GB2041948A

GB2041948A - Expansible Rubber/Resin Blend and Foam Produced Therefrom

Info

Publication number: GB2041948A
Application number: GB8002785A
Authority: GB
Original assignee: Armstrong Cork Co
Current assignee: Armstrong World Industries Inc
Priority date: 1979-01-29
Filing date: 1980-01-28
Publication date: 1980-09-17
Also published as: ES8101100A1; GB2041948B; DE2943145A1; FR2447389B1; JPS55102634A; AU523740B2; JPS5627531B2; CA1120200A; DE2943145C2; ES484439A0; AU5052579A; FR2447389A1

Abstract

An expansible resin/rubber blend suitable for the manufacture of a chemically blown, predominantly closed cell form with a density in the range of about 1.8-4 pounds/cu. ft. (28.8864 Kg/cm<3>), comprises (1) 100 parts of butadiene-acrylonitrile rubber, (2) 40-200 parts of vinyl chloride resin, and (3) 25-200 parts of polymethylmethacrylate.

Description

SPECIFICATION Expansible Rubber/Resin Blend and Foam Produced Therefrom This invention relates to a composition comprising a thermoplastic resin and an elastomer, hereinafter referred to as a resin/rubber blend, to foamable compositions comprising the blend, and to articles comprising foamed compositions formed therefrom.

Resin/rubber blends are useful in making low density foams of a predominantly closed cell structure. In the form of sheets of cylinders, these low density, closed cell foams are useful as heat insulating material. When appropriately shaped, the foams serve as expansion joint and sealers generally.

In all of these applications, it is the general rule that the lower the density, the better the product, provided strength, structural integrity, and improved, i.e., reduced, thermal conductivity can be maintained during the useful life of the product. Since it is generally true that the product becomes more flimsy as the density is diminished, it has been necessary to use higher density foams than would be chosen if thermal characteristics were the only criterion in order to maintain the required mechanical performance characteristics. Typical products made from resin/rubber blends have in the past had densities in the range of about 4.5-6 pounds/cu.ft. (72-96 kg/cm3). These products have generally been satisfactory.

The patent best exemplifying the prior products is U.S. 2,849,028, which describes the use of a two-component resin/rubber blend to form predominantly closed cell products having the properties and utilities described above. The resin/rubber ratios have been varied over the years since the issue of this patent, and the actual resins and rubbers have also varied over the years, but these are the products, with their densities in the range of about 4.5-6 pounds/cu.ft. (72-96 kg/m3), that have been the standard in the industry.

U.S. 2,788,333 also shows a two-component resin/rubber blend for making a foam product.

Other patents disclose various modifications of resin/rubber blends, including mixtures of polyvinyl chloride, butadiene-acrylonitrile rubbers to form foamed products.

Summary of the Invention The present invention provides a resin/rubber blend suitable for use in the manufacture of substantially closed cell, low density foams on being blown at elevated temperature by means of a chemical blowing agent, the blend comprising 100 parts by weight of a nitrile-butadiene rubber containing 20-45 percent by weight of acrylonitrile; 40-200 parts by weight of a vinyl chloride resin which may be polyvinyl chloride, a vinyl chloride-vinyl acetate copolymer, or mixture thereof; and 25200 parts by weight polymethylmethacrylate, provided that the polymethylmethacrylate is present in the blend in an amount of at least 9 percent by weight of the three specified components of the blend.

The resin/rubber blend of the present invention may be foamed, using a chemical blowing agent, into products having densities in the range of 1.8-4 pounds/cu.ft. (28.8-64 kg/m3), and products having densities of about 3 pounds/cu.ft. (48 kg/m3) may be routinely produced reproducibly on a commercial scale. These lower density products have improved thermal conductivity, in addition to the obvious advantages of cost saving in material and shipping.

Butadiene-acrylonitrile rubbers (NBR) suitable for use in the present invention are standard items of commerce. The Mooney viscosity advantageously lies between 25 and 90. The NBR advantageously contains between 20 and 45 percent by weight acrylonitrile, preferably about 30 percent by weight. It is commercially available and may be used in the present invention in the form of a dry rubber. In describing the resin/rubber blend of the present invention, it is convenient to base the proportions of all other components on 100 parts by weight of the NBR. The phrase "relative proportions" as used herein therefore means that the amounts of the several ingredients are adjusted on a basis of 100 parts by weight NBR, no matter what actual weight of the NBR is actually used.In some instances, as will be seen in the examples, a 70/30 NBR/resin mixture is used, but the other ingredients will be calculated as if 100 parts by weight NBR were used.

The second ingredient in the resin/rubber blend of the present invention is a vinyl chloride resin.

This term includes the homopolymer polyvinyl chloride (PVC) and the copolymer vinyl chloride-vinyl acetate (VCVA). Polyvinyl chlorides are standard items of commerce, made by solution, suspension, or emulsion polymerization, and are generally considered to be low molecular weight with a relative viscosity up to about 2.2. The PVC is commercially available, and may be used, in the form of a white powder.

The VCVA normally contains about 1.5-20 percent by weight vinyl acetate, and preferably contains 10-1 5 percent by weight. It, too, is a standard item of commerce and is sold and may be used in the present invention in the form of a white powder.

To achieve the unusually low density foams of the present invention, the vinyl chloride resin must be used in an amount of about 40--200 parts by weight for each 100 parts by weight of the NBR. This amount of 40-200 parts by weight of this resin may be either 100% PVC or 100% VCVA. Put another way, either of these two vinyl chloride resins functions in the present invention, allowing the production of low density foams. Alternatively, mixtures of the two may be used in any proportions, including those in which the mixture contains a mere trace of either in almost 100% of the other. As a practical matter, it is usually preferable to use a mixture of the two vinyl chloride resins, and the mixture would usually be about 1:1.This 1:1 ratio will often be varied according to the exigencies of local supplied, local forming equipment, the views of the foreman running the line, and other such intangibles.

Advantageously, the ratio PVC:VCVA is in the range 70:40 to 40:70.

The third ingredient in the resin/rubber blend of the present invention, which is crucial to the production of the unusually low density foams, isthe PMMA. Again, the PMMA is an item of commerce sold and may be used in the invention in the form of a free-flowing white powder. It is sometimes sold and mixed with small amounts of copolymers of methylmethacrylate, and these normally have little or no deleterious effect on the compositions of the present invention. It is preferred that over half of the PMMA powder pass through a 200 mesh screen, since the small particle size appears to aid in forming a good blend.The molecular weight of these PMMA's normally varies around a central point of about 1,000,000; and the most useful PMMA's are sold in a molecular weight range of about 700,000 to about 1 250,000. Such PMMA's are normally sold as processing aids for PVC. Their presence aids the physical processing of PVC when the PMMA is present in an amount of 1-2 percent by weight of the PVC, up to a maximum 5 percent by weight. The amount of PMMA used in the compositions of the present invention is in the range of about 25-200 parts by weight PMMA per 100 parts by weight NBR, with the proviso that the resin/rubber blend contain at least 9 percent by weight PMMA of the total composition of NBR, vinyl chloride resin, and PMMA.It is the presence of the PMMA in the system, in the amounts defined herein, that allows the production of the substantially closed cell, unusually low density foams of the present invention.

The compounding of the resin/rubber blend of the present invention, as well as the compounding of the complete foamable system in which it is used, may proceed in a manner conventional for rubber/resin systems. Rubbers, resins, fillers, plasticizers, waxes, fire retardants, smoke suppressants, and any other conventional ingredients in these foams would normally be first blended on a mill or a Banbury in accordance with conventional procedures. The rubber may first be broken down, if desired, and any other of these ingredients then added. When that portion of the final composition is suitably mixed, the curing agent system and the blowing agent may then be added.An advantage of the resin/rubber blend of the present invention is that it calls for no special handling beyond that normally used in the art of blending rubbers and resins to make foamable mixtures.

At the same time, the resin/rubber blend of the present invention lends itself to compounding to achieve in the finished foam product any particular or special properties normally obtained in such products having the higher density of conventional blends. Variations in plasticizers and in the amounts of plasticizers will produce variations in the softness or rigidity of the resulting foam according to convention standards. Pigments can be added as desired to achieve any needed coloring. Flame resistance and smoke suppression can be taken into account in compounding in the usual ways. Any conventional fillers may be used, including, for example, the clays, finely ground or precipitated calcium carbonate, silicates, the carbon blacks, hydrate alumina and titanium dioxide.

The blowing agent to be used will advantageously be nitrogen-producing, chemical blowing agent which produce a closed cell structure. Many of such blowing agents are known, and include, for example, dinitroso pentamethylene tetramine, p,p' oxybis (benzene sulfonyl hydrazide), benzene sulfonyl hydrazine, p-toluene sulfonyl semicarbazide, and, preferably, azodicarbonamide.

Curing agent systems may be any system capable of producing foamed products from resin/rubber blends, many being conventional in the art.

Any suitable plasticizer may be used, including, for example, tricresyl phosphate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl phthalyl butyl glycolate and dibutyl sebacate. Lubricants may be, for example, stearic acid, the paraffins, ceresin wax, or wax mixtures. Fire retardants include, for example, antimony trioxide and other metal oxides, and chlorinated paraffins.

Once the complete composition has been prepared, it may be shaped as desired. To form pipe insulation, standard extruders may be used to extrude cylinders in the desired sizes. Sheets may be formed by extruding, calendering, or molding. Specially shaped objects may be formed by molding.

Once the finished composition has been shaped into the desired form, it is heated to a temperature sufficient to decompose the blowing agent and cure the system. The foamable compositions of the invention expand linearly, in that finished, foamed dimensions consistently bear a constant relationship to the unfoamed composition. Temperature for expansion and cure will normally be in the range of about 220--3600F.'(1 04--1820C) depending to a large extent on the thickness of the unfoamed composition td be expanded. Depending on the exact thickness dimension, sheets may be expanded at around 2900F. (1 43 OC) and tubes can be expanded at around 3400F. (171 OC), on an average.

As mentioned earlier, the principal advantage of the present invention is the ability to form unusually low density products in a reproducible manner. The present products show a significant improvement i.e. lowering in smoke density on burning by virtue both of the low density of the product and the presence of the PMMA. At the same time, the thermal conductivity of the products used in heat insulation improves, i.e., is lowered, from a prior value of about 0.27 to a new value of about 0.25 Btu.

-in/hr.ft2 OF. (W/mk).

The following examples illustrate the invention; Example I and Run Nos. 1 to 4 of Example II being for comparison.

Example I The following formulation and compounding procedure is conventional and well known in the art.

The following ingredients were placed in a Banbury, blended to a temperature in the range of 2350--2900F. (113 to 1 430C), and cooled: Parts by Ingredients Weight NBR/PVC blend 70/30 100 stearic acid 1 magnesium silicate 60 carbon black 10 Kaolin clay 30 dioctyl phthalate 20 octyl diphenyl phosphate 15 wax blend 2 diphenylamine-diisobutylene reaction product 2 The following ingredients in the amounts stated were then added and blended to a temperature in the range of 1000--2000F (38-930C):: Parts by Ingredients Weight zinc oxide 5 surface coated urea 1.5 azodicarbonamide 20 benzothiazole disulfide 0.8 zinc diethyl dithiocarbonate 0.8 diorthotolyl guanidine 0.8 sulfur 2.5 The finished composition represents a conventional foamable composition for producing, on appropriate heating, closed cell products having a density in the range of about 4.5-6 pounds/cu. ft.

(72-96 kg/m3).

Example II A series of nine compositions was made up, including the composition of Example I as a control and as a representative of prior technology. The compositions other than the control had differing quantities of PMMA, vinyl chloride resin or blowing agent to illustrate the invention. While each composition contains 100 parts by weight of a 70/30 mixture of NBP/vinyl chloride resin, the addition of further VCVA changes the proportions. The mixing procedure was the same for all nine compositions, and each final composition was extruded to form a tube which was then free-blown at a temperature in the range of 2500---3400 F. (121-171 OC) to form a predominantly closed cell. The -following table shows the differing formulae and the results in each case.

Run Data 1 2 3 4 5 6 7 8 9 NBR/PVC 100 100 100 100 100 100 100 100 100 PMMA - - 7 13 35 81 97 20 97 VCVA - - - - - - - 65 97 Total PMMA/100 NBR O 0 10 19 50 116 139 29 139 Total VC resin/100 NBR 43 43 43 43 43 43 43 136 182 PMMA, percent 0 0 7 12 26 45 49 11 33 Azodicarbonamide, percent 7 10 10 10 10 10 10 10 8 Density, lbs./ft.3 4.5 3.6-6.5 4.6 4.7 2.9 3.4 3.6 3.2 3.8 Density kg/m3 72 57.6-10.4 73.6 75.2 46.4 54.4 57.6 51.2 60.8 Following are the comments on each of the above runs:: Run 1 produced a good tube, typical of the prior art, and having about the lowest reproducible density of the prior art of 4.5 pounds/cu. ft. (72 kg/m3).

Run 2 produced a product having longitudinal splits down the outer surface, and different portions of the same run produced tubes of differing density and size. Run 2 illustrates the point that it is not possible to achieve lower density tubes in prior resin/blend mixtures simply by increasing the amount of blowing agent used.

Runs 3 and 4 produced tubes having no improvement in density and having longitudinal splits rendering the tubes unsatisfactory, illustrating the effect of insufficient PMMA.

Runs 5, 6, 7, and 8 produced good, reproducible, low density tubes.

Run 9 produced a good, usable tube and illustrates the point that reducing the blowing agent level slightly did not take the tube out of the very low density range.

Example Ill To illustrate the use of a vinyl chloride resin consisting solely of VCVA, the following resin/blend composition was prepared in the usual manner: Parts by Ingredients Weight NBR 95 polybutadiene (processing aid) 5 VCVA 110 PMMA 40 This resin/blend composition was compounded in the usual way with the usual fillers, plasticizers, fire retardents, wax blend, azodicarbonamide blowing agent, and a curing system. The final foamable composition was extruded in the form of tubes and heated and expanded in the usual manner to form a predominantly closed cell tube. The tubes were excellent in appearance, soft and flexible, reproducible, and had a density of 3.3 pounds/cu. ft. (52,8 kg/m3).

Claims

1. A resin/rubber blend comprising: (a) 100 parts by weight of a nitrile-butadiene rubber; (b) 40-200 parts by weight vinyl chloride resin selected from the group consisting of polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, and mixtures thereof; and (c) 25-200 parts by weight polymethylmethacrylate, the polymethylmethacrylate being present in a proportion of at east 9 percent of the total weight of (a), (b), and (c).

2. A blend as claimed in claim 1 ccntaining a mixture of polyvinyl chloride and vinyl chloride-vinyl aceTate copolymer.

3. A blend as claimed in claim 2 in which the polyvinyl chloride:vinyl chloride-vinyl acetate copolymer ratio is in the range of 70:40 to 40:70.

4. A blend as claimed in any one of claims 1 to 3, wherein the Mooney viscosity of the nitrile/butadiene rubber is within the range of from 25 to 90.

5. A blend as claimed in any one of claims 1 to 4, wherein the nitrile/butadiene rubber contains between 20 and 45 percent by weight acrylonitrile.

6. A blend as claimed in claim 5, wherein the rubber contains about 30 per cent by weight acrylonitrile.

7. A blend as claimed in any one of claims 1 to 6, wherein the vinyl chloride resin is or contains polyvinyl chloride, the relative viscosity of which is not more than 2.2.

8. A blend as claimed in any one of claims 1 to 6, wherein the vinyl chloride resin is or contains a vinyl chloride/vinyl acetate copolymer, with a vinyl acetate content of 1.5 to 20% by weight.

S. A blend as claimed in claim 8, wherein the vinyl acetate content of the copolymer is from 10 to 15% by weight.

10. A blend as claimed in claim 1, substantially as described in Example Ill or in any one of Run Nos. 5 to 9 of Example II.

11. A low density, predominantly closed cell foam composition comprising: (a) 100 parts by weight of a nitrile-butadiene rubber; (b) 40-200 parts by weight vinyl chloride resin selected from the group consisting of polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, and mixtures thereof; and (c) 25-200 parts by weight polymethylmethacrylate the polymethylmethacrylate being present in a proportion of at least 9 percent by weight based in the total weight of (a), (b) and (c).

12. A foam as claimed in claim 11 having a density in the range of 1.8-4 pounds/cu. ft.

13. A foam as claimed in claim 11 or 12, wherein the composition is as specified in any one of claims 2 to 9.

14. A foam as claimed in claim 11, substantially as described in Example Ill or in any one of Run Nos. 5 to 9 of Example II.

1 5. A heat-insulating foam product as claimed in claim 11 having a thermal conductivity of about 0.25 Btu. in./hr ft2 OF.