JPH028621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is known that poly(ethylene glycol) can be added to polyoxymethylene to lower the melt viscosity (Japanese Patent Publication No. 37-8816). This is done to avoid processing at high temperatures that could cause decomposition. However, this method is not very useful. This is because commercially available poly(ethylene glycol) contains impurities, and known polyoxymethylene stabilizers,
When used with, for example, those described in Alsup and Lindvig US Pat. No. 2,993,025, stabilization is lost. Known stabilizers for polyoxymethylene to improve thermal stability are superpolyamides with melting points below 220°C. The use of polyamides that soften at high temperatures to thermally stabilize polyoxymethylene is described in US Pat. No. 4,098,843 to Johnson. In this method, the use of these high temperature softening polyamides also reduces mold deposits. Polyamide, which softens at high temperatures, is predispersed in a suitable carrier resin,
Reduce particle size when dispersed in polyoxymethylene. Currently in the industry, mold and die deposits,
Poly(ethylene glycol) without increasing the amount of polyamide stabilizer to have a negative effect on the surface appearance and ultimately the physical properties
There is no suggestion how to solve the problem of worsening stabilization when added to polyoxymethylene. Although it is shown in US Pat. No. 4,098,843 that an advantage over US Pat. It is necessary to add large amounts of additives. It would be desirable to have polyoxymethylene molding compounds that do not have this destabilizing effect when poly(ethylene glycol) is present. In accordance with the present invention, it has been found that small amounts of predispersed polyamide stabilizers are surprisingly effective in providing thermal stability when relatively large amounts of technical poly(ethylene glycol) are present. Ta. Using the present invention, the advantages of predispersed stabilizer mold deposits are retained without the use of large amounts of additives that would lead to deterioration of surface quality and other properties. A surprising and unexpected feature of the present invention is that the poly(ethylene glycol) to polyamide ratio is high;
At the same time good stability of the formulation is maintained. In other words, for a given amount of poly(ethylene glycol) added, surprisingly, the amount of pre-dispersed polyamide is significantly lower than when no polyamide is pre-dispersed in the carrier resin. Excellent stabilization can be obtained even in cases where More specifically, the compositions of the present invention include (a) polyoxymethylene, (b) poly(ethylene glycol) in an amount of 0.1 to 10%, preferably 0.5 to 5% by weight of the formulation, and (c) poly(ethylene glycol) of the formulation. Consisting essentially of a dispersion comprising 0.15 to 3%, preferably 0.4 to 2.0% by weight of polyamide in a carrier resin, said polyamide comprising about
10 to 50% by weight, present in the carrier resin as particles with a particle size of about 5 microns or less, the carrier resin being inert to the oxymethylene polymer, and having a melting point below the melting point of the oxymethylene polymer. A polyoxymethylene formulation characterized by: Oxymethylene polymers that can be used in the present invention include a wide range of homopolymers and copolymers known in the art. These polymers are generally addition polymers of formaldehyde, and the polymer chain other than the terminal portion has a series of methylene-oxygen bonds of the general formula -(CH ₂ -O) _o -, with n is an integer of at least 500. The polymer chain also has the general formula , where m is an integer from 1 to 5, and R ₁ and R ₂ are inert substituents that do not cause undesirable reactions in the polymer. Such additional components of the polymeric chain are a minor part of the repeating units, and their proportion is preferably less than 40%, particularly preferably less than 5%, of the oxymethylene repeating units. The poly(ethylene glycol) used in the present invention is a known commercially available material. Its molecular weight is
100 to several hundred. One example is the product under the trade name "Carbowax." Impurities that impair stabilization and impair thermal stability are not known with certainty, but may be residues of the catalyst used in the polymerization of ethylene oxide. It is economically advantageous to use commercially available poly(ethylene glycol) in polyoxymethylene formulations. Although purified poly(ethylene glycol) meets the requirements of the present invention, it is expensive. Polyamides can vary widely in composition and molecular weight. Polyamide has carboxamide bonds is selected from a number of polymeric polyamides known in the art in which the polyamide is an integral part of the polymeric chain. In these polyamides, preferably R in the carboxamide bond is hydrogen, alkyl or alkoxy group.
The molecular weight of polyamides can vary widely, with a degree of polymerization of about 50-500. The particular polymeric carrier resin in which the stabilizing polyamide is dispersed must be chosen so that it melts below the processing temperature of the oxymethylene polymer and is inert to the oxymethylene polymer. Processing temperatures are typically about 170° to 240°C, preferably 190° to 220°C. Furthermore, in order to produce a satisfactory dispersion of polyamide, the carrier resin must have a decomposition temperature higher than the melting point of the polyamide. A wide variety of carrier resins may be used within this guideline, as will be apparent to those skilled in the art. Among such carrier resins are, for example, polyethylene and copolymers of ethylene with methyl acrylate, ethyl acrylate, vinyl acetate, acrylonitrile, carbon monoxide, or methyl methacrylate, especially about 15 to 30% by weight of methyl methacrylate. Contains a melting coefficient of approximately 0.5~
100, preferably about 2 to 20 ethylene/methyl acrylate copolymers. Among still other materials that can be used as carrier resins are methacrylate and acrylate polymers, such as polymethyl methacrylate containing about 4-15% ethyl acrylate, polyester copolymers, polyether esters, polystyrene, styrene/acrylonitrile copolymers, etc. Polymers, polyethylene oxide, and mixtures of two or more of these polymers are included. In making the compositions of this invention, the polyamide and carrier resin are first combined at a temperature above the melting points of both. These ingredients are generally mixed in a high shear mixer as known in the art to disperse the polyamide as particulates in the carrier resin. Polyamide is approx.
It must be atomized to less than 5μ, preferably less than about 2μ. The polyamide/carrier resin should contain about 10-50% by weight polyamide, preferably about 25-40% by weight. Any convenient equipment can be used to form the mixture of carrier resin and polyamide stabilizer so long as the particle size of the dispersed polyamide is as small as required. In one preferred method of compounding, the polyamide and carrier resin particles are first dry compounded and then melt extruded in a high shear double screw extruder and the extruded strands are then cut. The polyamide/carrier resin blend is then combined with an oxymethylene polymer and poly(ethylene glycol).
The oxymethylene polymer and carrier resin are mixed at a temperature above the melting point of the carrier resin and below the melting point of the polyamide to obtain a substantially uniform dispersion of the polyamide in the oxymethylene formulation. The amount of polyamide/carrier resin blend used will vary depending on the amount of oxymethylene polymer and poly(ethylene glycol) used and the desired stability. Generally, however, the polyamide/carrier resin will comprise about 0.15-3, preferably about 0.4-2.0% by weight of the final product. Various additives such as pigments, antioxidants, etc. can be included in the compositions of the invention at various stages of formulation. For example, compatibilizers can be added to polyamide and carrier resin formulations, typically polyamide/
It can be incorporated in an amount of about 0.5 to 30% by weight of the carrier resin dispersion. When using ethylene polymers or copolymers as carrier resins, it is advantageous to add various compatibilizers, such as:
i.e. copolymers of acrylic acid and methacrylic acid with ethylene, partially neutralized with alkali or alkaline earth metals, such as zinc; grafting of these partially neutralized compounds with low molecular weight polyamides. copolymers; and ethylene-propylene polymers thermally grafted with fumaric acid, maleic acid, and ethyl hydrogen maleate. When the carrier resin is a methacrylate or acrylate polymer, particularly suitable compatibilizers include methacrylate or acrylate copolymers with acidic or basic functionality. The composition of the present invention can be used to make various molded articles by molding. The invention is illustrated by the following examples, in which all proportions are by weight unless otherwise specified. EXAMPLES Formulation Method The compositions in Table 1 were made by dry blending the ingredients and feeding the mixture into a laboratory extruder of the type indicated. The molten extrudate was in the form of a ribbon, and the stabilization factor was determined after quenching, cutting, and drying. In Table 1, it is indicated as pp (predispersed polyamide). After mixing the ingredients, the stabilizer dispersion was extruded through a co-rotating, self-wiping, double-screw extruder. The truncated predispersed stabilizer product was used in polyoxymethylene compositions. This method was published in Jeonson's U.S. patent.
No. 4,098,843, and the method for measuring the particle size of polyamide is described in that patent. The thermal stability of the formulation was measured by the volume of gas evolved at 259°C. A 0.5 g sample was heated to 259° C. in a calibrated syringe in a nitrogen atmosphere for 30 minutes. The volume of gas evolved during a 5 minute to 30 minute interval is used as a measure of thermal stability. Table 1 below shows the thermal stability results of the compositions of the present invention (Examples 1-4 in the table), and these results are compared with the control compositions (Control Examples A-I in the table). The obtained results were compared. The results will be discussed next. Compositions A-D of Table 1 are polyoxymethylene stability factors (SI) with or without antioxidants and/or commercially available poly(ethylene glycol).
is in the range of 24 to 36. Composition E is polyoxymethylene without poly(ethylene glycol) plus the stabilizer described in US Pat. No. 2,993,025 (66/610/6 polyamide). SI has decreased to about 9. Composition F is poly(ethylene glycol)-free polyoxymethylene plus predispersed polyamide (pp) as described in US Pat. No. 4,098,843. SI drops to about 7. Compositions E and F therefore demonstrate the effect of adding polyamide in the absence of poly(ethylene glycol). Composition G
When industrial poly(ethylene glycol) is added to polyoxymethylene containing the 66/610/6 nylon stabilizer described in U.S. Pat. No. 2,993,025, thermal A significant decrease in physical stability occurs. On the other hand, when poly(ethylene glycol) is present, if the predispersed polyamide (pp) is added at a significantly lower concentration than the polyamide concentration described in U.S. Pat. As you can see, SI
is significantly lower at 11.5. For composition 1, pp is 0.45
% by weight. The polyamide is only about 1/3 pp, so the polyamide concentration is practically only 0.15% by weight. Therefore, although the polyamide concentration of Composition 1 is only 1/5 of that of Composition G,
A product with excellent thermal stability is obtained. It is believed that polyamides act as acid and formaldehyde detergents. This is because these decomposition products interact with the amide functional groups of the polyamide. The much lower concentration of amide functionality in pp stabilizers makes it difficult to recommend over 66/610/6 in cases of questionable stability, such as in the case of modification with poly(ethylene glycol). do not have. On the contrary,
The pp stabilizer seems to be less effective because it contains only 1/3 of the polyamide even at the same stabilizer concentration and poly(ethylene glycol) concentration. Composition H is a polyoxymethylene containing 66/610/6 stabilizer and poly(ethylene glycol).
This is the addition of EMA. The lack of significant change in SI indicates that it is not the carrier resin that is responsible for the surprisingly effective stabilization of pp. Composition 2, an example of the present invention, combines two stabilizers and shows that pp is effective when the 66/610/6 stabilizer is present. Compositions 3 and 4, as well as I, contain lower molecular weight polyoxymethylenes than those used in the compositions described above. Composition I is 0.75% 66/610/6 stabilizer
and 1.1% poly(ethylene glycol), with an SI of approximately 18. Composition 3 is similar to I, but with 0.45% pp instead of 66/610/6 stabilizer.
is used. This also contains only 1/5 polyamide. In this case as well, an excellent improvement in thermal stability is seen, with an SI of 11. In composition 4, the concentration of poly(ethylene glycol) is 3.0%
PP is 1.3% and polyamide 0.43
%. The amount of poly(ethylene glycol) was almost three times that of Control Example I.
The pp system of Composition 4 has a significantly lower SI than Composition I, with a
It is 11. 【table】

Claims (1)

Claims: 1. (a) polyoxymethylene (b) poly(ethylene glycol) at 0.1 to 10% of the formulation, and (c) a dispersion comprising polyamide in a carrier resin at 0.15 to 3% of the formulation. and the polyamide in the dispersion consists essentially of
10 to 50% by weight, present in the carrier resin as particles with a particle size of about 5 microns or less, the carrier resin being inert to the oxymethylene polymer, and having a melting point below the melting point of the oxymethylene polymer. A polyoxymethylene formulation characterized by: 2. A formulation according to claim 1, wherein the polyoxymethylene is a homogeneous polymer. 3 Poly(ethylene glycol) is 0.5% of the formulation.
3. A formulation according to claim 1 or 2, present in an amount of ~5% by weight. 4. A formulation according to claim 1 or 2, wherein the dispersion comprising polyamide in the carrier resin is present in an amount of 0.4 to 2.0% by weight of the formulation. 5. A formulation according to claim 3, wherein the dispersion comprising polyamide in the carrier resin is present in an amount of 0.4 to 2.0% by weight of the formulation. 6 Poly(ethylene glycol) is 0.5% of the formulation.
5. A formulation according to claim 4, present in an amount of ~5% by weight. 7. A formulation according to claim 5, wherein the carrier resin is a copolymer of ethylene.