JPH02217220A - Production of polyethylene-based foam - Google Patents

Abstract

PURPOSE:To obtain a polyethylene-based foam which equips cushioning properties, softness and toughness and is suitable for packaging by mixing a specified ethylene-alpha-olefine copolymer with low-density PE at a specified blending ratio and extruding the obtained resin composition from the tip of an extruder to form the foam. CONSTITUTION:alpha-olefine content is regulated to 8-40wt.% and density is regulated to 0.88-0.92g/cm<3>. Composition consisting of 40-80wt.% ethylene-alpha-olefine copolymer and 60-20wt.% low density PE is mixed. A foaming agent is added to this resin composition and further various additives are added in accordance with necessity. This mixture is introduced into an extruder, heated and mixed therein and made molten mixed gel. Thereafter a foam is obtained by extruding this gel in the atmosphere through the mouthpiece of the extruder.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a polyethylene foam suitable for cushioning packaging materials, which has both flexibility and toughness particularly suitable for packaging products with complex shapes. The present invention relates to a method for producing a polyethylene foam.

(Prior Art) In recent years, polyethylene foams have been suitable as cushioning packaging materials because they have good cushioning properties.

In particular, thin sheet-shaped foams made by extruding and foaming low-density polyethylene are widely used because they are easy to obtain of high quality.

By the way, low-density polyethylene foam sheets have no problems when packaging objects with simple shapes, but when they are used to package objects with complex shapes, the sheet has little elongation, so the adhesion to the packaged items is insufficient. In some cases, the sheet may break, significantly impairing its cushioning properties.

0.92 in JP-A-60-222222 for the purpose of improving the elongation and tensile strength of low-density polyethylene foam sheets.
Ethylene-α with a density of 0 to 0.940 g/am3
- A method for obtaining an extruded polyethylene foam sheet by using an olefin copolymer alone or by mixing it with low density polyethylene is disclosed. However.

The foamed sheet obtained by this method has a high tensile strength and is difficult to break, but because the tensile modulus is too high, it does not elongate much under low loads, so it is not used as a packaging material. In some cases, it lacks adhesion to the packaged item and also lacks a supple texture.

Furthermore, shrink packaging using a blown film of polyethylene, polypropylene, etc. is available as a packaging with improved adhesion to the packaged item. However, in shrink packaging, it is necessary to pass the packaged item through a heat shrink tunnel in order to wrap it tightly, which requires a complicated process, and it also has disadvantages in that it lacks cushioning properties and texture.

(Problems to be Solved by the Invention) The present inventors have conducted intensive research to obtain a foam that has cushioning properties, flexibility, and toughness suitable for packaging products with complex shapes that require impact resistance. , by mixing 40-80% by weight of a highly flexible ethylene-α-olefin copolymer with a specific density and 60-20% by weight of low-density polyethylene and extruding it as a foamable molten gel. The inventors have discovered that a foam suitable for the purpose of the invention can be obtained, and have completed further detailed studies to complete the present invention.The purpose of the present invention is to:

An object of the present invention is to provide a method for producing a polyethylene foam that has cushioning properties, flexibility, and toughness and is suitable for packaging.

(Means for Solving the Problems) The present invention provides ethylene-α-
A foaming agent is added to a resin composition consisting of 40-80% by weight of an olefin copolymer and 60-20% by weight of low-density polyethylene, and the mixture is heated and mixed in an extruder to form a melt-mixed gel. This is a method for producing a polyethylene foam, characterized by obtaining an extruded foam.

The ethylene-α-olefin copolymer used in the present invention particularly needs to have excellent flexibility and α-
Olefin content is 8~40% by weight and density is 0.88~
If the α-olefin content is less than 8% by weight or exceeds 0.92g/aj, the structural rigidity of the resin is too high. One of the objectives, flexibility, is not satisfied, and the α-olefin content is 40%.
Exceeds weight S. Alternatively, if the ethylene-α-olefin copolymer has a content of less than 0.88 g/d, the flexibility of the resin becomes excessive, and problems such as blocking of the resin in the extruder hopper are likely to occur, making stable production difficult.

The α-olefin copolymerized with ethylene is butene-
1,hexane-1,4-methylpentene-1, octene-1, etc., and the higher the α-olefin content, the lower the resin density and the higher the flexibility.

The low-density polyethylene used in the present invention is a polyethylene with branched long chains manufactured by a high-pressure method, and in order to obtain a high-foamed product, the melt flow rate is J0.1 to 10.
g/10 minutes is desirable.

In the present invention, the mixture of ethylene-α-olefin copolymer and low-density polyethylene must be a composition consisting of 2 parts by weight of low-density polyethylene for every 40-80 parts by weight of ethylene-α-olefin.

If the amount of low-density polyethylene in the above composition exceeds 6 parts, the flexibility and toughness of the resulting foam will be significantly reduced, making it impossible to achieve the desired purpose, and if the amount added is less than 20% by weight, high foaming It is difficult to form foams, and only foams with poor cushioning properties can be obtained.

Foaming agents that are essential components of the present invention include propane, butane, pentane, pentene, and methyl chloride.

methylene chloride, trichloromonofluoromethane, dichlorodifluoromethane, monochlorotrifluoromethane,
Volatile hydrocarbons and halogenated hydrocarbons such as monochlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, P -P
'Organic decomposition type blowing agents such as oxybisbenzenesulfonyl hydrazide and inorganic decomposition type blowing agents such as sodium bicarbonate can be used.N2 gas, carbon dioxide gas, etc. can also be used, but particularly preferred blowing agents are butane and dichloromethane. It is tetrafluoroethane. The above blowing agent is usually 3~
It is used in addition of 30 parts by weight.

In addition, fine inorganic powders such as talc, calcium carbonate, and silica, and fine organic powders such as calcium stearate and zinc stearate are added as foam regulators, and a small amount of higher fatty acid ester of polyhydric alcohol is used as a dimensional stabilizer. You may.

Furthermore, the composition of the present invention may contain an ultraviolet absorber, an antioxidant, an antistatic agent, a coloring agent, etc. depending on the purpose.

The method for producing the polyethylene foam of the present invention is carried out by a conventionally known method using an ordinary extruder.

That is, in the present invention, a foaming agent and other various additives as necessary are poured into an extruder into a resin composition, heated and mixed in the extruder to form a melted mixed gel, and then extruded at a temperature of 100 to 150°C. The foam is obtained by extruding it into the atmosphere through the machine nozzle.The shape of the foam depends on the shape of the nozzle.
Rod-shaped body, plate-shaped body.

Although it is possible to extrude into sheets and other shapes, the method of the present invention is particularly effective for forming sheets.

The foam extruded by the method of the present invention, especially the foam sheet, has both flexibility and toughness, and as a packaging material, has good adhesion to the packaged object and is difficult to break.

Note that the density of the foam obtained in the present invention can be easily adjusted by changing the amount of blowing agent added.6 For example, when the amount of blowing agent added is reduced.

The resulting foam sheet has a relatively high density.

It has a supple suede-like texture and feel, and can be used as packaging material, as well as clothing, rugs, etc.

In addition, if a large amount of foaming agent is added, the resulting foam sheet becomes a highly foamed, low-density foam sheet, which has excellent cushioning properties and is stretched during extrusion molding, making it suitable for use as a packaging material. , After wrapping the packaged item, the sheet shrinks by performing heat treatment,
Adhesion to the packaged object can be further strengthened.

Next, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 3 Foamed sheets were manufactured using the resin composition and foaming agent shown in Experiment No. 1 in Table 1. That is, a resin composition 100 consisting of 45 parts by weight of an ethylene-butene-1 copolymer having a butene-1 content of 18% and a density of 0.885 g/cj and 55 parts by weight of low-density polyethylene having a density of 0.920.
1.0 parts by weight of talc and 2 parts by weight of butane as a blowing agent
0 parts by weight was added, mixed in an extruder, heated and melted, and extruded using a die having an annular opening with an opening thickness of 0.41 to obtain a foamed sheet.

Table 2 shows the properties of the foamed sheet obtained.

Examples 2-3 Ethylene-α-olefin copolymers and low-density polyethylene having various α-olefin contents and densities shown as experiment numbers 2-3 in Table 1 were prepared as shown in Table 1. Talc is added to a resin composition that is a blend of both in a ratio of 1.0 to 1.0.
The parts by weight and the blowing agents shown in Table 1 were mixed, and an extrusion 1 foam sheet was obtained in exactly the same manner as in Example 1. Table 2 shows the properties of the foamed sheet obtained.

Comparative Example A foamed sheet was produced in the same manner as in Example except that the resin composition and the type and amount of blowing agent shown in Experiment Nos. 4 and 5 in Table 1 were used. Table 2 shows the properties of the foamed sheet obtained.

(Effects) As described above, the foam obtained from the resin composition obtained by mixing the specific ethylene-α-olefin copolymer defined in the present invention with low density polyethylene at a specific blending ratio is A cushioning packaging material with excellent flexibility and toughness.

Polyethylene foams can be produced that are particularly suitable for packaging objects with complex shapes.

Applicant: Sekisui Plastics Co., Ltd.

Claims (1)

[Claims] 1 α-olefin content is 8 to 40% by weight and density is 0
．． A blowing agent was added to a resin composition consisting of 40 to 80% by weight of an ethylene-α-olefin copolymer with a yield of 88 to 0.92 g/cm^3 and 60 to 20% by weight of low density polyethylene, and the mixture was put into an extruder. A method for producing a polyethylene foam, which comprises heating and mixing to form a melt-mixed gel, and then extruding from the tip of an extruder to obtain a foam.