DE1629526A1 - Manufacture of foamed resins - Google Patents

Description

DRS. EULE & BERG IfIr * "KVWl i 4» .. »

DIPt -ING STAPF I ^ * ♦ £ * XPI »ί ⁸ MUNICH 13, the 1 9th YEAR.

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PATENTANWÄLTE phone number 3ί42ί5

Telegram address i PATENTEULE MOnchen-

Bank connectioni

Bayerische Vereinsbank MOndien 453100

Pomchack account in India £ 5,343

Drs. Eule & Berg, DIpI. Ing.Stapf, 8 MDndien 13, Kurf Orstenplalz 2
Your Zeldien

UnierZtldiin Attorney's file: 15 635

MONSANTO GHEMXOALS LIMITED Monsanto House, 10-18 Victoria Street, London S.W. 1

Manufacture of foamed resins.

The present invention relates to the manufacture of foamed ones Resins, and more particularly a process for producing foamed polyolefin resins by an extrusion process.

009886/1773

Gasei R-436 '. . -2-

Foamed resins have heretofore been extruded However, attempts to extrude polyolefins in foamed lOrm generally encountered difficulties, in that the properties of the extruded foams are in many cases not entirely satisfactory was. A process has now been developed which makes it possible to manufacture products of good quality.

The invention comprises a process for making a foamed polyolefin resin in which the product, this is achieved by extruding a foamable mixture comprising a polyolefin resin and a volatile one Pneumatogenic, with a gas under elevated conditions Temperature is treated.

The polyolefin is one which has been obtained by polymerizing an olefin, "preferably one which that contains no more than four carbon atoms in the molecule. Polyethylene is particularly valuable however, polypropylene, for example, is also useful. A polyethylene can be made either by a high pressure or Low-pressure processes can be produced, being an example the latter is under a "Ziegler" method Use of an organometallic catalyst. However, the invention is particularly applicable to polyethylene, which is produced by a high pressure process

009886/1773

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became.

The pneumatogen is a volatile substance that makes one Has a boiling point (at atmospheric pressure) lower than the extrusion temperature? the preferred pneumatogens are the aliphatic hydrocarbons with up to four carbon atoms, such as Ethane, ethylene, propane, n-butane, iso-butane and butadiene, however, the invention is also applicable to polyolefin foams, made using neopentane or carbon dioxide as a pneumatogen. An example a normally liquid pneumatogen is n-pentane or a mixture of pentanes

The gas with which the foamed polyolefin resin is treated is, according to the method of the present invention is preferably air. However, it can be any gas be that is essentially inert to the polyolefin and the permanent gases that meet this condition, for example nitrogen, are very useful. A low boiling fluorocarbon such as chlorotrifluoromethane can also be used as the gas.

The process is carried out at an elevated temperature which is typically above about 4O ⁰ C; elevated temperatures between 50 ° and 100 ⁰ C, preferably from 60 ° to 90 ⁰ C sindoft very suitable ..

009886/1773 -

The pressure of the gas employed can be atmospheric or above atmospheric, and if above atmospheric it can be, for example, between 20 and 200 (2.41 and 15.1), such as from 40 to 100 pounds per square inch gauge (3.81 to 8.03 kg / cm ² ).

The period of time over which the foamed polyolefin resin is treated with the gas is relatively short. Quite often, periods of just a few minutes are sufficient for example between 5 and 30 minutes, however, in some cases longer periods of time, for example from 1 to 20 hours, or preferably from 2 to 10 hours, may sometimes be desirable.

In many cases, advantages can be obtained by using the method of the present invention a foamed polyolefin resin as it comes out of the extruder, in which case it is appropriate, to use an elevated temperature at atmospheric pressure. For example, the extruded foam can pass through a suitable heated tunnel or oven.

Where the gas treatment is carried out under increased pressure, the same is slowly built up and discharged to

Avoid destroying the foamed structure and pre- 009886/1773

BATH ORIGINAL

preferably is also where a combination of increased ! Temperature and pressure are used »the pressure is removed, before allowing the temperature to drop to room temperature. ·

Conventional methods can be used in the initial production of the extruded foam. For example, the weight of pneumatogen used can be, for example, up to half the weight of the polyolefin and, for example, between 5 and 40% by weight, preferably from 10 to 15% by weight, of the polyolefin is often a suitable proportion. The extrusion ÜJemperatur is preferably between 9O ⁰ C and 120 ⁰ C, preferably between 100 ⁰ C and 115 ⁰ C; often, an extrusion temperature of about 11O ⁰ C have used In these Extrudierlemperaturen to extrusion pressures from 200 to 5000 pounds per square inch (14 "1 and 351.5 kg / cm) and preferably between 300 and 3000 pounds per square inch (21.1 and 210.9 kg / em) proved to be suitable. Preferably, the polyolefin also contains a germ or. nucleating agent that assists in the formation of large numbers of fine cells. A wide range of nucleating agents can be used, including finely divided inert solids such as silica or alumina (in conjunction with zinc stearate if desired) *, or small amounts of a substance that are below the extrusion temperature

-6 formation of a gas decomposed, can be used.

An example of the latter class of nucleating agents is sodium bicarbonate, in conjunction if desired with a weak acid such as tartaric acid or citric acid. A small amount of the nucleating agent, for example up to 5 wt. # Des Polyolefin, is usually effective.

Simple extrusion molds can be used, but it is preferred to use a mold which has a relatively ' allows high resistance to flow of the polyolefin. A form like that in the British Patent application No. 25001/63 is described which involves the manufacture of comparatively large extruders Sections allowed is suitable.

The method of the present invention may for example be used for producing foamed polyolefins "having a density of less than 5 pounds per cubic foot (2.27 kg per 0.0283 m ^) _f, for example, 1 or 2 pounds per cubic foot (0.454 kg or 0.907 kg per

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0.0283 m), although an improvement in the Production of high density foamed polyolefins is achieved, for example, Ms up to 10 pounds per cubic foot ^

(4s, 54 kg per 0 * 0283 m ³ ) ₀

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The invention is illustrated by the following example.

Example '·

This example describes the production of foamed Polyethylene by a process in accordance with the present invention and illustrates the improvement achieved.

A piston press with a cylinder capacity of 300 mm was equipped with an orifice valve and an extrusion die consisting of a single circular opening 0.040 "(0.1016 cm) in diameter and 0.1" (0.254 cm) guide channel length connected to the outlet valve was attached, and was heated ^{to 100 0 C by a steam coil.} The extrusion cylinder was charged with 150 g of polyethylene granules with a density of 0.92 and a melt index of 2.0, in which 3.3% by weight of finely divided silicon dioxide had been dispersed as a nucleating agent. Then, 50 g of liquid butane was added at -10 ⁰ C and the extruder was sealed and heated to 110 ⁰ C for one hour "A nitrogen pressure of 300 pounds per square inch (136 kg per 6.452 cm ²⁾ was set in the piston press, and the extruder was still closed, a further half hour at 110 ⁰ C '009886/1773

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held.

The valve was then opened and a strand of foamed polyethylene 0.15 inch (0.5810 cm) in diameter and 1.5 pounds per cubic foot (0.681 kg per 0.0283 m ⁵ ) density was released into the atmosphere extruded. The extrusion speed was 60 feet per minute (914 cm per minute) and nitrogen pressure was maintained in the piston press throughout the extrusion. The extrudate collapsed after extrusion

The extruded foam was divided into four portions labeled A, B, C and D. Part A was kept in the air; Part B was kept for 20 hours at 70 ⁰ O in air at atmospheric pressure; Part G was held for 30 minutes at 100 Ω under 100 pounds per square inch gauge (8.03 kg / cm) air pressure? and portion D was ^{stored at 100 °} C. for 3 hours under a nitrogen pressure of 20 pounds square inch gauge (2.41 kg / cm ² ).

Part A had not regained its elasticity after four weeks, but the other parts had each other all recovered from the described treatment and the improvement, which results from the method of the present invention can therefore be seen.

0 & 9886/1773 _ — __

Claims (1)

Patent claims: 1 .J Process for producing a foamed polyolefin resin, characterized in that the product resulting from the extrusion of a foamable mixture comprising a polyolefin resin and a volatile pneumatogen, emerges with a gas under elevated conditions Temperature is treated. 2. The method according to claim 1, characterized in that that the polyolefin is polyethylene. 5. The method according to any one of claims 1 or 2, characterized characterized in that the pneumatogen is an aliphatic hydrocarbon with up to four Carbon atoms. · '. 4. The method according to any one of the preceding claims, characterized in that the gas with which the foamed resin is treated, air is. 5. The method according to any one of the preceding claims, characterized in that the gas treatment is carried out at a temperature between 5O ⁰ C and 100 ⁰ O. 6. The method according to one of the preceding claims, 009886/1773 "- _ ^ ORIGINAL BATHROOM -10- characterized in that the gas treatment at a pressure which is above atmospheric pressure, is carried out. 7. The method according to claim 6, characterized in that the pressure is from 40 to 100 pounds per square inch gauge (3.81 to 8.03 kg / em). 8. The method according to any one of the preceding claims, characterized in that the resin with the gas over is treated for a period of 2 to 10 hours. 9. The method according to any one of the preceding claims, characterized in that the foamed polyolefin produced has a density of less than 5 pounds per cubic foot (2.27 kg per 0.0283 m ⁵ ). 10. The method according to claim 1, essentially as described in the example. 11. Foamed polyolefin resin, characterized in that it has been produced by a method according to any one of the preceding claims. 009886/1773