JPS636582B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polypropylene and polypropylene containing 2 to 20% by weight of 1.2-
The polybutadiene and optionally the crosslinking and/or blowing agent are mixed at a temperature below the decomposition temperature of the crosslinking or blowing agent and formed into the desired shape, followed by treatment with high energy radiation at a dose of 2 to 20 Mrad and The present invention relates to a process for producing crosslinked and foamed mixtures containing polypropylene, which comprises crosslinking and optionally foaming by heating in an oven.

Such a method is described in German Patent No. 2839733. In this process, products are obtained which have both the advantageous and disadvantageous thermal properties of polypropylene. Disadvantageous properties include their high susceptibility to embrittlement, especially at low temperatures.

JP-A No. 47-49825 also discloses elastic rubber-like 1.4-
A method for foaming polyolefins containing 0.3 to 40 parts by weight of polybutadiene by direct gas action or physical methods is described. If 1,4-polybutadiene is included, small and stable cells will be formed, but it will lead to a decrease in thermal stability under elevated temperatures, and to that extent, it will deteriorate the heat resistance of the resulting foam. Become.

DE 2937528 relates to a foam based on a mixture of a propellant and a thermoplastic resin such as polypropylene, 1,2-polybutadiene or other thermoplastic resins, such as ethylene-alpha-olefin copolymers, Although this foam is characterized by particularly high thermal stability, a homogeneous cell structure and an excellent appearance, the possibilities of vacuum forming processes are limited and the strength becomes brittle at low temperatures in the freezing point range.

Also, West German Publication No. 1694130 describes a method for producing a foam which consists of mixing polyolefin, 1,4-polybutadiene rubber and an organic peroxide, molding and then heating to crosslink and foam. It is being Although this blowing agent is very soft and flexible, its low hardness makes it unsuitable for the production of load-bearing jackets.

The object of the invention is to provide a process for the production of crosslinkable and optionally foamable mixtures containing polypropylene, which makes it possible to produce highly valuable structural materials. The mixture exhibits good temperature stability in the freezing point range, comparable to the properties of pure polypropylene, and complete absence of the embrittlement known for polypropylene, as well as good stability in the temperature range -20 to +30°C. It is characterized by strength and hardness. Plate-shaped semi-finished products from this mixture can be deformed by applying vacuum methods. Also, the highly fine cell structure and glossy surface of the material from which the mixture is foamed is comparable to other known high value foams.

This object is achieved according to the invention in the initially mentioned method by adding 10 to 50% by weight of low-pressure polyethylene or high-pressure polyethylene, based on polypropylene, to the mixture raw material.

The mixture used in the process of the invention consists primarily of polyethylene and polypropylene and small amounts of free-flowing 1,2-polybutadiene.

This mixture has innovative properties not found in the properties of the raw materials. This new property is not transient, and in this respect has never been seen before.

The method of the present invention makes it possible to manufacture structural members with excellent heat deformation resistance. In order to measure this heat deformation resistance, bulk density was measured according to Example 1.
A foam with 30Kg/ ^m3 was produced. A 10 mm thick plate was cut from this foam and formed into a cylindrical cap with an outer diameter of 120 mm and a height of 60 mm using a commercially available vacuum forming machine. Hot storage of this cap at 150°C in a circulating oven resulted in a diameter reduction of 3.3% and a reduction in height of 4.8%. When using polypropylene foam with the same bulk density,
Comparable results were obtained.

In another test, the plate-like foam described above was manufactured according to Example 1 and stored in a circulating oven at a temperature of 150° C. for 24 hours, resulting in a shrinkage of about 1% in the longitudinal and transverse directions. occurred. A comparable pure polypropylene foam also showed a shrinkage of about 1% in the machine and transverse directions. The temperature was then increased to 160° C. in both cases, and both the pure polypropylene foam and the foam according to the invention shrunk significantly. From this, it can be inferred that the foam according to the present invention has almost the same heat deformation resistance as pure polypropylene, even though it contains a considerable amount of low-pressure polyethylene with a softening point of 130°C.

Next, a sample of the foam according to Example 1 was
Torsional vibration tests were conducted according to DIN53445.
For this test, 4.1Hz, transition temperature (Tu¨) = -40
It was found that the maximum attenuation rate occurred at °C (Fig. 1). Such a damping maximum is exhibited by neither pure polypropylene foam (FIG. 2) nor pure polyethylene foam (FIG. 3).

The behavior of the material at low temperatures can be elucidated from the maximum value of such a damping rate. According to FIG. 1, the foam according to the invention has a transition temperature of -40°C, and it becomes brittle only below this temperature.
Pure polypropylene foam becomes brittle already at temperatures of approximately +7°C. In this respect, the workpiece according to the invention is superior to pure polypropylene foam near the freezing point.

Figures 4 and 5 show the relationship between the damping behavior and temperature of various workpieces. Curve A in FIG. 4 shows the damping behavior of the foam from the mixture according to Example 1;
The B curve in the figure shows the damping behavior of a control body of the same size and bulk density from pure polypropylene. The trends of both curves are almost the same. Only at temperatures above 150°C does a strong drop occur.

In the case of the control body made of non-foamed low-pressure polyethylene, a comparable trend of reduction is already shown at a temperature of 130° C. (FIG. 5).

When low-pressure polyethylene is used as an additive in the mixture of the present invention, the required amount of crosslinking agent (peroxide content or radiation dose) can be reduced by 10 to 20%, which is the same as when high-pressure polyethylene is added. The results were obtained. In this respect, the selection of the mixture according to the invention is particularly significant also from an economic point of view.

The method according to the invention is also suitable for producing crosslinked, non-foamed polyolefin materials. This processed material can in particular be reprocessed into load-bearing structural materials. Furthermore, in the temperature range of -40 to 150°C, it characteristically has properties that are considered to clearly surpass those of known polyolefin processed materials.

Next, the present invention will be explained in more detail based on examples.

Example 1 Low pressure polypropylene (melt index)
230/5g/10min=10) 66.3 parts by weight, low pressure polyethylene (melt index 190/2.16g/10
min = 4.6; ρ = 0.927-0.929 g/cm ³ ) and 15 parts by weight of azodicarbonamide were added to polybutadiene (molecular weight
3000, 1, 2 (90% by weight) was mixed with 5.6 parts by weight. The mass temperature during mixing was adjusted to 175-185°C. The homogeneous mixture in the extruder was shaped into a strip through a wide slit nozzle and then crosslinked by means of an electron beam with a surface dose of 7 Mrad. The crosslinked product thus obtained was passed through a circulation oven on a screen belt and foamed. The residence time in the furnace was 8 minutes at a temperature of 215°C. This foam plate has a homogeneous cell structure and 30
It had a density of Kg/ ^m3 .

The gel content of this processed material was measured in boiling xylene as follows.

Boil 1g of the material in 100ml of xylene for 5 minutes,
Washed three times with 50 ml each of hot xylene.

By weighing the non-dissolving furnace liquor after drying it for 16 hours at 105°C,
The gel content of the starting material amount was calculated.

Gel content was 67%.

The test results for this foam are shown in curve A in FIGS. 1 and 4.

Example 2 Low pressure polypropylene (melt index
230/5g/10min=10) 85 parts by weight and 15 parts by weight of azodicarbonamide were mixed into polybutadiene (molecular weight 3000, 1, 2 content 90%) in a twin-screw extruder.
5.6 parts by weight. The mass temperature during mixing is 175
The temperature was adjusted to ~185°C. The homogeneous mixture in the extruder was shaped into a strip through a wide slit nozzle and crosslinked by electron beam with a surface dose of 8 Mrad. The crosslinked product was placed on a screen belt and passed through a circulating oven to foam. The residence time was 8 minutes at a temperature of 215°C. The foamed zone obtained had a homogeneous cell structure and a density of 30 Kg/ ^m3 .

The test results for this foam material are shown in curve B in FIGS. 2 and 4.

The differences between the products of Example 1 and Example 2 are clearly visible in the figure. The foam produced by the method of the present invention exhibits a transition point at -40°C, but pure polypropylene (Figure 2) and pure low-pressure polyethylene (Figure 3)
No transition occurs at this temperature.

The above results are also verified in other examples.

Example 3 Polypropylene (melt index 230/5
g/10 min = 10) 74.3 parts by weight, low pressure polyethylene (melt index 190/2.16 g/10 min = 4.6;
20.7 parts by weight of ρ=0.927~0.929g/m ³ ) and 5 parts by weight of azodicarbonamide were mixed into polybutadiene (molecular weight 3000, 1,2 content 90% by weight) 5.3 in a twin screw extruder.
% by weight and reprocessed as in Example 1.

The foam material obtained has a bulk density of 75Kg/ ^m3 ;
Gel content was 69%.

Figure 6 shows the logarithmic attenuation rate according to DIN53445.

Example 4 Polypropylene (melt index 230/5
g/10 minutes = 10) and 5 parts by weight of azodicarbonamide were mixed with 5.3% by weight of polybutadiene (molecular weight 3000; 1,2 content 90% by weight) in a twin-screw extruder, and reprocessed in the same manner as in Example 2. processed.

The resulting foam had a bulk density of 80 Kg/m ³ and a gel content of 70%.

Figure 7 shows the logarithmic attenuation rate according to DIN53445.

[Brief explanation of the drawing]

Figure 1 shows the results of a torsional vibration test according to DIN 53445 for the foam of the invention, Figure 2 is a similar diagram to Figure 1 for a pure polypropylene foam, and Figure 3 shows the results of a pure low-pressure polyethylene foam. A diagram similar to Figure 1 for a foam; Figure 4, A, for a foam of the invention, B, a diagram showing the damping behavior versus temperature for a pure polypropylene foam, and Figure 5, for an unfoamed foam. FIG. 6 is a diagram similar to FIG. 1 regarding another foam of the present invention, showing the relationship between damping behavior and temperature for low-pressure polyethylene;
FIG. 7 is a view similar to FIG. 1 regarding yet another foam of the present invention.

Claims (1)

[Claims] 1 for polypropylene and 2 for polypropylene
~20% by weight of 1,2-polybutadiene with a molecular weight of 500 to 10,000 and optionally crosslinkers and/or
or by mixing the blowing agent at a temperature below the decomposition temperature of the crosslinking agent or blowing agent, shaping it into the desired shape, and then treatment with high-energy radiation at a dose of 0.5 to 20 Mrad and/or heating in a furnace. A process for producing crosslinked and optionally foamed mixtures containing polypropylene, which comprises crosslinking and optionally foaming, in which the mixture raw material contains 10 to 50% by weight of low-pressure or high-pressure polyethylene, based on the polypropylene. A method characterized by adding.