CA1118131A - Reinforced polyoxymethylene molding composition capable of forming composite articles exhibiting improved physical properties - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An improved fiber reinforced polyoxymethylene molding composition is provided which when molded forms a composite article having improved physical properties (e.g. tensile strength and Izod impact strength). In admixture with the polyoxymethylene polymer and fibrous reinforcement (e.g.
glass fiber) is provided a minor amount (as defined) of a certain poly-carbodiimide (as defined) or a combination of the polycarbodiimide and a high molecular weight thermoplastic phenpoxy resin. It is believed that the polycarbodiimide either alone or in combination with the thermoplastic phen-oxy resin function primarily by a complex mechanism which is incapable of simple explanation to enhance the adhesion between the chemical functional-ity of the oxymethylene polymer chain and the fibrous reinforcement.

Description

--- lil8:131-Background of the Invention The present invention relates to improved fiber reinforced polyoxymethylene moldîng compositions. More specifically, this invention relates to fiber reinforced polyoxymethylene molding composi-tions which form composite articles of improved physical properties.
As is well known, polyoxymethylene, or polyacetal, is a thermo-plastic resin which finds wide utility in the manufacture of molded articles. Molded articles of exceptional strength and toughness are obtained when the polyoxymethylene resin is intimately combined with various reinforcing agents. It has been found, however, that various additi~es are required to provide the desired physical properties to the molded articles prepared from the reinforced polyoxymethylene polymers.
Inferior physical properties commonly can be traced to poor adhesion between the polyoxymethylene polymer and the fibrous reinforcement.
Thus, for example, reinforced polyoxymethylene polymers as described in United States Patent No. 3,455,867 provide increased strength in molded articles through the use of chemical coupling agents.
Polyoxymethylene compositions containing certain carbodiimides are disclosed in British Patent No. 993,600 where the carbodiimides primarily serve an anti-aging role.
The patent broadly suggests the use of mono- and polycarbodi-imides, but the specific working examples are limited to the use of severely hindered carbodiimides such as 2,6,2',6'-tetraisopropyldiphenylcarbodiimide and the polycarbodiimide of 1,3,5-triisopropyl-benzene-2,4-diisocyanate.

United States Patent No. 3,901,846 discloses that the incorp-oration of small amounts of specific high molecular wei~ght phenoxy resins in intimate mixtures of the polyoxymethylene polymers and reinforcing agents provides the desired improved physical properties as well as improved surface effects in molded articles.
The non analogous use of carbodiimides in the prepara-tion of polyoxymethylene polymers is also disclosed in United States Patent Nos. 3,170,896 and 3,135,718.
In the past certain polycarbodiimides have been employed as heat and hydrolysis stabilizers for polyesters as well as in a variety of other areas as illustrated in United States Patent Nos. 3,193,522; 3,193,523; 3,296,190; 3,575,931; and 3,835,098;
United States Serial No. 715,946, filed August 19, 1976; United States Serial No. 753,384, filed December 22, 1976; British Patent Nos.
1,056,202; 1,231,975; and 1,330,036; Japanese Document No. 75-00044 ~summarized in Chemical Abstract, 17232w, Vol. 82, 1975); Belgian Patent No. 626,176 ~summarized in Chemical Abstract, 2054f, Vol. 61, 1964); and Preparation of Carbodiimides from Isocyanates, by W. Neumann and P. Fischer, 1 Angew. Chem. Internat. Edit. 625 ~1962).
In light of this prior art, it is an object of the present invention to provide an improved reinforced polyoxymethylene molding composition capable of forming composite articles exhibiting improved physical properties.

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It is another object of this invention to provide rein-forced polyoxymethylene composite articles having physical properties which are superior to those of the phenoxy modified fiber reinforced polyoxymethylene articles of the prior art.
It is yet another object of this invention to provide polyoxymethylene molded articles of improved physical properties employing a specifically defined class of polycarbodiimide not employed heretofore in the art to modify the reinforced polyoxy-methylene molding resins.
These and other objects of the invention will become apparent from the following summary and description of preferred embodiments.
Summary of the Invention It has now been found that a particular class of poly-carbodiimides, particularly, unhindered aromatic polycarbodiimides having up to one methyl substituent per aromatic ring and having at least three carbodiimide groups per molecule, improve the physical properties of the resulting fiber reinforced composite articles when combined with the polyoxymethylene and fibrous reinforcement in an amount of about O.S to S percent by weight based on the total weight of the composition.
In particular, the present invention provides an improved fiber reinforced polyoxymethylene molding composition capable of forming composite articles exhibiting improved physical properties comprising an admixture of (1) a polyoxymethylene polymer, (2) about 2 to 60 percent by weight based on the total weight of the composition of a fibrous reinforcement, and (3) about 0.5 to 5 percent by weight based on the total weight of the composition of a polycarbodiimide which is ~a) derived from an aromatic isocyanate which is unsubstituted or substituted with up to one metnyl group per aromatic ring and (b) contains at least three carbodiimide units per polycarbodiimide molecule.

~i ~ 81 In another aspect of the invention it has been found that the polycarbodiimide, when employed in combination with a high molecular weight thermoplastic phenoxy resin which has heretofore been known in the art to improve the physical proper-ties of reinforced polyoxymethylene polymers, provides a synergistic improvement in the physical properties o~ the reinforced polyoxymethylene composite articles: particularly glass-reinforced polyoxymethylene articles.
Thus, the present invention also provides an improved fiber reinforced polyoxymethylene molding composition capable of forming composite articles exhibiting improved physical properties comprising an admixture of (1) a polyoxymethylene polymer, (2) about 2 to 60 percent by weight based on the total weight of the composition of a fibrous reinforcement, and (3) about 0.6 to 5 percent by weight based on the total weight of the composition of a polycarbodiimide which is (a) derived from an aromatic isocyanate which is unsubstituted or substituted with up to one methyl group per aromatic ring and (b) contains at least three carbodiimide uni.ts per polycarbodiimide molecule, and a high molecular weight thermoplastic phenoxy resin; the weight ratio of the polycarbodiimide to phenoxy resin being in the range of 1:16 to 50:1.

- 4a ----` 1118~31 Descri tion of Preferred Embodiments p As used herein the term "polyoxymethylene" is intended to include both homopolymers, including so-called capped homopolymers, i.e., acylated homopolymers, as well as capolymers. Such polymers which may be produced according to methods well-known in the art, have recurTing -OCH2 units and are typically prepared by the polymerization of anhydrous formal-dehyde or by the polymerization of trioxane.
Particularly useful in this invention is polyoxymethylene copoly-mer having at least one chain containing recurring oxymethylene (-OCH2-) units interspersed with -OR- groups in the main polymer chain wheTe R is a divalent radical containing at least two carbon atoms directly linked to each other and positioned in the chain between the two valences with any substituents on said R radical being inert, i.e., substituents which will not induce undesirable reactions. Preferred copolymers contain from about - 60 to about 99.6 mole percent of recurring oxymethylene groups. In a pre-ferred embodiment R may be, for example, an alkylene or substituted alkylene group containing at least two carbon atoms.
Among the copolymers which are utilized in accordance with the in-vention are those having a structure comprising recurring units of the for-mula:
~-OC~12~

wherein n is zero or an integer of from 1 to 5, and wherein n is zero in from 60 to 99.6 percent of the recurring units. Rl and R2 are inert substituents, that is, substituents which will not cause undesirable reac-tions.
A preferred class of copolymers are those having a structure com-prising recurring units wheTein from 60 to 99.6 percent of the recurring X

- 111E~13~`

units are oxymethylene units. These copolymers are prepared by copolymer-izing trioxane with a cyclic ether having the structure:

CH2 (CH2)n where n is 0, 1, or 2.
Examples of other preferred polymers include copolymers of triox-ane and cyclic ethers containing at least two adjacent carbon atoms such as the copolymers disclosed in United States Patent No. 3,027,352.
Among the specific ethers which may be used are ethylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, 1,3-dioxane, trimethylene oxide, penta-methylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, neopentyl formal, pentaerythritol diformal, paraldehyde, tetrahydrofuran, and butadiene mon-oxide.
The preferred polymers utilized in accordance with the invention are moldable thermoplastic materials having a weight average molecular weight of at least about 35,000, a melting point of at least about 150C., and an inherent viscosity of at least about 0.8 (measured at 60C. in a 0.1 weight percent solution in p-chlorophenol containing 2 weight percent of alpha-pinene~.
Commonly the polyoxymethylene polymer is pre-stabilized to a sub-stantial degree. Such stabilization may take the form of stabilization bydegradation of the molecular ends of the polymer chain to a point ~here a relatively stable carbon-to-carbon linkage exists at each end. For example, such degradation may be effected by melt hydrolysis such as that disclosed in United States Patent No. 3,318,848, or by solution hydrolysis such as that described in United States Patent No. 3,219,623. Mixtures of polyoxy-methylene polymers stabilized by melt hydrolysis and by solution hydrolysis may, of course, be used. The polyoxymethylene may also include conventional stabilizers such as an antioxidant and/or an acid scavenger. Generally, . 6 -,~ .

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these stabilizers will be present in a total amount of less than about 3 percent by weight based on the weight of the polyoxymethylene polymer.
The polycarbodiimides which may be used in the present invention are selected from a particularly deflned group. It has heen found that only those polycarbodiimides which both ~a) are derived from one or more aromatic diisocyanates which are either unsubstituted or contain up to one methyl substituent on each aromatic ring, and (b) contain at least three carbodiimide units per polycarbodiimide molecule will achieve the desired result. It is believed that the specific polycarbodiimide defined herein either alone or in combination with the thermoplastic phenoxy resin func-tions primarily by a complex mechanism which is incapable of simple explan-ation to enhance the adhesion between the chemical functionality of the oxymPthylene polymer chain and the fibrous reinforcement. Carbodiimides having less than three carbodiimide units per polycarbodiimide molecule are not suitable for use in the present composition because they are too volat-ile for practical use at the temperatures typically encountered in a mold-ing, e.g., injection molding, operation and may tend to exude during mold-ing. Additionally, such carbodiimides tend not to mix well with the poly-oxymethylene.
The polycarbodiimide should be such that it is miscible with the polyoxymethylene polymer in the molten sta~e. The polycarbo~iimide useful in the present invention may have number average molecular weights of gen-erally from about 450 to about 10,000 typically from about 800 to about 8,000, and preferably from about 1,000 to about 6,500. Polycarbodiimides having molecular weights greater than about 10,000 may not dissolve in the polyoxymethylene melt and thus may not be useful in the present invention.
Polycarbodiimides which are useful in the present invention typ-ically include poly(tolyl carbodiimide), poly(4,4'-diphenylmethane carbo-diimide), poly(3,3'-dimethyl-4,4'-biphenylene carbodiimide), poly(p-phenyl-ene carbodiimide), poly (m-phenylene carbodiimide), poly(3,3'-dimethyl-~B~3~

4,4'-diphenylmethane carbodiimide), and mixtures thereof. Preferred poly-carbodiimides include poly(tolyl carbodiimide), polyt4,4'-diphenylmethane carbodiimide), and mixtures thereof. The poly(4~4'-diphenylmethane carbo-diimide) is particularly preferred because its carbodiimide groups are most readily available for interaction between the oxymethylene polymer and the fibrous reinforcement. Additionally, it imparts only a light yellow color to the blend. The poly(tolyl carbodiimide) has slightly less available carbodiimide groups and imparts a more intense color to the blends.
The polycarbodiimide may be prepared in any manner known to those skilled in the art, for example, by heating the aromatic diisocyanate com-pounds defined above in the presence or absence of a solvent. The formation of the polycarbodiimide is accompanied by the evolution of carbon dioxid0 gas.
Although the polycarbodiimides useful in the present invention may be prepared without the use of a catalyst, much higher temperatures (ca 300C.) are needed in the absence of a catalyst. For certain polycarbodi-imides, the use of such high temperatures may result in the formation of large quantities of side products and colored products. Thus, the poly-carbodiimides may be typically prepared by heating the isocyanates in the presence of a catalyst such as the phosphorus containing catalysts described in United States Patent Nos. 2,853,473, 2,663,737, and 3,755,242, and also in Monagle, J. Org. Chem. 27, 3851 ~1962). Phospholine oxides such as those described in Campbell et al, J. Amer. Chem. Soc. 84, 3673 (1962) are pre-ferred catalysts. A particularly preferred catalyst is l-ethyl 3-methyl-3-phospholine-l-oxide.
The polycarbodiimide formation reaction is preferably carried out under an atmosphere of argon or other dry inert gas so as to-minimize the amount of water which may be in contact with the Teactants since isocyanates tend to react rapidly with water at elevated temperatures.
Aromatic diisocyanates which may be used in preparing the desired 5~, 13~

polycarbodiimides include, for example, toluene diisocyanate, 4,4'-diphenyl-methane diisocyanate, 3,3'-dimethyl-4,4'-diphenylene diisocyanate, p-phenyl-ene diisocyanate, m-phenylene diisocyanate, 3,3'-dimethyl-~,4'-diphenyl-methane diisocyanate, and mixtures thereof.
Preerred aromatic diisocyanates are toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and mixtures thereof.
The aromatic diisocyanates are preferably employed in an essen-tially pure state but may contain minor amounts (i.e., less than about 2 percent by weight) of other compounds such as ureas, amines, and traces of water and/or acid. The term "toluene diisocyanate" is meant to include

2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or any combination of these isomers. Mixtures of the 2,4- and 2,6-isomers typically contain either 80 parts by weight 2,4-toluene diisocyanate and 20 parts by weight 2,6-toluene diisocyanate, or 65 parts by weight 2,4-toluene diisocyanate and 35 parts by weight 2,6-toluene diisocyanate.
Small amounts (i.e., 50 percent by weight or less) of aromatic monoisocyanates may also be used in conjunction with the aromatic diisocyan-ates in the preparation of the polycarbodiimides which are employed in the process of the present invention. These mono-isocyanates act as chain stop-pers and help control the molecular weight and viscosity of the resultingpolycarbodiimides. The amount of aromatic monoisocyanate used depends upon the particular diisocyanate employed, but generally from about 20 to about 50, typically from about 25 to 45, and preferably from about 30 to about 40 percent by weight of the monoisocyanate and correspondingly generally from about 50 to about ~0, typically from about 55 to about 75, and preferably from about 60 to about 70 percent by weight of diisocyanate based upon the total weight of the isocyanate compounds may be employed.
Aromatic monoisocyanates which m~y be used in this way include, for example, p-chlorophenyl isocyanate, m-chlorophenyl isocyanate, phenyl isocyanate, p-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-tolyl ~.1813~

isocyanate, m-tolyl isocyanate, o-tolyl isocyanate, p~nitrophe~yl iso cyanate, m-nitrophenyl isocyanate, and mixtures thereof.
Phenyl isocyanate, p-chlorophenyl isocyanate, m-chlorophenyl iso-cyanateJ and mixtures thereof are preferred monoisocyanates for use in the present invention.
Monoisocyanates alone may not be used to prepare the polycarbodi-imides since polymeric carbodiimides would not result from the heating of monoisocyanates alone.
The polycarbodiimide is typically employed in the reinforced poly-oxymethylene resin composition in an amount of from about 0.5 to 5 percentby weight based on the total weight of the composition, and more typically in an amount of from about 1 to 3 percent by weight based on the total weight of the composition. Amounts of polycarbodiimide of less than about 0.5 percent may require extensive mixing with the polyoxymethylene to achieve the desired improvement in physical properties whereas amounts o much greater than about 5 percent by weight may not significantly improve the physical properties over the lower amounts and tend to cause unaccept-able discoloration of the compositions. Any of the polycarbodiimides in-cluded within the description set forth above may be used alone or in mix-ture with other of the polycarbodiimides to achieve the desired effect.
In a second aspect, or embodiment, according to the present in-vention, improved thermoplastic reinforced polyoxy~ethylene compositions are provided by the incorporation of both the polycarbodiimide and a spec-ific high molecular weight phenoxy resin in the compositions. The phenoxy resins which may be utilized according to the invention are those described in United States Patent No. 3,901,846. These resins are high molecular weight thermoplastic resins which are produced from 2,2'-bis(4-hydroxy-phenyl)propane and epichlorohydrin according to the procedure as described in United States Patent No. 3,356,646. The basic chemical structure of the phenoxy resins is similar to that of epoxy resins. They are, however, a

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separate and unique resin class, differing from epoxies in several import-ant characteristics:
1. Ph~noxy resins are tough and ductile thermoplastics. Their weight average molecular weight ranges from about 15,000 to 75,000, prefer-ably from about 20,000 to 50,000 compared with 3~0 to 13,000 foT convention-al epoxies which crosslink on polymerization.
2. Phenoxy resins do not have terminal highly reactive epoxy groups and are thermally stable materials with a long shelf life.
3. The phenoxy resins can be used without further chemical con-version. They require no catalysts, curing agents or hardeners to be use-ful products while epoxy resins require catalysts, curing agents or harden-ers to be useful.
The phenoxy resins utilized herein can be characterized by a re-peating structure:

~ ~ U OH U

and have a weight average molecular weight range from about 15,000 to 75,000. As is obvious, the terminal structure is completed with hydrogen atoms or some suitable end capping groups.
The polycarbodiimide and phenoxy resin are typically incorporated in the reinforced polyoxymethylene compositions in a combined amount of from about 0.6 to 5 percent by weight based on the weight of the total composition, and more typically in an amount of from about 1 to 3 percent by weight based upon the total composition. Amounts of less than about 0.6 percent by weight for the combined weight of polycarbodiimide and phenoxy resin do not give the desired improvement or may require extensive mixing with the polyoxymethylene. Amounts much greater than about 5 percent by ~l~B131 weight do not provide significantly greater improvements and thus do not appear to be warranted. The ratio of polycarbodiimide to phenoxy resin commonly will be in the range of from about 1:16 to 50:1. Preferably, the amount of polycarbodiimide employed is at least equal to the amount of phen-oxy resin employed. When both the polycarbodiimide and the phenoxy resin are utilized, the minimum quantity of polycarbodiimide should be about 0.5 percent by weight based upon the total weight of the composition, and the minimum quantity of phenoxy resin should be about 0.1 percent by weight based upon the total weight of the composition.
1~ The physical properties of composite articles prepared from rein-forced polyoxymethylene compositions containing bo~h the polycarbodiimide and the phenoxy resin tend to be significantly better than the physical properties of moldings produced from unmodified reinforced polyoxymethylene molding compositions and are also better than those of moldings prepared from reinforced polyoxymethylene molding compositions containing an amount of polycarbodiimide alone or of phenoxy resin alone (on a weight basis) equal to the total amount of the two combined additives. For a given amount of phenoxy resin the physical properties of the moldings appear to increase with an increasing amount of polycarbodiimide.
The polyoxymethylene, fibrous reinforcement, and polycarbodiimide and, in the second aspect of the invention, the phenoxy resin, may be mixed or blended in any convenient manner. Thus, for example, in a preferred em-bodiment the polycarbodiimide, or polycarbodiimide and phenoxy may be simul-taneously intimately mixed with the reinforcing agent and the oxymethylene polymer. Mixing time involving the fibrous reinforcement should be kept to a minimum so as to avoid attrition of the fibrous reinforcement. For in-stance, mixing of all components may satisfactorily be carried out for 0.5 to 3 minutes (e.g. 1 to 2 minutes) while the components are present in a ZSK extruder provided at a melt temperature of about 400 to 405F.
The reinforcing agents as utilized herein can be intimately mixed 1J.1.~.131 with the other components by either dry blending or melt blending, blend-ing in extruders, heated rolls or other types of mixers. Also, the rein-forcing agents can be blended with the monomers in the polymerization reac-tion as long as the polymeriza~ion reaction is not affected. The types of fibrous reinforcements which can be used are those generally ~nown in the art for reinforcing thermoplastic molding resins and include among others, glass fibers (chopped strand or continuous rovings), asbestos fibers, cellu-losic fibers, and synthetic fibers such as graphite fibers. Best results, however, with the polycarbodiimide and with the combination of the polycarbo-diimide and phenoxy resin have been obtained with glass fiber reinforced polyoxymethylene compositions. The amount of reinforcing agent can range from about 2 to about 60 weight percentJ and preferably 5 to 50 weight per-cent, based on the weight of the total molding composition.
The reinforced polyoxymethylene molding compositions of the inven-tionJ in addition to the polyoxymethylene polymerJ reinforcing agent and polycarbodiimide and, if desiredJ the phenoxy resinJ optionally may also in-clude a minor quantity of additives conventionally employed in non-reinforced polyoxymethylene molding compositions both polymeric and non-polymeric, such as lubricity agents, dyesJ and conventional antioxidants and acid scavengers.
A typical molding composition to which the additives according to the present invention are added may compriseJ for example: 57 to 89.9 per-cent by weight polyoxymethyleneJ 10 to 40 percent by weight glass fiber, 0.1 to 2.0 percent by weight antioxidant, and 0.05 to l.0 percent by weight acid scavenger. A preferred composition which may be modified according to the invention includes 69 to 79.8 percent by weight polyoxymethylene polymerJ
20 to 30 percent by weight glass fiberJ 0.15 to 0.5 percent by weight anti-oxidant, and 0.1 to 0.5 percent by weight acid scavenger. For instanceJ
72.9 parts by weight of a polyoxymethylene resin which incorporates 015 part antioxidant and 0.1 part acid scavenger can be mixed with 25 parts of glass 3U fiber and 1.5 parts of the polycarbodiimide, or 71.4 parts by weight of a 111~;131 polyoxymethylene resin which incorporates 0.5 part antioxidant and 0.1 part acid scavenger can be mixed with 25 parts glass fiber, 1.5 parts by weight of the polycarbodiimide, and 1.5 parts by weight of the phenoxy resin. The exact composition chosen, however, will be dependent on the de-sired properties of the molded article as will be apparent to one of ordin-ary skill in the art.
Molded articles prepared from the thermoplastic reinforced poly-oxymethylene molding compositions according to the invention show a distinct improvement in physical properties as compared to articles prepared from the fiber reinforced polyoxymethylene which does not contain the polycarbodi-imide or the polycarbodiimide and the phenoxy resin. For example, composi-tions containing from about 5 to 50% by weight glass and from about 0.5 to 5 percent by weight polycarbodiimide ~based upon the total weight of the composition) commonly evidence up to a 75 percent increase in tensile strength and up to a 40 percent increase in Izod impact values.
The following examples will serve to further illustrate the inven-tion without limiting the same.
Examples Blends of ~1) polyoxymethylene polymer, glass fibers, polycarbodi-imide and ~2) of polyoxymethylene polymer, glass fiber, polycarbodiimide andphenoxy as shown in the Table were prepared by feeding the materials to a ZSK extruder and compounding them for 1 to 2 minutes. The various composi-tions were thereafter molded into tensile bars on a 2-1/2 oz. Stubbe m~ld-ing machine under the following conditions:
Cylinder Temperature410F.
Mold Temperature 180F.
Cycle Times ~Sec.) Injection 10 Cooling 20 Delay 2 Total 32 111~131 Screw ~RP~I) 80 Injection Pressure (psi) 9,000 to 18,000 The polyoxymethylene polymer employed in the Examples was a poly-oxymethylene copolymer prepared from trioxane and 2 percent by weight of ethylene oxide and had a weight average molecular weight of approximately 68,000. The oxymethylene polymer additionally was a polymer blend consist-ing of a 67 percent by weight portion which had been melt hydrolyzed in accordance with United States Patent No. 3,318,848, and a 33 percent by weight portion which had been solution hydrolyzed as described in United States Patent No. 3,219,623. The polyoxymethylene polymer also had been "stabilized" or "prestabilized" prior to blending by employing a standard additive package and including 0.5 percent 2,2'-methylene-bis-t4-methyl~6-tertiary butyl phenol) antioxidant, and 0.1 percent cyanoguanidine acid scavenger. The glass fibers were chopped strands having a length of 3/16 inch and a diameter of 50 to 55 x 10 5 inch. The glass fibers were sold commercially by Owens-Corning Fiberglas Corp. under the designation OCF 409.
As the additives there were employed a polycarbodiimide namely, poly(4,4'-diphenylmethane carbodiimide) having a number average molecular ; weight of about 5,000 (sold by the Upjohn Company and hereinafter described as PCDI), and a thermoplastic phenoxy resin prepared from epichlorohydrin and 2,2-bis(4-hydroxyphenyl) propane having a weight average molecular weight of about 30,000.
The physical properties of the moldings prepared from the blends according to the invention are included in the Table. For comparative pur-poses also are shown the physical properties of moldings made from blends similarly prepared but employing, instead of the polycarbodiimide or poly-carbodiimide and phenoxy: (1) phenoxy alone, (2) a mixture of the poly-carbodiimide and the diepoxide of the reaction product of 2,2'-bis(4-hydroxyphenyl)propane and epichlorohydrin having a number average molecular weight in the range of from 8,000 to 12,000 and sold under the mark EpiRe~

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560 ~hereinafter described simply as the epoxy) and t3) methylene diphenyl-diisocyanate (hereinafter described as MDI; employed heretofore to improve the physical properties of reinforced polyoxymethylene compositions but which is unsafe to use because of its toxicity).

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~1~813:1 The comparative results show that the polycarbodiimide provides vastly improved physical properties over the control containing no additives and which are better than those provided by the use of phenoxy resin alone The combined use of the polycarbodiimide and phenoxy resin tends to provide improvements greater than that achieved through the use of either additive alone and greater than that provided by the combined use of the polycarbodi-imide and the epoxy. Moldings prepared from the compositions according to the present invention show slightly less improvement than those prepared from compositions containing the MDI additive but without the toxicity prob-lems inherent in the use of MDI. Additionally, the compositions accordingto the invention require molding conditions similar to those required for compositions including only the phenoxy additive. Higher molding pressures, however, are required for ~I modified compositions.
Similar outstanding results are obtained employing other polyoxy-- methylenes, polycarbodiimides and phenoxy resins within the scope of the in-vention as defined above.
In commonly assigned Canadian Application Serial No. 292,351, filed December 5, 1977 concurrently herewith of Robert Edelman, entitled "Produc-tion of An Improved Non-Reinforced Polyoxymethylene Moiding Composition ~hich Forms Reduced Mold Deposits Upon Molding" is claimed a process for forming a non-reinforced polyoxymethylene molding composition wherein a small amount of a certain polycarbodiimide serves a non-analogous role ~i.e. elim-ination of mold deposit~ than that of the polycarbodiimide in the present composition.
Although the invention has been described in conjunction with cer-tain preferred embodiments, it is not limited thereto but instead includes all those embodiments within the scope and spirit of the appended claims.

,~

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An improved fiber reinforced polyoxymethylene molding composi-tion capable of forming composite articles exhibiting improved physical properties comprising an admixture of (1) a polyoxymethylene polymer, (2) about 2 to 60 percent by weight based on the total weight of the composi-tion of a fibrous reinforcement, and (3) about 0.5 to 5 percent by weight based on the total weight of the composition of a polycarbodiimide which is (a) derived from an aromatic isocyanate which is unsubstituted or substi-tuted with up to one methyl group per aromatic ring and (b) contains at least three carbodiimide units per polycarbodiimide molecule.

2. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 1 wherein the fibrous reinforcement is glass fiber in an amount of about 5 to 50 percent by weight based on the total weight of the composition.

3. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 2 wherein the polyoxymethylene polymer has an inherent viscos-ity of at least 0.8 (measured at 60°C. in a 0.1 weight percent solution in p-chlorophenol containing 2 weight percent of alpha-pinene), a weight aver-age molecular weight of at least 35,000. and a melting point of at least 150° C.

4. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 3 wherein the polyoxymethylene polymer is a copolymer compris-ing about 60 to about 99.6 mole percent recurring -OCH2- groups.

5. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 4 wherein the polyoxymethylene polymer has been pre-stabilized by melt hydrolysis prior to admixture with components (2) and (3).

6. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 4 wherein the polyoxymethylene polymer is pre-stabilized by the addition of an antioxidant and an acid scavenger.

7. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 6 wherein said antioxidant is 2,2'-methylene-bis-(4-methyl-6-tertiary butyl phenol), and said acid scavenger is cyanoguanidine.

8. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 4 wherein said polycarbodiimide is selected from the group consisting of poly(tolyl carbodiimide), poly(4,4'-diphenylmethane carbodi-imide), poly(3,3'-dimethyl-4,4'-biphenylene carbodiimide), poly(p-phenylene carbodiimide), poly(m-phenylene carobodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethane carbodiimide), and mixtures thereof.

9. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 2 wherein the polyoxymethylene polymer is a mixture of a melt hydrolysis stabilized polymer and a solution hydrolysis stabilized polymer,

10. An improved fiber reinforced polyoxymethylene molding composi-tion capable of forming composite articles exhibiting improved physical properties comprising an admixture of (1) a polyoxymethylene polymer, (2) about 2 to 60 percent by weight based on the total weight of the comp-osition of a fibrous reinforcement, and (3) about 0.6 to 5 percent by weight based on the total weight of the composition of a polycarbodiimide which is (a) derived from an aromatic isocyanate which is unsubstituted or substi-tuted with up to one methyl group per aromatic ring and (b) contains at least three carbodiimide units per polycarbodiimide molecule, and a high molecular weight thermoplastic phenoxy resin; the weight ratio of the poly-carbodiimide to phenoxy resin being in the range of 1:16 to 50:1.

11. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 10 wherein the phenoxy resin has the repeating structure:

and a weight average molecular weight of from about 15,000 to 75,000.

12. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 11 wherein the fibrous reinforcement is glass fiber in an amount of about 5 to 50 percent by weight based on the total weight of its composition.

13. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 12 wherein the polyoxymethylene polymer has an inherent vis-cosity of at least 0.8 (measured at 60°C. in a 0.1 weight percent solution in p-chlorophenol containing 2 weight percent of alpha-pinene), a weight average molecular weight of at least 35,000, and a melting point of at least 150° C.

14. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 13 wherein the polyoxymethylene polymer is a copolymer compris-ing about 60 mole to about 99.6 mole percent of recurring -OCH2- groups.

15. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 14 wherein the polyoxymethylene polymer has been pre-stabil-ized by melt hydrolysis prior to admixture with components (2) and (3).

16. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 14 wherein the polyoxymethylene polymer is pre-stabilized by the addition of an antioxidant and an acid scavenger.

17. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 16 wherein said antioxidant is 2,2'-methylene-bis-(4-methyl-6-tertiary butyl phenol), and said acid scavenger is cyanoguanidine.

18. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 14 wherein said polycarbodiimide is selected from the group consisting of poly(tolyl carbodiimide), poly(4,4'-diphenylmethane carbodi-imide), poly (3,3'-dimethyl-4,4'-biphenylene carbodiimide), poly(p-phenyl-ene carbodiimide), poly(m-phenylene carbodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethane carbodiimide), and mixtures thereof.

19. The improved fiber reinforced polyoxymethylene molding composi-tion of Claim 12 wherein the polyoxymethylene polymer is a mixture of a melt hydrolysis stabilized polymer and a solution hydrolysis stabilized polymer.

20. A fiber reinforced injection molded polyoxymethylene composite article exhibiting improved physical properties formed from the molding composition of Claim 1.