JP2002225108A - Method for manufacturing polyolefin multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a method for manufacturing not a thick foamed sheet but a thin foamed film of a polyolefin having excellent buffering properties (cushioning property), heat insulation, strength, moistureproofness and the like. SOLUTION: The method for manufacturing the polyolefin multilayer film comprises the steps of co-extruding a polyolefin resin by using two or three extruders to two types three-layer film, three types three-layer film or three types five-layer film. The method further comprises the steps of adding a chemical foaming agent of 0.1 to 1.9 pts.wt. to the central polyolefin resin, co- extruding so that a thickness of the film not filled with an outside foaming agent becomes thinner than the foaming layer to prepare an internally foamed polyolefin multilayer film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a co-extruded polyolefin foamed film having excellent cushioning properties (cushioning properties), heat insulating properties, strength and moisture resistance. This foamed film is suitable as a substitute for various papers. It is.

[0002]

2. Description of the Related Art A conventional polyolefin foam sheet is a thick sheet foamed immediately after chemical crosslinking or electron beam crosslinking, and it has been difficult to produce a thin film of 200 μm or less. Also, it is not economical because a cross-linking step is required. In addition, non-crosslinked foaming is caused by the breaking of the foam cells, resulting in 10
It is difficult to form a thin foam film having a thickness of 0 μm or less.
Only those having a thickness of not less than 00 μm and an expansion ratio of not more than 2 were produced.

JP-A-5-50485 discloses a thick sheet (about 1 to 5 mm thick) of a co-extruded multilayer of nylon / adhesive layer / foamed polyolefin / adhesive layer / nylon. It is described that if the expansion ratio is not less than 1.5, the sheet becomes rough and has no practical value even in the case of a sheet. JP-A-6-91795 discloses a high-rigidity and lightweight T-die method foamed laminated resin sheet having a large thickness. A thermoplastic resin containing 20 to 40% of an inorganic filler is provided on both sides to increase rigidity, and a foam layer is provided in an intermediate layer to reduce the weight of a sheet which is heavier than the inorganic filler.
A large amount of a foaming agent of 2 to 3.5 parts by weight is added to 100 parts by weight of the resin in order to make the intermediate layer highly foamed, and large foam cells are generated in the foamed layer. The thickness of the obtained sheet is 300 to 500 μm. In short, the purpose of the invention is different from that of the present invention, and therefore, the configuration of the invention is also different. JP-A-6-182884 is a sheet and a composite material having spherical closed cells. The thickness and thickness of the foamed resin sheet are 2 to 8 mm, and the purpose and contents are different from those of the invention of the present application. Japanese Patent Application Laid-Open No. 2000-902 is a composite sheet of a crosslinked resin foam and an inorganic fiber sheet, and has a different purpose and content from the invention of the present application which features a non-crosslinked resin foam.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a method for producing a thin multi-layer foamed film of a non-crosslinked polyolefin which could not be produced by the prior art. is there.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and comprises coextruding a polyolefin resin by using two or three extruders to obtain two or three types.
In the method for producing a multi-layer, three-layer or three-layer or three-layer five-layer polyolefin film, 0.1 to 1.9 parts by weight of a chemical foaming agent is added to the central polyolefin resin, and A method for producing an internally foamed polyolefin multilayer film, comprising coextruding from a die such that the thickness of a film that cannot enter is smaller than that of a foamed layer.

A multilayer film having a wide range of applications in the most general method in which the intermediate layer is a foamed layer is a multilayer film in which each layer is independent.
It is a seed three-layer film. In this case, the types and compositions of the resins of the outer layer films on both sides can be changed depending on the application. In the case of two types and three layers, the outer layer films on both sides are made of the same material, and different functions cannot be given to the outer layer films as in the case of three types and three layers, but the cost can be reduced most. In the case of a three-layer, five-layer film, the cost is higher, but the type and composition of the resin of the film can be changed according to the application more than in the case of a three-layer, three-layer film, and the application of functions becomes diverse.

In the present invention, the internally foamed polyolefin multilayer film can employ any one of a blown film forming method and a T-die film forming method. However, in general, in the T-die film forming method, it is somewhat difficult to reduce the temperature fluctuation and the pressure fluctuation in the width direction of the T-die. As a result, uneven foaming occurs and the film thickness tends to fluctuate in the width direction. Therefore, it is necessary to pay attention to the molding apparatus and the molding operation so that they do not occur. Generally, it is used for forming a thick film, but the thickness of the film of the present invention is also possible.

On the other hand, in the blown film forming method, since a circular die is used, it is easy to reduce the temperature fluctuation and the pressure fluctuation as described above. Therefore, there is an advantage that the uneven thickness accuracy is easily maintained at a high level. It is suitable for forming a thin film as in the present invention.

In the present invention, the thickness of the outer layer film is made smaller than that of the foamed film of the intermediate layer in order to provide a buffering effect, heat insulation and the like.

In the present invention, as the polyolefin, various polyethylenes such as low-density polyethylene (hereinafter referred to as LDPE), linear polyethylene (hereinafter referred to as LLD), high-density polyethylene (hereinafter referred to as HDPE), and various types of ethylene are used. A system copolymer (EEA or the like) and polypropylene (hereinafter, referred to as PP) can be used.

In the present invention, the intermediate layer has a melt flow index at 190 ° C. (hereinafter referred to as MF) in terms of balance between strength and waist.
Called R. ) 0.1 to 10 g / 10 min, preferably 0.1 to 10 g / 10 min.
4 to 5.0 g / 10 min HDPE or high density L
An LLD produced by a metallocene-based catalyst or a single-site catalyst having a DPE having an MFR of 0.1 to 10 g / 10 min, preferably 0.4 to 5.0 g / 10 min in the outer layer is suitable.

In the present invention, since the outside is made of a non-foamed polyolefin, the foamed layer of the intermediate layer can be foamed uniformly, and a thin foamed film can be formed. With a conventional single-layer film, it is difficult to form a non-crosslinked foamed film of 150 μm or less, and the expansion ratio is 2 times or less.

In the present invention, a chemical blowing agent which decomposes at the molding temperature to generate gas is used as the blowing agent, and azodicarbonamide, sodium bicarbonate / citric acid, etc. are suitable. The amount of the chemical foaming agent to be added is 0.1 to 1.9 parts by weight of the chemical foaming agent with respect to the central polyolefin resin.
It is 3 to 1.2 parts by weight.

When the amount of the foaming agent is less than 0.1 part by weight (based on 100 parts by weight of the polyolefin resin, the same applies hereinafter), the desired film is not formed due to insufficient foaming. The cells are broken, and a uniform foamed film cannot be obtained.

The polyolefin resin of the outer layer includes charcoal
Additives such as a matting agent such as talc, a rust inhibitor such as slaked lime, a weathering agent, an antistatic agent, a flame retardant, a pigment, a lubricant and an antiblocking agent can be added in appropriate amounts as required.

In the present invention, in order to obtain a molded multilayer foam film having good moldability and excellent cushioning properties, heat insulation properties, strength and moisture resistance, the foaming ratio of the foamed layer is set to 1.
When the thickness of the multilayer foamed film is less than 20 μm, the film is cut and becomes difficult to form. When the thickness is 300 μm or more, the stability of the film immediately after being extruded (in the case of inflation molding). In such a case, the stability of the bubble tends to deteriorate, so that the thickness of the multilayer foamed film is preferably 20 μm to 300 μm.

The molding temperature varies depending on the grade to be used, the type and amount of the foaming agent, the expansion ratio, etc., but is 170 to 210 ° C. for the inflation system and 20 for the T-die system.
0-240 ° C is preferred.

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited thereto.

[0019]

Example 1 Using a three-type, three-layer T-die molding apparatus with a die width of 1.5 m, HDR having an MFR of 1.5 g / 10 min and a density of 0.955 g / cm ³ for the intermediate layer, LLD (MFR1.5
g / 10 min, density 0.920 g / cm ³ ) and HD
0.5 parts of an azodicarbonamide-based blowing agent was added to PE, 2 parts of a brown pigment was added to the outer layer 1, and 8 parts of slaked lime was added to the outer layer 2 for the purpose of rust prevention.

The thickness of the obtained multilayer film is determined by taking-up speed 2
At 0 m / min, (outer layer) 15 μm / (intermediate foam layer) 40
μm / (outer layer) 15 μm Total thickness 70 μm, take-off speed 1
At 0 m / min, (outer layer) 30 μm / (intermediate foam layer) 80
μm / (outer layer) 30 μm Total thickness was 140 μm, and the expansion ratio of the intermediate foam layer was 2.5 times. Each of the obtained films exhibited excellent stiffness (rigidity) and moisture resistance, and the film strength was good as a foamed film.

[0021]

Example 2 A three-layer, three-layer inflation molding apparatus having a die diameter of 150 mm was used, and an MFR of 1.3 g was used for the intermediate layer.
/ 10 minutes, LDPE having a density of 0.926 g / cm ³ , and LLD (MF
R1.5 g / 10 min, density 0.930 g / cm ³ ), and a baking soda / citric acid based blowing agent 0.5
Parts and the outer layer 2 were added with 2 parts of a brown pigment,
Molded at 0 ° C. At this time, the outer layer 1 was subjected to a corona treatment of 50 dynes in order to improve printability.

The thickness of the obtained multilayer film is set at a take-up speed of 2.
At 0 m / min, (outer layer) 20 μm / (intermediate foam layer) 70
μm / (outer layer) 20 μm The total thickness was 110 μm, the expansion ratio of the intermediate foam layer was 2.3 times, and the foam cells were denser than in Example 1.

In the above-mentioned film, the intermediate layer is made of LDPE. However, since the high-density product is used and the LLD produced with the metallocene catalyst is also high-density, the stiffness (rigidity) and moisture-proofness are the same as in Example 1. And the film strength was good as a foamed film.

[0024]

Comparative Example 1 The same HDPE (MFR 1.5 g /
For 10 minutes, the same foaming agent was added to a density of 0.955 g / cm ³ ), and a single-layer film was tested with various changes in the amount added and the resin temperature. A foamed film having an expansion ratio of 1.2 times or more was obtained. And the film was as thick as 250 μm.

[0025]

Comparative Example 2 MFR 1.0 g / 10 min, density 0.920
0.5 parts of a baking soda / citric acid-based blowing agent was added to g / cm ³ LDPE, and the mixture was molded at a resin temperature of 190 ° C. using a single-layer inflation molding apparatus. When the expansion ratio is 1.5 times or more, it is difficult to form a film of 200 μm or less due to breakage of the foam cells.

[0026]

According to the present invention, it is possible to produce a polyolefin thin foam film which has been conventionally difficult to form, and as a film excellent in cushioning property (cushioning property), heat insulating property, cost, strength, moisture resistance, etc., such as kraft paper. It can be suitably used as a substitute for various papers and for packaging various industrial materials used outdoors.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) B29L 7:00 B29L 7:00 9:00 9:00 (72) Inventor Teru Kobayashi 2- Ikebukuro, Minami-Ikebukuro, Tokyo 27-9 Tamapoli Stock Company In-house (72) Inventor Takumi Maruyama 2-27-9 Tamapoli Stock Company In-house F-term (reference) AK04D AK04E AK05A AK05B AK05C AK05D AK05E AK07A AK07B AK07C AK07D AK07E AK63A AK63B AK63C AK63D AK63E BA03 BA05 BA06 BA10A BA10C CA01B CA08A CA08C CA13A CA13C CA14A CA14C CA22A CA22C CA30A CA30C DJ01B EH232 GB90 JD04 JJ02 JK01 JK11 4F207 AA03 AA04 AA05 AA08 AA11 AB02 AB05 AB09 AB12 AB16 AE02 AG01 AG03 AG20 AH53 KA01 KA11 KA19 KB26 KB28 KF04 KK81 KL84

Claims (5)

[Claims] 1. A method for producing a polyolefin multilayer film, comprising coextruding a polyolefin resin using two or three extruders to form a two-, three-, three- or three-layer five-layer film. 0.1 to 1.9 parts by weight of a chemical foaming agent is added to the central polyolefin resin, and the extruded film is coextruded from a die so that the thickness of the film not containing the foaming agent becomes thinner than the foamed layer. For producing an internally foamed polyolefin multilayer film. 2. The method for producing an internally foamed polyolefin multilayer film according to claim 1, wherein the resin extruded from the die is formed into a film by an inflation method or a T-die method. 3. The foaming ratio of the foamed layer is 1.5 to 5 times,
The method for producing an internally foamed polyolefin multilayer film according to claim 1 or 2, wherein the total thickness of the multilayer film is 20 µm to 300 µm. 4. The polyolefin resin is polyethylene or polypropylene, and the outer layer resin has a rust preventive such as charcoal or talc as a matting agent, slaked lime, a weathering agent, an antistatic agent,
A flame retardant, a pigment and the like are compounded, wherein
4. The method for producing an internally foamed polyolefin multilayer film according to claim 2 or 3. 5. The method for producing an internally foamed polyolefin multilayer film according to claim 4, wherein the polyethylene is a linear low-density polyethylene or a high-density polyethylene produced by a metallocene catalyst or a single-site catalyst.