JPH09216318A - Multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film for heat sealing which maintains stable heat sealability by using linear polyethylene on the heat sealing surface of the cover material of a molded vessel with polyethylene as the sealing surface and has releasing strength easy for tearability and excellent external appearance of the release part. SOLUTION: The multilayer film 10 comprises a polypropylene layer 1 of a support layer, a release layer 2 of composition of olefin copolymer rubber and polypropylene and a polyethylene layer 3 sequentially formed in this order, wherein the thicknesses of the layers 2 and 3 are 0.5 to 2 and 2 to 3.5μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an easily peelable heat sealant layer used for a lid material of a laminated container having a polyethylene layer as a heat seal surface, which has stable heat sealability, easy peelability and peeling. It belongs to a multi-layer film which has low stringing properties when it is made.

[0002]

In order to stably heat-seal a lid material used for a molding container having a polyethylene layer as a heat-sealing surface, the stability of foreign matter-adhering seal and the hot work required for high-speed filling heat-sealing A linear polyethylene (hereinafter, referred to as LLDPE) has been used as a material having a sealing property. However, LLDP
When E was used, there was a problem that the heat sealing strength and breaking strength were strong and it was difficult to open. The present invention is LL
An object of the present invention is to provide a multilayer film for heat-sealing, which maintains the heat-sealing stability of DPE, has peeling strength for easy opening, and has less stringiness at the peeling portion and has an excellent appearance. Is.

[0003]

In order to achieve the above object, a multilayer film for heat-sealing of the present invention comprises a support layer made of polypropylene, a release layer made of a composition of olefinic copolymer rubber and polypropylene, and In a multilayer film in which the polyethylene layer is configured in this order,
The release layer and the polyethylene layer (hereinafter referred to as PE layer) have thicknesses of 0.5 to 2 μm, 2 to 3 ...
It is a multilayer film having a thickness of 5 μm. The release layer is a multi-layer film in which the olefin copolymer rubber and the polypropylene have a weight ratio of 10: 2.5 to 40. The PE layer is obtained by catalytic polymerization of ethylene and 4-methylpentene-1, and contains at least 89% by weight of a polymer unit derived from ethylene and has a density of 0.910 to 0.925 g / cm. It is a multilayer film of LLDPE of ³ (hereinafter, g / cm ³ which is a unit of density is omitted).

[0004]

2. Description of the Related Art A polyethylene resin is used for a heat sealant layer used as a lid material for a molding container having a PE layer as a heat seal surface, and in particular, when a liquid material or the like is filled, a perfect heat seal can be achieved. When the sealing property is required, LLDPE, which is excellent in foreign matter-adhering heat sealing property and hot heat sealing, has been used.

When the sealing portion needs to be openable, heat sealing of low-density polyethylene and polypropylene, polystyrene copolymer, etc. is impeded in the portion corresponding to the PE layer of the molding container or lid. Attempts have been made to facilitate opening by mixing with a resin.
However, the provision of a heat sealant layer other than the above LLDPE deteriorates the hot sealing property and the foreign substance adhering sealing property of LLDPE, resulting in poor heat sealing such as defective heat sealing. There was a problem in that the contents leaked out and the quality was altered.

Further, the heat-sealing portion is made of LLDPE to stabilize the hot-sealing property and the foreign substance-adhering sealing property.
Further, in order to provide easy opening, a heat sealant layer having a multi-layer structure has also been proposed. For example, by lowering the adhesive force between the heat-sealing portion and the resin layer in contact with it, the resin layer on the heat-sealing surface is cut, and the interface peelability is used to provide easy opening or contact with the heat-sealing resin. A technique has also been disclosed in which the heat-sealed portion can be easily peeled off by cohesively breaking the resin. However, the above method cannot be stably cut and opened because the LLDPE, which is the resin of the heat seal portion to be cut, is not well cut, and the resin of the heat seal portion causes stringing at the time of breakage. Therefore, it had a bad appearance.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A multilayer film for a heat sealant of the present invention comprises a polypropylene layer (hereinafter referred to as a PP layer) 1 as a supporting layer, an olefinic copolymer rubber and polypropylene as shown in FIG. In the multilayer film with the release layer 2 and the PE layer 3 made of the composition, the thicknesses of the release layer 2 and the PE layer 3 are 0.5 to 2 μm, respectively.
m is a multilayer film 10 formed with a thickness of 2 to 3.5 μm. The release layer 2 is the multilayer film 10 in which the weight ratio of olefinic copolymer rubber and polypropylene is 10: 2.5 to 40.

The PP layer, which is the supporting layer of the present invention, serves as a substrate for forming a multilayer film, has a tensile strength of 300 kg / cm ³ , an elongation of 200% or more, and causes cohesive failure. There is no polypropylene, and a grade that can be cast sheet or melt extrusion coated is used. The polypropylene may be either a homopolymer or a copolymer. Preferably, in order to stabilize the adhesion to the release layer, a copolymer with α-olefin or an ethylene / vinyl acetate copolymer, an ethylene / acrylic acid copolymer, an ethylene / acrylic acid ester copolymer, an ionomer, etc. It is a blend with. In addition, a crushed product of scraps or scraps at the time of film formation may be appropriately added to the PP layer.

The PP layer can be formed by a coextrusion cast film capable of forming a multilayer film together with a release layer and a PE layer, or by melt coextrusion coating with a thickness of 10 to 50 μm on another substrate film. Thickness is 1
5 to 60 μm. The multilayer film of the present invention is preferably subjected to the coextrusion film forming method from the viewpoint of thinning the release layer and the PE layer. In the co-extrusion film forming method, a T-die method using a flat die or an inflation method using an annular die can be applied. In the T-die method, either a black box type coextrusion or a multi-manifold type may be used. Also in the case of the inflation method, a known die can be used. Further, the surface of the PP layer on which the release layer is not provided is preferably subjected to corona discharge treatment, ozone treatment or the like in order to stabilize the adhesion to the substrate film or the printing film. When the other base film is provided by coextrusion coating, it is preferable to apply, for example, an isocyanate anchor coat to the base film.

The peeling layer is strongly adhered to the PP layer and the PE layer at the time of film formation and can be peeled from the PP layer by cohesive failure of the peeling layer, and is required to be cut with less stringing. It The present invention can satisfy the above requirements by appropriately changing the weight composition of the olefin-based copolymer rubber and the polypropylene to strictly regulate the thickness and the thickness of the PE layer to be laminated.

The release layer comprises homopolypropylene (hereinafter referred to as homoPP) or a copolymer of propylene and α-olefin, and an ethylene / vinyl acetate copolymer or ethylene / acrylic acid copolymer which is an olefin copolymer rubber. It is a composition with a polymer, an ethylene / acrylic acid ester copolymer, an ionomer, ethylene / butene rubber, ethylene / propylene rubber and the like. And its thickness is 0.5
When the thickness is less than μm, the heat sealing strength between the PE layer and the PP layer is weak and the function as a heat sealant layer with stable sealing cannot be satisfied. On the other hand, when it exceeds 2 μm, the heat seal strength (peeling strength) is so strong that the function as the easily openable heat sealant layer cannot be exhibited.

As the PE layer of the present invention, a PE layer made of LLDPE is used to stabilize the hot sealing property. When the thickness of the PE layer is less than 1 μm, the PE layer 36 provided on the base material layer 4 of the laminated material 43 shown in FIG. The inter-sealing property cannot be obtained, and the heat sealing becomes unstable. On the other hand, when the thickness exceeds 5 μm, there is a problem that the heat-sealed PE layer 31 is difficult to cut and stringing is large when opening, and it is preferable to set the PE layer to 2 to 3.5 μm. Therefore, the PE layer is added to the layers 2-3.
5 μm, the release layer is 0.5 to 2 μm, and the total thickness is 2.
The release layer and the PE layer, which are required to be processed into a thin film in the multilayer film so as to have a thickness of 5 to 5.5 μm, are preferably formed by a multilayer coextrusion process together with the PP layer. Also, PE
Layer 3 is obtained by catalytic polymerization of ethylene with 4-methylpentene-1, contains at least 89% by weight of units of polymer derived from ethylene and has a density of 0.910-0.
In the case of LLDPE of 925, particularly excellent hot-sealing property can be obtained.

Further, as shown in FIG. 2, the PE layer 3 which is the heat-sealing surface of the multilayer film is a laminated material 43 which becomes a container.
Is heat-sealed with the PE layer 36 of
When it is adhered to the E layer 36 and peeled off, it peels off like the cohesive failure portion 32. And PE of multilayer film
The layer 3 remains as the PE layer 31 on the side of the laminated material 43, and the periphery of the cohesive failure portion 32 of the peeling layer 2 is good without stringing. In any layer or all layers constituting the above-mentioned multilayer film 10, known additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent may be added, if necessary. Lubricants, nucleating agents, organic and / or inorganic pigments, dyes and the like can be added as appropriate.

[0014]

EXAMPLE The release layer 2 was made of homo PP (melt flow rate specified in JIS K7210 = 7.0 g / 10 min (hereinafter, abbreviated as MFR ... and g / 10 min)) and MFR3.5 ethylene. Butene rubber (hereinafter E
And described as BM) in the proportions shown in Table 1. Further, a propylene / ethylene random copolymer (ethylene content 3% by weight, MFR 7.0, hereinafter referred to as random PP) was used as the PP layer 1, and PE described in Table 1 was used.
Layer 3 was supplied to a T-die type co-extrusion film forming apparatus having a pipe-joining type feed block (black box type), and a sample 1 of a three-layer example having a resin temperature of 240 ° C. and a thickness shown in Table 1 The multilayer film 10 of ~ 5 was produced.
Samples 1 to 3 of the examples are LL obtained by catalytic polymerization of an olefin having 6 carbon atoms with 4-methylpentene-1 and ethylene.
It is a DPE having a density of 0.915 and an MFR of 7.0. Further, Sample 4 is LLDPE obtained by catalytic polymerization of α-olefin having 4 carbon atoms and ethylene, and has a density of 0.
920, MFR 7.0.

[0015]

[Comparative Example] In the same apparatus as in the example, as shown in Table 1, the release layer 2 was a composition of random PP and EBM, the thickness of which was 2.0 μm and 0.5 μm, and PE. The thickness of the layer 3 is changed to 1-2 μm and P
Samples 1 to 3 of Comparative Examples using EBM instead of the E layer 3 were prepared. Table 1 shows the layer configurations of the multilayer films of Examples and Comparative Examples. (Below margin)

[0016]

[Table 1]

A lid member was prepared by dry-laminating the PP layer of each sample of the examples and comparative examples and a polyester film having a thickness of 25 μm using a polyurethane adhesive. On the other hand, a low-density polyethylene having a thickness of 50 μm as the PE layer 36 and a polyester sheet having a thickness of 300 μm as the base material layer 4 were composited by dry lamination to prepare a laminated material 43 for a container shown in FIG.

The PE layer 3 of the lid member and the PE layer 36 of the laminated sheet 43 were evaluated for heat sealability, hot sealability and appearance when peeled by the following evaluation methods.
Table 2 shows the evaluation results. * 1 Peel strength: At each temperature shown in Table 2, the PE layer 3 of the lid material and the PE layer 36 of the laminated sheet were pressed at a pressure of 3 kg / cm ² ,
Heat sealing was performed under a condition of a time of 1 second, and the strength was measured by peeling at a peeling angle of 90 ° and a pulling speed of 300 mm / min. * 2 Hot sealability: P of the lid material at each temperature shown in Table 2
The E layer 3 and the PE layer 36 of the laminated sheet are pressed at a pressure of 3 kg / cm.
^{2. After} heat-sealing under the condition of time of 1 second, immediately after heat-sealing, an external force of 50 g is applied to the heat-sealed surface in a state where it is not cooled and solidified, and the peeling distance is evaluated. A material having a small peeling distance is a material having excellent hot sealability. * 3 Peeling portion: The appearance of the peeling portion (cohesive failure portion 32) of the sample whose peel strength was measured is visually evaluated. ◎: Good with no stringiness ○: Good with almost no stringiness * 4 Overall evaluation ◎: Good in appearance, peel strength and hot sealability ○: Some of appearance, peel strength and hot sealability Inferior, but no practical problem. B: Any of appearance, peel strength, and hot sealing property was slightly inferior, and there were some problems as a product. X: The appearance, peeling strength, and hot sealing property were poor, and there was a problem as a product. (Below margin)

[0019]

[Table 2]

In all the samples of the examples, good results were obtained in terms of peel strength, hot sealability, and appearance of the peeled portion. In particular, Samples 1 to 3 used, in which LLDPE obtained by catalytic polymerization of ethylene and 4-methylpentene-1 were used, had good hot sealability. On the other hand, the sample 1 of the comparative example had an insufficient hot sealability because the PE layer was thin, and the sample 2 had a peel strength of 500 gf / 15 mm.
It is weak, and Sample 3 has a problem in hot sealability.

[0021]

From the results shown in Table 2, the examples have stable heat-sealing strength (peeling strength) and hot heat-sealing contributing to the stability of heat-sealing. Is a multilayer film for heat-sealing having a good appearance that causes cohesive failure without stringing. In addition, as shown in FIG. 2, the peeling portion is the PE layer 3 of the lid material.
Is heat-sealed with the PE layer 36 of the laminated material to form the PE layer 3
It is heat-sealed as No. 1 and remains in the laminated material when peeled off. Then, the cohesive failure part 32 from which the PE layer 31 was peeled off exhibited a good effect without stringing.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a layer configuration of a cross section of the present invention.

FIG. 2 is a cross-sectional view showing the concept of a peeling portion of a multilayer film heat-sealed in a container.

[Explanation of symbols]

 1 PP layer 2 Release layer 3, 31, 36 PE layer 4 Base material layer 10 Multilayer film 32 Cohesive failure part 43 Laminated material

Claims (3)

[Claims] 1. A multilayer film comprising a support layer made of polypropylene, a release layer made of a composition of an olefin-based copolymer rubber and polypropylene, and a polyethylene layer in this order, and the thickness of the release layer and the polyethylene layer. Is 0.5 to 2 μm and 2 to 3.5 μm, respectively.
Is a multilayer film. 2. The multilayer film according to claim 1, wherein the release layer comprises an olefinic copolymer rubber and polypropylene in a weight ratio of 10: 2.5 to 40. 3. The polyethylene layer is obtained by catalytic polymerization of ethylene and 4-methylpentene-1, and contains at least 89% by weight of a polymer unit derived from ethylene, and has a density of 0.910. 0.925 g / cm ³
3. The multi-layer film according to claim 1 or 2, which is the linear low-density polyethylene.