DE1121801B - Process for the production of foams containing urethane groups - Google Patents

Description

INTKRNAT. KL. C 08 g

GERMAN

PATENT OFFICE

ANME LDETAG:

NOTICE THE REGISTRATION AND ISSUE OF THE EDITORIAL:

J 18311 IVd / 39b

June 22, 1960

JANUARY 11, 1962

It is known to produce polyurethane foams by reacting organic polyisocyanates with hydroxyl-containing polyisocyanates To make polymers and water; it has also been proposed to use polyurethane foams to prepare in such a way that one organic polyisocyanates with mixtures of polyesters and Converts polyethers and water. It has been proposed in particular to use flexible polyurethane foams superior water absorption properties using blends of polyesters and polyethylene glycol to manufacture. However, the use of polyethylene glycol provides foams which are inferior in terms of hydrolytic stability. On the other hand, satisfactory foams generally not from mixtures of polyesters and polyethers other than polyethylene glycol be made because the gas from the foams Mixture escapes and, as a result, unattractive foams of high density form.

In "Modem Plastics", May 1958, pp. 145 to 154, the production of polyurethane foams is made from Described polyesters made from acids obtained by polymerizing unsaturated long chain Fatty acids were obtained, these foams being cured in an oven or were subjected for a week or more at room temperature.

It has now been found that mixtures of certain polyethers and polyesters from long-chain acids including the long-chain acids of the type described in "Modem Plastics" give foams, which do not require post-curing and which have excellent compressibility among others have good physical and mechanical properties.

Thus, according to the invention, there is provided a process for the production of urethane groups Foams proposed by reacting organic polyisocyanates, water, polyethers and polyesters with the characteristic that the polyethers are those with more than 2 carbon atoms in each repeating unit and at least two hydroxyl groups per molecule and as polyester those with Carboxylic acid residues with a chain of at least 11 consecutive carbon atoms are used were, said acid residues in an amount of at least 40 percent by weight of the total Carboxylic acid residues are present in the polyester and the amount of polyether applied between 30 and 95% of the total weight of the polyether and polyester.

Method of manufacture

of urethane groups

Foams

Applicant:

Imperial Chemical Industries Limited, London

Representative:

Dr.-Ing. H. Fincke, Berlin-Lichterfelde, Drakestr. 51, Dipl.-Ing. H. Bohr and Dipl.-Ing. S. Staeger,

Munich 5, patent attorneys

Claimed priority:

Great Britain dated June 26, 1959 (No. 21 975) and May 13, 1960

Roxburgh Richmond Aitken

and William John Lanigan,

Manchester, Lancashire (UK),

have been named as inventors

The polyether must have more than 2 carbon atoms in each repeating unit, as polyether with a lower carbon to oxygen ratio, such as polyethylene glycol, the resultant Making foams too hydrophilic and therefore prone to hydrolysis. Suitable polyethers can be prepared, for example, by using cyclic oxides such as 1,2-alkylene oxides, e.g. B. 1,2-propylene oxide, 1,2- and 2,3-butylene oxides and epichlorohydrin, trimethylene oxide and tetrahydrofuran according to previously has polymerized known methods, for example using basic catalysts, such as sodium or potassium hydroxides, or of acidic catalysts such as fluorosulfonic acid with subsequent Hydrolysis of the end groups to form the desired terminal hydroxyl groups. Just Polyethers containing two hydroxyl groups per molecule can be obtained, for example, by the cyclic oxide has been polymerized in the presence of a compound which is only 2 reactive Hydrogen atoms per molecule, for example water, glycols such as ethylene, diethylene and propylene glycols

and primary monoamines such as ethylamine.

Polyethers containing more than two hydroxyl groups per molecule can, for example, have a cy-

109 759/433

clic oxide in the presence of a compound containing more droxyacyloxystearic acids, in which the acyl group can be than 2 reactive hydrogen atoms per molecule, for example formyl and acetyl, by for example ammonia and compounds containing hydroxylation of unsaturated fatty acids containing at least three groups, such as the from tene polyhydroxy acids, such as those obtained by hydrolysis of hydroxyl, primary and secondary amino groups, soybean or linseed oils, and poly-existing groups. Thus, merized unsaturated fatty acids such as dioleic acid include those used to make polyethers with more than two and trilinoleic acid. Also included are hydroxyl groups per molecule of suitable compounds, monocarboxylic acids without other ester-forming groups, for example polyhydroxy compounds such as glycerol, _pen and with chains of at least eleven carbon atoms following one another - trimethylolethane, trimethylolpropane, triethanol, for example lauric, amine, pentaerythritol, sorbitol, cane sugar and phenol - Stearic, oleic and linseed oil acids and mixtures of such formaldehyde reaction products, polyamines, such as acids, which can be obtained by hydrolysis of naturally pre-ethylenediamine, hexamethylenediamine, tolylenediamine, upcoming oils and fats. Diaminodiphenylmethane and diethylenetriamine, and monocarboxylic acids of this type are used in conjunction with mono- and dialkanolamines, such as mono- and di- 15 with branched components, which are more ethanolamines and mono- and dipropanolamines. as two reactive groups, such as carboxyl, more than two hydroxyl groups per molecule ent- hydroxyl and amino groups, per molecule in a holding polyether can also contain such an amount from a cyclic that on each monocarbon oxide of the type already mentioned and a diepoxide acid residue in the polyester there is at least one residue of one or another polyfunctional cyclic oxide, branched component, which more, for example, glycidol, can be obtained. as two reactive groups, such as carboxyl,

Polyethers are preferably used if they contain hydroxyl and amino groups per molecule, which more than half of the repetitive suitable branched components are the ones already Units propylene glycol units of the formula named polyols, dialkanolamines, such as diethanol

CH 25 amine and dipropanolamine, and polybasic carbon

1 ³ acids, as they are mentioned below.

' _{rH n} _ The amount of residues of acids that make up a chain

- LH · C-HjU - _of at least 11 consecutive carbons. Such polyethers may contain heratoms, for example, and are such that they can be adjusted to a minimum by polymerizing 1,2-propylene-at least 40 percent by weight of the total acid residue oxide or a larger amount of this oxide in the polyester. In a mixture with another cyclic oxide or the amount of acid residues which contain a chain of at least 11 consecutive carbon atoms, for example by polymerizing propylene oxide, in the presence of a preformed hydroxylating polyatom, is at least 50 percent by weight of the ethers with repeating units other than 35 total Acid residues.

Propylene glycol units with the formation of a block-other in connection with those already described

copolymers. long fatty acid chains are acid residues present

In the method of the invention, the normal ones of carboxylic acids have at least two wisely used polyethers contain molecular weights of carboxyl groups per molecule and 2 to at least 200. There are preferably polyethers 40-10 carbon atoms between the carboxyl groups with molecular weights from 1000 to 10000. Among such acids are dicarboxylic acids, turned. for example amber, adipine, alkyladipine, pime

For use in the method of the invention, lin-, cork-, alkylcork-, azelaic and sebacic acids, suitable polyesters can be made according to the usual metho- and higher-basic carboxylic acids, for example, for example by condensing polyvalent carballylic, pyromellitic and citric acids to form alcohols are produced with polyfunctional carboxylic acids.

be put. The alcohols can, for example, polyesters and polyesters, which are long fatty

Diols such as ethylene, 1,2-propylene, 1,3-butylene, acid residues can be used individually Diethylene, triethylene and decamethylene glycols, and will. Optionally, a polyester blend can be used Polyols with more than two hydroxyl groups per molecule, 50, provided that at least 40% and such as glycerol, pentaerythritol, sorbitol, polyallyl alcohol, preferably at least 50 percent by weight of and triethanolamine. Mixtures of more than one whole can be present in the polyester mixture high-quality alcohols must be used. Acid residues are those which form a chain of min-

At least 11 consecutive carbon atoms containing primary or secondary amino groups Compounds can be used to make polyesters 55, and that at least one of the polyesters 20 are also included, which contains a low to 80% carboxylic acid residues, which is a chain Amount of amide bonds, e.g. residues of at least 11 consecutive carbon-amino alcohols and diamines, such as mono- and diatoms, and 80 to 20% carboxylic acid residues ethanolamine and hexamethylenediamine. with 2 to 10 carbon atoms between the carb

The polyesters used must contain residues of carboxyl groups, based on the total weight of the acid residues present in at least the polyester.
11 consecutive carbon atoms are preferably used in the process of the invention

point. Among such acids are those containing polyesters with at least predominantly hydroxyl terminated a carboxyl group and at least groups used, in particular polyester, which another hydroxyl or carboxyl group each 65 hydroxyl numbers between 45 and 100 and acid numbers To understand molecule, for example castoroleic acid, have less than 10 because the using the castor oil obtained by hydrolysis of castor oil- such polyesters in general acidic mixture, dihydroxystearic acid, hy- have particularly good mechanical strength.

Polyesters with these desirable hydroxyl and acid numbers are made using such amounts made of polyester-forming components that the hydroxyl and amino groups in excess the carboxyl groups are present.

Especially valuable are polyesters with melting point below 2O ⁰ C.

Polyurethane foams with particularly valuable properties are obtained when the amount of polyether between 50 and 80 percent by weight of the total weight of polyether and polyester. The polyethers and polyesters can be used as such; but in certain cases it is advantageous to use these polymers in the form of their reaction products with organic polyisocyanates. These Reaction products can, for example, by reacting the polyester or polyether with a larger than the stoichiometric amount of an organic polyisocyanate at temperatures from 15 to 140 ° C can be produced for a period of up to 6 hours. The reaction can optionally go through Accelerated addition of a catalyst for the urethane-forming reaction of the type described earlier for example a basic compound such as a tertiary amine or a non-basic one Metal compound such as manganese acetylacetonate or dibutyltin dilaurate.

The other starting materials and the methods generally used in the process of the invention may be those used in the manufacture of polyurethane foams Prior art are described more fully.

Examples of suitable organic polyisocyanates are: aliphatic diisocyanates, such as hexamethylene diisocyanate, aromatic diisocyanates such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, Diphenylmethane-4,4'-diisocyanate, 3-methyldiphenylmethane-4,4'-diisocyanate, m- and p-phenylene diisocyanates, chlorophenylene-2,4-diisocyanate, naphthylene -1,5-diisocyanate, diphenyl-4,4'-diisocyanate, 4,4'-diisocyanate-3,3'-dimethyldiphenyl and diphenyl ether diisocyanate and cycloaliphatic diisocyanates such as dicyclohexylmethane diisocyanate. Applicable Triisocyanates are aromatic triisocyanates such as 2,4,6-triisocyanatotoluene and 2,4,4'-triisocyanatodiphenyl ether. Examples of other suitable organic polyisocyanates are the reaction products of excess Diisocyanate with polyhydric alcohols which have more than two hydroxyl groups per molecule contain, such as trimethylolpropane and uretedione dimers and isocyanurate polymers of diisocyanates, for example of toluene-2,4-diisocyanate. Mixtures of polyisocyanates can be used. Examples Suitable mixtures are the polyisocyanate mixtures which are obtained by phosgenating the mixed Polyamine reaction products of formaldehyde and aromatic amines, such as aniline and o-toluidine, are preserved.

The implementation of polyesters and polyethers or their reaction products with polyisocyanates, with water and, if necessary, organic polyisocyanate can be carried out continuously or discontinuously Way to be carried out according to the methods relating to the polyurethane foams. the The amount of water used is usually between 0.5 and 8%> preferably between 2 and 6 percent by weight, the total weight of the polyester and polyether.

The implementation of the foam-forming components can be accelerated or modified as a result, that they can be used in the presence of catalysts for the polyurethane-forming reaction described earlier Type, examples of which are: tertiary amines, such as dimethylcyclohexylamine, dimethylbenzylamine, N-methylpyrrolidine, Ν, Ν, Ν ', Ν'-tetramethylbutylene-l, 3-diamine, N-methylmorpholine, triethylenediamine, basic inorganic compounds such as the

ίο Hydroxides and carbonates of alkali metals, and non-basic metal compounds such as dibutyltin dilaurate and other metal complexes, for example Heavy metal complexes with ß-diketones, such as manganese acetylacetonate.

Surfactants can also be added to the foam-forming mixture, for example Salts of long-chain fatty acids, salts of sulfates or sulfonates of high molecular weight organic Compounds, non-ionic compounds,

such as the reaction products of ethylene oxide with a long-chain alcohol, acid or amine or with an alkylphenol and polyethylene oxide-polypropylene oxide block copolymers, as well as liquid polydialkylsiloxanes and polysiloxane-polyalkylene oxide block copolymers. The added amount of surfactant is normally between 0.5 and 5 ° / ₀ and preferably between 1 and 3 weight percent of the total weight of the polyester and polyether.

Other additives can be added to the reaction mixture at a suitable stage, for example Plasticizers, fillers, coloring substances, pigments, antioxidants, flame retardants and additional propellants, such as low-boiling organic liquids, for example fluorinated alkanes.

The products of the process have exceptionally desirable properties. So have the products unusual resistance to hydrolysis and excellent mechanical properties. In particular products can be obtained which have unusually low density with good tensile strength, Combine (rebound) elasticity and load-bearing ability. An important benefit of the procedure is that foams are made with the desired properties, without the need long heat curing, for example in an oven. In many cases it can be entirely due to heat curing be waived.

The forms of application include upholstery, mattresses, pads, packaging, sponges for washing and toys.

The invention is illustrated by the following examples. Parts and percentages relate to Weight.

Preparation of the polyether prepolymers A

100 parts of polypropylene glycol with molecular weight 2000 and a water content of 0.2 ° / ₀ WUI in the nitrogen atmosphere, with 40 parts of a 80: 20 mixture of 2,4- and 2,6-tolylene diisocyanates in the course of 1 hour at 110 ⁰ C. touched. The polyether prepolymer A had a viscosity of 16 P at 25 ° C. and contained 9.9% isocyanate groups.

Manufacture of polyester B

824 parts of diethylene glycol, 40 parts of pentaerythritol, 779 parts of adipic acid and 788 parts of a mixture

of polymerized unsaturated C ₁₈ acids, which _3e of 75% C-dicarboxylic acids and 25% (^ tricarboxylic acids consisted were heated and stirred in a stream of carbon dioxide gas at 250 ⁰ C, while the reaction water was removed by distillation. The polyester product B had an acid number of 2.6, a hydroxyl number of 69.3 and a viscosity of 190 at 25 ° C.

Manufacture of polyester C

864 parts of diethylene glycol, 40 parts of pentaerythritol, 487 parts of adipic acid and 1967 parts of the mixture used to prepare the polyester B polymerized unsaturated acids were heated and stirred in a carbon dioxide gas stream at 250 ⁰ C, while the reaction water was removed dutch distillation. The polyester product C had an acid number of 2.6, a hydroxyl number of 56.7 and a viscosity of 270 P at 25 ° C.

Manufacture of polyester D

824 parts of diethylene glycol, 40 parts of pentaerythritol, 779 parts of adipic acid and 788 parts of a mixture of polymerized unsaturated C ₁₈ acids, which consisted of 10% Qg-monocarboxylic acids, 77% C _3e -dicarboxylic acids and 13% (^ -tricarboxylic acids, were heated and in stirred for a carbon dioxide gas stream at 25O ⁰ C, while the reaction water was removed by distillation. the polyester product D had an acid number of 3.0, a hydroxyl number of 68.5 and a viscosity of 190P at 25 ⁰ C.

Manufacture of the polyester E

814 parts of diethylene glycol, 45 parts of pentaerythritol, 973 parts of adipic acid and 1192 parts of the through Acids obtained from hydrolysis of castor oil were heated and stirred in a stream of carbon dioxide gas at 250 ° C, while the water of reaction was removed by distillation. The polyester product E had an acid number of 6.6, a hydroxyl number of 56.3 and a viscosity of 25 P at 25 ° C.

Manufacture of the polyester F

459 parts of pentaerythritol and 1333 parts of the acids obtained by hydrolysis of coconut oil were obtained heated and stirred in a stream of carbon dioxide gas at 250 ° C., while the water of reaction is distilled was removed. If the reaction product had an acid number less than 5, were 615 parts of diethylene glycol and 1266 parts of adipic acid were added. Stirring and heating to 250 ° C im A stream of carbon dioxide gas was added with removal of the water of reaction to produce the polyester F continued, which had the acid number 17.3, hydroxyl number 43.8 and viscosity 209 P at 25 ° C.

Production of the polyester G

481 parts of diethylene glycol, 22.5 parts of pentaerythritol and 628.5 parts of adipic acid were heated and at 250 ° C. in a stream of carbon dioxide gas, the water of reaction formed being removed. The polyester product G had an acid number of 4.5, a hydroxyl number of 68.6 and a viscosity of 150 P. at 25 ° C.

30th

Preparation of the polyether prepolymer H

150 parts of a polyether produced by adding propylene oxide to glycerine with a molecular weight of 3000 and a water content of 0.05% were mixed with 58.3 parts of an 80:20 mixture of 2,4- and 2,6-tolylene diisocyanate in a nitrogen atmosphere Stirred at 110 ^° C. for an hour. The polyether prepolymer H had a viscosity of 25.6 P at 25 ^° C. and contained 9.6% isocyanate groups.

example 1

For mixtures of the polyether prepolymer A, polyester B and tolylene diisocyanate with a content of 80% of the 2,4- and 20% of the 2,6-isomer, a mixture of N, N-dimethylcyclohexylamine, Emulsifier (reaction product of p-octylphenol with 7.5 mol of ethylene oxide) and water added. While the reaction mixture was still liquid, it was poured into a mold poured and allowed to expand.

The foamed products thus produced were cut open, leaving a cross section of more uniform Pore structure became visible. Foam manufacturing details and properties of the products are given in the following table:

Components

Parts by weight of the components in the mixtures

Polyether prepolymer A

Polyester B

Tolylene diisocyanate

Dimethylcyclohexylamine.

Emulsifier

water

280

3
4th
6th

266 10

4.25 2.3
3
6 252
20th
8.5
2.3
3
6th

224

40

17th

2.3

196
60

25.5
2.3
3
6th

168
80
34

2.3

140
100

42.5
2.3
3
6th

112

120

2.3

84 140 59.5 2.3 3 6

56

160

68

1.2

Physical nature

Test results of the foams

Compressibility (%)

Compressibility after 4 hours
long heating to 125 ° C (%) ...

Compression modulus at 40% compression (kg / cm ² )

Tensile strength (kg / cm)

Density (g / cm ³ )

15.5 9.2 9.4 6.8 7.3 7.9 8.0 10.3 9.4 13.5 4.3 5.1 5.1 4.8 4.8 5.4 5.9 9.4 8.6 15.0 0.018
0.89
0.035 0.017
0.86
0.032 0.015
0.69
0.031 0.018
0.63
0.030 0.019
0.61
0.030 0.019
0.57
0.028 0.019
0.48
0.028 0.014
0.40
0.026 0.017
0.45
0.026 0.019
0.49
0.027

0.020

0.35

0.029

Example 2

70 parts of A were Polyäthervorpolymeres ° / ₀ of the mixed 2,4- and 20% of the 2,6 isomer with rapid stirring, with 50 parts Polyester D and 20.7 parts of tolylene diisocyanate with a content of 80 s. A mixture of 1.2 parts of N, N-dimethylcyclohexylamine, 2 parts of an emulsifier (reaction product of p-octylphenol with 7.5 mol of ethylene oxide) and 3 parts of water was added to the resulting mixture, with continued stirring. The reaction mixture was poured into a mold while still liquid and allowed to expand. The foamed material produced in this way was cut open, the highly resilient foam showing a cross section with a uniform pore structure. The product had a low permanent set of 1.3 ⁰ I ₀ , which was not significantly reduced when heated at 125 ° C. for 4 hours, a density of 0.028 g / ccm, tensile strength of 0.45 kg / cm and a compression modulus 40 ° / ₀ iger compression of 0.016 kg / cm ² .

Example 3

70 parts of polyether prepolymer A were mixed with 50 parts of polyester E and with rapid stirring 20 parts of tolylene diisocyanate with a content of 80% of the 2.4 and 20% of the 2,6 isomers. 1.2 parts of dimethylcyclohexylamine and 2 parts of an emulsifier were added to the resulting mixture (Reaction product of p-octylphenol with approximately 7.5 moles of ethylene oxide) and 3 parts of water were added. The reaction mixture was poured into a mold while still liquid and allowed to expand calmly. The material produced in this way was cut open, with a highly resilient foam with uniform pore structure could be seen in the cross-section.

Example 4

70 parts of polyether prepolymer A were mixed with 50 parts of polyester F and 20 parts of tolylene diisocyanate with a content of 80% of the 2.4 and 20% of the 2,6 isomers. A solution of 0.7 parts of triethylenediamine was added to the resulting mixture with vigorous stirring added in 3 parts of water. The reaction mixture was poured into a mold while it was still liquid and let it foam. The material produced in this way was cut open, with the strong resilient foam showed a uniform pore structure in cross section.

Example 5

70 parts of polyether prepolymer A were mixed with 37.5 parts of polyester C, 14.5 parts with rapid stirring Parts of polyester G and 20 parts of tolylene diisocyanate with a content of 80% of the 2,4-isomer and 20% of the 2,6 isomer mixed. The resulting mixture became a mixture with further stirring from 1.2 parts of HN-dimethylcyclohexylamine, 2 parts an emulsifier (reaction product of p-octylphenol with about 7.5 mol of ethylene oxide) and 3 parts Water added. The reaction mixture was poured into a mold while still liquid left to foam.

The material produced in this way was cut open, the highly resilient foam having a uniform cellular structure in cross section with a density of 0.029 g / ccm, a tensile strength of 0.45 kg / cm, a compression modulus at 40% compression of 0.011 kg / cm ² and a compression set of 10%, which was after 4 hours of heating is reduced to 125 ⁰ C at 5%.

Example 6

70 parts of polyether prepolymer A were taken under

ίο rapid stirring with 50 parts polyester C and 45 parts of tolylene diisocyanate with a content of 80% of the 2,4-isomer and 20 percent by weight of the 2,6 isomers mixed. A mixture of 1.2 parts was added to the above mixture with further stirring Dimethylcyclohexylamine, 2 parts of an emulsifier (reaction product of p-octylphenol with about 7.5 moles of ethylene oxide) and 5.5 parts of water were added. This still liquid product was turned into a Mold poured and left to foam.

The material produced in this way was cut open, the highly resilient foam showing a cross section with a uniformly cellular structure. The product had a density of only 0.017 g / cc and a compression modulus at 40% compression of 0.021 kg / cm ² .

Example 7

Fifty parts of a polypropylene glycol with the molecular weight of about 2000 were under rapid Stirring with 50 parts of polyester B and 20.3 parts of tolylene diisocyanate with a content of 80% of the 2.4 and 20% of the 2,6 isomer mixed. The resulting mixture was added with vigorous stirring a solution of 0.5 part of triethylenediamine in 3 parts of water was added. The still liquid reaction mixture was poured into a mold and left to foam.

The material produced in this way was cut open, with the highly resilient foam in cross section showed a uniformly cellular structure.

Example 8

70 parts of polyether prepolymer H were mixed with 50 parts of polyester D and 20 parts of tolylene diisocyanate with a content of 80% of the 2,4-isomer and 20% of the 2,6-isomer mixed. A solution of 1.2 parts of Ν, Ν-dimethylcyclohexylamine, 2 parts of an emulsifier (reaction product of p-octylphenol with approximately 7.5 mol of ethylene oxide) and 3 parts of water were added. The still liquid reaction mixture was in a Mold poured and left to foam.

The foam produced in this way was cut open, its cross section being uniform cellular structure.

Claims (6)

PATENT CLAIMS: 1. A process for the production of foams containing urethane groups by reacting polyethers and polyesters, organic polyisocyanates and water, characterized in that polyethers with more than 2 carbon atoms in each repeating unit and at least two hydroxyl groups per molecule and polyester such with Carboxylic acid esters with a chain of at least 11 consecutive carbon atoms used '■ ·> · ^: 109759/433 with the acid residues in an amount of at least 40 percent by weight of the total Carboxylic acid residues are present and the amount of polyether used is between 30 and 95 percent by weight of the total weight of polyether and polyester. 2. The method according to claim 1, characterized in that such a polyether is used becomes, in the molecule of which more than half of the repeating units as 1,2-propylene glycol residues are present. ■ ■. : 3. The method according to claim 1 or 2, characterized in that a polyether with a Molecular weight from 200 to 10,000 is used. . 4. The method according to claim 1 to 3, characterized in that polyester with hydroxyl numbers between 45 and 100 and acid numbers less than 10 can be used. 5. The method according to claim 1 to 4, characterized in that polyesters with a melting point below 20 ⁰ C are used. 6. Embodiment according to claim 1 to 5, characterized in that the foaming under The addition of 0.5 to 8% water, based on the total weight of the polyester and polyether, takes place. : Considered publications:
"Modern Plastics", May 1958, pp. 150, 152. β 109 759/433 1.62