JPS61238831A - Crosslinked polyethylene resin foam - Google Patents

Abstract

PURPOSE:The titled foam excellent in heat resistance and compression set, comprising a polymer blend comprising a specified random ethylene/propylene copolymer and a linear PE. CONSTITUTION:A heat-decomposable blowing agent (e.g., azodicarbonamide) and, optionally, a crosslinking agent which can generate radicals upon heating are added to a polymer blend comprising a random ethylene/propylene 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 and a linear PE (B) of MI of 0.1-50g/10min, a density of 0.915-0.945g/cm<3> and a m.p. of 115-135 deg.C. The obtained mixture is formed into a sheet and expanded to obtain a crosslinked polyethylene foam having an area intensity ratio (R) determined from a <13>C-NMR spectrum and represented by the equation of 20-300, a gel fraction of 15-45%, a compression set (S) in the range of S<=0.3M+3 (wherein M is an apparent expansion ratio).

Description

Detailed Description of the Invention [Industrial Application Field] The present invention comprises an ethylene-propylene random copolymer (A>) and two monomers of linear polyethylene (8) as essential components.
The present invention relates to a crosslinked ethylene foam having excellent properties in both heat resistance and compression set, which is made of a blend polymer containing the following components.

[Prior Art] Cross-linked low-density polyethylene foam has been known as a foam that has uniform, fine closed cells and has excellent cushioning and heat insulation properties, and this foam has been used for bath mats, It is widely used for insulation folded plate roofs laminated with steel plates and as an insulation material for various other industrial applications.

Foams made of low-density polyethylene have a low softening temperature and are suitable for use in fields that require heat resistance, such as automobile interior materials and air conditioners, which have recently become required to be heat-molded. There was a problem. However, with the remarkable spread of automobile interior materials and air conditioners,
There is an increasing demand for heat insulating materials with higher heat resistance, and in response to these demands, linear low density polyethylene with a higher melting point is blended with the low density polyethylene, and this blend polymer is produced. An attempt has been made to use it as a material for foam (Japanese Unexamined Patent Publication No. 1983
-53929).

However, foams made of highly crystalline polymers such as linear low-density polyethylene have a disadvantage that they have poor compression set and tend to become stiff after long-term use.

[Problems to be Solved by the Invention] An object of the present invention is to not only have superior heat resistance compared to the foam made of the above-mentioned low-density polyethylene, but also to solve the disadvantages of the foam made of the above-mentioned linear polyethylene. It is an object of the present invention to provide a crosslinked polyethylene foam having excellent performance even in certain compressive strain characteristics.

[Means for Solving the Problems] The object of the present invention is to: A: Contain a propylene component as a copolymer component in an amount ranging from 15 to 30% by weight, and have a melting point (Tm) of 100 to 118°C.
B: A blend polymer whose essential components are an ethylene-propylene random copolymer having a crystallization temperature (Tm) of 85 to 100°C and a linear polyethylene having a melting point (Tm) of 115 to 135°C. [R-I30/2・I20] The area intensity ratio (R) according to the 1 3C-NMR spectrum is 20 to 300. This can be achieved by using a crosslinked polyethylene resin foam having a gel fraction of 15 to 45% and a compression set (S) of 850.3M+3 (where M is the apparent expansion ratio).

The foam of the present invention is composed of a blend polymer whose essential components are an ethylene-propylene random copolymer (A>(1-3) and linear polyethylene (B). B) preferably accounts for at least 90% by weight based on the total amount of the polymer blend making up the foam.

The ethylene/propylene random copolymer constituting the foam of the present invention (A> means that the copolymerization rate of propylene is 1
in the range of 5-30% by weight, with a Tm of 100-118°C, preferably 105-115°C and 85-100°C.
It is characterized by having a TmC of preferably 87 to 97°C.

Here, l'-m and TmC are values detected by a differential scanning calorimeter (DSC), respectively.

In other words, having Tm and Tmc in the above range means that the copolymer still has 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 foam becomes less flexible and does not exhibit the effect of improving compression set. On the other hand, if the propylene content exceeds 30% by weight, the polymer becomes completely amorphous and loses heat resistance, which is not preferable.

In addition, it is important that the copolymer (A) of the present invention has a melting point (Tm>) and a crystallization temperature (Tmc) within the above range; if the melting point is outside the above range, for example, T
If m is less than 100°C, the heat resistance of the foam will deteriorate, and T
If m exceeds 118°C, crystallinity increases and the compression set of the foam worsens, which is undesirable, and the crystallization temperature (T
If mc) is outside the above range, for example, if TmC is less than 85°C, the morphological stability of the foam during high-temperature use will decrease, and if it exceeds 100°C, the processability will be poor when molding a foam sheet. This is undesirable because it becomes difficult to manufacture products with stable quality and performance, and the characteristics of the foam increase.

Linear polyethylene (
B) is preferably 0.1 to 50 gi1om+
n, melt flow rate (value determined according to the measurement method specified in ASTM-D-1238), 0.9
Density of 15 to 0.945 g/Cm3 (ASTM-D-1
505)
and polyethylene consisting of ethylene having a melting point of 115 to 127°C and an α-olefin having 4 to 20 carbon atoms,
That is, so-called linear low-density polyethylene and medium-density polyethylene are preferable.

More specifically, α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexeno, 4
- Methyl-1-pentene, 1-octene, etc.; linear low-density polyethylene consisting of at least one or two or more of these α-olefins or α-olefin containing a small amount of propylene component The above-mentioned linear low density polyethylene can be exemplified.

These low-density polyethylenes can be obtained by polymerizing ethylene and α-olefin in a ratio that provides a predetermined density using a medium/low pressure method.

In general, the linear polyethylene used in the present invention has a high crystallinity density of 0 obtained by medium/low pressure polymerization.
．． Polyethylene having a melting point of 940 to 0.970C and a melting point of 125 to 135C may be used.

The blending ratio of the blend polymer having the two components (A> and (B)) of the present invention as essential components is within the range of 20 to 300, preferably 25 to 200 in area intensity ratio (R) according to 13C-NMR spectrum. Gayo(, also, the gel fraction is 1
5 to 45%, preferably 20 to 40%, more preferably 25 to 35%, and in addition satisfies the following formula: S≦0.3M+3, preferably S≦0.3M+1 (However, M is the apparent The permanent compression set (S
It is necessary to have >.

That is, in the present invention, the area intensity ratio (R) according to the 13C-NMR spectrum is important for increasing the expansion ratio of the foam and imparting heat resistance and compression set, and the 13Q NMR spectrum in the above range It is possible to achieve the object of the present invention only when the areal strength ratio (R>) is satisfied. When this R is smaller than 20, the rubber elasticity of the resulting foam increases, and the compression set property However, it becomes difficult to obtain a foam with good heat resistance, and when R exceeds 300,
This is not preferable because the rubber elasticity becomes insufficient and the compression set decreases.

If the gel fraction is lower than 15%, the heat resistance will be insufficient, and if it exceeds 45%, the heat resistance will be good, but it will become sticky and the compression set will deteriorate, which is not preferable.

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

A known thermally decomposable blowing agent such as azodicarbonamide, dicarbonate, Nitrosopentamethylenetetramine and the like and, if necessary, a crosslinking agent that generates radicals when heated are mixed, and the mixture is held at a temperature at which the foaming agent and crosslinking agent do not decompose, and molded, for example, into a sheet shape. This shaped sheet material is crosslinked using any known method such as an ionizing radiation crosslinking method or a chemical crosslinking method so that the gel fraction becomes 15 to 45%.

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 ~5Q Mrad. 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 100 parts by weight of the blend polymer of the present invention for electron beam crosslinking. You may.

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, and 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 used as appropriate. Can be applied.

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 thus obtained crosslinked polyethylene resin foam of the present invention has excellent heat resistance and compression set characteristics ranging from low expansion ratios to high expansion ratios, and has excellent cushioning properties and Because of its excellent heat insulating properties, it can be developed and used in many applications such as various packing materials, adhesive tape bases, mat base materials, automobile interior parts, other clothing, building materials, and medical applications.

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), compression set (S), apparent expansion ratio (M) by 13C-NMR spectrum
etc. 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 melting after once melting and recrystallization was defined as the melting point (Tm). Moreover, TmC was defined as TmC by the exothermic peak temperature due to recrystallization when the temperature was lowered after melting.

(2>130-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 and I20 is defined as R= 30/2·I2°.

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

First, in a '1Qmmφ NMR sample tube, orthodichlorobenzene (1.4cc) and deuterated benzene (0.2cc
) in a mixed solvent such that the solid content concentration of the sample was adjusted to 20% by weight, and then heated to a frequency of 25. OOMHz, 130-NMR at 120°C by pulsed FT method as mode.
was measured.

(3) Compression set (S) Measured according to the measurement method specified in JIS-6767-1976.

Samples measuring 5 cm x 50 m square were stacked to a thickness of about 25 mm and left for 22 hours under a compressive strain of 25% of the total thickness (to). Thereafter, the thickness (tl) after releasing the compressive strain and leaving it at room temperature for 24 hours was measured, and the compression set (S) was calculated according to the following formula.

S (%) = 100x (to-tl)/l.

(4) Apparent foaming ratio (M) This value is expressed as the reciprocal of the apparent density of the foam, and is measured by cutting the foam into a 10 cm x 10 cm square, measuring the weight and thickness, and dividing this weight by the volume. Weight per volume 1/
cm3).

(5) Heat resistance The heat shrinkage rates in the vertical, horizontal, and thickness directions due to heat treatment are shown according to the measurement method specified in JIS-6767. Specifically, a measurement sample (foam) is marked with a square mark of 100 meters both vertically and horizontally to measure its thickness, and then heat treated in a hot air oven at 90° 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 size of the dimensional change (thermal shrinkage rate) due to this heat treatment.

Heat shrinkage rate: within ±3.02 〇 [Accepted] Heat shrinkage rate: 3.0-5. O: Δ Heat shrinkage rate exceeding ±5.0:

(6) Gel fraction: Take about 0.2 CI of the shredded foam and accurately weigh it (this value is defined as Wl). After immersing this foam in tetralin at 135°C for 3 hours, the insoluble portion is taken out, washed with methanol, air-dried, vacuum-dried, and then accurately weighed (this value is designated as w2). Values of Wl and W2 From this, the gel fraction is calculated using the following formula.

Gel fraction (%) = 100-W2/W1 Examples 1 to 5, Comparative Examples 1 to 4 Ethylene and propylene were polymerized using a catalyst system containing an organometallic compound and a titanium compound to form ethylene and propylene with different contents of propylene. A propylene random copolymer was created.

Azodicarbonamide was added as a blowing agent to 100 parts by weight of a blend polymer consisting of these ethylene propylene random copolymers and linear polyethylene,
After mixing in a Henschelmi mixer, it was melt extruded to form a shaped sheet.

In Examples 3 and 4 and Comparative Example 3, the linear polyethylene had a density of 0.963. High-density polyethylene with a melting point of 132°C and a melt flow rate of 8Q/10 parts was used, and 2 parts by weight of divinylbenzene was added as a crosslinking aid. Further, only in Comparative Example 4, 5 parts by weight of didonylbenzene was added.

In other Examples and Comparative Examples, linear low-density polyethylene with a density o of 925, a melting point of 124° C., and a melt flow rate of 8Q/10 minutes was used, and no crosslinking aid was used. In addition, the amount of azodicarbonamide added is as follows in Example 3.
And Comparative Example 1 was 10 parts by weight, and all other Examples and Comparative Examples were 12 parts by weight. These molded sheets were exposed to an electron beam irradiation device (IR-
2> was irradiated with a dose of 5 Mracj for crosslinking. These crosslinked sheets were foamed by heating to 225-230"C on a salt bath. Evaluation tests were conducted on the resulting foam sheets. The results are shown in Table 1.

From the table, when the requirements of the present invention in Examples 1 to 4 were satisfied, foams with a high expansion ratio and excellent compression set and heat resistance were obtained. R defined in the present invention in Comparative Examples 1 and 2
If the requirements are not met, the compression set is poor (
Comparative Example 1) and poor heat resistance (Comparative Example 2).

Furthermore, the ethylene-propylene random copolymer of Comparative Example 3 whose propylene content did not satisfy the specifications of the present invention had low melting point and low crystallization temperature, resulting in low heat resistance of the foam.

Roughly speaking, in Comparative Example 4, the compression set was poor because the gel fraction did not satisfy the specifications of the present invention.

Claims (1)

[Claims] (1) A: As a copolymerization component, the propylene component is 15 to 15%
It contains an amount in the range of 30% by weight and has a melting point of 100-118°C (
B: a blend polymer whose essential components are a linear polyethylene having a melting point (Tm) of 115 to 135°C. , The area intensity ratio (R) according to the 13_C_-_N_M_R spectrum shown by the formula [R=I_3_0/2・I_2_0] is 20 to 300, and the gel fraction is 15 to 4.
5%, and a compression set (S) of S≦0.3M+3 (where M is the apparent expansion ratio).