KR20010081920A - Polyoxymethylene Resin Compositions Having Improved Molding Characteristics - Google Patents

Abstract

polyoxymethylene with improved curing time and reduced shrinkage, comprising a) a polyoxymethylene polymer, b) a polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus c) a waxy denucleation product and d) a nucleus Composition.

Description

Polyoxymethylene Resin Compositions Having Improved Molding Characteristics}

The present invention relates to polyoxymethylene (hereinafter also referred to as polyacetal) with improved moldability and physical properties of molded articles.

Polyacetal resins are usually prepared by polymerizing formaldehyde monomers or formaldehyde trimers (trioxane). Acetal homopolymers are homopolymers of formaldehyde (e.g. Delrin® acetal resin, E.I.du Pont de Nemours and Company). Acetal copolymers are produced, for example, by copolymerizing alkylene oxide with, for example, trioxane.

Polyoxymethylene resins are widely used in, for example, electrical and electronic applications, automotive applications, and precision mechanical applications because of their high mechanical strength, excellent wear resistance, fatigue resistance, formability, and the like.

Polyoxymethylene resins are the most crystalline of engineering polymers and, therefore, freeze quickly in the mold. However, such resins also have a high degree of shrinkage. Recently, nucleation products have been introduced into polyoxymethylene resins to improve curing time and reduce shrinkage. However, it is preferable to improve further, especially if the toughness can be improved. In addition, it is desirable to remove or substantially remove voids in the molded article.

Summary of the Invention

The present invention includes blends of polyoxymethylene resins with polyalkylene / unsaturated carboxylic acid lower alkyl ester nucleates, waxy denucleates and nucleants. Such compositions improve cure time, reduce shrinkage, and improve elongation. In addition, distortion in asymmetrical parts is reduced. The composition of the present invention is used to remove or substantially eliminate voids in the molded article. Statistically designed experiments are conventionally unrecognized between additives, ie, alkylene acrylate (methacrylate) polymer nucleates such as polyethylene methacrylate (EMA), waxy denuclear products such as polyethylene wax, and nuclei such as talc. Demonstrated synergism.

1A and 1B show the crystallization 1/2 hour plots for various polyoxymethylene resin compositions.

2A, 2B and 2C show photographic copies of rod cuts formed from polyoxymethylene resins containing various additives.

3A and 3B show photographic copies of rod cuts formed from polyoxymethylene resins containing various additives.

4A and 4B show photographic copies of rod cuts formed from polyoxymethylene resins containing various additives.

The present invention is polyoxymethylene resin and

a) polyalkylene / unsaturated carboxylic acid lower alkyl ester nucleates,

b) waxy denucleation products and

c) nuclear bodies

A composition comprising a combination of

In particular, the composition comprises polyoxymethylene and

a) 0.5 to 3 weight percent polyalkylene / unsaturated carboxylic acid lower alkyl ester nucleation product,

b) 0.1 to 1% by weight waxy denucleation product and

c) 0.01-3% by weight of nuclide

It contains a blend of.

Preferred compositions are polyoxymethylene resins and

a) 1-3 weight percent polyalkylene / unsaturated carboxylic acid lower alkyl ester nucleation product,

b) 0.1 to 1% by weight waxy denucleation product and

c) 0.01-3% by weight of nuclide

It contains a blend of.

Weight percentages are based on total composition. The remainder of the composition consists of polyoxymethylene resin and other additives.

Polyoxymethylene resins that can be used in the present invention include a wide variety of homopolymers and copolymers known in the art. These polymers are generally formaldehyde polymers, except for the chain ends, in which the polymer chain consists of a series of methylene to oxygen bonds. In addition, the polymer chain may comprise residues of the formula:

R _1- (C) _m -R ₂

Wherein m is an integer from 1 to 5 and R ₁ and R ₂ are inert substituents which do not result in an undesirable reaction in the polymer. This additional component of the polymer chain is present as a small proportion of repeat units.

More specifically, the "polyoxymethylene resin" component as used herein includes homopolymers of formaldehyde or cyclic oligomers of formaldehyde whose end groups are capped by esterification or etherification; Or cyclic oligomers of formaldehyde or formaldehyde with other monomers which provide an oxyalkylene group having at least two adjacent carbon atoms in the main chain, wherein the terminal groups may be terminated with hydroxyl or capped by esterification or etherification. Copolymers.

The polyoxymethylene resins used in the present invention may be linear or substantially linear with only minor amounts of branched chains and generally have a weight average molecular weight of 40,000 to 175,000, preferably 50,000 to 150,000. Preferably, the polyoxymethylene resin does not contain a measurable amount of branching. The molecular weight can conveniently be determined by gel permeation chromatography in m-cresol at 160 ° C. or alternatively in hexafluoroisopropanol at room temperature. Polyoxymethylene resins of high or low weight average molecular weight may be used, but depending on the desired physical and processing properties, they provide an optimal balance of good mixing of the various components to be melt blended in the composition, thereby providing physical properties in the parts made from such compositions. In order to obtain the desired combination of polyoxymethylene resins having the above weight average molecular weight are preferred.

As described above, the polyoxymethylene resin may be a homopolymer having different weight average molecular weights, copolymers having different weight average molecular weights, or mixtures thereof. The copolymer may also contain one or more monomers generally used to prepare the polyoxymethylene composition. Commonly used comonomers include alkylene oxides and formaldehyde having 2 to 12 carbon atoms and cyclic addition products of such alkylene oxides. The amount of comonomer is 20% by weight or less, preferably 15% by weight or less and most preferably about 2% by weight. Commonly used comonomers include ethylene oxide, dioxalane and butylene oxide. In general, polyoxymethylene homopolymers are preferred over copolymers because of their high tensile strength and rigidity. Preferred polyoxymethylene homopolymers include polymers in which the terminal hydroxyl groups are capped by chemical reactions to form ester or ether groups, preferably acetate or methoxy groups, respectively.

Polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleates are generally copolymers or terpolymers of lower alkenes (C ₂ -C ₄ ) with lower alkyl esters of unsaturated acids. Examples of polymeric nucleates useful in the present invention are ethylene-based polymers of the formula E / X / Y, preferably E / X. In formula E / X, X is ethylene and Y is unsaturated carboxylic ester.

Unsaturated carboxylic acid esters include alkyl (C ₁ -C ₈ , preferably C ₁ -C ₄ ) esters of unsaturated carboxylic acids having 3 to 8 carbon atoms. Exemplary unsaturated acids include acrylic acid and methacrylic acid. Specific examples of esters are methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl Methacrylate, n-butyl methacrylate and isobutyl methacrylate, of which ethyl acrylate and methyl methacrylate are preferred.

Preferred ethylene methyl acrylate copolymer ("EMA") components are generally commercially available materials and can be prepared by known means. The amount of methyl acrylate in the EMA is generally from 3 to 40% by weight, preferably from 15 to 25% by weight of the EMA.

In addition, the polyalkylene / unsaturated carboxyl lower alkyl ester nucleation additive is of formula E / X / Y, wherein E is ethylene, X is selected from methyl methacrylate, ethyl acrylate and butyl acrylate, and Y is Selected from glycidyl methacrylate and glycidyl acrylate, glycidyl methacrylate being preferred for Y). Formula E / X / Y consists essentially of 5 to 99% of E, 0 to 35% of X, and 0.5 to 10% of Y.

Examples of ethylene-based random polymers consist essentially of 90 to 99% by weight of ethylene and 1 to 10% by weight of glycidylmethacrylate. Preferably, this ethylene / glycidyl methacrylate ("EGMA") random polymer consists essentially of 90 to 97% by weight of ethylene and 3 to 10% by weight of glycidyl methacrylate ("GMA"). have.

Another preferred ethylene-based random polymer is essentially 60 to 98.5 weight percent ethylene, 0.5 to 35 weight percent butyl acrylate ("BA") and 1 to 10 weight percent glycidyl methacrylate ("GMA"). ) Preferably, this ethylene / butyl acrylate / glycidyl methacrylate (“EBAGMA”) random polymer consists essentially of 55 to 84 weight percent ethylene, 15 to 35 weight percent BA and 1 to 10 weight percent GMA Consists of Most preferably, the EBAGMA random polymer consists essentially of 57.5 to 74 weight percent ethylene, 25 to 35 weight percent BA and 1 to 7.5 weight percent GMA.

Ethylene-based random polymer components can be prepared by techniques readily available to those skilled in the art. Examples of EBAGMA random polymers are described in US Pat. No. 4,753,980.

The waxy denucleating component is a substance that can be dispersed in the polyacetal resin and can be liquid at normal room temperature. In addition, if the material is solid at normal room temperature, the polyacetal must be fluidized at a temperature lower than the temperature at which it is to be processed or molded. Examples of useful wax denucleating components are natural or synthetic waxes such as hydrocarbon and polymer waxes. Hydrocarbon waxes include mineral, petroleum, paraffin or microcrystalline waxes and synthetic waxes such as ethylenic polymers or chlorinated naphthalenes. Polymeric waxes include polyethylene, polypropylene and ethylene / propylene copolymers. Preferred materials include paraffin wax and polyethylene wax. Good blending is obtained when the components are mixed together in a twin screw extruder, which is the preferred mixing device.

Nuclei useful in the present invention may be any finely divided solid, such as boron nitride, talc, silica, polyimide, branched or crosslinked acetal copolymers or terpolymers, melamine-formaldehyde resins, calcium carbonate, diatomaceous earth, dolomite Or other commonly known nucleolus for polyoxymethylene. Boron nitride, terpolymers or talc are preferred, and branched terpolymers are most preferred. Nuclei can optionally be surface treated by standard processes.

Branched or crosslinked poly (oxymethylene) useful as nucleus in the present invention can be obtained by the following method:

a. Trioxane is copolymerized with at least one compound capable of reacting and copolymerizing trioxane polyfunctionally, and optionally copolymerizing with at least one compound capable of reacting and copolymerizing trioxane consistently,

b. Branching or crosslinking to linear poly (oxymethylene) having lateral or chain-linked functional groups in sequence;

c. Trioxane is copolymerized with at least one compound and a branched or crosslinked polyether capable of reacting and copolymerizing with trioxane consistently, or linear poly (oxymethylene) is reacted with a branched or crosslinked polyether.

Small average particle sizes are preferred for nuclei. The average particle size of the nucleus should be less than 20 μm, preferably less than 10 μm, most preferably less than 5 μm.

The nucleus can be an encapsulated nucleus. Encapsulated nucleus as used herein consists essentially of the encapsulated polymer and nucleus.

The encapsulating polymer may be any suitable molten polymer, ie any polymer that melts at the processing temperature of the polyoxymethylene resin of the encapsulated nucleus. Exemplary encapsulated polymers include linear low density polyethylene ("LLDPE"), high density polyethylene ("HDPE"), and polypropylene, each of which has a solid density of 1 g / cm 3 or less as measured by ASTM D1505. Preferably, the encapsulating polymer is LLDPE or HDPE. Encapsulated polymers lack long chain polymer branches or are mostly linear in their molecular structure. The lack of long chain branching is due to the way in which encapsulated polymers are made.

Encapsulated polymers are selected from the group of polymers known in the art. Encapsulated polymers are commercially available or can be prepared by other techniques readily available to those skilled in the art. In general, encapsulated polymers are prepared by polymerizing ethylene or ethylene and alpha-olefin comonomers in solution or gas phase using coordination catalysts, in particular Zieglar or Phillips type catalysts.

The LLDPE encapsulated polymer has a melt index of 5 to 55 grams / 10 minutes as determined by ASTM D 1238 method, Condition E. HDPE encapsulated polymers preferably have a melt index of about 0.5 to 7 grams / 10 minutes as measured by ASTM D 1238 method, Condition E. Compositions containing LLDPE or HDPE with melt indices outside this range can obtain material shapes with good porosity values, but are not desirable, such as reduced stability or separation of polyoxymethylene and LLDPE or HDPE (ie, delamination). It is possible to produce blended resins and extruded material shapes having different properties.

Additives or ingredients that may have an adverse effect on the oxidative stability or thermal stability of polyoxymethylene should be avoided.

Compositions useful in the present invention may optionally comprise other ingredients, modifiers, and thermal stabilizers and co-stabilizers, antioxidants, colorants (including pigments), toughness enhancers (e.g., thermoplastic polyurethanes), other than those described above, UV stable, including reinforcing agents, hindered amine light stabilizers, especially when hindered nitrogen is a tertiary amine group or hindered amine light stabilizer contains both piperidine or piperazinone rings and triazine rings Additives commonly used in polyacetal compositions, including agents (eg, benzotriazole or benzophenone), glasses and fillers. Suitable thermal stabilizers include polyamides (including nylon terpolymers of nylon 66, nylon 6/10 and nylon 6 and polyamide stabilizers of US Pat. No. 3,960,984); Meltable hydroxy containing polymers and copolymers including ethylene vinyl alcohol copolymers and stabilizers described in US Pat. Nos. 4,814,397 and 4,766,168; Non-melt hydroxy containing or nitrogen containing polymers and especially polyacrylamides described in US Pat. No. 5,011,890; And microcrystalline cellulose; Polybeta-alanine (described in German Publication Application 3715117); Polyacrylamide; Or stabilizers disclosed in US Pat. Nos. 4,814,397, 4,766,168, 4,640,949 and 4,098,984; And mixtures of any of the above. Conventional antioxidants include triethylene glycol bis (3- (3'-t-butyl-4'-hydroxy-5'-methylphenyl) propionate, as well as antioxidants including the compounds disclosed in US Pat. No. 4,972,014, Hindered phenols such as N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinamide) and mixtures thereof.

The compositions disclosed herein can be prepared by mixing all the components with the acetal polymer by methods known in the art at temperatures above the melting point of the acetal polymer. Intense mixing devices such as rubber mills, internal mixers such as "Banbury" and "Brabender" mixers, single or multi blade internal mixers with external or frictionally heated cavities, "Ko- Multi-barrel mixers such as "Kneader", "Farrel Continuous Mixers", injection molding machines, and single screw and twin screw, co-rotating and counter-rotating extruders are used to make thermoplastic polyacetal compositions It is known to do. Such devices may be used alone or in combination with a variety of devices, such as static mixers, mixing torpedos, and / or valves, gates, or screws designed for this purpose, to increase internal pressure and / or mixing strength. Extruders are preferred and twin screw extruders are most preferred. Of course, such mixing must be carried out below the temperature at which significant decomposition of the polyacetal component occurs. Generally, the polyacetal composition is melt processed at 170 to 290 ° C., preferably 185 to 240 ° C., most preferably 195 to 225 ° C.

Molded articles can be prepared from the compositions of the present invention using methods known in the art, including compression molding, injection molding, extrusion, blow molding, rotational molding, melt spinning and thermoforming. Injection molding is preferred.

Examples of shaped articles include sheets, profiles, rods, films, filaments, fibers, strapping, tapes, tubing, and pipes. Such shaped articles can be post-treated by orientation, stretching, coating, heat treatment, painting, stratification and plating. Such molded articles and the remaining pieces therefrom can be ground and remolded.

It is understood by those skilled in the art that various modifications and substitutions can be made to the invention described above without departing from the spirit and scope of the invention. Accordingly, the invention is illustrated by way of example and not limitation.

Experiment

The following experiments were designed using experimental design software known as "EChip" (available from ECHIP, Hockessin Delaware). The designed experiment included a copy so that the statistician could measure the experimental error. Because this is a designed experiment, it is not always possible to compare experimental pairs with only one variable. Instead, they had to rely on statistical analysis to analyze the results. Samples were prepared using polyoxymethylene (POM) capped with acetate having a weight average molecular weight nominally 72,000. The examples listed in the table were made using a Werner and Pfeiderer 40 mm twin screw extruder. A 50 pound (22.7 kg) sample was prepared at 200 pounds per hour (90.7 kg / h). The machine was operated at 225-400 rpm with a barrel temperature setting of 200-225 ° C. Samples containing P561 wax and no EMA were difficult to perform because the wax was hindered by the melting of the POM, so high temperatures and mechanical RPMs were used here. EMA is a copolymer of 80% ethylene, 20% methyl acrylate and EMAC® SP2205 (available from Chevron Chemical) with a melt index of 2 g / 10 min. P561 is a nonpolar hydrocarbon wax (commercially available from Moore and Munger). Celcon® U-10 is a branched acetal terpolymer (Hoechst-Celanese (currently manufactured by Ticona)). Ultratralc 609 is a talc supplied by Barretts Minerals, Inc. Zemid® 641 is 40% talc (manufactured by DuPont) in polyethylene. U-Talc 609 / EMA is a 40% dispersion of ultratalk in EMA. U-Talk 609 / P561 is a 40% dispersion of Ultratalk in P561.

Crystallization half time was measured using differential scanning calorimetry (DSC). 10 mg of resin was heated to 210 ° C. at 50 ° C./min in Perkin-Elmer DSC 7 and held for 3 minutes, then rapidly cooled to 158 ° C. at 200 ° C./min and completed It was kept at that temperature until Half-life was obtained from the peak position of the crystallization exotherm.

In-mold crystallization time was obtained from a plot of the melt pressure curve during injection molding of the sample into a 1 × 8 × 0.070 inch bar. The DSC and in-mold crystallization data measured for the material were then statistically analyzed using the "EChip" DOE software to graphically show the effects of EMA and P561 waxes. Waxes with the effect of normally slow crystallization (increased DSC half-life) in the presence of talc-based nucleation "zemide" now have the opposite effect and increase the rate of crystallization (crystallization of DSC samples crystallizing at 158 ° C). Half-life decreases).

In addition, from the examination of the data in Table 2 below, EMA and wax have little effect on the in-mold crystallization time, either individually or together, but with greater than 0.08% of the nucleus itself when only 0.04% of the talc nucleus is used together. It can be seen.

A plot of the crystallization half-life of the composition containing various amounts of EMA and P561 in the polyoxymethylene resin is shown in FIG. 1A. 1B shows a plot of crystallization half-life for a polyoxymethylene composition containing 0.080% nucleolus (zemid) and various amounts of EMA and P561.

As shown in Table 3 below, samples containing polyoxymethylene resins and additives were formed by cycles that were too short to produce parts without voids by non-nucleated resins by injection molding. The rod was cut longitudinally to reveal the internal structure. Photographic copies of the cut bars are shown in FIGS. 2A, 2B and 2C. Sample 1 (FIG. 2A), which is an example of the present invention, is substantially free of voids compared to the bars shown in FIGS. 2B and 2C which do not contain the three additives used in the present invention.

The additives shown in Table 4 below were combined together on a 40 mm W & P twin screw extruder and then molded into 1/4 inch thick tensile test rods with molding cycles too short for unmodified control resin 3. The rods were then processed 1/8 inch thick to show internal porosity. The control of Sample 3 had many pores while Sample 14, which is the subject of the present invention, had few. Sample 14 is more preferred for molding use.

Photographic copies of the processed rods showing internal porosity are shown in FIGS. 3A, 3B and 4A and 4B. 3A corresponds to Sample 3 of Table 4, FIG. 3B corresponds to Sample 6 of Table 4, FIG. 4A corresponds to Sample 12 of Table 4, and FIG. 4B corresponds to Sample 14 of Table 4.

Claims (10)

a) polyoxymethylene polymer, b) polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus, c) waxy denucleation products and d) nucleant Composition comprising a. The method of claim 1, a) 0.5 to 3 weight percent polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus, b) 0.1 to 1% by weight waxy denucleation product and c) 0.01-3% by weight of nuclide Composition comprising a. The polyoxymethylene of claim 1, wherein the polyoxymethylene is a homopolymer of formaldehyde or a cyclic oligomer of formaldehyde in which the end group is capped by esterification or etherification; Or cyclic oligomers of formaldehyde or formaldehyde with other monomers which provide an oxyalkylene group having at least two adjacent carbon atoms in the main chain, wherein the terminal groups may be terminated with hydroxyl or capped by esterification or etherification. A composition that is a copolymer. The composition of claim 1 wherein the polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus is a copolymer or terpolymer of lower alkene (C ₂ -C ₄ ) and lower alkyl ester of unsaturated acid. The unsaturated carboxylic acid lower alkyl ester is an alkyl ester of an unsaturated carboxylic acid having 3 to 8 carbon atoms. The method of claim 4 wherein the unsaturated carboxylic acid lower alkyl ester is methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate. The composition is rate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate or isobutyl methacrylate. The composition of claim 1 wherein the nucleus is a finely divided solid. The nucleus according to claim 7, wherein the nucleus is boron nitride, talc, silica, polyimide, branched or crosslinked acetal copolymer or terpolymer, melamine-formaldehyde resin, calcium carbonate, diatomaceous earth, dolomite or encapsulated polymer and nucleus. A composition that is an encapsulated nucleus. a) polyoxymethylene polymer, b) polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus, c) waxy denucleation products and d) nuclear bodies Molded article comprising a. a) preparing a polyoxymethylene polymer component, and b) melt blending the polyoxymethylene polymer prepared in step a) with a combination of i) polyalkylene / unsaturated carboxylic acid lower alkyl ester polymer nucleus, ii) waxy denucleation and iii) nucleus Method for producing a polyoxymethylene composition comprising a, curing time is improved, shrinkage is reduced.