HK1057761B - Toughened polyacetal resin composition - Google Patents

Description

Toughened polyacetal resin composition

Technical Field

The present invention relates to a blend composition comprising a polyacetal resin (also referred to herein as polyoxymethylene) that exhibits a toughness superior to that of polyacetal without sacrificing other desirable properties inherent in polyacetal resins. More specifically, the present invention provides a polyacetal resin composition comprising a small amount of thermoplastic polyurethane, which is prepared by: a polyacetal masterbatch component is prepared in which a thermoplastic polyurethane is present at proportionally high levels, and this masterbatch component is subsequently blended with further polyacetal resin to reduce the proportional amount of polyurethane in the final blended composition to the desired level.

Background

Polyacetal resins prepared by polymerizing a starting material such as formaldehyde monomer or trioxane (i.e., formaldehyde trimer) exhibit excellent mechanical and physical properties such as tensile strength, stiffness, fatigue resistance, slip resistance, chemical resistance, and the like. Comonomers may also be present. It is widely used for mechanical parts, electronic parts, automobile parts and the like. However, for certain shaped articles obtained by shaping conventional compositions containing substantially only polyacetal resin, it is desirable to have a toughness greater than heretofore possible with such conventional compositions.

Improvement in toughness of polyacetal resin compositions has heretofore required addition of a substantial amount of a toughening agent to the composition. However, the addition of substantial amounts of toughening agents to polyacetal compositions is often disadvantageous because the stiffness and formability of the composition can be adversely affected, making formation difficult, and can also adversely affect the handling and manufacturing costs.

Many techniques are known in connection with improvement of impact resistance by adding various additives to a polyacetal resin composition. For example, the prior art for improving impact resistance involves blending a toughening agent such as polyurethane into polyoxymethylene [ Japanese Kokai publication Sho 59(84) -155452, Japanese Kokai publication Sho 59(84) -155453 and Japanese Kokai publication Sho 61(86) -19652 ].

U.S. Pat. No.5,286,807 discloses polyoxymethylene compositions having from 5 to 15% by weight of a thermoplastic polyurethane having a soft segment glass transition temperature of less than 0 ℃ and dispersed as discrete particles in the polyoxymethylene in order to achieve exceptional impact resistance as measured by Gardner impact.

U.S. Pat. No.4,804,716 discloses polyoxymethylene compositions having 15 to 40 weight percent of a thermoplastic polyurethane having a soft segment glass transition temperature of less than-15 ℃ and dispersed as individual particles in the polyoxymethylene in an attempt to achieve exceptional impact resistance as measured by Gardner impact.

Japanese Kokai publication Hei-4-198355 discloses a polyoxymethylene resin composition comprising 100% by weight of a polyoxymethylene resin and 1 to 150% by weight of a thermoplastic polyurethane to provide a molded article excellent in impact resistance and mechanical properties as well as surface appearance and heat aging resistance.

Japanese Kokai publication Hei-7-207115 discloses a polyacetal resin composition comprising a thermoplastic elastomer, preferably a polyurethane or a thermoplastic elastomer having a molecular weight of 1 to 3000kg/cm²A polyolefin elastomer of elastic modulus, which is dispersed in the form of fine particles and in the average distance between fine particles given by a prescribed formula, in order to improve impact resistance.

Japanese Kokai publication Hei-5-262957 discloses a polyacetal resin composition comprising 99 to 40% by weight of a polyacetal, 1 to 60% by weight of a polyester-based thermoplastic polyurethane elastomer and 0.01 to 10% by weight of a polyol having 3 hydroxyl groups in the molecule, which is prepared by melt-mixing these components under shearing conditions at a temperature in the range of 180 to 250 ℃.

Despite the introduction of the above-described compositions, there remains a need for means of improving the toughness of polyacetals in a composition without adversely affecting other inherent properties of the polyacetal resin. When preparing a blended composition from polyacetal and polyurethane, it may also be desirable to do so in a manner that inhibits any significant degradation of the polyurethane and any yellowing of the polyacetal due to the presence of the higher temperatures encountered during processing and shaping of the polyurethane.

Extensive studies by the inventors have led to the blended compositions of the present invention in which greater toughness is achieved than is characteristic of polyacetal alone, but in which there is no compensatory decrease in other desirable properties inherent to the polyacetal resin.

Disclosure of Invention

In one aspect, the present invention relates to a blend composition comprising, in admixture, (a) a polyacetal masterbatch component, and (b) a polyacetal dilution component.

In another aspect, the present invention relates to a process for making a blend composition comprising the steps of: (a) preparing a polyacetal masterbatch component from a polyacetal resin and a thermoplastic polyurethane, (b) blending the polyacetal masterbatch component with a polyacetal dilution component, and (c) recovering a blended composition.

In yet another aspect, the present invention relates to a toughened composition comprising (a) a polyacetal resin, and (b) a thermoplastic polyurethane having a soft segment with a glass transition temperature of less than-30 ℃, wherein

(i) The toughening compositions are prepared by mixing a polyacetal masterbatch component with a polyacetal dilution component,

(ii) said polyacetal masterbatch component being prepared by mixing a polyacetal resin with a thermoplastic polyurethane, said thermoplastic polyurethane being about 10 to about 60 weight percent of the masterbatch component, and

(iii) the toughened composition has a total thermoplastic polyurethane content of from about 1 to about 15 weight percent.

In a further aspect, the present invention relates to an article of manufacture prepared from the blend composition of the present invention.

Detailed description of the invention

The blended compositions of the present invention are prepared by blending a polyacetal masterbatch component with a polyacetal dilution component. The polycondensation masterbatch component is prepared by blending a polyacetal resin and a polyurethane, preferably a thermoplastic polyurethane. The polyacetal dilution component is a polyacetal resin. The polyurethane is present in the polyacetal masterbatch component in a substantially higher amount than it is present in the final blend composition. Thus, the polyacetal dilution component serves to dilute the relative amount of the polyurethane from the higher level characteristic of the masterbatch component to the lower level desired in the final blend composition. The process of the present invention involves preparing a blend composition in the manner described above.

The polyacetal resins used herein to prepare the polyacetal masterbatch component and the polyacetal dilution component include homopolymers of formaldehyde or formaldehyde cyclic oligomers whose terminal groups are terminated by esterification or etherification; but also copolymers of formaldehyde or cyclic oligomers of formaldehyde with other monomers which yield oxyalkylene groups having at least two adjacent carbon atoms in the backbone, the terminal groups of the copolymer being either hydroxyl-terminated or terminated by esterification or etherification.

The polyacetals used in the compositions of the invention may be branched or linear and have either unprotected or protected end groups. The polyacetal resin generally has a number average molecular weight in the range of about 10,000 to about 100,000, preferably about 20,000 to about 70,000, more preferably about 35,000 to about 70,000. The molecular weight can be conveniently determined by gel permeation chromatography in m-methylphenol at 160 ℃ using a DuPont PSM bimodal column kit with nominal pore sizes of 60 and 1000 *.

As indicated above, the polyacetal used in the present invention may be either a homopolymer, a copolymer or a mixture thereof. The copolymer may contain one or more comonomers, such as those typically used in the preparation of polyacetal compositions. More commonly used comonomers include alkylene oxides of 2 to 12 carbon atoms and cyclic adducts thereof with formaldehyde. The amount of comonomer is not more than 20% by weight, preferably not more than 15% by weight, more preferably not more than 2% by weight. The most preferred comonomer is ethylene oxide. Generally, polyacetal homopolymers are preferred over copolymers for their greater stiffness. Preferred polyacetal homopolymers include those in which the terminal hydroxyl groups have been terminated by chemical reaction to form ester or ether groups, preferably acetate or methoxy groups, respectively.

The polyurethanes useful in the present invention are prepared by reacting a polymer soft segment precursor, such as a dihydroxy polyester or a polyalkylene ether glycol, having at least two hydroxyl groups per molecule (a "polyol") and a molecular weight of at least about 500, preferably about 550 to about 5000, and more preferably about 1000 to about 2500. The polyol is reacted with an organic diisocyanate in a ratio such that a substantially linear polyurethane polymer is obtained, despite some branching. A diol chain extender having a molecular weight of less than about 250 may also be incorporated. The molar ratio of isocyanate to hydroxyl in the polymer is preferably from about 0.95 to 1.08, more preferably from 0.95 to 1.05, and most preferably from 0.95 to 1.02. In addition, monofunctional isocyanates or alcohols can also be used to control the molecular weight of the polyurethane.

Suitable polyester polyols include the polyesterification products of one or more dihydric alcohols with one or more dicarboxylic acids. Suitable dicarboxylic acids include adipic acid, succinic acid, sebacic acid, pimelic acid, azelaic acid, thiodipropionic acid, citraconic acid, and mixtures thereof, as well as small amounts of aromatic dicarboxylic acids. Suitable dihydric alcohols include ethylene glycol, 1, 3-or 1, 2-propylene glycol, 1, 4-butanediol, 1, 3-butanediol, 2-methylpentane-1, 5-diol, diethylene glycol, pentane-1, 5-diol, hexane-1, 6-diol, dodecane-1, 12-diol, and mixtures thereof. Furthermore, hydroxycarboxylic acids, lactones and cyclic carbonates, such as epsilon-caprolactone and 3-hydroxybutyric acid, may be used in the preparation of the polyesters. Preferred polyesters for use as the polyol include polyhexamethylene adipate, polyhexamethylene-1, 4-butanediol adipate, mixtures of these adipates, and poly-epsilon-caprolactone.

Suitable polyether polyols include the condensation products of one or more alkylene oxides with minor amounts of one or more compounds having active hydrogen-containing groups such as water, ethylene glycol, 1, 2-or 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol and mixtures thereof. Suitable alkylene oxide condensates include condensates of ethylene oxide, 1, 2-propylene oxide, butylene oxide, and mixtures thereof. Suitable polyalkylene ether glycols can also be prepared from tetrahydrofuran. Furthermore, suitable polyether polyols may also contain comonomers, in particular as random or block comonomers, for example ether diols derived from ethylene oxide, propylene oxide and/or Tetrahydrofuran (THF). Alternatively, THF polyether copolymers with small amounts of 3-methyl THF can also be used.

Preferred polyethers for use as the polyol 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 essentially hydrocarbon in nature, such as polybutadiene diol.

Suitable organic diisocyanates include 1, 4-tetramethylene diisocyanate; 1, 6-hexamethylene diisocyanate; cyclopentane-1, 3-diisocyanate; 4, 4' -dicyclohexylmethane diisocyanate; 2, 4-toluene diisocyanate; 2, 6-toluene diisocyanate; isomer mixtures of 2, 4-and 2, 6-toluene diisocyanate; 4, 4' -methylenebis (phenyl isocyanate); 2, 2-diphenylpropane-4, 4' -diisocyanate; p-phenylene diisocyanate; m-phenylene diisocyanate; xylene diisocyanate; 1, 4-naphthalene diisocyanate; 1, 5-naphthalene diisocyanate; 4, 4' -biphenyl diisocyanate; azobenzene-4, 4' -diisocyanate; m-or p-tetramethylene diisocyanate; 1-chlorobenzene-2, 4-diisocyanate. 4, 4' -methylenebis (phenyl isocyanate); 1, 6-hexamethylene diisocyanate; 4, 4' -dicyclohexylmethane diisocyanate and 2, 4-toluene diisocyanate are preferred.

Secondary amide linkages, including those derived from adipoyl chloride and piperazine, and secondary urethane linkages, including those derived from bischloroformates of PTMEG and/or butanediol, may also be incorporated into the polyurethane.

Suitable diols for use as chain extenders in the preparation of thermoplastic polyurethanes include those containing carbon chains either free or interrupted by oxygen or sulfur bonds, including 1, 2-ethanediol; 1, 2-propanediol; isopropyl-a-glyceryl ether; 1, 3-propanediol; 1, 3-butanediol; 2, 2-dimethyl-1, 3-propanediol; 2, 2-diethyl-1, 3-propanediol; 2-ethyl-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' -cyclohexanedimethanol; thiodiglycol; diethylene glycol; dipropylene glycol; 2-methyl-1, 3-propanediol; 2-methyl-2-ethyl-1, 3-propanediol; dihydroxyethyl ether of hydroquinone; hydrogenated bisphenol a; dihydroxy ethyl terephthalate; and dimethylol benzenes, and mixtures thereof. Hydroxyl-terminated oligomers of 1, 4-butanediol terephthalate can also be used to give a polyester-polyurethane-polyester repeating structure. Diamines may also be used as chain extenders to give urea linkages. Preferred are 1, 4-butanediol, 1, 2-ethanediol and 1, 6-hexanediol.

In the preparation of thermoplastic polyurethanes, the isocyanate to hydroxyl ratio should be close to 1 and the reaction is a one-step reaction. The polyurethanes used in the compositions of the present invention typically have a soft segment, i.e., a soft segment having a glass transition temperature of less than about-30 ℃ that is formed as a result of the incorporation of the polyol.

Using the polyacetal blend compositions of the present invention, one may knead known additives conventionally used in the engineering silk clothes resins to obtain the desired properties. These optional additives include, for example, lubricants, nucleating agents, mold release agents, antistatic agents, surfactants, organic polymeric materials; and inorganic or organic, fibrous, particulate or tabular fillers. These additives may be used either singly or in combination of two or more kinds, and are used at a content level not impairing the effects of the present invention.

Representative lubricants that may be used in the polyacetal compositions of the present invention include, but are not limited to, silicones, such as dimethylpolysiloxane and modifications thereof; oleamide; erucamide; stearamide; di-fatty amides, such as bisamide; a nonionic surfactant; hydrocarbon waxes; chlorinated hydrocarbons; fluorocarbons; fatty acids, including hydroxy fatty acids; esters, including lower alcohol esters of fatty acids; alcohols, including polyols, polyglycols; and metal soaps such as metal salts of bay oil, stearic acid, and the like.

Further, it is desirable to add an antioxidant to prevent thermal deterioration of the resin and to suppress formation of fish eyes and lumps (to break down non-uniform lumps). Hindered phenol type antioxidants are the most preferred in the present invention. Most preferred are those antioxidants having a melting point above 100 c, especially above 120 c.

It may also be desirable to add a thermal stabilizer to the composition of the present invention. These include polyamide compounds, especially nylon terpolymers, hydroxyl-containing polymers, and non-melting nitrogen-containing or hydroxyl-containing compounds, such as polyamide-6, polyamide-6/12-copolymers, polyamide-6/66/610-terpolymers, polyamide-6/66/612-terpolymers, ethylene-vinyl alcohol copolymers, acrylamide (co) polymers, acrylamide/N, N-methylenebisacrylamide copolymers.

To prepare the compositions of the present invention, a polyurethane is compounded with a polyacetal, and then melt-mixed and extruded to prepare a polyacetal masterbatch component. The amount of polyurethane used for incorporation into the polyacetal masterbatch component should be adjusted so that when the polyacetal masterbatch component is blended with the polyacetal dilution component, the resulting blend composition has a final polyurethane content in the range of about 1 to about 15 wt.%, although lower amounts, such as about 1 to about 10 wt.%, about 1 to about 5 wt.% or less, or about 1 to about 4 wt.%, also give the desired results. In the blended composition formed from the mixture of the polyacetal masterbatch component and the polyacetal dilution component, the total polyurethane content in the range as described above achieves an excellent balance between impact resistance and other inherent and desirable properties of the polyacetal resin.

The polyurethane content in the final blend composition as described above can be obtained by preparing the polyacetal masterbatch component from these components in a ratio of about 40 to about 90% by weight of polyacetal and about 10 to about 60% by weight of polyurethane, preferably about 60 to about 75% by weight of polyacetal and about 25 to about 40% by weight of polyurethane. Once the polyacetal masterbatch component is prepared, it is typically combined with the polyacetal dilution composition in the proportions of about 5 to about 60 wt% masterbatch component and about 40 to about 95 wt% dilution component, preferably about 10 to about 40 wt% masterbatch component and about 60 to about 90 wt% dilution component. As a result of the preparation of the blend compositions of the present invention, the polyurethane is dispersed in the polyacetal matrix as fine particles having a particle size in the range of about 0.2 to about 5 μm.

The toughened polyacetal blend compositions of the present invention may be prepared by any of the well-known methods of preparation. For example, by using an extruder, either or both of the polyacetal masterbatch component and the polyacetal dilution component may be added as a dry powder, as a concentrate, or as a solution, and may be blended, melted, and extruded together at the same time in the extruder. Furthermore, the preparation of the polyacetal masterbatch component from polyacetal and polyurethane, and the subsequent compounding of the masterbatch component with the polyacetal dilution component, can be carried out in the same mixer in a suitably timed and staged sequence. Further, the pellets produced from the masterbatch component and the pellets produced from the diluent component may be mixed and supplied to a molding machine for producing molded articles. Further, in a molding machine equipped with an appropriate screw, the polyacetal masterbatch component and the polyacetal dilution component can be directly supplied to the production of a molded article.

The process of the present invention involves preparing a blend composition in the manner described above.

Shaped articles such as parts can be prepared from the polyacetal blend compositions of the present invention. Any of the forming processes customary in the plastic forming industry may be used including, for example, compression molding, vacuum forming, injection molding, extrusion molding, blow molding, rotary molding, melt spinning, and hot molding. Injection molding is particularly preferred for obtaining parts suitable for the composition of the present invention. For example, gears, buckles, and toy parts can be made from the compositions of the present invention. The process of forming the composition of the invention as described above may be combined with the process of making the composition of the invention as described above.

Examples

The present invention and its advantageous technical effects are described by tests performed on sample materials. The inventive examples (examples 1-5) were compared to various comparative formulations (comparative examples A-E) that did not exhibit the performance of the inventive compositions. These examples are provided for the purpose of illustrating the present invention and should not be construed as limiting the scope of the present invention.

Test method

In these examples and comparative examples, polyacetal blend compositions and shaped articles prepared therefrom were characterized as determined by the following test methods:

the impact resistance is determined according to ISO 179/1eA (Charpy impact). Each sample was injection molded according to ISO 3167 as a tensile bar which was allowed to sit at room temperature (approximately 25 ℃) for at least one week after molding and prior to testing.

Flexural modulus was determined according to ISO 178. Each sample was injection molded according to ISO 3167 into tensile bars that were allowed to sit at room temperature for at least one week after molding and before testing.

The elongation is determined according to ISO 527-1/-2. Each sample was injection molded according to ISO 3167 into tensile bars that were allowed to sit at room temperature for at least one week after molding and before testing.

Composition (I)

The polyacetal resin used in these examples and comparative examples was Delrin^*500 end-capped Polymer (hereinafter CP500) and Delrin^*100 end-capped polymers (hereinafter CP100), both of which are polyacetal homopolymers manufactured by DuPont (E.I. du Pont de Nemours and Company, Wilmington, Del.). As the polyurethane (hereinafter referred to as TPU) used to prepare the polyacetal masterbatch component, a thermoplastic polyurethane as described in US 4,804,716 was used.

Preparation of

70 wt% CP100 and 30 wt% TPU were mixed in an extruder (Toshiba twin screw extruder) at 220 ℃ and 310rpm, and the resulting resin was pelletized to prepare pellets of master batch composition. The resulting masterbatch pellets were mixed with CP500 and diluted to give a blend composition in which the polyurethane was present at a much lower level than 30 wt%. The content levels of the polyurethanes in the blend compositions obtained in examples 1 to 5 are shown in Table 1. Controls A-E were those obtained by adding the polyurethane at the same level of content as in the blend composition of each of these examples, but without first preparing the masterbatch component prior to the addition of the polyacetal dilution component.

The evaluation results are shown in Table 2, and it was confirmed that, when a blend composition was prepared by preparing a polyacetal masterbatch component prior to mixing with a polyacetal dilution component, a blend composition was obtained in which the impact resistance was improved while maintaining a good balance with other inherent and desirable properties of the polyacetal resin.

TABLE 1

Sample (I)	Wt.% masterbatch	Wt.％CP100	Wt.％TPU	Wt.％CP500	Net Wt.％TPU
						Example 1	5.0	-	-	95.0	1.5
Comparative example A	-	3.5	1.5	95.0	1.5
						Example 2	10.0	-	-	90.0	3
ControlExample B	-	7.0	3.0	90.0	3
						Example 3	15.0	-	-	85.0	4.5
Comparative example C	-	10.5	4.5	85.0	4.5
						Example 4	20.0	-	-	80.0	6
Comparative example D	-	14.0	6.0	80.0	6
						Example 5	33.3	-	-	66.7	10
Comparative example E	-	23.3	10.0	66.7	10

TABLE 2

Sample (I)	Notched Charpy impact (KJ/m)2)	Flexural modulus (MPa)	Elongation (%)
				Example 1	9.43	3017	38.00
Comparative example A	9.28	3005	27.15
				Example 2	10.02	2896	50.55
Comparative example B	9.88	2883	27.95
				Example 3	12.52	2737	42.35
Comparative example C	11.27	2774	26.00
				Example 4	13.69	2617	40.45
Comparative example D	10.89	2677	26.85
				Example 5	14.91	2343	38.50
Comparative example E	11.91	2413	32.15

Claims (11)

1. A toughened composition comprising (a) a polyacetal resin, and (b) a thermoplastic polyurethane containing a soft segment having a glass transition temperature of less than-30 ℃, wherein

(i) The toughening compositions are prepared by mixing a polyacetal masterbatch component with a polyacetal dilution component,

(ii) said polyacetal masterbatch component being prepared by mixing a polyacetal resin with a thermoplastic polyurethane, said thermoplastic polyurethane being 10 to 60% by weight of the masterbatch component and said thermoplastic polyurethane being dispersed in the polyacetal as particles having a particle size of 0.2 to 5 μm, and

(iii) the total thermoplastic polyurethane content of the toughened composition is 1-15 wt%.

2. A composition according to claim 1, wherein the polyacetal resin utilized in the polyacetal masterbatch component or as the polyacetal dilution component is a homopolymer.

3. A composition according to claim 1, wherein the polyacetal resin utilized in the polyacetal masterbatch component or as the polyacetal dilution component is an acetal copolymer.

4. A composition according to claim 3, wherein the acetal copolymer is prepared from formaldehyde and ethylene oxide.

5. The composition according to claim 1, further comprising one or more additives selected from the group consisting of: stabilizers, impact modifiers, reinforcing agents, antistatic agents, antioxidants, plasticizers, lubricants, fillers, and colorants.

6. The composition according to claim 1, in the form of a manufactured article.

7. A process for making a blend composition, comprising: (a) preparing a polyacetal masterbatch component from a polyacetal resin and a thermoplastic polyurethane, (b) blending the polyacetal masterbatch component with a polyacetal dilution component, and (c) recovering a blended composition, wherein the thermoplastic polyurethane is dispersed in the polyacetal as particles having a particle size of 0.2 to 5 μm.

8. A process according to claim 7 wherein the polyurethane content in the blend composition is from 1 to 15% by weight.

9. A process according to claim 7, wherein the polyacetal resin utilized in the polyacetal masterbatch component or as the polyacetal dilution component is a homopolymer or a copolymer.

10. A process according to claim 7 wherein the polyurethane contained in the polyacetal masterbatch component has a soft segment glass transition temperature of less than-30 ℃.

11. A process according to claim 7 wherein step (b) comprises a step of admixing the polyacetal masterbatch component with a polyacetal dilution composition and one or more additives selected from the group consisting of: stabilizers, impact modifiers, reinforcing agents, antistatic agents, antioxidants, plasticizers, lubricants, fillers, and colorants.