US2613189A

US2613189A - Cellular material and blowing agent therefor

Info

Publication number: US2613189A
Application number: US183100A
Authority: US
Inventors: Donald V Sarbach
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1950-09-02
Filing date: 1950-09-02
Publication date: 1952-10-07
Anticipated expiration: 1969-10-07

Description

Patented Oct. 7 1952 CELLULAR MATERIAL AND BLOWING AGENT THEREFOR Donald V. Sarbach, Cuyahoga Falls, Ohio, as-

signor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application September 2, 1950, Serial No. 183,100

19 Claims.

This invention relates to a cellular material such as a cellular rubber composition and pertains more specifically to a blowing agent and a method of using the same in the manufacture of vulcanized sponge rubber.

The object of this invention is to provide a blowing agent which is more effective than those hitherto known and which produces a product having superior properties.

Another object is to provide a method of making a cellular material from a plastic composition which material is characterized by having a soft texture and by having cells of uniform size which are for the most part interconnected.

Two general types of synthetic cellular material are well known, one in which the individual cells are discrete chambers separated from each other by a wall of material, the other in which the individual cellsare interconnected to provide a product which is pervious to fluids. In making products of the latter type, two general methods have been employed, the first of which involves beating or whipping air into a liquid dispersion or solution of the binder material to form a froth or foam, then gelling or setting the foam; the second involves dispersing in the solid binder material an ingredient which will liberate gas upon heating to form bubbles or cells. In this latter method, finely-divided sodium bicarbonate has been one of the principal blowing agents employed up until the present time. This ingredient reacts to liberate carbon dioxide upon subsequent heating of the composition. If desired, acidic materials may be present, such as the cottonseed fatty acids commonly employed in rubber compounding in order to accelerate liberation of the gas.

However, the results obtainable with sodium bicarbonate have not been entirely satisfactory in that even by using a large proportion of this ingredient it has been impossible to reduce the apparent density of the finished product to the desired point. Furthermore, the cells in the finished product are larger than is desired for many purposes and are not uniform in size but vary over a wide range. Consequently the products tend to be stiff and boa-rdy and of varying compressibility. Y

I have now discovered that by adding to sodium bicarbonate a small amount of an amide having the formula (CH2N2): where a: is a small integer, these disadvantages are overcome and a highly desirable product is obtained. This result apparently is due to a synergistic effect be tween these two ingredients since the amide by itself produces only a small degree of blow, much less than that of an equal amount of sodium bicarbonate. The amides which I have found to be particularly effective are cyanamide, dicyandiamide and melamine, of which melamine is preferred because of the superior results which it produces. A mixture of sodium bicarbonate and amide containing from 2 to 30% by weight of amide is satisfactory although from 3 to 10% is preferred, the best results being obtained by the use of about 5% of amide by weight of the. mixture.

It has been found desirable and convenient to mix the sodium bicarbonate and amide in finely-divided form prior to incorporating the mixture in the material to be blown. However, if desired, the two ingredients may be separately dispersed in the material to be blown. The precise particle size of the bicarbonate and of the amide is not critical. I have found commercial baking soda to be quite satisfactory, and the particle size of the amide is preferably of the same order of magnitude as that of the bicarbonate. Material which will pass a No. 50 U. S. Standard sieve is satisfactory, although it is preferred to use material which is fine enough to pass a No. U. S. Standard sieve.

The amount of this new blowing agent which should be used will vary, of course, depending upon the plasticity of the uncured composition and the apparent density desired in the finished product. Satisfactory results have been obtained by using from 2 to 30% of the blowing agent by weight of the binder material such as rubber. However, it is preferred in most cases to employ from 3 to 10% by weight.

My new blowing agent may be used with any heat-softening or thermoplastic binder material which is capable of being blown to a cellular product by means of sodium bicarbonate alone. regardless of whether the material is hardened or set in its cellular condition merely by cooling or by a chemical reaction such as vulcanization. Among such binder materials are phenol aldehyde resins, urea formaldehyde resins, melamine formaldehyde resins, polyethylene, polyisobutylene, polyvinyl resins such as polyvinyl acetals, plasticized polyvinyl chloride, various copolymers of vinyl chloride with other polymerizable materials, and natural or synthetic rubbers such as caoutchouc (a polymer of isoprene) and various other rubbery conjugated diene polymers such as the rubbery polymers of butadiene-1,3, chloroprene, 2,3-dimethyl butadicne and the like and rubbery copolymers of these materials with each ,189 I v: m

alone as a blowing agent, it is desirable but not.v

essential that some acidic ingredient bepresent in the composition to react with the sodiun'i'bicarbonate upon heating to liberate a gas and cause cell formation. Preferably'thisacidic ingredient is an organic acid such asthe iatty acids commonly employed in rubber compounding.

The following specific examples are intended as illustrations of my invention but not as 9. 'mmcation thereon.

Example 1 .LThe following, composition was prepared by mixing. the ingredients on a roll mill, thesodium bicarbonate being added last:

rans by weight Crude rubber 100.0

Whiting -85.0 Channel black -2.'0 Zinc oxide 15.0 Sulfur i a MiheraLoil 10.0 Cottonseed fatty acid 20.0 fiei ola m 2- Sincere. wax 2.0 Accelert'or benzothia yl' disul de) 0.6 Sodium bicarbonate (commercial baking soda) 20.0

Total 2491s The composition was heatedin a mold at 300 F.v for 30 minutes to cause cellformation and vulcanization. By usingvarious amounts of this rubbercomposition it was determined that 100 gramsofthecomposition was required to produce a cellular product completely filling a standard mold (18 cu. in.), the product having an-apparent density of .22 oz. per cu. in, When less than 100. g. of the composition was employed/the material failed to fill out the mold completely during the blowing stage.

.The.,.product in this case was stiff and boardy and the individual cells varied consideraly in size from about to about in diameter. This non-uniformity in size of, the cells resulted in. the product having varying compressibility at different spots, one area being quite firm while another adjacent area was relatively soft.

Example 2 :per.cu.,in. The product was characterized by a soft texture and very'uniiorm cell size, (about 3 :1), which was considerably smaller than the cell size of the product prepared using sodium b1- carbonate alone.

' Example 3 i The sodium bicarbonate of Example 1 was re-- placed with parts by weight of a mixture of "IO parts by weight of sodium bicarbonate with 30 parts by weight of melamine. The results obtained were similar to those of Example 2.

Example 4 :'I hesodium bicarbonate of Exampleiljwas replaced with 5 parts by weight of a mixture of 95 ;parts by weight of sodium bicarbonate and 5 parts of cyanamide and treated as in Example 1. .Inthis case it was found that the 5 parts of new blowing -agent was approximately equivalent in blowing power to, 2 0 parts of sodium bicarbonate,

about 100g. of the composition being required to fill thestandard mold. In addition, the product was similar to that of Examples 2 and 3 in tex ture'and'uniformity of cell size.

Example 5 The sodium bicarbonate of Example 1 was replaced with 5 parts by weight of amixtureof 95 parts by weight'of sodiurn'bicarbonate' with 5 parts vofdicyandiamide'and treated as in Examplel.,.. p

The results in this casewere appr ximates the same as those obtained in Example 4.

Exampleo The sodium biaiboaaeiqf.E ample}; was re-,-

placed with 10 parts by weightlof amiXturei fQS parts by weight of sodium bicarbonatefwithfl parts; of melamineand treated-as in nxam leig Theresults. were similar tothose in Exampleb.

"Similar results were obtained using as; little" as, 2 partsby weight'of'the newblowmgagefit other binder materials such asv phenolic resins,-

polyvinyl resins or the like, the various minor changes in the other ingredients usually present in the. compositionwill be .apparentfto those skilled in the art. VulcaniZable syntheticrubberssuoh asbutadiene-styrene copolymers, butadiene-isobutylene copolynie'rs, r'ieoprerie, and the'like, may be used in, place of the crude rubber inthe recipe given in Example 1 of course, with only the conventionalchanges in amount and kind of vulcanizing agent, accelerator, plas ticizer, etc, as are well knowntotheart Obvious variations and modifications which are within the scope of the appended claims will be apparent to those. skilled in the art.

1. A blowing agentcomprisingamixture of solid, -finely divided sodium bicarbonate with from 2 to 30%, by weight'of the mixture, ofa solid, finely-divided amide selected from the class consisting of cyanamide, dicyandiamide, and

v melamine.

. mixture, of finely-divided cyanamide.

, sisting of cyan'amide, dicyandiamide, and mela- 3. A.blowing agent comprising solid, finelydivided sodium bicarbonate. having imiiormly mixed therewith from 3 to 10%, by weight of the 4. A blowing agent comprising solid, finelydivided sodium bicarbonate having uniformly mixed therewith from 3 to by weight of the mixture, of finely-divided dicyandiamide.

5. A blowing agent comprising solid, finelydivided sodium bicarbonate having uniformly mixed therewith from 3 to 10%, by weight or the mixture, of finely-divided melamine.

6. A composition capable of being blown to cellular form comprising a heat-softening binding material having dispersed therein a mixture in finely-divided form, of sodium bicarbonate with from 2 to by weight of the mixture, of an amide selected from the class consisting of cyanamide, dicyandiamide, and melamine.

7. A composition for making cellular material which comprises a vulcanizable rubbery diene polymer having dispersed therein a particulate mixture comprising sodium bicarbonate and from 3 to 10%, by weight of the mixture, of an amide selected from the class consisting of cyanamide,

dicyandiamide, and melamine.

8. A composition for making cellular material comprising a vulcanizable rubber containing dispersed therein from 2 to 30%, by weight of the rubber, of sodium bicarbonate and an amide selected from the class consisting of cyanamide, dicyandiamide, and melamine, said amide amounting to 2 to 30% of the total weight of said bicarbonate and amide.

9. A composition for making cellular material comprising a vulcanizable rubber containing dispersed therein from 2 to 30%, by weight of the rubber, of sodium bicarbonate and cyanamide, said amide amounting to 3 to 10% of the total weight of said bicarbonate and amide.

10. A composition for making cellular material comprising a vulcanizable rubber containing dispersed therein from 2 to 30%, by weight of the rubber, of sodium bicarbonate and dicyandiamide, said amide amounting to 3 to 10% of the total weight of said bicarbonate and amide.

11. A composition for making cellular material comprising a vulcanizable rubber containing dispersed therein from 2 to 30%, by weight of the rubber, of sodium bicarbonate and melamine, said melamine amounting to 3 to 10% of the total weight of said bicarbonate and melamine.

12. The method of making a spongy material which comprises dispersing in a heat-softening composition finely-divided sodium bicarbonate and an amide selected from the class consisting of cyanamide, dicyandiamide, and melamine, said amide amounting to 2 to 30% of the total weight of said bicarbonate and amide, and heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition.

13. The method of making a cellular sponge composition which comprises dispersing in a composition comprising a vulcanizable rubbery con jugated diene polymer from 2 to 30%, by weight of said polymer, of sodium bicarbonate and cyanamide, said amide amounting to 3 to 10% of the total weight of said bicarbonate and amide, and heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition and to vulcanize said composition.

14. The method of making a cellular sponge composition which comprises dispersing in a composition comprising a vulcanizable rubbery conjugated diene polymer from 2 to 30%, by weight of said polymer, of sodium bicarbonate and dicyandiamide, said amide amounting to 3 to 10% of the total weight of said bicarbonate and amide, and "heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition and to vulcanize said composition.

15. The method of making a cellular sponge composition which comprises dispersing in a composition comprising a vulcanizable rubbery conjugated diene polymer from 2 to 30%, by weight of said polymer, of sodium bicarbonate and melamine, said melamine amounting to 3 to 10% of the total weight of said bicarbonate and melamine, and heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition and to vulcanize said composition.

16. The method of making a cellular sponge composition which comprises dispersing in a composition comprising a vulcanizable rubbery conjugated diene polymer from 3 to 10%, by weight of said polymer, of sodium bicarbonate and melamine, said melamine amounting to about 5% of the total weight of said bicarbonate and. melamine, and heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition and to vulcanize said composition.

17. A composition for making cellular material which comprises a heat-softening binding material having dispersed therein a mixture in finelydivided form of sodium bicarbonate with from 2 to 30%, by weight of the mixture, of melamine.

18. A composition for making cellular material which comprises a heat-softening binding material having dispersed therein from 3 to 10%, by weight of said binding material, of a mixture in finely-divided form of sodium bicarbonate with from 3 to 10%, by weight of the mixture, of mela mine.

19. The method of making a spongy material which comprises dispersing in a heat-softening composition finely-divided sodium bicarbonate and melamine, said melamine amounting to to 10% of the total weight of said bicarbonate and melamine, and heating said composition to soften it and to liberate gas from said bicarbonate to form interconnected cells of uniform size dispersed throughout said composition.

DONALD V. SARI-EACH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,341,180 Jayne Feb. 8, 1944. 2,544,483 Baum Mar. 6, 1951 OTHER REFERENCES Schwarz India Rubber World, May 1946, pages 211 and 212.

Claims

6. A COMPOSITION CAPABLE OF BEING BLOWN TO CELLULAR FORM COMPRISING A HEAT-SOFTENING BINDING MATERIAL HAVING DISPERSED THEREIN A MIXTURE IN FINELY-DIVIDED FORM, OF SODIUM BICARBONATE WITH FROM 2 TO 30%, BY WEIGHT OF THE MIXTURE, OF AN AMIDE SELECTED FROM THE CLASS CONSISTING OF CYANAMIDE, DICYANDIAMIDE, AND MELAMINE.