JPS61188430A - Crosslinked polyethylene resin foam - Google Patents

Abstract

PURPOSE:The title foam excellent in flexibility and heat resistance and high in an expansion ratio, comprising an ethylene/propylene random copolymer specified in a m.p., a crystallization temperature, an area intensity ratio and a flexibility index. CONSTITUTION:An ethylene/propylene random copolymer of a propylene content of 15-30wt% is mixed with a heatdecomposable blowing agent (e.g., azodicarbonamide) and, optionally, a crosslinking agent which generates radicals upon heating and the obtained mixture is molded into a sheet, which is crosslinked to a gel content of 154n60% and expanded to obtain a crosslinked polyethylene resin foam having a melting temperature (Tm) in the range of 100<=Tm( deg.C)<=118, a crystallization temperature (Tmc) in the range of 85<=Tmc( deg.C)<=100, an area intensity ratio (R) as determined from a <13>C-NMR spectrum in the range of 3.0-12.0 and a flexibility index (N) <=9.5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a crosslinked ethylene-propylene foam having excellent properties in both flexibility and heat resistance.

[Prior Art] Conventionally, flexible foams are known from Japanese Patent Publication No. 44-470 and Japanese Patent Application Laid-Open No. 49-129757.・All of these foams are flexible, but the former foam is probably an ethylene/vinyl acetate copolymer.

Because it is composed of ethylene and propylene elastomers, its heat resistance is only about 60°C, and it can only be used for limited applications that do not require heat resistance. The foam has a partially crosslinked structure with unsaturated bonds inside the polymer, has strong rubber-like properties, and has high heat shrinkage, so there is a problem that it is difficult to obtain a product with a high expansion ratio. Ta.

[Problems to be Solved by the Invention] An object of the present invention is to provide a crosslinked polyethylene resin foam that not only has excellent flexibility but also has excellent heat resistance and a high expansion ratio.

[Means for Solving the Problems] The above object of the present invention is to contain a propylene component of 15 to 30% by weight as a copolymerization component.
melting point (Tm) and crystallization temperature (Tm
Ethylene, c> satisfies the following formulas (I> and (II))
It is made of a propylene random copolymer and has an area intensity ratio (R) of 3.0 to 12. O1 flexibility index (N>9.
This can be achieved by using a crosslinked polyethylene resin foam with a polyethylene resin foam of 5 or less.

(I>100≦rm (℃)≦118 Preferably,
105≦Tm(℃)≦115(II) 85≦
Tmc (°C)≦100, preferably 87≦Tmd (
°C)≦97 The ethylene/propylene random copolymer constituting the foam of the present invention has a copolymerization rate of propylene of 15
It is characterized in that it has Tm and TmC that are within the range of ~30% by weight and satisfy the above formulas (I> and (II)).

Here, Tm and TmC are values detected by a differential scanning calorimeter (DSC).

In other words, having Tm and TmC that satisfy the above formulas (I> and (II)) means that the copolymer still has crystallinity, and has EPR, EPT, EP
This shows that the polymer is clearly different from the non-quality ethylene/propylene elastomer such as DM.

In the copolymer of the present invention, if the propylene content is less than 15%, the crystallinity of the polymer increases and the melting point (Tm) increases, which is advantageous in terms of heat resistance, but the resulting This is not preferable because the flexibility of the foam decreases, and on the other hand, if it exceeds 30%, the polymer becomes completely amorphous and loses its heat resistance, which is not preferable.

In addition, the copolymer of the present invention has the formula (I') and (
It is important to have a melting point and crystallization temperature within the range specified by II), and if the melting point is outside the range of the above formula, for example, if Tm is less than 100°C, the heat resistance of the foam will be If Tm exceeds 118°C, the elongation will decrease and flexibility will be lost, which is undesirable.
If the temperature is less than 5℃, the shape stability of the foam during high-temperature use will decrease, and if it exceeds 100"C, the processability when molding a foam sheet will deteriorate, resulting in a product with stable quality and performance. This is undesirable because it becomes difficult to manufacture the foam and increases the variation in the properties of the foam.

The foam of the present invention has an area intensity ratio (R) of 13C-NMR spectrum in the range of 3.0 to 12°O1, preferably 4.0 to 10.0, and 9.5 or less, preferably 9 It has a flexibility index (N>) of less than or equal to .0.

Here, the flexibility index (N) is a value defined as follows, and the smaller the value of N, the better the flexibility.

N = (25% compression hardness) It also has excellent heat resistance and flexibility within the range shown by the flexibility index (N>).Normally, the flexibility of a foam depends on the expansion ratio, and even if the expansion ratio is the same, Flexibility varies depending on the properties of the polymer, especially the size of the crystallinity, but the foam of the present invention, which has an area intensity ratio (R) according to the 130-NMR spectrum in the above range, has flexibility with a wide range of practical performance. It holds.

Hereinafter, one embodiment of the method for producing a highly expanded crosslinked polyethylene resin foam according to the present invention will be described.

The ethylene/propylene random copolymer having the above copolymerization composition is mixed with a known thermally decomposable blowing agent such as azodicarbonamide, dinitrosopentamethylenetetramine, etc. and, if necessary, a crosslinking agent that generates radicals when heated. Then, it is held at a temperature at which the foaming agent and crosslinking agent described above do not decompose and is molded, for example, into a sheet shape. - This formed sheet material is crosslinked by any known method such as ionizing radiation crosslinking method or chemical crosslinking method. In this case, the degree of crosslinking is 15 to 6 in terms of gel fraction.
It is better to set it to 0%.

More specifically, in the case of the ionizing radiation crosslinking method, α, β, γ, X-rays, electron beams, neutron beams, etc. are used as high-energy rays, and a high-energy electron beam irradiation machine is usually used. The sheet material is crosslinked by irradiating the sheet material with an electron beam at a dose of ~50 Mracj. In this case, 0.1 to 10 parts by weight of various known crosslinking aids, such as divinylbenzene, diallyl phthalate, trimethylolpropane triacrylate, etc., are added to the ethylene/propylene copolymer for electron beam crosslinking. You can. Instead of this radiation irradiation, it is also possible to add an ultraviolet sensitizer such as benzophenone and crosslink by irradiating ultraviolet rays. ′ In addition, in the case of chemical crosslinking method, dicumyl peroxide,
Crosslinking methods using organic peroxides such as ditertiary butyl peroxide, silane crosslinking methods in which a vinyl silane such as vinyltrimethoxysilane is kneaded with these crosslinking agents to form a graft, and then crosslinked by a siloxane condensation reaction. It can be applied as appropriate.

The thus obtained crosslinked molded article is heated in a hot air atmosphere or on a salt bath to rapidly decompose the foaming agent contained within the molded article, thereby converting it into a foam.

In addition, to the extent that the object of the present invention is not impaired, various polymers such as polyethylene, polypropylene, polybutylene, and chlorinated polyethylene may be added to the ethylene resin composition used in the production of the foam of the present invention in small amounts up to 10% by weight. Can be added and mixed, and as necessary, lubricants, antioxidants, ultraviolet absorbers, colorants, antistatic agents, flame retardants, and other properties can be added to the extent that the purpose of the present invention is not impaired. Various inorganic substances can be added for desired purposes.

In general, the crosslinked polyethylene resin foam of the present invention can be coated with an adhesive on at least one surface thereof by corona discharge treatment, coating, etc., and then laminated to improve its workability. By laminating plastic films, sheets, other foam sheets, or metal foils, or by adding composite structures using extrusion lamination, etc.
That is, various processing techniques can be applied.

[Effects of the Invention] The crosslinked polyethylene resin foams of the present invention thus obtained have excellent flexibility and heat resistance, ranging from low expansion ratios to high expansion ratios. Taking advantage of its excellent texture, it can be used and developed in many applications such as various packing materials, adhesive tape bases, matte base materials, insulation materials, cushioning materials, clothing, pharmaceuticals, etc. that take advantage of its excellent texture. .

Hereinafter, the effects of the present invention will be roughly and specifically explained based on Examples.

In addition, in the present invention, melting point (Tm>), crystallization temperature (
Tmc), area intensity ratio (R) by -13C-NMR spectrum, and heat resistance are values measured by the following method.

(1) Tm and TmC DSC-2 differential scanning calorimeter manufactured by PerkinElmer (
Using DSC), the endothermic peak temperature of the melting of the oxidized resin that was once melted and recrystallized was taken as the melting point (Tm>). It was set as 1'-mC.

(2) Area intensity ratio (R
) In the integral curve of the 13C-NMR spectrum, 29~
The area intensity between 31 ppm is I30, and 19.5 to 20
．． When the area intensity between 5 ppm is I20, it was defined by R=I30/2·I20.

The method for measuring the 13C-NMR spectrum is as follows.

First, in a 10 mmφ NMR sample tube, add orundichlorobenzene (1.4 cc) and deuterated benzene (0.2 cc).
After adjusting the solid content concentration of the sample to 20% by weight in the mixed solvent of
Co., Ltd.] at a frequency of 25. 130-NMR was measured at 120° C. using the pulse FT method at OOMHz and mode.

(3) Flexibility index (N> This is the value displayed by the following formula.

N= (25% compression hardness) x (expansion ratio) where, 25
The % compression hardness is measured according to the measuring method specified in JIS-6767-1976, and the expansion ratio is expressed as the reciprocal of the apparent density of the foam.

The apparent density was determined by cutting the foam into a 10 cm x 10 cm square, measuring the weight and thickness, and dividing the weight by the volume to show the weight per unit volume ffi (Q/cm3).

(4) Heat resistance The heat shrinkage rates in the vertical, horizontal, and thickness directions due to heat treatment are shown in accordance with the measuring method specified in JIS-6767. Specifically, the measurement sample (
A square mark of 1 Qcm in both the vertical and horizontal directions was made on the foam, and the thickness was measured, followed by heat treatment in a hot air oven at 80° C. for 22 hours.

After cooling to ¥300,000, the vertical, horizontal, and thickness dimensions were measured, and the following judgment was made based on the magnitude of dimensional change (thermal shrinkage rate) due to this heat treatment.

Heat shrinkage rate within ±5.0% 20 [passed], heat shrinkage rate exceeding ±5.0:

Examples 1 to 5, Comparative Examples 1 to 2 Ethylene and propylene were polymerized using a catalyst system containing an organometallic compound and a titanium compound to create ethylene/propylene random copolymers with different contents of propylene.

To 100 parts by weight of these, 5 to 15 parts by weight of azodicarbonamide as a blowing agent was added, mixed in a Henschelmi mixer, and melt-extruded to obtain a molded sheet.

This sheet was irradiated with a dose of 5 Mrad using an electron beam irradiation device (IR-2 manufactured by Nissin High Voltage Co., Ltd.).These crosslinked sheets were foamed by heating to 225 to 230°C on a salt bath. An evaluation test was conducted on the obtained foam sheet.The results are shown in Table 1.

From the table, it can be seen that the foam sheets of Examples 1 to 5 that satisfy the requirements of the present invention are high-grade foams that are excellent in both flexibility and heat resistance. On the other hand, the propylene content and Tm specified in the present invention in Comparative Examples 1 and 2.

Sheets that did not satisfy requirements such as Tmc and R had low flexibility (Comparative Example 1), low heat resistance, and low expansion ratio (Comparative Example 2).

Claims (1)

[Claims] (1) As a copolymerization component, the propylene component is 15 to 30%
% by weight, and whose melting point (Tm) and crystallization temperature (Tmc) satisfy the following formulas (I) and (II), and has the formula [R=I_3_0/2. I_2_0] The area intensity ratio (R) according to the ^1^3C-NMR spectrum is 3.0 to 12.0, and the flexibility index (N) is 9.
．． 5 or less. (I) 100≦Tm (℃)≦118 (II) 85≦Tmc (℃)≦100