Application of George W. Polly, Jr, 331 F.2d 628 (C.C.P.A. 1964)

This appeal is from the decision of the Patent Office Board of Appeals which affirmed the rejection of claims 1-14 in application serial No. 762,931, filed September 24, 1958, entitled "Modified Polyoxymethylene." No claims are allowed.

The invention relates to stabilized polyoxymethylene and is thus described in appellant's specification:

"Polyoxymethylene polymers, having recurring — CH₂O — units have been known for many years. They may be prepared by the polymerization of anhydrous formaldehyde or by the polymerization of trioxane which is a cyclic trimer of formaldehyde. Polyoxymethylene varies in thermal stability and in molecular weight, depending on its method of preparation.

* * * * * *

"Although polyoxymethylenes prepared by some methods are much more stable against thermal degradation than those prepared by other methods, it is nevertheless desirable for many uses that the thermal stability be increased.

"It has been found in accordance with this invention that polyoxymethylenes may be stabilized against thermal degradation by reaction with isocyanates and preferably with compounds containing two or more isocyanate groups. [Emphasis ours.]

* * * * * *

"The isocyanate which may be used in accordance with this invention may be either aliphatic or cyclic. Compounds containing two or more isocyanate groups are preferred. Among the specific isocyanate compounds which may be used are aromatic diisocyanates * * *, aromatic monoisocyanates * * *, aliphatic monoisocyanates * * *, aliphatic diisocyanates * * * and triisocyanates * * *.

"The reaction is carried out in a system wherein the isocyanate and the polyoxymethylene are in intimate admixture. The polyoxymethylene may be in the form of finely divided solid particles, as in a slurry, but for best results the polyoxymethylene and the isocyanates are dissolved in a common solvent. * * *

* * * * * *

"The temperature of the reaction is suitably at least about 20°C. and preferably from about 140° to about 180°C.

Appellant's examples disclose comparative tests in which samples of both untreated polyoxymethylene and polyoxymethylene treated with isocyanate are subjected to temperatures conventional for molding operations. Decomposition rate data show greater thermal stability for the treated material.

Claims 1-4 are drawn to composition, 5-14 to method. Claims 1, 4, 5 and 6 are representative:

"1. The reaction product of normally solid resinous polyoxymethylene with an isocyanate.

"4. High molecular weight polyoxymethylene, having an inherent viscosity of at least 1.0, measured at 60°C. in a 0.1% solution in p-chlorophenol containing 2% alpha pinene, said polyoxymethylene being thermally stabilized by combination with from about 0.1 to about 10 weight percent of a diisocyanate, based on the weight of the polyoxymethylene.

"5. Method for improving the thermal stability of polyoxymethylene which comprises reacting said polyoxymethylene with an isocyanate.

"6. Method for improving the thermal stability of polyoxymethylene, having an inherent viscosity of at least 1.0, measured at 60°C. in a 0.1% solution in p-chlorophenol containing 2% alpha pinene and which loses less than 5.0% in weight per minute when maintained at 222°C in a circulating air oven, which comprises reacting said polyoxymethylene with a compound consisting essentially of an isocyanate."

The following prior art is relied on:

 DuPont British Patent 557,873 Dec. 9, 1943 DuPont British Patent 748,856 May 9, 1956

British 557,873 (hereinafter '873) deals with a process for making formaldehyde polymer by mixing formaldehyde monomer with isocyanate and aliphatic acyl ketene.¹  After mixing the constituents in any order at below -20°C., a polymerization is effected under pressure at a temperature of -20° to +30°C. In reciting the objects of the invention the patent states:

"Another object is the preparation of high molecular weight polymers of formaldehyde of reduced brittleness, little or no tendency to decompose at their melting points, and of good flow characteristics at moulding temperatures. A still further object is the preparation of tough, unusually stable, polymers of formaldehyde." [Emphasis ours.]

The patent further says:

"The resultant polymer melts in the 165-175°C. range. It shows a greater thermal stability than formaldehyde polymers prepared in the absence of isocyanates and aliphatic acylethenone, decomposing only slowly up to 200°C., whereas formaldehyde polymers prepared similarly but without the aliphatic acyl ketene, as hereinbefore defined, and isocyanate decompose rapidly even at temperatures as low as 175°C." [Emphasis ours.]

The quantity of isocyanate and ketene used depends upon their molecular weights, the patent stating:

"The isocyanate or isothiocyanate is used in relatively small amounts between 0.01-2.0 mole per cent, of the formaldehyde employed. The exact amount of isocyanate is dependent upon its molecular weight, 2 — 4 isocyanate groups to each thousand formaldehyde molecules generally being most effective."

The function of isocyanate in the polymerization process is said to be as follows:

"Although the exact manner in which these modifying agents [isocyanates and ketenes] function is not known, it is believed that one or both of these modifying agents facilitate the formation of stable, high molecular weight formaldehyde polymers both by removing impurities and by reacting with the terminal methylol groups of the polymer." [Emphasis ours.]

British 748,856 (hereinafter '856) deals with stabilizing formaldehyde polymers

"* * * by incorporating certain stabilizing agents therein, namely:

"(a) hydrazines, substituted hydrazines or hydrazides,

"(b) secondary or tertiary monomeric aromatic amines,

"(c) phenols or substituted phenols, or

"(d) ureas, thioureas and their substitution products.

* * * * * *

"The stabilizing agent is added in an amount of not more than 10% of the weight of the polymer, a preferred range being from 0.1% to 5%. It can be incorporated in the polymer in various ways: it may be introduced during or after the formation of the formaldehyde polymer, in the form of a solution in a suitable solvent or be milled into the polymer." [Emphasis ours.]

Formaldehyde polymers thus stabilized are admittedly similar in molecular weight to appellant's.

Regarding the problem of polyoxymethylene stabilization, the patent says (all emphasis ours):

"This invention relates to improvements in high molecular weight formaldehyde polymers and, more particularly to compositions of such polymers which have stability against heat and improved toughness characteristics.

"It is known that polymers of formaldehyde of moderately high molecular weight can be made which initially possess desirable properties. * * * but they degrade quickly when heated to an elevated temperature, such as 105°C., as shown by the generation of formaldehyde fumes and the embrittlement of films prepared therefrom.

"It is believed that the chain of a formaldehyde polymer having recurring — CH₂O — units is subject to attack by three separate mechanisms. * * * The third attack is believed to start at the end of the polymer chain to cause the end formaldehyde unit to be broken away and then the next unit and so on until a strong unit is reacted [sic, reached?] that will not break away."

The examiner rejected claims 1 and 5 as "substantially fully met" by '873, and rejected all claims as "unpatentable over British patent 748,856 taken together with British patent 557,873." We find it unnecessary to consider the rejection of claims 1 and 5 as "substantially fully met."

As to claims 1-14, all claims, the examiner said:

"The later British patent ['856] meets each claim with the exception that compounds of groups other than the isocyanate group are used as stabilizers for the polyformaldehyde. The types of compound used for this stabilizing purpose are quite diverse. They have, with the exception of one class of compounds (the phenols) one thing in common; each class contain [sic] nitrogen atoms bonded to carbon atoms. * * *

"It is not deemed inventive to add to this list of -N-C compounds, still another type — namely the isocyanates, especially since the earlier British patent, (557,873), already teaches the use of isocyanates in polyformaldehyde resin compositions, wherein a thermally-stable polyformaldehyde resin composition is produced from formaldehyde, or from `depolymerized' polymers of formaldehyde."

The board affirmed the examiner saying simply:

"British Patent No. 557,873 indicates that one or more of the modifying agents [isocyanates and ketenes] facilitate the formation of thermally stable, high molecular weight for maldehyde polymers. The patent clearly indicates that the isocyanate reacts with the terminal methylol groups of the polymer. For the reasons indicated above, as well as those set forth in the Examiner's Answer, we conclude that the appealed claims are not patentable over the references." [Emphasis ours.]

The gist of appellant's arguments before this court regarding the rejection of claims 1-14, which we take to be an obviousness rejection under 35 U.S.C. § 103, is that the examiner's above-quoted statement concerning -N-C compounds is erroneous and displays a "woeful ignorance of elementary organic chemistry"; that compounds (a) to (d), supra, in '856 are "diverse classes of compounds," functioning in various ways as stabilizers and certainly do not suggest isocyanates as stabilizers; that the statement in '873 that isocyanates stabilize polyoxymethylene "by reacting with the terminal methylol groups of the polymer" is "speculative" and "vague and uncertain"; that '873 employs as stabilizers isocyanates and ketenes together and there is "no teaching * * * that either of these compounds is effective by itself"; and that the reaction conditions in '873 are such that one does not obtain a product of isocyanate with "normally solid resinous polyoxymethylene" as required by appellant's claims 1 and 5.

Notwithstanding appellant's arguments, we find no reversible error in the board's decision. In our view, the British patents considered together clearly teach one skilled in the art (1) that isocyanates stabilize polyoxymethylene, at least in part, by reacting with terminal methylol groups and (2) that such stabilization occurs when isocyanate is mixed with formaldehyde before polymerization or after formation of polyoxymethylene. Appellant appears to have confirmed the teachings of the art but in so doing, in our opinion, has done nothing unobvious.

While we do not agree with the examiner that the four classes of stabilizers listed in '856 render obvious per se an analogous use of isocyanates, we agree with the board that such use is obvious in view of patent '873 which "clearly indicates that the isocyanate reacts with the terminal methylol groups of the [polyoxymethylene] polymer." In our opinion, such teaching, in view of the later teaching in '856 that preformed polyoxymethylene may be stabilized against "end-attack" thermal degradation, renders appellant's process and product obvious within the meaning of 35 U.S.C. § 103.

For reasons above stated, the decision of the board is affirmed.

Affirmed.