JPS61188432A - Crosslinked polyethylene resin foam of high expansion ratio - Google Patents

Abstract

PURPOSE:The title foam excellent in flexibility and heat resistance and high in an expansion ratio, comprising a blend polymer comprising a specified ethylene/propylene random copolymer and a linear PE. CONSTITUTION:A blend polymer obtained by blending an ethylene/propylene random copolymer (A) of a propylene content of 15-30wt%, a m.p. of 100-118 deg.C and a crystallization temperature of 85-100 deg.C with a linear PE (B) of a m.p. of 115-135 deg.C and a density of 0.940-0.970 at a B/A blend ratio of 0.10-5.70 is mixed with a heat-decomposable blowing agent (e.g., azodicarbonamide) and, optionally, a crosslinking agent which generates radicals upon heating, and the obtained mixture is formed into a sheet, which is crosslinked to a gel content of 15-60% and expanded to obtain a crosslinked polyethylene resin foam having an area intensity ratio (R) as determined from a <13>C-NMR spectrum in the range of 3.0-74.0 and a flexibility index <=12.0.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a blend polymer comprising an ethylene-propylene random copolymer and a linear polyethylene as essential components, which has excellent properties in both flexibility and heat resistance. This invention relates to a cross-linked ethylene/propylene foam with a high expansion rate.

[Prior Art] Conventionally, flexible foams are known from Japanese Patent Publication No. 44-470 and Japanese Patent Application Laid-Open No. 49-129757.

Both of these foams are flexible, but because the former foam is composed of ethylene/vinyl acetate copolymer, its heat resistance is only about 60°C, so it cannot be used unless heat resistance is required. The latter type of foam made from ethylene-propylene elastomer has a partially cross-linked structure with unsaturated bonds inside the polymer, and has strong rubber-like properties. There was a problem in that it was difficult to obtain a product with a high expansion ratio because of its high heat shrinkability. □ [Problems to be Solved by the Invention] An object of the present invention is to provide a crosslinked polyethylene-based 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 object of the present invention is to (contain a propylene component in an amount in the range of A > 15 to 30@1%, have a melting point (Tm) of 100 to 118°C and a temperature of 85 to 1%;
Blend ratio (B/A) of ethylene-propylene random copolymer having a crystallization temperature (Tmc) of 00°C and (B) linear polyethylene having a melting point (Tm) of 115 to 135°C is 0.10. ~5
．． 70, and has an area intensity ratio (R) of 3.0 to 74. O, flexibility index (N) is 12.
This can be achieved by using a crosslinked polyethylene resin foam with a high expansion rate of 0 or less.

The foam of the present invention is composed of a blend polymer of an ethylene-propylene random copolymer (A>) and linear polyethylene (B).

Ethylene-propylene random copolymer of the present invention (A>
The copolymerization rate of propylene is within the range of 15 to 30% by weight, and the temperature is 100 to 118°C, preferably 105 to 1
Tm of 15°C and 85-100°C, preferably 87
It is characterized by having a TmC of ~97°C.

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

In other words, having Tm and TmC in the above range means that the copolymer has residual crystallinity, and is different from non-quality ethylene-propylene elastomers such as EPR, EPT, and EPDM. This shows that the polymers are clearly different.

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 Poma becomes completely amorphous and loses its heat resistance, which is not preferable.

In addition, the copolymer of the present invention has a melting point within the above range (
Tm) and crystallization temperature (Tmc), and if the melting point is outside the range of the above formula, 1. For example, if Tm is less than 100°C, the heat resistance of the foam will deteriorate;
Moreover, if Tm exceeds 118°C, it is undesirable because the elongation decreases and flexibility is lost, and if the crystallization temperature is outside the range specified by the formula, for example, if TmC is less than 85°C, the foam Form stability decreases when used at high temperatures, resulting in
If the temperature exceeds 00°C, the processability when molding foam sheets deteriorates, making it difficult to manufacture products with stable quality and performance, and increasing the variation in the properties of the foam, which is undesirable. .

1. Linear polyethylene (B) is 115 to 135
One such polymer has a melting point (Tm>) in the range of 0.1 to 50 °C.
0/10m1n (7) Melt 7 Low Rate (ASTM
-D-1238>, 0°915 to 0.945Q/
Density in cm3 (ASTM-D-1505>, 115-1
Ethylene with a melting point of 27°C and α- having 4 to 20 carbon atoms
Examples include polyethylene consisting of olefin, that is, so-called linear low-density polyethylene and medium-density polyethylene.

More specifically, the α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 4
One or more α-polyolefins selected from -methyl-1-pentene, 1-octene, etc. can be mentioned, and these α-olefins may contain a small amount of propylene component.

The linear polyethylene of the present invention can be obtained by polymerizing ethylene and α-olefin in a ratio that provides a desired density using a medium/low pressure method.

Furthermore, as another linear polyethylene, high crystallinity density obtained by medium/low pressure polymerization is O0940-0.
970. There is high density polyethylene with a melting point of 125-135°C.

The blend ratio (B/A> of (A> and (B)) is 0.10 to 5.70, preferably 0.17 to 4.70 in weight ratio.
(B/A> is preferably within the range of 0. If B/A> is lower than 0.10, it will tend to stick when molding a sheet etc., making it difficult to set casting conditions. 70
Exceeding this is not preferable because the resulting foam will have insufficient flexibility.

The foam of the present invention made of such a blend polymer has an area intensity ratio (R
) and has a flexibility index (N) of 12.0 or less, preferably 10.0 or less.

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

N=(25% compression hardness) First, it has excellent heat resistance and flexibility within the range indicated 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, the flexibility differs depending on the properties of the polymer, especially the degree of crystallinity. The foam of the present invention having an area strength ratio (R) is
It maintains flexibility with a wide range of practical performance.

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 (A) having the above-mentioned copolymerization composition is blended with linear polyethylene (B) within the above-mentioned range, and then a known heat-decomposable blowing agent such as azodicarbonamide or dinitrosopenta is added. Methylenetetramine, etc. and, if necessary, a crosslinking agent that generates radicals when heated are mixed, and the foaming agent and crosslinking agent are kept at a temperature that does not decompose and molded, for example, into a sheet shape.This molded sheet shape The material is crosslinked by applying any known method such as ionizing radiation crosslinking method or chemical crosslinking method.In this case, the degree of crosslinking is 15 in terms of gel fraction.
It is best to set it to ~60%.

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 Mrat:j. 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. It's okay. 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,
A crosslinking method using an organic peroxide such as tertiary butyl peroxide, a silane crosslinking method 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, etc. 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, various polymers such as high-pressure process/low-density polyethylene, polypropylene, polybutadiene, chlorinated polyethylene, etc. may be added to the ethylene resin and composition used for producing the foam of the present invention, to the extent that the purpose of the present invention is not impaired. can be added and mixed in small amounts up to 10% by weight to 100 parts by weight of the blend polymer of the present invention, and if necessary, lubricants and antioxidants can be added as well, within a range that does not impair the purpose of the present invention. agent,
Ultraviolet absorbers, colorants, antistatic agents, flame retardants, various inorganic substances that impart other properties, and the like can be added for desired purposes.

Furthermore, the cross-linked polyethylene resin foam of the present invention can be laminated with an adhesive applied to at least one surface thereof by corona discharge treatment, coating, etc., to improve its workability, and can be used as a plastic material. By laminating films, sheets, other foam sheets, or metal foils together, or by extrusion lamination, etc., to create a composite structure.
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 heat resistance and heat resistance, 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 feel. I can do it.

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 (
The endothermic peak temperature of melting and recrystallization using DSC> was defined as the melting point (Tm>).In addition, TmC was once melted and then the exothermic peak temperature of recrystallization during cooling was defined as the melting point (Tm>). It was designated as TmC.

(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 is defined by R=I30'72·I2a.

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

'・First, 10mmφNMR
After adjusting the solid content of the sample to 20% by weight in a mixed solvent of orthodichlorobenzene (1.4cc) and deuterated benzene (0.2CG) in a sample tube, JNM
Using the 2FX100 device [manufactured by JEOL Ltd.], frequency 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)
The foaming ratio is measured in accordance with the measuring method specified in Section 6, and the foaming ratio is expressed as the reciprocal of the apparent density of the foam.

To determine the apparent density, cut the foam into a 1100m x 100 square, measure the weight and thickness, and divide this weight by the volume to find the weight per unit volume! (Q/cm3).

(4) Heat resistance In accordance with the measuring method specified in JIS K-6767, the thermal shrinkage rates in the vertical, horizontal, and thickness directions due to heat treatment were also shown. Specifically, a square mark of 10 am each vertically and horizontally is placed on the measurement sample (foam),
After measuring the thickness, heat treatment is performed in a hot air oven at 80° C. for 22 hours. After cooling to room temperature, the vertical, horizontal and thickness dimensions were measured, and the following judgment was made based on the magnitude of six dimensional changes (thermal shrinkage rate) due to this heat treatment.

Heat shrinkage rate within ±3.0%: ○ [Passed] Heat shrinkage rate
3.0 to 5.0: Δ Heat shrinkage rate exceeding ±5.0: X The dimensional change due to the heat treatment was measured 5 to 10 times and determined.

Examples 1 to 7, Comparative Examples 1 to 3 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.

This ethylene/propylene random copolymer was blended with linear polyethylene, and 5 parts by weight of azodicarbonamide was added as a blowing agent to 100 parts by weight of this blended polymer.
~15 parts by weight were added, mixed in a Henschelmi mixer, and then melt extruded to obtain a molded sheet.

As the linear polyethylene, Example 6 and Comparative Example 2
Here, high-density polyethylene having a density of 0.9630/cm3, a melting point of 132°C, and a melt flow rate of 8C1/10 minutes was used, and 2 parts by weight of divinylbenzene was added as a crosslinking aid. In other examples and comparative examples, the density is 0.92
5. Linear low-density polyethylene with a melting point of 124° C. and a melt flow rate of 8 q/10 minutes was used, and no crosslinking aid was added.

Further, the amount of azodicarbonamide added was 15 parts by weight in Example 5, 5 parts by weight in Example 6, and 10 parts by weight in all other Examples and Comparative Examples.

These sheets were irradiated with a dose of 5 Mrad using an electron beam irradiation device (Nissin High Voltage Co., Ltd. IR-2).
Crosslinked. These crosslinked sheets were placed on a salt bath at 225~
Foaming was effected by heating to 230°C. 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 7 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, in Comparative Examples 1 and 2, the blend ratio specified in the present invention (K> was not satisfied, so the heat resistance was poor (Comparative Example 1), and the product lacked flexibility (Comparative Example 2). . In addition, in Comparative Example 3, since the propylene content of the ethylene propylene random copolymer (A> is outside the range specified in the present invention), both the melting point and the crystallization temperature are low, and the heat resistance of this foam Sexuality was insufficient.

Claims (1)

[Claims] (1) (A) Contains a propylene component in an amount ranging from 15 to 30% by weight, and has a melting point (Tm) of 100 to 118°C and a
Blend ratio (B/A) of ethylene/propylene random copolymer having a crystallization temperature (Tmc) of 5 to 100°C and (B) linear polyethylene having a melting point (Tm) of 115 to 135°C is 0. .10 to 5.70, and has an area intensity ratio (R) of 3.0 to 74. 0, flexibility index (N) is 1
A crosslinked polyethylene resin foam with a high expansion rate of 2.0 or less.