Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1999-08-26
2002-07-09
Woodward, Ana (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C524S538000, C525S432000
Reexamination Certificate
active
06416704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nylon compositions having improved surface aesthetics. More particularly, the invention pertains to nylon compositions of containing a nylon 6 homopolymer and a nylon-6,6,6 copolymer which has improved surface qualities while maintaining its physical properties. The invention also pertains to a method for preparing molded articles of from such nylon compositions. Nylons formed herein are useful to create injection molded articles having a good surface appearance and good performance at a low cost.
2. Description of the Related Art
It is known in the art to prepare blends of nylon homopolymers and copolymers. Typically, nylons are used to manufacture molded articles having good properties such as hardness, high tensile strength, toughness and aesthetics. The clarity of nylons, combined with the ease of molding them into articles of various shapes and surface textures, have resulted in many practical uses of nylons. However, when a nylon composition is modified to improve surface quality, the physical properties are often compromised. Properties such as cavity pressures, mold temperatures, cycle times and cooling times are affected, resulting in a greater production cost. Therefore, it has long been of interest to improve the appearance of a nylon while maintaining its strong physical properties.
Many attempts have been made to improve the various properties of a nylon composition through blending certain nylon homopolymers and copolymers. For example, U.S. Pat. No. 4,683,170 teaches a blend of nylon polymers which is used to form single and multilayer films. The nylon composition has low temperature extrusion processability and high heat resistance for heat sealing operations. U.S. Pat. No. 4,945,129 teaches certain polyamide compositions of which are combinations of nylon polymers and copolymer. The nylon composition has high impact strength and good toughness at low temperatures.
These references t each certain blends of nylon polymers, but do not teach the specific blend of a nylon 6 homopolymer with a nylon 6,6,6 copolymer having the characteristics of the present invention which include good surface appearance. The present invention solves the problems in the prior art by teaching a nylon composition useful for molding articles with good surface appearance and good performance at a low cost.
SUMMARY OF THE INVENTION
The invention provides a nylon composition comprising a substantially uniform blend of:
a) a first polyamide which is a nylon 6,6,6 copolymer formed from about 65 to about 75 weight percent of caprolactam and from about 25 to about 35 weight percent of hexamethylenediamine and adipic acid in a 1:1 ratio; and
b) a second polyamide which is nylon 6 homopolymer,
wherein the composition comprises from about 7 to about 20 weight percent of said first polyamide and from about 80 to about 83 weight percent of said second polyamide.
The invention also provides a nylon article comprising a substantially uniform blend of:
a) a first polyamide which is a nylon 6,6,6 copolymer formed from about 65 to about 75 weight percent of caprolactam and from about 25 to about 35 weight percent of hexamethylenediamine and adipic acid in a 1:1 ratio; and
b) a second polyamide which is nylon 6 homopolymer,
wherein the composition comprises from about 7 to about 20 weight percent of said first polyamide and from about 80 to about 83 weight percent of said second polyamide.
The invention further provides a method of forming a molded article comprising:
i) forming a substantially uniform, molten nylon composition comprising a mixture of
a) a first polyamide which is a nylon 6,6,6 copolymer formed from about 65 to about 75 weight percent of caprolactam and from about 25 to about 35 weight percent of hexamethylenediamine and adipic acid in a 1:1 ratio; and
b) a second polyamide which is nylon 6 homopolymer, wherein the composition comprises from about 7 to about 20 weight percent of said first polyamide and from about 80 to about 83 weight percent of said second polyamide; and
ii) molding said nylon composition to form an article.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the present invention, a substantially uniform nylon composition is prepared by blending a first polyamide of a nylon 6,6,6 copolymer and a second polyamide of poly(caprolactam) (nylon 6) homopolymer. The nylon 6,6,6 copolymer (also sometimes referred to as nylon 6/66) is prepared through a condensation reaction of caprolactam, hexamethylene diamine and adipic acid by techniques well known in the art. Preferably, the nylon 6,6,6 copolymer comprises from about 65 to about 75 parts by weight of nylon 6 and from about 25 to about 35 by weight of nylon 6,6. More preferably, the nylon 6,6,6 copolymer comprises from about 68 to about 72 parts by weight of nylon 6 and from about 28 to about 32 parts by weight of nylon 6,6, and most preferably from about 69 to about 71 parts by weight of nylon 6 and from about 29 to about 31 parts by weight of nylon 6,6. This copolymer is also referred to as poly(caprolactamhexamethylene adipamide).
The nylon 6 homopolymer is prepared through a condensation of caprolactam by techniques well known in the art. The nylon 6,6,6 copolymer is prepared by condensing from about 65 to about 75 weight percent of caprolactam and from about 25 to about 35 weight percent of hexamethylenediamine and adipic acid in a 1:1 ratio. General procedures useful for the preparation of polyamides are well known to the art, and the details of their formation are described under the heading “Polyamides” in the Encyclopedia of Polymer Science and Technology, published by John Wiley & Sons, Inc, Vol. 10, pps.487-491, (1969).
The polyamides used in the practice of this invention may be obtained from commercial sources or prepared in accordance with known preparatory techniques. For example, nylon 6 can be obtained from AlliedSignal Inc., Morristown, N.J. under the trademark CAPRON®. Suitable variants of CAPRON® nylon resins for use in the present invention include CAPRON® nylon 8200, a balanced nylon 6 having a formic acid viscosity (FAV) of 75, CAPRON® nylon 8202, a balanced nylon 6 having an FAV of 45, CAPRON® nylon 1767, a balanced nylon 6 having an FAV of 35, CAPRON® nylon 8224HSL, a balanced nylon 6 containing a lubricant and a heat stabilizer, and having an FAV of 60, and CAPRON® nylon 1250, an amine-terminated nylon 6 with a FAV of 60.
The number average molecular weight of each polyamide homopolymer or copolymer may vary widely. Such are sufficiently high to form a free standing film but sufficiently low to allow melt processing of the blend. Such number average molecular weights are well known to those of skill in the film forming art and are usually at least about 5,000 as determined by gel permeation chromatography (GPC). Another measure of molecular weight is by the FAV method (ASTM D-789). This method provides a means of quickly determining molecular weight and can be comparable to the molecular weight as determined by the GPC method. In this method, a solution of 11 grams of aliphatic polyamide in 100 ml of 90% formic acid at 25° C. is used. In the preferred embodiments of the invention, the number average molecular weight of each polyamide ranges from about 5,000 to about 100,000, and in the preferred embodiment it ranges between about 10,000 to about 60,000. Most preferred are those in which the number average molecular weight of each polyamide ranges from about 20,000 to about 40,000.
The weight percent of the first polyamide in the nylon composition ranges from about 7 percent to about 20 percent. More preferably the weight percent the first polyamide in the nylon composition ranges from about 10 percent to about 18 percent.
The weight percent of the second polyamide in the nylon composition ranges from about 80 percent to about 83 percent. More preferably the weight percent of the second polyamide in the nylon composition ranges from about 10 percent to about 18 percent.
The composition may be formed by dry blend
Krolick Thomas J.
Smith Clark W.
Sundar Rajendra A.
Allied-Signal Inc.
Criss Roger H.
Woodward Ana
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