JPH0375574B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to certain polyoxymethylene compositions that have exceptional impact properties. Polyoxymethylene compositions generally include homopolymers of formaldehyde or cyclic oligomers of formaldehyde, such as homopolymers of trioxane (whose end groups are end-capped by esterification or etherification), as well as formaldehyde or its rings. Copolymers of the formula oligomers and oxyalkylene groups having at least two adjacent carbon atoms in the main chain, the end groups of which may have hydroxyl end groups or be end-capped by esterification or etherification. should be understood to include the following: The proportion of comonomers can be up to 20% by weight. Relatively high molecular weight, i.e.
Compositions based on polyoxymethylene of 20,000 to 100,000 can be prepared using techniques commonly employed when using thermoplastic materials, such as compression molding, injection molding,
It is useful in the production of semi-finished and finished products either by extrusion, blow molding, rotational molding, melt spinning, stamping and thermoforming. Finished products made from such compositions have highly desirable physical properties, such as high stiffness,
It has strength, chemical stability and solvent resistance.
However, in some applications it may be desirable to obtain greater impact resistance than has heretofore been possible with common polyoxymethylene compositions. U.S. Patent No. 2993025 (July 18, 1961)
Alsup et al.); U.S. Patent No. 3,027,352 (Mar. 1962);
U.S. Pat. No. 3,743,614 (July 3, 1973, Wolters et al.); U.S. Pat.
No. 3787353 (January 22, 1974, Isii et al.); U.S. Patent No. 3960984 (June 1, 1976, Kohan);
and U.S. Patent No. 4,098,843 (July 4, 1978;
Johnson) disclose various polyoxymethylene compositions, both based on homopolymers and copolymers, and various techniques for stabilizing such compositions. US Patent No.
No. 2993025 discloses stabilizing polyoxymethylene compositions by blending them with synthetic polyamides. US Pat. No. 3,027,352 discloses that the thermal stability of certain polyoxymethylene copolymer compositions is improved compared to corresponding homopolymers. U.S. Patent No. 3,743,614
It is disclosed that polyoxymethylene compositions are stabilized by compounding them with combinations of alkaline earth metal compounds and esters of (alkyl-hydroxylphenyl)-carboxylic acids and polyols. U.S. Pat. No. 3,787,353 describes polyoxymethylene compositions having the formula R( _NHCOCH2X )n, where R is a hydrocarbon group, X is a cyano or carbamoyl group, and n is from 2 to 6. It discloses that it can be stabilized by blending with a compound of US Patent No. 3,960,984 discloses stabilizing polyoxymethylene compositions by blending them with amide oligomers. US Pat. No. 4,098,843 discloses stabilizing polyoxymethylene compositions by compounding them with a dispersion of polyamide in some carrier resin. The polyoxymethylene compositions described in the patents cited above can be modified in accordance with the present invention into compositions characterized by exceptional impact resistance. Various additives have been used with polyoxymethylene compositions to improve the toughness and impact resistance of such compositions. The exceptional degree of impact resistance reached in the present invention has not been achieved heretofore. Furthermore, the compositions of the present invention achieved an exceptional degree of impact resistance with minimal sacrifice of other desirable properties of such compositions. U.S. Patent No. 3,795,715 (March 5, 1974)
Cherdon et al.) prepared polyoxymethylene compositions with 0.1 to 10 parts by weight of (a) an average molecular weight of 1,000 to 1,000,000, (b) a softening temperature below the crystalline melting point of the polyoxymethylene, and (c) a describes improving the impact resistance of polyoxymethylene compositions by blending with a polymer having a second-order transition temperature of +30°C, the latter polymer having a diameter
It exists in the form of particles of 0.1-5 microns. Such copolymers include polyethylene, ethylene/
Includes propylene copolymers, homopolymers or copolymers of (meth)acrylic esters, and homopolymers or copolymers of vinyl esters. Moderate improvements are disclosed as measured by drop weight impact testing. U.S. Patent No. 4,277,577 (July 7, 1981, Burg.
et al.) is similar to that disclosed in U.S. Pat. No. 3,795,715 above, but from 0.001 to 20% by weight of the third polymer, which can be a segmented thermoplastic copolyester or polyurethane.
A polyoxymethylene composition is disclosed that also contains. U.S. Patent No. 3,850,873 (November 26, 1974)
Wurmb et al.) improved the physical properties (including impact resistance) of glass fiber reinforced polyoxymethylene compositions by blending them with 0.5-10% by weight of high molecular weight polyurethane. This is disclosed. Polyurethane is not specified except in two examples. Moderate improvements in impact resistance are disclosed. U.S. Patent No. 1381106 (January 22, 1975)
Discloses improving the impact resistance of polyoxymethylene block copolymers by copolymerizing an elastic terpolymer with a molecular weight of at least 100,000 with the polyoxymethylene block copolymers via urethane, ureido, thiourethane or thiouraid linkages. are doing. U.S. Patent No. 3,476,832 (November 4, 1969)
Pritchard discloses improving the impact resistance of thermoplastic oxymethylene polymers by blending them with up to 20% by weight of a rubbery polymeric material having a glass transition temperature below 0°C. ing. Preferably, the rubbery material is dispersed as small average diameter particles of 20 microns or less. Thermoplastic polyurethanes are not mentioned and only modest increases in impact resistance are reported. U.S. Patent No. 3,642,940 (February 15, 1972, Burg.
et al. disclose improving the impact resistance of polyoxymethylene molding compositions by blending them with a two-phase composition of an elastic polymer and a hard polymer. ing. Thermoplastic polyurethane is not mentioned as a possible elastic component of the two-phase mixture. U.S. Patent No. 3,749,755 (July 31, 1973)
Bronstert et al.) improved the impact resistance of polyoxymethylene molding compositions by blending them with an elastomeric graft copolymer having a glass transition temperature below -20°C. is disclosed. Thermoplastic polyurethanes are not mentioned. Other examples of various additives other than thermoplastic polyurethanes for improving the impact resistance of polyoxymethylene compositions are U.S. Pat. No. 3,975,459 (August 17, 1976, Schmidt et al.); Patent No. 4017558
No. (April 12, 1977, Schmidt et al.);
No. 48-15954 (February 28, 1973); and JP-A-52
-019752 (February 15, 1977). None of the references discussed or listed above report the exceptional impact resistance achievable with the present invention. The present invention relates to certain polyoxymethylene compositions characterized by exceptional impact resistance. As used herein, the term "polyoxymethylene" refers to homopolymers of formaldehyde or cyclic oligomers of formaldehyde whose end groups are end-capped by esterification or etherification, and formaldehyde or its rings. Copolymers of the formula oligomers and oxyalkylene groups having at least two adjacent carbon atoms in the main chain, the end groups of which may have hydroxyl end groups or be end-capped by esterification or etherification. possible). It has been discovered that certain polyoxymethylenes can be formulated into compositions with exceptional impact resistance that is considerably harder than the levels of impact resistance previously achieved with such polyoxymethylenes. More specifically, a certain kind of high molecular weight polyoxymethylene is mixed with a certain kind of thermoplastic polyurethane elastomer having a low glass transition temperature, and the ratio of the thermoplastic elastomer is 5 to 15% by weight, and the thermoplastic polyurethane elastomer is a polyoxymethylene. When melt compounded so as to be homogeneously mixed with the oxymethylene and dispersed throughout as discrete particles therein, the resulting composition passes the Standard Gardner Test (ASTM D-3029, Method G). ,
Shape and dimensions D) using a weight of 3.6Kg (8b) and 7.62 x 12.7 x 0.16 cm (4" x 5" x 1/
The polyoxymethylene compositions of the present invention are characterized by exceptional impact resistance when measured by injection molding into 9J" plaques.
(80in-b), preferably 17J (150in-b)
-b), in the most preferred case 25J (225in-
b) Will be characterized by a larger Gardner impact value. This could be contrasted with unmodified polyoxymethylene, which would exhibit a Gardner impact value of about 1.8 J or less. In fact, some of the compositions of the present invention are so impact resistant that they exceed the range measured in the standard Gardner impact test, which is approximately 36 J (320 in-
b) means a greater Gardner impact value;
characterized by Exceptionally high impact resistance, i.e. 9J (80in−
b) It has been discovered that polyoxymethylene compositions with higher Gardner impact values can only be made when several important parameters or conditions coexist. In particular, exceptionally impact resistant polyoxymethylene compositions require that the polyoxymethylene polymer have a certain molecular weight. More particularly, the polyoxymethylene polymer can be branched or linear and has a molecular weight of 20,000 to 100,000, preferably 25,000 to 90,000, more preferably 30,000 to
It must have a number average molecular weight of 70,000, most preferably 35,000 to 40,000. The melt viscosity of polyurethane at a certain temperature cannot be measured accurately. This is because the preferred compounding temperature is very close to the decomposition temperature of the polyurethane. Thus, the intrinsic viscosity of the polyurethane is used instead. Melt viscosity is related to intrinsic viscosity, but is not necessarily directly proportional. The preferred melt viscosity (or intrinsic viscosity) for the polyurethane in a given composition will depend on the chemical type of the polyurethane and the melt viscosity (or intrinsic viscosity) of the polyoxymethylene. For example, polyurethane is ADIP/BDO/
MDI type, for example, polyurethane B in the table below, and the molecular weight of polyoxymethylene is m
- It can be conveniently determined by gel permeation chromatography in cresol at 160° C. using a Dupont PSM type bimodal column kit with nominal pore sizes of 60 and 1000 Å. If the molecular weight of polyoxymethylene polymer is too high,
Processing limitations may occur and it may be difficult to blend polyoxymethylene with thermoplastic polyurethane in a short time and at temperatures low enough to prevent significant decomposition of both components. The reason for this is that compounding of polyoxymethylene and thermoplastic polyurethane is usually carried out at temperatures relatively close to the temperature at which the thermoplastic polyurethane will decompose given sufficient time. When the molecular weight of polyoxymethylene is too high, the amount of mechanical energy required to achieve homogeneous mixing of the formulation components is very large, so keeping the compounding temperature below the decomposition temperature of the polyurethane is
Even when externally cooling the mixing equipment it may be difficult. Furthermore, if the molecular weight of the polyoxymethylene is too high, there will be excessive orientation of the polyoxymethylene during molding of the thin strips and the Gardner impact value will be low. If the molecular weight of the polyoxymethylene is too low, the melt viscosity of the polyoxymethylene will be low and the polyurethane will disperse as discrete particles throughout the polyoxymethylene.
Achieving homogeneous and thorough mixing with polyurethane may be difficult. As an alternative way to characterize polyoxymethylene by its number average molecular weight, polyoxymethylene can be characterized by its melt flow rate.
Polyoxymethylenes suitable for use in the compositions of the present invention have a melt flow rate of 0.1 to 30 g/10 min (ASTM D-1238, Procedure A, Condition G, 1.0 mm diameter).
(using a 0.0413 inch) orifice). Preferably, the melt flow rate of the polyoxymethylene used in the composition of the invention is 0.5
~10g/10min, most preferably 5g/10min for homopolymers and 9g/10min for copolymers
It would be a minute. As indicated above, the polyoxymethylene can be a homopolymer, a copolymer or a mixture thereof. The copolymer can contain one or more comonomers commonly used in making polyoxymethylene compositions. More commonly used comonomers include alkylene oxides of 2 to 12 carbon atoms. When choosing a copolymer, the amount of comonomer should be 20% by weight
It will preferably be less than 15% by weight, most preferably about 2% by weight. The most preferred comonomer is ethylene oxide, and the preferred polyoxymethylene copolymer is a dipolymer of formaldehyde and ethylene oxide, where the amount of ethylene oxide is about 2% by weight. in general,
Polyoxymethylene homopolymers are preferred over copolymers due to their greater stiffness. The most preferred homopolymers for use in the compositions of the invention are those having a molecular weight of about 38,000 and in which the terminal hydroxyl groups are end-capped by chemical reaction to form ester or ether groups, preferably acetate or methoxy groups, respectively. This is what we are doing. The proportion of polyoxymethylene in the composition of the invention should be 85-95% by weight of the composition. Therefore, the thermoplastic polyurethane is
It will constitute 15% by weight. The compositions of the invention include compositions containing only polyoxymethylene and polyurethane in the proportions mentioned above, and other ingredients, modifiers and/or additives, such as
Polyamide stabilizers, for example, U.S. Pat.
3960984 and 4098843, antioxidants, pigments, colorants, coloring agents, carbon black, reinforcing agents and fillers, maintaining the aforementioned proportions of polyoxymethylene and polyurethane. It should be understood that it encompasses compositions that are Within the limits mentioned above and assuming all other parameters to be equal, the higher the proportion of thermoplastic polyurethane, the higher the impact resistance of the compositions of the invention.
However, at higher levels of polyurethane, the incremental benefit in terms of Gardner impact value decreases. Therefore, in order to achieve the exceptional impact resistance of the compositions of the present invention and other highly desirable properties normally present in polyoxymethylene compositions, a polyurethane content of 8 to 12% by weight is preferred. Compositions are generally preferred, with compositions containing about 10% by weight polyurethane being most preferred. Another important parameter necessary for the production of polyoxymethylene compositions characterized by exceptional impact resistance is the selection of specific thermoplastic polyurethanes derived from at least one aromatic diisocyanate. Thermoplastic polyurethanes suitable for use in the compositions of the invention can be selected from those commercially available or can be manufactured by known methods. (For example, Rubber Technology, 2nd edition, Maurice
Morton (1973), Chapter 17, Urethane Elastomers,
DAMeyer, especially pages 453-456). Polyurethanes are produced from the reaction of polyester or polyether diols with diisocyanates and optionally further reaction of such components with chain extenders, such as low molecular weight polyols, preferably diols, or with diamines to form urea bonds. derived from forming. Polyurethane elastomers are generally composed of soft segments, such as polyester or polyester diols, and hard segments, usually derived from the reaction of low molecular weight diols with diisocyanates. Polyurethane elastomers without hard segments can be used to prepare the compositions of the present invention. however,
The most useful compositions of the invention will contain both soft and hard segments. In preparing thermoplastic polyurethanes useful in the compositions of the present invention, the thermoplastic polyurethanes have at least 2 hydroxyl groups/molecule and have at least about 500, preferably from about 550 to 5000, most preferably from about 1000 to
A polymeric soft segment material having a molecular weight of about 2500, such as a dihydric polyester or polyalkylene ether diol, is combined with an organic diisocyanate such that a substantially linear polyurethane polymer results, although some side chains may be present. React in proportion. Diol chain extenders of molecular weight less than about 250 can also be incorporated. The molar ratio of isocyanate to hydroxyl in the polymer is
Preferably about 0.95 to 1.08, more preferably about 0.95
~1.05, most preferably less than 0.95-1.00.
Additionally, monofunctional isocyanates or alcohols can be used to adjust the molecular weight of the polyurethane. Suitable polyester polyols include polyesterification products of one or more dihydric alcohols and one or more dicarboxylic acids. Suitable dicarboxylic acids include adipic acid, succinic acid, sebacic acid, suberic acid, methyladipic acid, glutaric acid, pimelic acid, azelaic acid,
Includes mixtures containing thiodipropionic acid and citraconic acid and small amounts of aromatic dicarboxylic acids. Suitable dihydric alcohols include 1,3- or 1,2-propylene glycol, 1,4-butanediol, 1,3-butanediol, 2-methylpentanediol-1,5, diethylene glycol, 1,5- Includes pentanediol, 1,6-pentanediol, 1,12-dodecanediol and mixtures thereof. In addition, hydroxyl carboxylic acids, lactones,
and cyclic carbonates, such as ε-caprolactone and 3-hydroxylbutyric acid, can be used in the production of polyesters. Preferred polyesters are poly(ethylene adipate), poly(1,4-butylene adipate)
and mixtures thereof with adipate polyε-caprolactone. Suitable polyether polyols are compounds having one or more alkylene oxides and small amounts of one or more active hydrogen-containing groups, such as water, ethylene glycol, 1,2- or 1,3- Includes condensation products with propylene glycol, 1,4-butanediol and 1,5-pentanediol, and mixtures thereof.
Suitable alkylene oxide condensates include those of ethylene oxide, 1,2-propylene oxide and butylene oxide and mixtures thereof. Suitable polyalkylene ether glycols can also be prepared from tetrahydrofuran. Furthermore, the polyether polyols can contain ether glycols derived from ethylene oxide, propylene oxide and/or tetrahydrofuran (THF) as comonomers, especially irregular or block comonomers. Alternatively, THF polyether copolymers with small amounts of 3-methyl THF can be used. Preferred polyethers include poly(tetramethylene ether) glycol (PTMEG), poly(propylene oxide) glycol, copolymers of propylene oxide and ethylene oxide, and copolymers of tetrahydrofuran and ethylene oxide. Other suitable polymeric diols include those that are primarily hydrocarbon in nature, such as polybutane diol. Suitable aromatic diisocyanates are 2,6-tolylene diisocyanate, isomeric mixtures of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 2, 2-diphenylpropane-4,4'-diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, xylene diisocyanate, 1,4-
naphthylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diphenyl diisocyanate, azobenzene-4,4'-diisocyanate, m- or p-tetramethylxylene diisocyanate and 1-chlorobenzene-2,
Contains 4-diisocyanate. 4,4'-methylenebis(phenyl isocyanate) and 2,
4-Tolylene diisocyanate is preferred. Secondary amide linkages, including those derived from adipyl chloride and piperazine, and PTMEG
Secondary urethane linkages may also be present in the polyurethane, including bis-chloroformate and/or butanediol. Dihydric alcohols suitable for use as chain extenders in the production of thermoplastic polyurethanes include:
those containing carbon chains that are either unhindered or interrupted by oxygen or sulfur bonds, including, for example: 1,2-ethanediol, 1,2-propanediol, isopropyl-a-glyceryl ether,
1,3-propanediol, 1,3-butanediol, 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-butyl-1, 3-propanediol, 2-methyl-2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-butanediol, 2 , 5-hexanediol, 1,5-pentanediol, dihydroxycyclopentane, 1,6-hexanediol, 1,4-cyclohexanediol, 4,4'-
Cyclohexane dimethylol, thiodiglycol, diethylene glycol, dipropylene glycol, 2-methyl-1,3-propanediol,
2-Methyl-2-ethyl-1,3-propanediol, dihydroxyethyl ether of hydroquinone, hydrogenated bisphenol A, dihydroxyethyl terephthalate and dihydroxymethylbenzene and mixtures thereof. Hydroxy-terminated oligomers of 1,4-butanediol tephthalate can also be used to form polyester-urethane-polyester repeat structures. Diamines can also be used as chain extenders to form urea linkages. 1,4-butanediol, 1,2-
Ethanediol and 1,6-hexanediol are preferred. In the production of thermoplastic polyurethanes, the isocyanate to hydroxyl ratio should approach unity and the reaction can be a one-step or two-step reaction. Catalysts can be used and the reaction can be carried out in the presence or absence of a solvent. Besides what has been explained above regarding polyurethane selection, the most important property of thermoplastic polyurethanes is the glass transition temperature (Tg) of the soft segments.
Whenever a glass transition temperature is reported here, it is a Dupont mounted on a Type 990 DTA fixture.
981 Dynamic Mechanical Analysis
It was measured using a Dynamic Mechanical Analysis Cell. The cell uses liquid nitrogen as the refrigerant and is 3.2cm long to hold the sample.
(1.25 inch) gap can be used. The amplitude was set at 0.2 cm. A heating rate of 2.5°C/min was used from -170°C to 40°C, depending on the signal amplitude. Readings were taken in 1°C increments. Plot the storage modulus and loss modulus,
Then, the main loss modulus peak was defined as the glass transition temperature of the soft segment. It has been discovered that the lower the glass transition temperature of a soft segment of thermoplastic polyurethane, the higher the impact resistance, assuming all other parameters are equal.
Compositions of the invention with exceptional impact resistance can be made when the glass transition temperature of the soft segments of thermoplastic polyurethane is below 0°C. Preferably, the glass transition temperature of the polyurethane soft segments is below -10°C, more preferably -15°C.
below -30°C, most preferably below -30°C. Combinations or mixtures of thermoplastic polyurethanes can also be used in the compositions of the present invention. These parameters discussed above were found to be of paramount importance in determining whether a polyoxymethylene/thermoplastic polyurethane composition with exceptional impact properties can be produced. As can be seen, the optimal compositions, i.e. those that have the highest impact resistance while maintaining reasonable levels of other properties important in polyoxymethylene compositions and fabricated articles, are those that The results will be obtained when selecting materials and conditions that represent optimal values for each of the most important parameters. For example, to try to obtain an optimal composition, a moderate molecular weight (e.g., about 30,000
~40,000) and a thermoplastic polyurethane with a low soft segment glass transition temperature (e.g., about -35°C) and about 90% by weight polyoxymethylene and about 10% by weight thermoplastic polyurethane. and should be formulated in such a way that these two components are homogeneously mixed and the thermoplastic polyurethane is dispersed as small discrete particles in the polyoxymethylene. At the same time, it is clear that by departing from the optimum values for one or more of the most important parameters discussed above, the impact resistance is exceptional, although perhaps not as high as in the optimum composition. Compositions of the invention could be prepared. However, each of these parameters is independent of each other, and the consequences of deviation from the optimal value for each of these parameters are cumulative. Thus, when chosen to perform around some or all of these parameters, one prepares polyoxymethylene/thermoplastic polyurethane compositions that are useful, but whose impact resistance is less than exceptional. Is possible. thus,
It becomes important to define what is considered exceptional impact resistance. For the purpose of defining this invention, impact resistance is
3.6 according to ASTMD-3029, Method G, Geometry D
Measured using a Kg weight (Gardner impact).
Each sample was injection molded as a 3 inch x 5 inch x 1/16 inch plaque. The plaques were allowed to stand at room temperature for at least two days after molding and before testing. Twenty-five samples of each composition were tested at room temperature and the average value determined by the Bruceton Staircase Method was reported. As mentioned above, when the polyoxymethylene thermoplastic polyurethane compositions of the present invention are characterized by a Gardner impact rating of greater than 9J, preferably greater than 17J, more preferably greater than 25J, most preferably greater than 34J, It is considered to have exceptional impact resistance. Accordingly, the composition of the invention comprises: (a) 5 to 15% by weight of at least one thermoplastic polyurethane, said polyurethane being derived from at least one aromatic diisocyanate, the glass transition of the soft segments thereof; temperature is 0℃
and (b) 85 to 95% by weight of at least one polyoxymethylene polymer, said polyoxymethylene polymer having a molecular weight of 20,000 to 100,000, wherein said weight % consists essentially of component (a) ) and (b), the thermoplastic polyurethane is dispersed as discrete particles throughout the polyoxymethylene polymer, and the composition is characterized in that the Gardner impact value is greater than 9 J. shall be. As mentioned above, various other ingredients, modifiers and/or additives can be included in the compositions of the present invention so long as the aforementioned properties of the polyoxymethylene and polyurethane are maintained. While the parameters discussed above are the most important when determining whether a particular polyoxymethylene/thermoplastic polyurethane composition is characterized by exceptional impact resistance, other parameters impact resistance may be affected to a lesser extent. For example, the molecular weight of the soft segment of the thermoplastic polyurethane will affect the properties of the composition. If the molecular weight of the soft segment is too low, the glass transition temperature will not be low enough. This is believed to be due to incomplete separation of the soft segment from the hard segment. If the molecular weight of the soft segment is too high, crystallization will occur and the glass transition temperature of the polyurethane will be too high. Generally, the molecular weight of the soft segment should be about 500 to about 5000, preferably about 850 to 3000, more preferably about 1000 to 2500, and the most preferred polyurethane is about
It has a soft segment with an average molecular weight of 2000. The desired soft segment average molecular weight can be achieved using a narrow molecular weight or a broad molecular weight distribution.
In fact, with a formulation of a polyurethane with a very high molecular weight and a very low molecular weight soft segment (outside the range mentioned above), such that the average molecular weight of the soft segment is within the range mentioned above, i.e.
Polyurethanes with extremely broad molecular weight distributions for soft segments can be used to prepare the compositions of the present invention. Similarly, the melt viscosity of the thermoplastic polyurethane at the time of compounding will affect the properties of the composition. If the melt viscosity is too low, it will be difficult to disperse the polyurethane into discrete particles. If the melt viscosity is too high, the thermoplastic polyurethane becomes difficult to process at its decomposition temperature. It is believed that an important aspect regarding the melt viscosity of polyurethane is how it approaches the melt viscosity of polyoxymethylene at the processing temperature. As a practical matter, it has been found to be particularly preferred that the intrinsic viscosity of the polyurethane be between 0.75 and 1.50 at compounding temperatures and when the polyoxymethylene is an acetate end-capped homopolymer of a number average molecular weight of about 38,000. It should be understood that intrinsic viscosity is only one means of evaluating the approximate melt viscosity of a polyurethane, and that the actual parameter in question is the melt viscosity at the compounding temperature. Therefore, one starts with a polyurethane with a very low intrinsic viscosity and then during the compounding operation, for example, the starting material polyurethane has a very low intrinsic viscosity, but is further polymerized or cross-linked and thus the polyurethane It is possible to modify the polyurethane by increasing the effective melt viscosity of the polyurethane to a desired level. Alternatively, one could start with a polyurethane with a high intrinsic viscosity and degrade or hydrolyze it during formulation to obtain the desired effective viscosity. Alternatively, a blend of high and low molecular weight polyurethanes could be used. The moisture content of the composition, particularly the polyurethane, will influence the results achieved. Water is known to react with polyurethane, causing it to degrade and reducing its effective molecular weight. Therefore, the drier the better. In any case, the components in the compositions of the invention and the compositions of the invention themselves contain less than 0.2% by weight, preferably 0.1% by weight, especially when there is no opportunity for water to escape, for example during injection molding. It should contain less water. The processing conditions used in preparing and molding the compositions of the present invention may also affect the impact resistance of the compositions. As previously mentioned, the polyurethane must be homogeneously mixed and dispersed in the polyoxymethylene as discrete particles and must remain so during the formation of the finished product.
These particles of polyurethane are approximately spherical in shape (i.e., the particles have an equal aspect ratio of approximately 1.0) or elongated (i.e., the particles have an aspect ratio substantially greater than 1.0), and the particle size The distribution of can be Gaussian, bimodal or multimodal.
If elongated, the particles can be slightly elongated and approximately oval in shape, or they can be highly elongated and resemble strands of thermoplastic polyurethane running through a continuous phase of polyoxymethylene. Thus, when referring to the compositions of the present invention, it is meant to include molded or shaped articles as well as melt compounded materials that can be subsequently shaped or shaped. The polyurethane can be dispersed in the polyoxymethylene using high-intensity mixing equipment capable of developing high shear above the melting points of the components. Examples of such equipment are rubber roll machines, internal mixers such as the "Banbury" mixer and the "Brabender" mixer, single or multi-blade internal mixers, such as the “Ko-kneader”; multi-barrel mixers, such as the Farrel Continuous Mixer;
Includes injection molding machines, and single- and twin-screw (rotating in the same or different directions) extruders. These devices can be used alone or in combination with static mixers, mixing torpedoes and/or various devices for increasing the internal pressure and/or intensity of the mixing, such as valves, gates or screws designed for this purpose. , can be used. Continuous devices are preferred. Twin-screw extruders, especially those incorporating high-intensity mixing sections, such as inverted pitch elements and kneading elements, are particularly preferred. The mixing equipment used in all of the examples of this application, unless otherwise specified, was a 28 mm co-rotating Werner and Pfleiderer twin screw extruder containing two working sections and a total 5 kneading elements, 2 reversal elements,
and a screw design with a vacuum port at approximately 70% of the distance from the feed throat to the die. All zones were set at 190°C.
The temperature of the melt coming out of the die is approximately 220-260℃
It was hot. A low flow of cooling water was used to reduce the temperature in some cases. The extruder is 225~
Operates at 250rpm, processing speed is 6.8~13.6Kg
(15-30 pounds)/hour. A blanket of nitrogen was maintained across the feed throat to exclude oxygen and preserve the dryness of the ingredients, and the strand exiting the die was quenched in water and cut into pellets. Deviations from these conditions are possible. For example, if the process rate is adjusted to compensate and no product is produced that does not melt or decompose,
Temperatures below 190°C or above 260°C are possible. However, 170-260℃ for melt compounding
is considered preferable; 185-240°C is preferable;
and most preferably 200-230°C. The melt temperatures shown are approximate values based on measurements taken at the die exit. Depending on the extruder geometry, there may be significant cooling between the last point of mixing and the die. Actual melting temperatures may be somewhat higher. The fabrication conditions used to manufacture the shaped article are equally important. This is because when manufacturing the shaped articles of the invention from previously melt compounded materials, the conditions occurring in the melt compounded materials, such as the distribution of thermoplastic polyurethane as discrete particles in polyoxymethylene, the composition. This is because it is important to maintain dryness. Shaped articles can be manufactured using several common methods, such as compression molding, injection molding, extrusion,
It can be made by blow molding, rotomolding, melt spinning, thermoforming and stamping. Examples of shaped articles include sheets, profiles, bars, films, filaments, fibers, straps, tapes, tubes, and pipes. Such shaped articles can be post-processed by orientation, stretching, coating, annealing, painting, laminating and plating. Unused shaped articles, rejected shaped articles or scrap compositions of the present invention can be crushed and reshaped. It should be noted that in addition to exceptional impact resistance, the compositions of the present invention can be used to make extruded bars with improved toughness, as demonstrated by increased elongation in standard tensile tests. be. Furthermore, a significant increase in elongation is evident in compositions with as little as 5% polyurethane. Moreover, when producing thick products, including rods, from polyoxymethylene, the polyoxymethylene usually shrinks during cooling and the cooling of the thick products takes place non-uniformly, i.e. from outside to inside. Therefore, voids often form in the center of such products. The composition of the present invention comprises:
It has been found that such a thick product will be produced with significantly fewer and/or smaller voids, and in some cases completely void-free. Generally, the conditions used to manufacture shaped articles will be similar to those described above for melt compounding. More specifically, melt temperatures and residence times can be used up to the point where significant decomposition of the polyurethane occurs. Preferably the melting temperature is about 170-250
C, more preferably about 185-240C, most preferably 200-230C. When injection molding the compositions of the invention, the mold is preferably cold to match as closely as possible the complexity of the shape being produced. That is, generally speaking, the colder the mold, the higher the impact resistance of the shaped article. However, the colder the mold, the harder it is to fill, especially when the passages are narrow or the shape is complex. Generally, the mold temperature is
10-120°C, preferably 10-100°C, most preferably the mold temperature will be about 50-90°C. Similarly,
The cycle time, which determines the total retention time in the melt, can be adjusted to suit the particular conditions encountered. For example, polyurethane can degrade if the total retention time in the melt is too long. If the cycle time is too short, the part may not fully solidify while the mold is still under pressure. Generally, the total retention time in the melt is about 3 to 15 minutes, with short times being preferred and consistent with the formation of high quality shaped articles. As an example, the 0.16 cm (1/16
inch) test samples were made on a 6 oz reciprocating screw injection molding machine with a cylinder temperature of 180-210°C.
Mold temperature from 25 to 120℃, minimum back pressure, screw speed from 60 to 120 rpm, fast ram speed, 30/15 to 60/30
It can be manufactured using a second shot/hold cycle and a general purpose screw. The samples were left undisturbed for at least two days between molding and testing. The specific molding conditions used in each of the examples are listed in the table below. In the following examples, certain embodiments of the invention and embodiments of control experiments in which one or more of the parameters discussed above were selected outside the range defining the limits of the invention are illustrated. A side-by-side comparison is shown. It will be appreciated that the compositions of the invention are characterized by exceptional impact resistance, whereas the control compositions are not. Unless otherwise specified,
All parts and percentages are by weight and temperatures are in degrees Celsius. Measurements not originally in SI units were converted as such and rounded as appropriate. In the examples below, the flexural modulus is
Determined according to ASTM 790, Geometry A, Method A on three samples and reports the average value. The samples were allowed to stand at room temperature for at least 2 days after molding. The chemical composition of each of the commercially available thermoplastic polyurethanes tested was
Associates (“Varian Associates”) XL type 200
It was determined using a nuclear magnetic resonance absorption spectrometer. A proton spectrum was used. Thermoplastic polyurethane is dissolved in diutero 1,1,2,2-tetrachloroethane at 2-5% solids,
Tested at 120°C. In the examples below, in addition to thermoplastic polyurethane and polyoxymethylene, three of the compositions tested (controls and examples in the table and
33 (with the exception of an acetate end-capped homopolymer with a number average molecular weight of approximately 38,000) containing 1.5% by weight of a polyamide oligomer stabilizer (as described in U.S. Pat. No. 3,960,984)
and 0.1% by weight of 4,4'-butylidene bis(6
-t-butyl-m-cresol) antioxidant. The acetate end-capped homopolymer of molecular weight approximately 38,000 in the Table and in the Control and Example 33 contains 0.4% by weight polyamide stabilizer (approximately 38% polycaprolactam, 35% polyhexamethylene adipamide, and 27% polyhexamethylene sebamide terpolymer) and
It contained 0.1% by weight of 2,2'-methylenebis(6-t-butyl-4-methylphenol). Additionally, the copolymers used in Examples 28-32 may contain the supplier's registered additives. Unless otherwise stated, polyoxymethylene refers to an acetate end-capped homopolymer (U.S. Pat.
No. 2998409). The use of stabilizers and antioxidants is not necessary for the operability of this invention. They were used to improve the thermal and oxidative stabilizers in the examples below and did not significantly affect the impact resistance of the compositions tested. The chemical composition, intrinsic viscosity, and glass transition temperature of each of the thermoplastic polyurethanes used in the Examples are summarized in the table below.

【table】

TABLE Gardner impact test plaques were injection molded in the following examples under various conditions depending on the composition being molded and the purpose of the experiment. The molding conditions are summarized in the table below.

【table】

EXAMPLE 1 Preparation of Thermoplastic Polyester Polyurethanes Thermoplastic polyurethanes suitable for use in the compositions of the invention can be selected from those commercially available or can be prepared by known methods. can. Typically suitable polyester polyurethanes were made as follows. A cylindrical reactor with a hemispherical bottom was used. The reactor had an inner diameter of about 95 mm and a height of about 160 mm.
It ended in a 55/50 internal joint. It is compatible with 10mm “Truebore” stirring guides on mechanical stirrers.
55/50 outer joint, thermometer (17.8mm immersion)
Used with a top made from a 10/30 joint for and an additional 29/26 joint for addition. The stirring blade was a glass propeller with a width of approximately 41 mm. 3280g “Rucoflex”
438.0 g of a mixture containing S102P55 (dried hydroxyl-terminated butylene adipate, hydroxyl number = 55) and 819.7 g of recently distilled 4,4'-methylene bis(phenyl isocyanate) was added to a cylindrical polymerization vessel. 1 drop (approximately 0.01g) of “DABCO” 33LV (in dipropylene glycol)
33% by weight trimethylene diamine) cyclic amine catalyst was added to this mixture. The catalyst was stirred into the diol mixture for 2 hours. Then 9 drops of DABCO33LV were added to 14.95g of butanediol (dried). After vigorous stirring for 4 minutes, the viscous mass was poured into a preheated pan (Teflon fluorocarbon polymer) in a vacuum oven at 100°C. The oven containing the pan and polymerization mixture was evacuated to a pressure of 9 inches (22.9 cm) Hg and swept with nitrogen. Polymerization was continued for 46 hours at 100° C. and 0.95 atmosphere nitrogen pressure. The resulting polymer (hereinafter referred to as Polyurethane A) was removed from the vacuum oven and cooled. The intrinsic viscosity measured for this polymer was 1.04 (0.1
% in DMF at 30°C). Next, polyurethane A is cubed (6 mm sides)
The samples were cut into pieces, melt compounded, injection molded and subjected to the Gardner test as described above. The Gardner impact value for a formulation of 10% of this polyurethane in polyoxymethylene homopolymer is 32.1J
It was hot. Examples 2-9 Effect of Thermoplastic Polyurethane Ratio Polyurethane B (detailed in the table above) was compounded into polyoxymethylene homopolymer in various ratios and injection molded into test plaques to determine the flexural modulus and Tested for Gardner impact with the following results.

Table: A series of experiments was conducted using an acetate end-capped polyoxymethylene homopolymer having a number average molecular weight of 63,000 with the following results.

Table: As is clear from the above results, compositions characterized by exceptional impact resistance can be prepared from compositions containing as little as 5% by weight of polyurethane, and generally As a result, the impact resistance grade becomes higher. Examples 10-13 Effect of Glass Transition Temperature of Polyurethane Flexible Segments Compositions were prepared using 10% by weight of each of four chemically similar thermoplastic polyurethanes and 90% by weight of polyoxymethylene homopolymer. .
All four types of polyurethane had PTMEG soft segments and BDO/MDI hard segments.
Furthermore, the intrinsic viscosities of the four polyurethanes were within a relatively narrow range. Plaques were prepared and tested as described above, and the results reported in the table below were obtained.

TABLE Examples 14-17 Effect of Polyurethane Intrinsic Viscosity As discussed above, it is most preferred that the melt viscosities of the polyurethane and polyoxymethylene be matched at the processing temperature. Intrinsic viscosity is used as an approximation, and this example reveals the optimal polyurethane intrinsic viscosity for one particular system. The compositions prepared for each of these four examples contained 5% polyurethane in polyoxymethylene homopolymer. The polyurethane used in each of these examples was essentially identical to Polyurethane B (listed in the table above) when chemically analyzed. All samples were prepared as described in Example 31 in the table above. The results are reported in the table below. Table Examples Intrinsic Viscosity Gardner (J) 14 0.64 13.9 15 0.96 34.2 16 1.36 32.9 17 1.91 8.8 Example 18 Effect of Mold Temperature A formulation containing 10% by weight polyurethane B and 90% by weight polyoxymethylene homopolymer Melt compounded and injection molded into plaques under the same conditions except that one portion of the plaque was prepared in a mold at 60°C and the other part in a mold at 100°C. Other processing conditions are detailed in the table above. Plaques from the 60°C mold had a Gardner impact value of 36J. The plaque from 100°C had a Gardner impact value of 7.3J. Examples 19-30 Comparison of various thermoplastic polyurethanes Various polyurethanes were blended at 10% by weight with 90% by weight polyoxymethylene homopolymer and injection molded into test plaques as described in the table above. It was then tested for Gardner impact. The results of these experiments and the intrinsic viscosity and glass transition temperature of each of the polyurethanes are summarized in the table below.

【table】

TABLE Examples 31-35 Compositions of polyoxymethylene copolymers Polyoxymethylene copolymers can also be used to prepare compositions characterized by exceptional impact resistance. In each of the following examples, 10% by weight of polyurethane B was added to the standard plaque as described above with 90% by weight of each of the listed polyoxymethylene copolymers and comparable polyoxymethylene homopolymers. injection molding and Gardner impact values were obtained as described in . The results are reported in the table below. All of the polyoxymethylene polymers in these examples are dipolymers containing approximately 2% by weight ethylene oxide, with the exception of Example 35, which is a homopolymer.

Table Example 36 Compositions Containing Mixtures of Different Polyoxymethylenes It is preferred to produce shaped articles of the invention from compositions of the invention containing a single polyoxymethylene, and the polyoxymethylene is approximately Although more preferred is an acetate end-capped homopolymer having a number average molecular weight of 38,000, products with exceptional impact properties can be prepared from compositions containing different blends of polyoxymethylenes. A portion of a melt compounded composition containing 30% by weight of polyurethane B in 70% by weight of an acetate end-capped polyoxymethylene homopolymer having a number average molecular weight of about 63,000 was mixed with two different low molecular weight polyesters. Dry blended with 2 parts each of oxymethylene. One was an acetate end-capped homopolymer having a molecular weight of approximately 38,000. The other is "Polyplastic" M90-, a dipolymer containing about 2% by weight of ethylene glycol.
It was 02. Each dry formulation was injection molded and tested for Gardner impact as described in the table above. These compositions each contain 10% by weight of polyurethane.
It gave Gardner impact values of 27.6J and 24.4J. Example 37 Improved elongation of extruded bar 93.6% polyoxymethylene homopolymer (66000 molecular weight), 5% polyurethane B, 0.2% lubricant, 0.75% polyamide stabilizer, 0.11% antioxidant and 0.3% UV stabilizer were prepared in a 28 mm twin screw extruder.
An additional 0.025% lubricant was added to the pellets of this composition as a surface coating. Bar stock was produced using a 2 inch (5.1 cm) TEC single screw extruder attached to a manifold and dual 70 mm bar extrusion dies. A dual positive take-off brake was used. The extrusion conditions were as follows. − Barrel, adapter and die temperatures:
340, 350, 360, 370, 370〓(171, 177, 182,
- Melt temperature: 375〓 (191℃) - Melt pressure: 650-750psi - Forming die water temperature: 85〓 (29℃) - Take-off speed: 1/2 inch (1.27cm) Bar specimens tested The sample was machined. A disk with a thickness slightly over 1/8 (0.32 cm) was cut from a bar using a lathe. The discs were inspected to see if any surface imperfections were present. The discs were thinned to a uniform thickness of 1/8 inch (0.32 cm) using a surface grinder. A center strip 1/2 inch (1.27 cm) wide was cut from the disc using a router. The specimen is 1/8 inch x 1/8 inch x 1 3/8 inch (0.32
cm×0.32cm×3.49cm). Test samples of each bar were tested according to the procedures described in ASTM D-638.
Tested for tensile strength and elongation. The results are listed in the table below.

Table: The polyoxymethylene compositions of the present invention can be used in extruded and finished products, such as bonding materials,
Useful in the construction of mechanical conveyors and small engine components. The exceptional impact resistance and exceptional abrasion resistance of these compositions, combined with other notable properties found in polyoxymethylene compositions, make these compositions suitable for applications such as gears and moving parts. Especially suitable.

Claims (1)

Claims: 1. An impact-resistant thermoplastic polyoxymethylene composition comprising: (a) 5 to 15% by weight of at least one thermoplastic polyurethane, said polyurethane derived from at least one aromatic diisocyanate; and the glass transition temperature of the soft segment is 0.
and (b) 85-95% by weight of at least one polyoxymethylene polymer, said polyoxymethylene polymer having a molecular weight of 20,000-100,000, wherein said weight % is the component ( Based solely on the total amount of a) and (b), the thermoplastic polyurethane is dispersed as discrete particles throughout the polyoxymethylene polymer, and the composition has a Gardner impact value greater than 9 J. Features an impact-resistant thermoplastic polyoxymethylene composition. 2. The composition according to claim 1, wherein the polyoxymethylene is a homopolymer. 3. The composition of claim 1, wherein the polyoxymethylene is a copolymer. 4. The composition of claim 3, wherein the polyoxymethylene contains at least one comonomer, said comonomer being an oxyalkylene group having at least two adjacent carbon atoms in the main valence chain. 5. The composition of claim 4, wherein said comonomer is selected from the group consisting of alkylene oxides of 2 to 12 carbon atoms. 6. The composition of claim 5, wherein the copolymer is a dipolymer and the comonomer is ethylene oxide. 7. The composition of claim 4, wherein the weight percent of comonomer in the polyoxymethylene copolymer is from 0.1 to 20.0. 8. The composition of claim 7, wherein the comonomer constitutes less than 15.0% by weight of the copolymer. 9. The composition of claim 8, wherein the comonomer comprises about 2% by weight of the copolymer. A composition according to claim 1 having a Gardner impact value greater than 10 17 J. 11. The composition of claim 1 having a Gardner impact value greater than 1125J. 12 Polyoxymethylene polymer is 25,000~
A composition according to claim 1 having a number average molecular weight of 90,000. 13 Polyoxymethylene polymer is 30,000~
A composition according to claim 1 having a number average molecular weight of 70,000. 14 Polyoxymethylene polymer is 0.1~
The composition of claim 1 having a melt flow rate of 30.0 g/10 minutes. 15 Polyoxymethylene polymer is 0.5~
The composition of claim 1 having a melt flow rate of 10.0 g/10 minutes. 16. The composition of claim 1, wherein the thermoplastic polyurethane constitutes 8 to 12% by weight of the composition. 17. The composition of claim 1, wherein the thermoplastic polyurethane comprises a soft segment having a molecular weight of at least 500. 18 Thermoplastic polyurethane has a molecular weight of 550~
A composition according to claim 1, comprising 5000 soft segments. 19 Thermoplastic polyurethane has a molecular weight of 1000~
A composition according to claim 1, comprising 2500 soft segments. 20. The composition of claim 1, wherein the thermoplastic polyurethane contains a diol chain extender having a molecular weight less than about 250. 21. The composition of claim 1, wherein the thermoplastic polyurethane has an isocyanate to hydroxyl ratio of 0.95 to 1.08. 22. The composition of claim 1, wherein the thermoplastic polyurethane has an isocyanate to hydroxyl ratio of 0.95 to 1.05. 23. The composition of claim 1, wherein the thermoplastic polyurethane has an isocyanate to hydroxyl ratio of 0.95 to less than 1.00. 24. The composition of claim 1, wherein the thermoplastic polyurethane is derived from the reaction of a hydroxyl-terminated polyester, a diol chain extender, and a diisocyanate. 25 Polyester is polyε-caprolactone,
25. The composition of claim 24 selected from the group consisting of poly(butylene adipate), poly(ethylene adipate) and mixtures thereof. 26. The composition of claim 1, wherein the thermoplastic polyurethane is derived from the reaction of a hydroxyl-terminated polyether, a diol chain extender, and a diisocyanate. 27 Polyethers include polytetramethylene ether glycol, poly(propylene oxide),
27. The composition of claim 26 selected from the group consisting of poly(ethylene oxide), copolymers of propylene oxide and ethylene oxide, and mixtures thereof. 28 The thermoplastic polyurethane is derived from the reaction of butylene adipate and 4,4'-methylene bis(phenylisocyanate) and 1,4-butanediol.
Composition according to item 5. 29. The composition of claim 24, wherein the diisocyanate is selected from the group consisting of 4,4'-methylenebis(phenyl isocyanate) and 2,4-tolylene diisocyanate. 30. The composition of claim 26, wherein the diisocyanate is selected from the group consisting of 4,4'-methylenebis(phenyl isocyanate) and 2,4-tolylene diisocyanate. 31. The composition according to claim 29, wherein the diisocyanate is 4,4'-methylenebis(phenyl isocyanate). 32 The glycol is selected from the group consisting of 1,4-butanediol, ethylene glycol and 1,6-hexanediol. Claim 24
Compositions as described in Section. 33. The composition of claim 32, wherein the glycol is 1,4-butanediol. 34. The composition of claim 1, wherein the thermoplastic polyurethane has a soft segment glass transition temperature of less than -10°C. 35. The composition of claim 1, wherein the thermoplastic polyurethane has a soft segment glass transition temperature of less than -15°C. 36. The composition of claim 1, wherein the thermoplastic polyurethane has a soft segment glass transition temperature of less than about -30°C. 37. An impact-resistant thermoplastic polyoxymethylene composition comprising: (a) 5 to 15% by weight of at least one thermoplastic polyurethane, said polyurethane being derived from at least one aromatic diisocyanate;
and (b) 85 to 95% by weight of at least one polyoxymethylene polymer, said polyoxymethylene polymer having a molecular weight of 20,000 to 100,000. and the foregoing weight percentages are based solely on the total amount of components (a) and (b), the thermoplastic polyurethane is dispersed as discrete particles throughout the polyoxymethylene polymer, and the composition is based on the Gardner In preparing impact resistant thermoplastic polyoxymethylene compositions with impact values greater than 9 J, thermoplastic polyurethane is combined with polyoxymethylene polymer under high shear at temperatures above the melting points of the components of the composition and A preparation method characterized by mixing at a temperature lower than the temperature at which decomposition occurs. 38 The temperature measured at the outlet of the die where the components are mixed is 170 to 260°C.
The method described in Section 7. 39 The temperature measured at the outlet of the die where the ingredients are mixed is 185-240°C. Claim 3
The method described in Section 8. 40 The temperature measured at the outlet of the die where the components are mixed is 200 to 230°C. Claim 3
The method described in Section 8. 41. The method of claim 38, wherein the high shear mixing is carried out in a twin screw extruder. 42. The method of claim 41, wherein the composition exiting the extruder is rapidly cooled.