DE1241976B - Process for the production of foamable molding compounds from alkenyl aromatic polymers - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C08f

German class: 39 b-22/06

Number: 1241976

File number: D 39236IV c / 39 b

Filing date: June 27, 1962

Open date: June 8, 1967

It is known to produce expandable thermoplastic polymer compositions by a normally solid styrene polymer in particle form with a mixture of water and a vaporizable organic liquid such as pentane or Petroleum ether, at temperatures between about 40 ° C and the softening temperature of the polymer brings into contact under pressure. The evaporable organic liquid penetrates or diffuses in the polymeric grains. After cooling, the grains are solid and can be expanded when heated will. They then form low density cell bodies.

^: Carrying out this process at temperatures below the softening temperature of the polymer has the disadvantage that it takes a relatively long time to achieve complete impregnation and penetration with the expansion or blowing agent. In the known processes, increasing the temperature is not recommended, since the individual polymeric particles then weld together and the entire batch occasionally solidifies; -SO 'that a uniform Pölymefmasse is formed which can not be used ⁱ for the intended purpose and-only can be removed with much time and effort from the plant.

It is already known to accelerate the impregnation and still prevent the ^{welding of the individual particles together by:} Softening temperature -provides. This ^: procedure shortens the working time somewhat, but does not prevent the particles ^{from welding together and} does not prevent the entire polymer mass from solidifying. Attempts have also been made to "shorten the treatment time" by introducing small amounts of a solvent into the polymer, either before or at the same time as the expansion or blowing agent is introduced. This process has the disadvantage that the foamable beads made in this manner contain some solvent for the polymer and therefore have "a substantially lowered softening temperature which is carried over to the foam products made from them. The foams made from these beads have In addition, a fairly large cell structure and thus a reduced insulation value.

Attempts have also been made to solidify and prevent the polymeric particles from adhering to one another in the Immersion or impregnation treatment by adding certain inorganic sweetness stabilizers Process for the production of foamable molding compositions from alkenyl aromatic polymers

Applicant:

The Dow Chemical Company,
Midland, me. (V. St. A.)

Representative:

Dipl.-Ing. F. Weickmann,

Dr.-Ing. A. Weickmann,

Dipl.-Ing. H. Weickmann

and Dipl.-Phys. Dr. K. Fincke, patent attorneys,

Munich 27, MöMstr. 22nd

Named as inventor:
Eugene Bruno Ulmanis,
Midland, me. (V. St. A.)

Claimed priority: ·. ■.

V. St. v. America June 27, 1961 (119 996)

to prevent. Such suspension stabilizers are alkaline earth carbonates, aluminum carbonates, alkaline earth carbonates, Alkaline earth phosphates and aluminum phosphates. These inorganic materials were used in amounts from 0.1 to 1 percent by weight of the polymer. Even here - it was still necessary the expansion or blowing agent at a temperature below or near the softening temperature to introduce the thermdplastischen polymer. Only when the whole expansion or Blowing agent is introduced at a temperature below or near the softening temperature, it becomes possible - to heat the mass under pressure to a temperature which is substantially above 'the Softening temperature of the polymer is. · ■■ "- ■ ·

-The inorganic suspending agents just described can be applied to the surface of the individual Particles adhere and are therefore expediently removed. Your presence at the final foaming party in any substantial or excess amount, the bonding and fusing can occur of the individual foamed particles make it difficult for one another.

The subject of the invention is a process for the production of foamable molding compounds from alkenylaromatic compounds Polymers. In the inventive

709 589/382

Process can include the addition of the expansion or blowing agent and / or the subsequent impregnation or immersion at any desired temperature above the softening temperature of the polymer, but below the decomposition temperature of the polymer.

Carboxymethylmethyl cellulose has already been used in the manufacture of foamable polymers from polystyrene. In the known procedure (French patent specification 1,243,155) , adhesives, including carboxymethylmethylceliulose, are used to coat the already impregnated polymers with a layer containing flame-retardant antimony oxide. The carboxymethyl methyl cellulose does not serve here as a dispersant for the blowing agent with which the polymer is to be impregnated, but as an adhesive. It was not foreseeable that the carboxymethylmethylceliulose, when used according to the invention, in which its adhesive effect is not at all important, could be used as an agent which prevents the sticking together of polymer beads. In the known process, treatment temperatures as high as those used in the process according to the invention are also not provided. It was surprising that at these high temperatures the carboxymethyl methyl cellulose would prevent the polymer particles from welding together.

The inventive method provides for the production of foamable, completely spherical or im essential spherical polymeric particles made of alkenyl aromatic polymers, for example in the shape of a pearl, an expansion or blowing agent in a particulate, thermoplastic polymer by dipping or Impregnation at a temperature above the softening temperature of the polymer, but below Bring the decomposition temperature of the polymer, at an elevated pressure in the presence of water and the dispersant. The water soluble dispersant is usually present in the aqueous phase in dissolved or finely dispersed form. Best results will be usually obtained at a temperature up to the melting temperature of the polymer. The inventive However, the process can also be successful at a temperature above the melting temperature of the polymer be performed. To keep the polymeric particles suspended in the medium, it is it is desirable to stir the mass or provide any other suitable means to prevent the keep polymeric particles in motion and suspended in the aqueous phase.

Accordingly, the method of the present invention for making foamy is perfect spherical or essentially spherical polymeric particles, for example in the form of pearls, before converting an expansion or blowing agent into a particulate, thermoplastic To incorporate polymer by immersion or impregnation at elevated temperature, am most effective at a temperature above but below the softening temperature of the polymer the decomposition temperature of the polymer, at an elevated pressure in the presence of Water and one or more of the dispersants. The water-soluble dispersant is normally present in the aqueous phase in dissolved or finely dispersed form. best

Results are usually obtained at a temperature up to the melting temperature of the polymer. However, the process according to the invention can also be carried out successfully at a temperature above the melting temperature of the polymer. In order to keep the polymeric particles suspended in the medium, it is desirable to stir the mass or provide some other suitable means to keep the polymeric particles agitated and suspended in the aqueous phase.

The dispersant is advantageously used in an amount comprised between 0.01 and 5 percent by weight of the water used in the process. The dispersants which are suitable for carrying out the process according to the invention include, in addition to carboxymethylmethyl cellulose, the water-soluble, sulfonated, vinyl aromatic polymers, such as, for example, sulfonated polyvinyl toluene. In some cases it may be preferable to use more than one of the aforesaid dispersants in combination.

The efficiency of the polymeric dispersants is highest with those organic _r water-soluble or water-dispersible polymers which have extremely high molecular weights. The efficiency is correspondingly lower when these polymers have a lower molecular weight. An increase in the proportion or concentration of the dispersant in the aqueous phase can result in at least some of the effectiveness being lost. This indicates that, for maximum economy, it is preferable to use polymeric dispersants which are medium or extremely high molecular weight. This applies in particular to the synthetic dispersants, which can be produced or obtained with molecular weights in the most varied of ranges. If the sulfonated polymers are not sufficiently soluble in acidic form, they can be used in the form of the water-soluble salts, especially in the form of alkali metal salts.

In some cases, particular advantages can be obtained by adding organic liquids which can be mixed with water and which have no dissolving or swelling effect on the polymer. Also — the foaming agent can be mixed into such organic liquids before it is pressed into the autoclave. The usual diluents which are suitable in this way include the lower alkyl alcohols such as methanol, ethanol, propanol, isopropanol, tert-butyl alcohol and monomethyl, monoethyl or monobutyl ethers of ethylene glycol usually in the range of no more than 1: 1 between dilution and foaming It should be noted here that such diluents for carrying out the invention are not necessary and that the advantages gained not make up for the specific circumstances and expenses in most cases .

The total time required to complete the immersion or impregnation process decreases rapidly with increasing temperatures. Instead of 40 hours or a similar time at or below the softening temperature of the polymer, only 1 hour or less is required

required when working at a temperature at or slightly below the melting temperature of the polymer will. Even shorter times are required at temperatures above the melting temperature of the polymer. The optimal temperature to be used in practice is given in the generally determined by the nature of the facility available. If the reaction is carried out in batches, so a certain million times is necessary to the mass of the polymeric particles in the aqueous Phase to be heated to the immersion or impregnation temperature. The duration of the minimal heating and Cool down time depends primarily on the training and size of the facility. Because to avoid it is to over-treat the polymeric particles at the high temperatures, i.e. longer at the treatment temperature to leave as necessary to get the desired impregnation and even distribution of the expanding or blowing agent in the polymeric particles, it is desirable to keep the temperature set in such a way that the optimal treatment time, which corresponds to the selected temperature, coincides with the predetermined heating and cooling cycle of the respective facility. Even with these restrictions it is now possible to reduce the treatment times to a fraction reduce those treatment times that are necessary to carry out the treatment according to the state of the art Technique required at or below the softening temperature of the thermoplastic polymer was.

Shorter treatment times and correspondingly higher treatment temperatures are continuous with one working processes possible in which smaller amounts or small portions of the dispersion the polymeric particles in the aqueous phase are each heated and cooled at any time.

The process of the invention relates to the treatment of alkenyl aromatic polymers. These include the normally solid homopolymers or copolymers of one or more monovinyl aromatic compounds, such as styrene, vinyl toluene, vinyl xylene, ethyl vinyl benzene, tert-butyl styrene, isopropyl styrene, chlorostyrene, dichloro styrene, bromostyrene, ethyl vinyl toluene, or a predominant amount of any or any amount of copolymer toluene of several of these monovinyl aromatic compounds with a minor amount of one or more other copolymerizable vinylidene compounds such as vinyl esters of aliphatic and aromatic acids, esters of acrylic and methacrylic acids, acrylonitrile, α-methylstyrene, methyl isopropenyl ketone and the like. The copolymers contain at least 50 percent by weight Styrene. Other thermoplastic styrene polymers that are useful in the process are the copolymers of about 85 to 99 percent by weight of at least one monovinyl aromatic compound and from about 1 to 15 percent by weight of a natural or synthetic rubber such as natural rubber, rubbery copolymers of styrene and butadiene, rubbery Copolymers of styrene, methyl isopropenyl ketone and butadiene, rubbery copolymers of acrylonitrile and butadiene, and mixtures of a predominant proportion of a normally solid styrene polymer and a minor proportion of natural or synthetic rubber. Thermoplastic copolymers of from about 99.5 to 99.99 percent by weight of at least one monovinyl aromatic compound and from 0.5 to 0.01 percent by weight of a divinyl aromatic compound such as divinylbenzoL divinyltoluene or divinylxylene can also be used.
The method according to the invention can be carried out using polymer particles of the most varied of sizes and shapes. The particles can be in the form of spheres, pearls, approximated spheres, or irregularly shaped, for example

ίο by grinding ,. Attrition or breakage of the solid polymer. The method can also be carried out with particular advantage with solid polymers which have the shape of elongated segments or sections of polymeric bodies. It is particularly advantageous if the polymer sections or segments are more molecularly oriented in at least one direction than in the other or the other directions.
In general, polymer particles are preferred whose largest dimensions are no greater than about 10 mm. For the subsequent processing of the end product, they are expediently in the form of pearls or spheres with a diameter between approximately 1 and 10 mm, preferably between 1 and approximately 5 mm. The final product can also be in the form of beads of larger dimensions.

The liquid foaming agents can be saturated aliphatic hydrocarbons, such as butane, isobutane, pentane, neopentane, hexane, heptane or mixtures of one or more such aliphatic hydrocarbons, which have a molecular weight of at least 56 and a boiling point not higher than 95 ^° C. at 760 mm have absolute pressure. Other suitable foaming agents are the perchlorofluorocarbons, such as:

CCl ₃ F

CCl ₂ F ₂

CClF ₃

CCl ₂ F-CCl ₂ F
CCIf ₂ -CCIF ₂
CClF _a -CCLF ₄

CF ₂ -CClF

I I

CF ₂ -CF ₂
CF ₂ -CClF

I I

CF ₂ -CClF

and tetraalkylsilanes, such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane and trimethyl-n-propylsilane, which have a boiling point not higher than 95 ° C at 760 mm absolute pressure. That liquid foaming agent is used in amounts ranging between about 0.05 to 0.4 g / mole of the volatile Fluid compound per 100 g of the normally solid thermoplastic polymeric starting material.

The length of time that the polymeric particles are heated in contact with the foaming agent depends in part on the dimensions of the polymeric particles used and in part on the temperature used in the process. The higher the temperature, the greater the rate of diffusion of the foaming agent into the polymeric particles and the shorter the time ₃ required to recover the beads or spheres.

An extension of the heating of the polymeric particles in contact with the foaming agent at the elevated temperatures for periods _5, the

are greater than necessary in order to ensure an even distribution of the expanding or foaming agent obtained, can lead to the fact that two or more polymeric particles agglomerate or stick to one another, stick, and that is to be avoided. When the treatment is completed, the entire contents of the closed Cooled vessel, namely to below the softening temperature of the polymer, preferably on a temperature below 40 ° C. The product is then removed and separated from the aqueous liquid and preferably dried at temperatures below 50 ° C.

Furthermore, as is known, organic, bromine-containing flame retardants and, if appropriate, peroxides can also be added as synergists. Preferred are the organic peroxides having a half life of at least 2 hours measured in benzene at IOO ⁰ C, are.

The organic bromide forming the flame retardant and the organic peroxide are preferred in an amount ratio between about 1: 1 and 10: 1 to one another. Usually they are in the Autolclav commonly entered or pressed in as a liquid mixture. Are the ingredients solids, so they can be mixed with a small amount of a solvent, for example with pentane, Hexane, heptane, methyl alcohol, ethyl alcohol, etc., so that a liquid solution or mixture is formed, which can be easily pressed into the autoclave. Are the organic bromide and the peroxide in the polymer granules diffused in; so everything is cooled in the closed vessel, then taken out and the polymeric product separated, washed and dried;

In carrying out the invention it is not necessary to use a large excess of propellant to use as it has been used up to now to speed up the impregnation and to reduce the treatment time to shorten it.

It is therefore no longer necessary to recover large amounts of the expanding or blowing agent after the end of the treatment. The process control can take place with somewhat wider tolerances without the uniformity of the action of the expansion or blowing agent being lost from batch to batch. The preferred proportion of the propellant for polystyrene in the finished foamable beads is between 4 and 6%. Sometimes it reaches about 7% j ^e according to the molecular weight of the polystyrene and the desired degree of foaming. An excess of the blowing or foaming agent of less than 1 or 2% is generally sufficient to ensure complete, even impregnation of the ^! To achieve polymer particles. In the known processes, excesses of up to 100% were used, so up to 12 and 14% of the expansion or blowing agent in relation to the amount of polymer were obtained. That made it necessary, at least? to recover half of the expanding or blowing agent that was originally added. When the method according to the invention is carried out, the blowing agent or expansion agent content in the finished beads or spheres is easily controlled to about 3 to 4% in relation to the total content of expanding agent or blowing agent. With the known method, an accuracy and uniformity of about% has only rarely been achieved on the same basis.

25th

30th

35

Example I.

A batch of 267 parts by weight of polystyrene having a viscosity of about 20 cps (measured on a lOgewichtsprozentigen solution of polystyrene in toluene at 25 ⁰ C, the polystyrene was in the form of ground particles having the specified below dimensions) was suspended in an aqueous solution, which consisted of 533 parts by weight of water, which contained 4.85 parts by weight of carboxymethylmethyl cellulose (1000 cP) and of 5.3 parts by weight of the ammonium salt of sulfonated polyvinyltoluene, which contained 77 percent by weight of ammonium sulfate together with 0.8 parts by weight of sodium lauryl sulfate, together with 4, Put 8 parts by weight of petroleum ether (boiling point 30 to 60 ° C) in a pressure-tight reaction vessel. The vessel contained air at room temperature and under atmospheric pressure in the remaining space before it was closed. The mixture was heated in the closed vessel to a temperature of 135 ^° C. with stirring. Normal pentane was then added to the vessel under pressure, namely 5 parts by weight of normal pentane per hour, the mixture in the vessel being further stirred and kept at a temperature of 135 ° C. until a total of 19.2 parts by weight of normal pentane had been added. After the addition of the normal pentane, heating and stirring were continued over a period of 2.25 hours. The total time for heating the polystyrene granules to a temperature of 135 ° C. in contact with the volatile hydrocarbons was 6 hours. The vessel was then cooled to a temperature of 25 ° C. and opened. The product was taken out, washed with water and dried in air at temperatures between 40 and 50 ° C. The product was in the form of spherical beads of the dimensions given below. The polystyrene starting material was in the form of granules of irregular dimensions as indicated below.

50-

Mesh size
after
US standard ' By
knife
mm Polystyrene
granulate
in the starting
material
Weight percent product
impregnated
Polystyrene beads
Weight percent 8th
- 10
• 1-2 ···
14th
-16
18th
20th
25th
■ 30 - 2.38
. -2.00
1.68
1.41
1.19
-1.00
0.84
0.71
0.59 0
0
0.3
4.5 -
57.0
29.4
7.8
0.7
0.3 - 0.6
0.9
29.6
62.0
6.2
0.7
0.0 100.0 100.0.

-6Ö The product has been analyzed. It was found to contain 6.24 percent by weight of the propellant in solution. A ^- content of the product was foamed by heating the granules in an open chamber with steam at temperatures of 99-102 ° C and were then dried. The foamed granules had a bulk density of 15.94 kg / cm ³ . The ground starting material contained relatively large proportions of very fine-grained material. Surprisingly and unexpectedly, the smaller particles were too

Claims (1)

grown together and formed larger round spherical particles. The larger particles in the starting material had a far less tendency to coalesce. This can readily be seen from the comparative sieve analysis given above. This phenomenon led to a narrowing of the size distribution instead of a broadening of the Size distribution, as would have been expected in itself. Example A batch of 300 parts by weight of a copolymer of 95% by weight styrene and 5% by weight of a rubbery copolymer, which in turn was formed from 70% by weight butadiene and 30% styrene, the copolymer being in the form of beads having a sieve with openings from 0.250 to 1, 68 mm passed according to US standard conditions, was suspended in an aqueous solution of 3000 parts by weight of water which contained 0.75% carboxymethyl methyl cellulose. This was done in a pressure-tight vessel made of stainless steel. The jar was closed and then 60 parts by weight of normal pentane was injected into the jar. The mixture was stirred and heated to a temperature of 125 ⁰ C for 6 hours and then cooled to 25 ⁰ C. After opening the vessel, the product was separated off by filtering, washed with water and dried. The impregnated copolymer beads contained 5.5 percent by weight normal pentane. After foaming, the foamed beads had a bulk density of 22.9 kg / cm ³ . Example III 35 A batch of 300 parts by weight of granulated polystyrene having a viscosity of 16.7 cP in terms of Segments of extruded rods 1.5 mm in diameter and 3.17 mm in length were placed in a solution suspended, which consisted of 3000 parts by weight of water, the 0.75 percent by weight carboxymethylmethyl cellulose (1000 cP, 55% active). This was done in a pressure-tight vessel made of stainless steel Stole. The jar was closed and 150 parts by weight of normal pentane was injected into the jar. The mixture was stirred and kept at a temperature of 160 to 166 ° C for 1.5 hours heated. This was followed by cooling to 95 ° C., and a batch of a liquid mixture of 60 parts by weight of normal pentane, 21 parts by weight of 1,2-dibromo - _ 1,1,2,2-tetrachloroethane and 15 parts by weight of dicumyl peroxide were pressed into the vessel. The resulting mixture was stirred, heated to a tem- ^F 'temperature of 95 ° C for 4.75 hours, then it was cooled to 25 ° C and open the vessel. The product was separated by filtering, washed and dried. The product was in the form of pearls. The impregnated beads contained 9 percent by weight normal pentane together with 1,2-dibromo-1,1,2,2-tetrachloroethane and dicumyl peroxide. The product was then foamed by heating. Cell-containing beads with a bulk density of 68.8 kg / cm ^{3 were obtained} . The foamed beads would extinguish themselves if they were lit in an open flame and the flame was removed. A portion of the impregnated beads was foamed into a cell-containing block in a porous form. Test pieces with a cross section of 6.3 x 25.4 mm and a length of 152 mm were cut from the cell-containing block. The test pieces were used to determine the self-extinguishing properties. For this purpose, a test piece of the foam was held in a horizontal position in an open flame, the 25.4 mm wide sides being vertical and the free end being lit by the open flame. Then the flame was removed. In ten foam test pieces tested in this way, in nine cases the flame went out immediately after the flame was removed, and in one case self-extinguishing took place in 6 seconds. Claim: Process for the production of foamable molding compositions from alkenyl aromatic polymers and blowing agents by impregnating the polymer with the blowing agent at one above the other Softening point of the polymer lying temperature and elevated pressure in the presence of Water and a dispersant, characterized in that one is used as the dispersant a sulfonated vinyl aromatic polymer or copolymer and / or carboxymethylmethyl cellulose used in an amount of 0.01 to 5 percent by weight, based on the water. Considered publications:
French patent specification No. 1243 155. 709 589/382 5.67 © Bnndesdruckerei Berlin