NO147989B - ALKENYL-AROMATIC THERMOPLASTIC FOAM, AND PROCEDURE FOR THE PREPARATION OF SUCH - Google Patents

Description

The invention relates to an alkenyl aromatic thermoplastic polymer foam body for insulation purposes, consisting of a rectangular plate having a minimum cross-sectional dimension of 6.35 mm and a minimum cross-sectional area of 51.6 cm, which plate contains a plurality of closed, non-connected gaseous fluorinated hydrocarbon-containing cells with an average size of 0.1-1.2 mm, and are of uniform cell structure and without discontinuities, produced by extrusion of a mixture of heat-softened polymer and a blowing agent mixture comprising fluorochloromethane, methyl chloride, ethyl chloride, chlorodifluoromethane or 1, 1-difluoroethane as a high-permeability blowing agent together with another, fluorinated hydrocarbon blowing agent. This foam body is characterized by the fact that the gas-containing cells contain one or more low-permeability foaming agents with formula

where is methyl, ethyl, chloromethyl, difluoromethyl, chlorofluoromethyl, fluoromethyl or trifluoromethyl, and R2 is hydrogen or chlorine, fluorine, methyl or trifluoromethyl, the emulsifying agent does not contain more than 3 C atoms, and the emulsifying agent is made up of a compound with more than 3 C -atoms if, as a halogen, it contains only 2 fluorine atoms. The invention also relates to a method for producing a polymer foam body as stated above, whereby a blowing agent mixture of fluorochloromethane, methyl chloride, ethyl chloride, chlorodifluoromethane or 1,1-difluoroethane as a high permeability blowing agent together with another, fluorinated hydrocarbon blowing agent is injected into a heat-softened polymer stream and mixed with it, after which the mixture is extruded through a die. This method is characterized in that one or more low-permeability emulsifiers with the formula are used as the second emulsifier, which is injected together with the high-permeability emulsifier

where R-^ is methyl, ethyl, chloromethyl, difluoromethyl, chlorofluoromethyl, fluoromethyl or trifluoromethyl, and R2 is hydrogen or chlorine, fluorine, methyl or trifluoromethyl, the evaporating agent does not contain more than 3 C atoms, and the evaporating agent consists of a compound with 3 C atoms if it contains only 2 fluorine atoms as a halogen.

Cell size is measured as the average cell diameter across the smallest cross-sectional dimension of the body (i.e.

e.g. with ASTM Method D2842-69), and the oblong body has a

cross-sectional area of at least 51.6 cm<2> and having a minimum cross-sectional dimension of at least 6.35 mm, the foam body having a water vapor permeability of not more than 3.02 metric perm cm and measured by ASTM Method C355-64 "Procedures for Desiccant Method", a density of 16-80 g/l with the additional limitation that the cells contain a low permeability desiccant having a permeability through the alkenyl aromatic resin polymer of no more than 0.017 x the permeability of nitrogen through the body, and a thermal conductivity of 0.07 ± 20% BTU-in/h/f t2 /°f(0 .24* 1 CT^^O^calcm/s cm2oc)>

One of the main uses for styrene polymer foam is in the area of thermal insulation. A styrene polymer foam for thermal insulation desirably has relatively small cells and excellent dimensional stability. It is also highly desirable that the insulation value of the foam is maintained for as long as possible. From a process standpoint, it has been desirable to use certain halogen-containing compounds, e.g.

e.g. dichlorodifluoromethane, in the production of extruded styrene polymer foam. It is currently believed that such compounds, when released into the atmosphere, can reduce the effectiveness of the ozone layer as a solar shield, and it is therefore desirable that fluorinated and/or chlorinated compounds which may possibly reduce the effectiveness of the ozone layer are generally eliminated from applications where they are eventually released to the atmosphere.

BRD publication 1 544 753 describes the basic procedure

for the production of extruded logs or planks of closed-cell thermo-plastic foam, whereby mixed blowing agents with specific vapor transmission rates are used.

US Patent 3,900,433 describes non-cellular styrene polymer beads - foamed in place - which are impregnated with a blowing agent mixture containing 0.5-20% by weight of an impregnation aid, e.g. methyl chloride or chlorofluoromethane.

None of the above-mentioned publications discloses or suggests a dimensionally stable foam product with a large cross-section made with a mixture of environmentally more acceptable foaming agents and which is particularly useful for thermal insulation in residential and industrial buildings, pipelines, tanks, etc., such as the product according to the present invention is. Furthermore, none of the specified publications describes such a spray agent mixture which is used in connection with the present invention.

Volatile, fluid blowing agents used in the method according to the invention are therefore a mixture of high-permeability blowing agents and low-permeability blowing agents. Either the high-permeability blowing agent and/or the low-permeability blowing agent can be a mixture of one or more suitable blowing agents. The low-permeability blowing agent in the mixture of blowing agents used for the production of foam in accordance with the invention advantageously constitutes 30-70% by weight of the foaming agent mixture.

Low permeability emulsifiers that fall under the above limitations are: 1,1,1-trifluoropropane, 2,2^-difluoropropane; 1,1,2,2-tetrafluoroethane; 1,1,1,2-tetrafluoro-2-chloroethane; 1,1,1-trifluoro-2-chloroethane; pentafluoroethane; 1,1,2-trifluoroethane; 1,1,1-trifluoroethane; octafluoropropane; and 1,1-difluoro-1-chloroethane and mixtures thereof. All the compounds mentioned above have the necessary permeability value and thermal conductivity.

The term "alkenyl aromatic thermoplastic polymer" refers to a solid polymer of one or more polymerizable alkenyl aromatic compounds. The polymer or copolymer comprises in chemically combined form at least 70% by weight of at least one alkenylaromatic compound with the general formula

where Ar represents an aromatic hydrocarbon radical or an aromatic halogen hydrocarbon radical of the benzene series, and R is hydrogen or methyl. Examples of such alkenyl aromatic polymers are the solid homopolymers of styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinyl-xylene, ar-chlorostyrene or ar-bromostyrene; and the solid copolymers of two or more of such alkenylaromatic compounds with small amounts of other easily polymerizable olefinic compounds, e.g. methyl methacrylate, acrylonitrile, maleic anhydride, citraconic anhydride, itaconic anhydride, acrylic acid and rubber-reinforced (either natural or synthetic) styrene polymers.

The production of alkenyl aromatic polymer foam bodies

in accordance with the invention is most conveniently done in a known manner, whereby the volatile, fluid blowing agent is injected into a heat-softened polymer stream in an extruder. From the extruder, the heat-softened gel is fed to a rotary mixer where a spiked rotor is enclosed in a housing that has a spiked inner surface that engages between the spikes on the rotor. The heat-softened gel from the extruder is fed to the inlet end of the mixer and comes out from the outlet end, the flow being in a generally axial direction.

From the mixer, the gel passes through coolers and from the coolers to

a die that extrudes a generally rectangular plate.

In the method according to the invention, it is often desirable to add a nucleating agent, e.g. talc, calcium silicate or indigo, for reduction of cell size.

A majority of foams were made by mixing polystyrene containing a commercial grade monochloropentabromocyclohexane flame retardant, barium stearate, magnesium oxide and a nucleating agent. The mixture was fed to an extrusion unit, a blowing agent was injected into the extruder housing continuously, and polystyrene foam was extruded as a rectangular plate with a cross-sectional dimension of approx. 2.54cm x 2.54cm. The foaming temperatures were from 112 to 118°C. All concentrations stated as parts or parts per 100 (pph) is parts by weight per 100 parts polystyrene resin. The feed rates, the blowing agent mixture and the physical properties are given in the following tables. The density is shown in grams/litre, the cell size in mm, and under the foaming agent the weight % and component of the foaming agent are shown.

The foams that were produced and are shown in the tables contained 3 parts per 100 of the flame retardant, 0.075 part per 100 barium stearate, 0.03 part per 100 magnesium oxide. The units of the measured K factor are BTU-in/h/ft /°F and are determined on samples sliced from the extrudate to such a thickness that all surfaces of the rectangular sample has been sliced from the rollable extruded plate to provide cut cells on each of the surfaces. Aging of the samples took place at room temperature, approximately 20 - 25°C. In the column "calculated K-factor" it is calculated values for the K-factor for the foam after 5 years at ambient temperatures in air, and the infinitely aged K-factor If one knows the density, cell size, blowing agent level, blowing agent composition, K-factor, permeability to the blowing agent, the first K-factor at extrusion, the K-factor at any point in the future can easily be calculated to a high degree

of accuracy. The K-factor below infinite aging value is the K-factor that the foam would have if the blowing agent in the cells were completely replaced by air. The extrusions shown in experiments 7 and 8 in the table do not produce a foam within the scope of the invention

frame, but is only for comparison purposes. If the cell size and the K-factor are considered, then it is obvious that for any of the emulsifier systems the K-factor will be the lower the smaller the cell size. It should also be noted from the first 6 lines in the table that the long-term insulation value is significantly improved by using a low-permeability sealant in conjunction with a high-permeability one. The unit of permeability is cm 3 /mil/100 in 2 /day/atm. = cm 3 /0.0254 mm/645cm 2/day/atm. The permeability to methyl chloride = 980; 1,1-difluoroethane= 8.4; chlorodifluoromethane=19; ethyl chloride=84; air=110; chlorofluoromethane= 329; and 1,1-difluoro-1-chloroethane=0.07.

Conversion factor for the expression BTU-in/h/ft<2>/°F is

3.4448 x 10~<4> (cal.-cm/sec. cm2 Qc) .

Table II shows the dimensional stability of different foams from Table I.

Foam in accordance with the invention has a

K-value after five years of aging at ambient temperature in air on

at least 1.0 x 10 cal. less than the K value for the same foam where the blowing agent has been replaced with air.

Claims (2)

1. Alkenyl aromatic thermoplastic polymer foam body for insulating purposes, consisting of a rectangular plate having a minimum cross-sectional dimension of 6.35 mm and a minimum cross-sectional area of 51.6 cm , which plate contains a plurality of closed, non-connected gaseous fluorinated hydrocarbon-containing cells having an average size of 0, 1-1.2 mm, and is of uniform cell structure and without discontinuities, produced by extruding a mixture of heat-softened polymer and a blowing agent mixture comprising fluorochloromethane, methyl chloride, ethyl chloride, chlorodifluoromethane or 1,1-difluoroethane as a high permeability blowing agent together with another fluorinated hydrocarbon blowing agent, characterized in that the gas-containing cells contain one or more low-permeability emulsifiers with formula where is methyl, ethyl, chloromethyl, difluoromethyl, chlorofluoromethyl, fluoromethyl or trifluoromethyl, and R2 is hydrogen or chlorine, fluorine, methyl or trifluoromethyl, the emulsifying agent does not contain more than 3 C atoms, and the emulsifying agent consists of a compound with 3 C -atoms if the halogen contains only 2 fluorine atoms. 2. Method for producing a polymer foam body according to claim 1, whereby a blowing agent mixture of fluorochloromethane, methyl chloride, ethyl chloride, chlorodifluoromethane or 1,1-difluoroethane as high permeability blowing agent together with another fluorinated hydrocarbon blowing agent is injected into a heat-softened polymer stream and mixed with it, after which the mixture is extruded through a die, characterized in that as the second emulsifier, which is injected together with the high-permeability emulsifier, one or more low-permeability emulsifiers with the formula where R^ is methyl, ethyl, chloromethyl, difluoromethyl, chlorofluoromethyl, fluoromethyl or trifluoromethyl, and R2 is hydrogen or chlorine, fluorine, methyl or trifluoromethyl, the emulsifying agent not containing more than 3 C atoms, and the emulsifying agent consisting of a compound with 3 C atoms if the halogen contains only 2 fluorine atoms.