Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-05-27
2001-03-06
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S147000, C524S414000, C524S461000, C524S495000, C524S555000
Reexamination Certificate
active
06197855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the production of synthetic polyamide compositions having a high degree of whiteness and color stability and improved molding cycle time.
2. Description of Related Art
Polymerization of suitable diamines with dicarboxylic acids to form polyamides is well known in the art and is of considerable commercial significance. Polyamides have a variety of uses. One important commercial use is resin for molding articles, especially articles that require toughness and the ability to withstand heat.
Nucleants have often been used to improved the molding cycle time or crystallization rate of polyamides. For example, U.S. Pat. No. 3,080,345 discloses using as a nucleating agent sodium phenylphosphinate, sodium isobutylphosphinate, magnesium oxide, mercuric bromide, mercuric chloride, cadmium acetate, lead acetate, or phenolphthalein. U.S. Pat. Nos. 3,585,264 and 4,866,115 also disclose using nucleating agents for improving the rate of crystallization of polyamides.
Hypophosphite compounds have been used as catalysts for polymerization of the polyamides, for example in U.S. Pat. Nos. 3,860,558; 3,173,898; and 3,691,131. In U.S. Pat. Nos. 3,860,558 and 3,691,131, metal hypophosphites are used along with a hindered phenolic compound as an antioxidant. In U.S. Pat. 3,173,898, hypophosphites of certain metals are used in small concentrations. The use of hypophosphites in the polymerization process also gives the polyamide a greater degree of whiteness and color stability.
One problem in polyamide manufacturing is that most nucleants are rendered much less effective in the presence of hypophosphite. Therefore, a need exists for polyamide compositions and manufacturing processes that will have the advantages imparted by the use of a nucleant, such as reduced molding cycle time, while still permitting the use of hypophosphites.
SUMMARY OF THE INVENTION
One aspect of the present invention is a polyamide composition that comprises (a) a polyamide other than nylon 2,2, (b) a phosphorous-containing whitening agent having Formula I:
Formula I:
wherein R is hydrogen, an alkyl group with 1 to 6 carbons, a cycloalkyl group with 5 to 6 carbons, or a phenyl or methylphenyl aromatic group, and M is hydrogen or a metal, and (c) nylon 2,2 in an amount effective to cause nucleation of the polyamide other than nylon 2,2. The polyamide of part (a) preferably is nylon 6,6, and the phosphorous-containing whitening agent of part (b) is preferably selected from the group consisting of hypophosphorous acid and metal salts thereof. More preferably, the phosphorous-containing whitening agent is a metal hypophosphite wherein the metal is selected from groups Ia, IIa, or IIb of the periodic table. Sodium hypophosphite is especially preferred.
In a particular embodiment, the composition contains the phosphorous-containing whitening agent in an amount between about 5 ppm and 500 ppm phosphorous by weight, more preferably between about 20 ppm and 80 ppm phosphorous by weight. The nylon 2,2 preferably is present in an amount between about 2 ppm and 2000 ppm by weight, more preferably between about 5 ppm and 50 ppm by weight.
Another aspect of the invention is a process for producing nucleated polyamide, comprising cooling a molten polyamide other than nylon 2,2 in the presence of a phosphorous-containing whitening agent and nylon 2,2 in an amount effective to cause nucleation of the polyamide.
The compositions of the present invention exhibit commercially desirable toughness, whiteness and color-stability, yet also have improved molding cycle times. The polyamide compositions of the invention can recrystallize at relatively high temperatures without substantial deterioration of the toughness of the end product. Higher recrystallization temperatures mean that the material needs less time to cool from the melt, because it hardens earlier as temperature drops from the melt. This improves molding cycle time and increases throughput and productivity.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The polyamides of the present invention are condensation polymers obtained by the polycondensation of amino carboxylic acids or of mixtures of diamines and dicarboxylic acids including interpolyamides obtained by the polycondensation of different polyamide forming components. Preferred polyamides are the class generally known as nylons. A particularly preferred polyamide is polyhexamethylene adipamide, nylon 6,6. This invention is useful for polyamides in all forms, but is especially useful for polyamide resins which are to be used for molding articles. Useful forms of polyamides include blends, alloys, and copolymers thereof. Preferred copolymers are copolymers of nylon 6,6 with nylon 6, nylon 6IA, nylon 6TA, and the like.
The phosphorous-containing whitening agents of the present invention are preferably hypophosphites, and more preferably hypophosphorous acid or metal hypophosphites, wherein the metal preferably is from group Ia, IIa or IIb of the periodic table. For example, the metal can be lithium, sodium, potassium, barium, magnesium, calcium, strontium or zinc. The transition metal manganese can also be used. The preferred metal hypophosphite is sodium hypophosphite.
The nylon 2,2 and the phosphorous-containing whitening agent can be incorporated into the polyamide before, during or after the polycondensation step. Preferably, the phosphorous-containing whitening agent is added during the polycondensation step to result in a white polymer. Yellowing of polymer due to oxidation during polycondensation cannot be reversed by subsequent addition of phosphorous-containing whitening agent; however, phosphorous-containing whitening agents do show efficacy as color stabilizers in subsequent melting and melt processing of the polymer. Thus the nylon 2,2 and phosphorous-containing whitening agent can be added to the polymer forming ingredients before the polycondensation step or during the polycondensation process and the reaction completed by heating. The nylon 2,2 can also be added to the already formed polyamide by adding it to the molten polyamide. Preferably, nylon 2,2 can be mixed with the solid polyamide. Alternatively, the solid polyamide in the form of lumps, pellets or chips may be coated or dusted with the ingredients and the polyamide then melted.
Preferably, nylon 2,2 can be incorporated into one set of polyamide pellets, while the phosphorous-containing whitening agent is incorporated into a second set of polyamide pellets. The two sets of polyamide pellets are then mixed and melted. In yet another embodiment, one set of polyamide pellets containing nylon 2,2 and the phosphorous-containing whitening agent are mixed and melted with a second set of polyamide pellets containing only the phosphorous-containing whitening agent.
The polyamide compositions of the present invention can further comprise conventional polymer additives known to those of skill in the art, including fillers, reinforcing agents, stabilizers, dyes, flame retarding agents, mold-release agents, plasticizers, pigments, ultraviolet light absorption agents, antistatic agents, lubricants, and the like which may be added in effective amounts and which do not deleteriously affect the compositions of the present invention.
REFERENCES:
patent: 3691131 (1972-09-01), Kelmchuk
patent: 4866115 (1989-09-01), Betz et al.
Ables Rickey W.
Lysek Bruce A.
Cain Edward J.
Howrey Simon Arnold & White , LLP
Solutia Inc.
Wyrozebski Katarzyna
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