the polyethylene layer.

In order to compensate for the low interfacial adhesion, an additional adhesive layer may be co-extruded between the polypropylene layer and the polyethylene layer, but in this case, there is a disadvantage in that an additional extruder is required in addition to the cost increase, and thus it is not widely used.

In addition to the method of coextrusion to form a film, there is also a method of forming a layer by laminating polyethylene after forming a polypropylene film and subjecting it to a surface treatment step, but the cost of reprocessing increases and the surface of the polypropylene surface increases with time. As the treatment effect decreases, the problem of lowering the interfacial adhesion force again occurs.

B.C. Poon et al. (Polymer, Vol 45, 893-903, 2004) used a method of blending polyethylene polymerized with a metallocene catalyst on a polyethylene layer to increase interfacial adhesion during coextrusion of polypropylene and polyethylene. However, even in this case, it is difficult to consider the underlying solution because there is a cost increase and the density must be lower than 0.90 g / cc due to the use of polyethylene polymerized with a metallocene catalyst.

The present invention has been made in order to solve the above problems, the problem to be solved by the present invention, in order to complement the advantages and disadvantages of polypropylene and polyethylene using an adhesive layer in the film forming a multi-layer film, or a post-treatment process The present invention is to provide a multilayer film having improved interfacial adhesion by coextrusion of polypropylene and polyethylene by a conventional multilayer film forming method without going through.

In order to solve the above problems, the multilayer film of the present invention is a multilayer film in which a polypropylene layer and a polyethylene layer are coextruded, and polyethylene is blended in the polypropylene layer or polypropylene is blended in the polyethylene layer. It features.

The content of polyethylene blended to the polypropylene layer is preferably 40 to 50% by weight, and the content of polypropylene blended to the polyethylene layer is preferably 20 to 50% by weight.

When the content of polyethylene blended to the polypropylene layer is less than 40% by weight, or the content of polypropylene blended to the polyethylene layer is less than 20% by weight, sufficient adhesive strength cannot be obtained between the polypropylene layer and the polyethylene layer. There is a problem that peeling between layers occurs.

The melt index (ASTM D 1238, 230 ° C., 2.16 kg) of the polypropylene constituting the polypropylene layer and the polyethylene layer is preferably 1 to 15 g / 10 minutes, more preferably 2 to 8 g / 10 minutes. Preferably, the melt index (ASTM D 1238, 190 ° C., 2.16 kg) of the polyethylene constituting the polyethylene layer and the polyethylene blended to the polypropylene layer is preferably 0.5 to 10 g / 10 minutes, and preferably 1 to 5 g / 10 minutes. More preferred.

If the melt index of the polypropylene used for multilayer film formation is less than 1 g / 10 minutes, the load increases during extrusion during film formation, the fluidity of the resin is low, and thus it is difficult to obtain desired productivity. The viscosity of the molten resin discharged is lowered, the thickness uniformity of the film is deteriorated, and film molding is not easy.

In addition, when the melt index of polyethylene used for multilayer film formation is less than 0.5 g / 10 minutes, the load increases during extrusion during film formation, the fluidity of the resin is low, and it is difficult to obtain desired productivity, and exceeds 10 g / 10 minutes. The viscosity of the molten resin discharged from the die is lowered, the thickness uniformity of the film is deteriorated, and film molding is not easy.

Although the said polypropylene is not specifically limited, It is preferable that it is a propylene homopolymer, a random copolymer of propylene and an alpha olefin, or a block copolymer of propylene and an alpha olefin.

Although the said alpha olefin is not specifically limited, It is preferable to select and use 1 or more types of the alpha olefin which has C2 or more.

Although the said polyethylene is not specifically limited, It is preferable that it is linear low density polyethylene.

Although not limited, the multilayer film of the present invention can be formed by a commonly used T-die casting method, and the same result can be obtained by conventional film forming such as an air-cooled blown film or a water-cooled blown film forming method. Can be.

As described above, the present invention, in order to improve the interlayer adhesion strength of the multilayer film composed of a polypropylene layer and a polyethylene layer, instead of a method of adding a separate adhesive layer between layers, another constituent layer resin in one of the constituent layers of the multilayer film To improve the adhesive strength by providing a film that can utilize the properties of polypropylene and polyethylene resin, especially when the polyethylene layer is a heat-adhesive layer and the polypropylene layer is used as a support layer, the interlaminar peeling properties are improved to When used for the multi-layer low temperature thermal adhesive film of the polyethylene layer it is possible to improve the interlaminar peel strength.

Hereinafter, the present invention will be described in more detail with reference to Examples. The examples are provided to illustrate the present invention by way of example and the scope of the present invention is not limited to these examples.

Film manufacturing

Next, the films of Examples 1 to 3 and Comparative Examples 1 to 3 were formed by a T-die casting method with the blending content of Table 1 below.

Melt index

Polypropylene was measured under conditions of 230 ° C. and 2.16 kg, according to ASTM D 1238 conditions.

Polyethylene was measured under conditions of 190 ° C. and 2.16 kg, according to ASTM D1238 conditions.

Thermal bond strength

Since it is difficult to directly measure the interlayer adhesive strength of the coextruded film, the film of each of the layers A and B of the examples below is formed into a film, and then the thermal adhesion strength is applied after performing thermal bonding under the conditions of ² kg / cm ² and 1 second. Measured.

Interlayer Peelability

Apart from the thermal adhesive strength evaluation for quantifying the interlaminar strength, in order to evaluate the interlaminar peelability under actual operation, the interlaminar peelability was evaluated after the film was coextruded into two layers. Adhesive strips having an adhesive strength of 200 N / m (= 0.3 kgf / 15 mm), which are generally used, were attached to both sides of the coextruded film in two layers, and then peeled. At this time, when the interlayer adhesive strength is lower than the adhesive strength of the adhesive tape, an interlayer peeling phenomenon occurs, and when the interlayer adhesive strength is higher than this, no peeling phenomenon occurs.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Floor A Polypropylene *
(weight%) 100 100 60 100 100 70 Polyethylene **
(weight%) 40 30 Floor B Polypropylene *
(weight%) 20 30 15 Polyethylene **
(weight%) 80 70 100 100 85 100 Thermal bond strength, kgf / mm 0.35 0.60 0.32 0.011 0.28 0.20 Delamination Peeling
Not Occurred Peeling
Not Occurred Peeling
Not Occurred Peeling
Occur Peeling
Occur Peeling
Occur

* Polypropylene: propylene homopolymer, melt index 8g / 10min

** Polyethylene: Linear low density polyethylene with melt index 0.9g / 10min, density 0.922g / cm ³

As can be seen in Table 1, in the case of Examples 1 to 3 of the present invention, it can be seen that the thermal adhesive strength exceeds 0.3kgf / mm, no interlayer peeling occurs.

Claims (4)

A multilayer film having a polypropylene layer and a polyethylene layer co-extruded, wherein the polyethylene is blended into the polypropylene layer or the polypropylene is blended into the polyethylene layer. The multilayer film of claim 1, wherein the polyethylene blended to the polypropylene layer is 40 to 50 wt%, and the polypropylene blended to the polyethylene layer is 20 to 50 wt%. According to claim 1, wherein the melt index of the polypropylene (ASTM D 1238, 230 ℃, 2.16kg) is 1 ~ 15g / 10 minutes, the polyethylene melt index (ASTM D 1238, 190 ℃, 2.16kg) is 0.5 ~ It is 10g / 10min, The multilayer film characterized by the above-mentioned. The multilayer film of claim 1, wherein the polypropylene is a propylene homopolymer, a random copolymer of propylene and an α-olefin, or a block copolymer of propylene and an α-olefin.