JP2003096231A - Molding material for foamed products containing foamed polyethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a molding material for foamed products at a low cost by changing a foamed polyethylene foamed product, which is crosslinked and poor in thermal fusion, to thermoplastic polyethylene so that the foamed polyethylene foamed product used in packaging materials, heat insulating materials for vehicles, buildings and so on and coated electric wires may possibly be recycled. SOLUTION: Polyethylene is combined with the crosslinked polyethylene foamed products which are cut into pieces or broken, and then they are kneaded together, while giving shearing stress at a temperature of the melting point of the polyethylene or higher, to give expansion molding-possible polyethylene molding materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding material obtained from expanded polyethylene used for a packaging material, a heat insulating material for automobiles and buildings, an electric wire coating, and the like. The present invention relates to a molding material for a foam, which is composed of a mixture of a crushed body and polyethylene.

[0002]

2. Description of the Related Art It is difficult for a cross-linked polyethylene foam to be subjected to a highly productive processing process by itself using an injection molding machine or an extrusion molding machine. Therefore, when trying to recycle the crosslinked polyethylene and use it, the crosslinked polyethylene is granulated or powdered and mixed with polyethylene or another thermoplastic resin as a filler,
Attempts are generally made to obtain molded articles by injection molding or extrusion molding. As disclosed in JP-A-6-145399, crosslinked polyethylene is powdered and mixed with polyethylene to form a foam. However, in the method of obtaining the foam by adding the crosslinked polyethylene to the polyethylene of the publication, the purpose of adding the crosslinked polyethylene fine powder is as a foam nucleating agent of the foam, and the particle size of the crosslinked polyethylene to be added is the maximum. 100 μm, the blending amount is polyethylene 100
Crosslinked polyethylene fine powder is 0.1 to 10 parts by weight.
Less than mass part. Further, in the method of utilizing crosslinked polyethylene disclosed in JP-A-11-100447 and JP-A-11-100448, the crushed body of the crosslinked polyethylene has a particle size of 50 mm or less, and the content of the crosslinked polyethylene is 95% by mass or less. However, the cross-linked polyethylene in this publication is unfoamed cross-linked polyethylene used for coating electric wires and the like, and the material obtained by this method is for use as a molding material without foaming and for foam molding. is not.

[0003]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a molding material for a foam by converting a cross-linked foamed polyethylene, which itself has poor heat melting property, into a thermoplastic polyethylene.

[0004]

The means adopted by the present invention is to obtain a foamable molding material from a cross-linked expanded polyethylene foam. The present inventors have conducted earnest researches for imparting meltability and fluidity to crosslinked polyethylene foam that is difficult to melt by itself, and as a result, surprisingly, it was found that It was discovered that a polyethylene molding material capable of foam molding can be obtained by mixing polyethylene into cut pieces or crushed bodies and kneading the mixture using a device that exerts a shearing force at a temperature equal to or higher than the melting temperature of polyethylene. Reached That is, in the present invention, polyethylene is added to cross-linked expanded polyethylene to form a mixture,
It is a foamed polyethylene molding material obtained by kneading while applying shearing force at a temperature equal to or higher than the melting temperature of polyethylene.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The molding material for a foam containing the crosslinked polyethylene of the present invention will be described in detail below.

The cross-linked expanded polyethylene used in the present invention is, for example, dicumyl peroxide or di-t-.
Foamed polyethylene that is chemically crosslinked by a chemical method using an organic peroxide such as butyl peroxide or t-butylcumyl peroxide or a silane compound, or foamed polyethylene that is electron beam crosslinked by electron beam irradiation. These cross-linked polyethylene foams may be partially melted by heating, but they are extremely difficult to melt as a whole, so they have poor fluidity, and the cross-linked polyethylene foam alone can be used for foam molding. , Polyethylene that cannot be injection-molded or extruded.

The crosslinked foamed polyethylene used in the present invention is cut into pieces or crushed bodies which can be put into a kneading extruder. The shape and size of the cut pieces or crushed pieces are regulated because they can be easily put into the cylinder from the hopper of the kneading extruder. The size of the cross-linked foamed polyethylene cut piece or crushed body is appropriately about 50 mm or less, preferably about 20 mm or less, and the shape is not particularly limited.

The content of cross-linked expanded polyethylene is 1
It is 0 mass% or more and 95 mass% or less. When the amount is 10% by mass or less, the significance of attempting to reuse cross-linked polyethylene foam, which has hitherto been unavailable, as a foam material is reduced. Further, in the present invention, the addition of uncrosslinked polyethylene is indispensable in order to make the crosslinked foamed polyethylene into a foam-moldable material, and therefore the upper limit of the content of the crosslinked foamed polyethylene is 95% by mass.

The polyethylene used in the present invention is LD
Examples thereof include polyethylene such as PE and HDPE and polyethylene modified with vinyl acetate. The amount of polyethylene added may be the minimum amount necessary for melt-molding the cross-linked expanded polyethylene, and may be 5% by mass or more.

Polyethylene is added to the cut and crushed pieces of cross-linked expanded polyethylene, and the mixture is mixed with a mixer such as a blender. The mixture is kneaded at a temperature equal to or higher than the melting temperature of polyethylene through a device to which a shear force is applied while heating, such as a biaxial kneading extruder, a stone mill type kneading extruder, a kneading open roll, or a Banbury mixer. Among these devices, the twin-screw kneading extruder and the stone mill-type kneading extruder have high productivity, excellent shearing and kneading performance, and small performance fluctuation due to kneading conditions, and therefore suitable for preparation of the material of the present invention. It can be given as a device. In the case of a kneading device having a plurality of metering ports capable of metering, the crosslinked foamed polyethylene and polyethylene may be kneaded while being charged from different charging ports of the device without premixing. Good.

By kneading the cross-linked foamed polyethylene and polyethylene at a temperature not lower than the melting temperature of polyethylene, a composite of both melted polyethylene can be obtained from the kneading device. This molten composite is
It can be supplied as a material for molding a foam by taking it out from the kneading device, crushing or cutting it into coarse particles or pelletizing.

The kneading temperature of both polyethylene mixtures is suitably a melting temperature of polyethylene or 100 ° C. higher than the melting temperature, preferably 5 ° C. to 70 ° C. higher than the melting temperature. In order to exert the shearing force of the kneader more effectively, the temperature is within the range of melting and kneading ability of the kneader,
It is desirable to be as low as possible.

Here, the material containing the crosslinked foamed polyethylene obtained can be made into a foamed molded product by using a conventional molding apparatus. Further, a material containing this cross-linked foamed polyethylene can be used as a masterbatch, and an arbitrary amount of polyethylene can be added to obtain a foamed molded product.
The material containing the foamed polyethylene can be injection-molded or extruded by itself or by adding polyethylene or another thermoplastic resin to the material. In the molding material of the present invention, polyethylene and a cross-linked polyethylene foam are partially alloyed. The degree of alloying is
It can be known by measuring the thermal properties of the DSC. 1
The melting behavior of DSC measured at a temperature rising rate of 0 ° C./min shows that the temperature of the endothermic peak is lower than that of polyethylene alone. The decrease in the temperature of the endothermic peak is 1 ° C. or more, and the highly alloyed one reaches 5 ° C. or more.

[0014]

The present invention will be described below with reference to examples, but the scope of the present invention is not limited by these examples.

[Example 1] 80% by mass of crosslinked polyethylene foam cut into about 1 cm square with a cutter knife,
Polyethylene pellets with a particle size of about 3 mm (Novatech LD
20 mass% (manufactured by Nippon Polychem) was added and mixed using a blender, and then a twin-screw kneading extruder (TZW15-30M).
G) is continuously charged, the cylinder temperature to 190 ℃,
Kneading was performed under the condition that the screw rotation speed was 400 rpm. The kneaded product was extruded from a nozzle, cooled and cut to obtain pellets having a particle size of about 3 mm.

[Example 2] 75% by mass of a cross-linked polyethylene foam sheet cut into about 1 cm square with a paper cutter and 25% by mass of polyethylene pellets (Novatec LD Japan Polychem) with a particle size of about 3 mm. Pellets having a particle size of about 3 mm were obtained in the same manner as in Example 1 except for the addition.

Example 3 A crosslinked polyethylene foam was crushed with a crusher to a diameter of 5 to 10 mm. Pellets having a particle size of about 3 mm were obtained in the same manner as in Example 1 except that 30 parts by mass of polyethylene pellets (Novatech LD Japan Polychem) having a particle size of about 3 mm were added to 70 parts by mass of the crushed polyethylene.

Foams were investigated to determine whether foams were obtained. [Example 4] 40 parts by mass of the pellet obtained in Example 1, L
DPE (Novatech LD Japan Polychem) 60 parts by mass, blowing agent azodicarbonamide (uniform AZ
10 parts by mass of Otsuka Chemical Co., Ltd.) and 1.5 parts by mass of a cross-linking agent dicumyl peroxide were mixed with a super mixer, and extruded into a sheet having a thickness of 2.0 mm at a barrel temperature of 125 ° C. using an extruder of 65φ. The obtained sheet was placed in an oven at 230 ° C. for thermal foaming and chemical crosslinking. When the obtained sheet was cut with a cutter knife, the appearance of bubbles in the cross section was good, and a foam having an apparent density of 0.028 g / cm ³ was obtained.

Example 5 Pellets 5 obtained in Example 2
A mixture of 0 parts by weight and 50 parts by weight of HDPE (manufactured by Novatec HD Nippon Polychem) was extruded from the middle of the extruder at an extrusion temperature of 150 ° C. while injecting CFC gas to obtain a polyethylene foam. When this foam was cut with a cutter knife, the appearance of bubbles in the cross section was good, and the foaming ratio was 73%.

Example 6 Pellets 9 obtained in Example 3
0 parts by mass, LDPE (Novatech LD Japan Polychem) 10 parts by mass, blowing agent azodicarbonamide (Uniform AZ manufactured by Otsuka Chemical Co., Ltd.) 10 parts by mass, and crosslinking agent dicumyl peroxide 1.5 parts by mass were mixed with a super mixer. Except for this, a sheet was extruded in the same manner as in Example 4. The obtained sheet was placed in an oven at 230 ° C. for thermal foaming and chemical crosslinking. When the obtained sheet was cut with a cutter knife, the appearance of bubbles in the cross section was good, and a foam having an apparent density of 0.033 g / cm ³ was obtained.

[0021]

INDUSTRIAL APPLICABILITY According to the present invention, a polyethylene foam molding material is obtained by adding polyethylene to a cross-linked polyethylene foam to form a mixture, and heating and kneading the mixture at a temperature not lower than the melting temperature of polyethylene. Since there is no difficulty in production and a polyethylene foam can be obtained at a low cost by the existing technology, the industrial value is great even when the crosslinked polyethylene foam is recycled.

Claims (3)

[Claims] 1. A foamed polyethylene molding material obtained by adding polyethylene to crosslinked foamed polyethylene to form a mixture, and kneading the mixture while applying shearing force at a temperature not lower than the melting temperature of polyethylene. 2. The expanded polyethylene molding material according to claim 1, wherein the content of the crosslinked expanded polyethylene is 10% by mass or more and 95% by mass or less. 3. The expanded polyethylene molding material according to claim 1, wherein the crosslinked expanded polyethylene is chemically crosslinked polyethylene.