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Title:
POLYCARBONATE COMPOSITION WITH REDUCED MOLD DEPOSITS
Document Type and Number:
WIPO Patent Application WO/2001/098402
Kind Code:
A1
Abstract:
Disclosed is a composition formed from the combination of an aromatic polycarbonate and an additive consisting of at least one bis (aralkylphenyl) pentaerythritol diphosphite, a preferred such additive being bis (2,4-dicumyl-phenyl)pentaerythritol diphosphite. Added to polycarbonate, the resulting composition is proven surprisingly useful in blow-molding large objects with reduced plateout compared to other commonly used additives. The composition is also useful for injection-molding.

Inventors:
KIM HONGKYU
FISCHER JOHN MICHAEL
Application Number:
PCT/US2001/013400
Publication Date:
December 27, 2001
Filing Date:
April 25, 2001
Export Citation:
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Assignee:
GEN ELECTRIC (US)
International Classes:
C08K5/527; (IPC1-7): C08K5/527; C08L69/00; C07F9/6574
Domestic Patent References:
WO2000078869A12000-12-28
Foreign References:
EP0885929A11998-12-23
US5112891A1992-05-12
US5438086A1995-08-01
EP0827981A21998-03-11
US5679284A1997-10-21
Attorney, Agent or Firm:
Snyder, Bernard (CT, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:
1. A method of producing an improved molding composition, comprising the steps of : providing an aromatic polycarbonate ; providing at least one bis (aralkylphenyl) pentaerythritol diphosphite of the general formula: wherein R', R2, R4, R5, R7, R8, R'°, and R"are selected independently from the group consisting of hydrogen and alkyl radicals of the formula CmH2m+l where m ranges from 1 to 4, including substituted derivatives thereof. Rn', Rn6, Rn9) and Rn are selected independently from the group consisting of hydrogen, aryl radicals, and alkyl radicals of the formula C7H2m+, where m ranges from 1 to 4 and n ranges from 0 to 3 with the proviso that the substituent be located at the ortho, meta, or para position with respect to the bridging methylene radical; and mixing said aromatic polycarbonate with said bis (aralkylphenyl) pentaerythritol diphosphite.
2. The method of claim 1 wherein about 0.01 to about 0.1 parts bis (aralkylphenyl) pentaerythritol diphosphite are mixed with one hundred parts polycarbonate.
3. The method of claim 1 wherein about 0.02 to about 0.9 parts bis (aralkylphenyl) pentaerythritol diphosphite are mixed with one hundred parts polycarbonate.
4. The method of claim 1 wherein about 0.03 to about 0.5 parts bis (aralkylphenyl) pentaerythritol diphosphite are mixed with one hundred parts polycarbonate.
5. The method of claim 1 wherein said bis (aralkylphenyl) pentaerythritol diphosphite comprises bis (2,4dicumylphenyl) pentaerythritol diphosphite.
6. The method of claim 2 wherein said bis (aralkylphenyl) pentaerythritol diphosphite comprises bis (2,4dicumylphenyl) pentaerythritol diphosphite.
7. The method of claim 3 wherein said bis (aralkylphenyl) pentaerythritol diphosphite comprises bis (2,4dicumylphenyl) pentaerythritol diphosphite.
8. The method of claim 4 wherein said bis (aralkylphenyl) pentaerythritol diphosphite comprises bis (2,4dicumylphenyl) pentaerythritol diphosphite.
9. The product produced by the method of claim 1.
10. The product produced by the method of claim 2.
11. The product produced by the method of claim 3.
12. The product produced by the method of claim 4.
13. The product produced by the method of claim 5.
14. The product produced by the method of claim 6.
15. The product produced by the method of claim 7.
16. The product produced by the method of claim 8.
17. A part blowmolded from the composition of claim 9.
18. A part injectionmolded from the composition of claim 9.
19. The method of claim 1 wherein said aromatic polycarbonate is a copolymer of bisphenolApolycarbonate.
20. The product of claim 9 wherein said aromatic polycarbonate is a copolymer of bisphenolApolycarbonate.
21. A method of estimating the amount of plateout likely to be produced when molding a particular resin, which method comprises extruding an amount of said resin using an extruder having a vent port affixed to a cold trap and subsequently determining the weight of materials trapped in said cold trap.
Description:
POLYCARBONATE COMPOSITION WITH REDUCED MOLD DEPOSITS FIELD OF THE INVENTION This invention relates to improved polycarbonate compositions in general, and bisphenol-A-polycarbonate compositions in particular, for molding operations.

BACKGROUND OF THE INVENTION Bisphenol-A-polycarbonate (BPA-PC) is one of the most versatile engineering plastics, having an attractive combination of toughness, transparency, and heat stability. This combination makes bisphenol-A-polycarbonate an ideal material for demanding applications where resistance to impact and good transparency are important. Processing of BPA-PC is typically carried out at elevated temperatures in order to reduce its high melt viscosity. Like most polyesters and other polycarbonates, BPA-PC is susceptible to hydrolysis and thermal degradation, especially at elevated temperatures. Thus, phosphorous-containing thermal stabilizers, in an amount that is effective to increase the melt stability of the polymer, are commonly added into the polycarbonate. Examples of such stabilizers include triphenyl phosphite, diphenylalkyl phosphites, phenyldialkyl phosphites, tri (nonyl- phenyl) phosphites, triauryl phosphite, trioctadecyl phosphite, tris (2,4-di-t-butyl- phenyl) phosphite, distearyl pentaerythritol diphosphite, diisodecyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, and tetrakis (2,4-di- t-butylphenyl) 4,4'-biphenylene diphosphite.

Although the addition of thermal stabilizers or antioxidants improves thermal stability of the polycarbonate, it often leads to mold deposits, or"plateout", that causes imperfection of a molded part surface and/or plugging of the vent lines of a mold.

In a typical blow-molding operation, a preform of molten plastic, or"parison", is extruded from an extruder, hanging downward into the cavity of a mold. After closing the mold, high pressure air is injected into the parison to cause the molten preform to inflate within the closed mold. After inflation of the parison and cooling of the blown part thus formed, the air is released, via an exhausting pin, through the same tube that was used to inflate.

When the parison is extruded in such an operation, the molten resin is prone to generate gaseous products that condense as plateout on the mold surface, mold vent lines, and in the exhausting pin and tubing. When these gaseous products condense on the mold surface they are prone to leave plateout and degrade the surface quality of the molded parts. When these gaseous products condense in the mold vent line, they tend to hinder air passage and also cause poor surface quality of the part. When these gaseous products condense and accumulate in the exhausting pin, they will often blow out during blowing stage and cause undesirable spots inside of the inflated molded parts. Air valve system and muffler (noise reduction) systems slowly clog from the plateout. The overall result is that typical blow-molding operations require chronic and periodic shutdown and cleaning of the plateout.

Although the quantity of plateout is not as large in injection molding as in blow molding, the effect of the plateout is also significant in injection molding process. The deposits of plateout cause inadequate replication of molded surfaces and leave undesirable surface features on molded parts.

What is needed is improved polycarbonate compositions for blow molding and injection molding that exhibit reduced gaseous emissions and plateout.

BRIEF SUMMARY OF THE INVENTION This invention describes an aromatic polycarbonate composition which results in reduced plateout (mold deposits), and maintains the advantageous processing and thermal properties of polycarbonates. This composition is formed by combining an aromatic polycarbonate with a bis (aralkylphenyl) pentaerythritol diphosphite.

A preferred additive is bis (2,4-dicumyl-phenyl) pentaerythritol diphosphite.

When the bis (aralkylphenyl) pentaerythritol diphosphites are added to polycarbonate, the resulting composition is proven surprisingly useful in blow- molding large objects with reduced plateout compared to other commonly used additives. Also this formulation can be used in injection molding objects which require detail replication with reduced plateout.

DETAILED DESCRIPTION OF THE INVENTION This invention describes an aromatic polycarbonate composition giving reduced plateout (mold deposits) while maintaining good processing and thermal properties. This composition comprises the combination of an aromatic polycarbonate and thermal-stabilizing additives, namely at least one bis (aralkylphenyl) pentaerythritol diphosphite of the general formula: wherein R', R2, R4, R5, R7, R8, Rl°, and R"are selected independently from the group consisting of hydrogen and alkyl radicals of the formula CmH2m+l where m ranges from 1 to 4, including substituted derivatives thereof. Rn3 Rn6, Rn9) and Rn are selected independently from the group consisting of hydrogen, aryl radicals, and alkyl radicals of the formula CmH2mAl where m ranges from 1 to 4 and n ranges from 0 to 3 with the proviso that the substituent be located at the ortho, meta, or para position with respect to the bridging methylene radical.

A preferred additive is bis (2,4-dicumyl-phenyl) pentaerythritol diphosphite, having the formula : Generally, in the preferred embodiment, bis (2,4-dicumyl- phenyl) pentaerythritol diphosphite will be the only bis (aralkylphenyl) pentaerythritol diphosphite utilized, but this is not required.

The polycarbonate composition comprising a diphosphite according to general formula (I) can be used in blow-molding large objects with reduced plateout and vent line plugging. Also this formulation can be used in injection molding objects which require detail replication together with reduced plateout. These additives are known to be useful as antioxidants when combined with polypropylene, as is described in Stevenson, et al., US 5,364,895 for"Hydrolytically Stable Pentaerythritol Diphosphites"issued November 15,1994, and US 5,438,086, issued August 1,1995, under the same title, the disclosures of both of which are incorporated by reference herein in their entirety. The references describe useful methods of making the additives with higher yield.

The present invention is directed to a thermoplastic resin composition, comprising an aromatic polycarbonate and a bis (aralkylphenyl) pentaerythritol diphosphite of Formula I. This resin composition comprising exhibits significantly reduced plateout and mold deposits under polycarbonate processing conditions. Thus the composition of the present invention exhibits improved resistance to thermal degradation and reduced plateout during blow molding and injection molding of polycarbonates.

As a general rule, there will be added to the polycarbonate an amount of the pentaerythitol diphosphite effective in providing heat-stabilization while reducing plateout in comparison to prior art stabilizers. In general, anywhere from about 0.01 to about 0.1 parts pentaerythitol diphosphite per hundred parts polycarbonate will be combined to create the composition of the invention. Preferably about 0.02 pph to about 0.09 pph will be combined, more preferable about 0.03 pph to about 0.05 pph.

The exact quantities will vary with circumstances, because one must make a tradeoff between how much heat stabilization is desired versus how much one wishes to reduce plateout. One can determine the optimum amount by experimenting with different concentrations used in different molding applications as described below.

EXAMPLES Although plateout is common during molding polycarbonate and other thermoplastic parts, it has been difficult to quantify and predict the degree of this occurrence prior to actual molding.

In order to quantify the plateout and quantitatively compare different thermal stabilizers, a twin screw extruder equipped with a vacuum vent and a set of screws with a venting design, was employed with a small leaking in the vent port. This leaking provides air-sweeping action in the vent area and helps to efficiently remove gaseous products generated during melt extrusion to a cold tap. The cold glass trap was to condense and accumulate the released gaseous (plateout) products at ice/water mixture temperature. A small length of fluorinated polymeric tubing was connected between the vent port and the trap. The twin screw set was designed and assembled to give an adequate melting, mixing, and melt surface area at the vent section for evaluation. After extrusion, the trap and tubing were weighed to quantify the plateout of the resin formulation.

Example 1 A linear grade of polycarbonate (Lexant) 100) was formulated with 3 different levels of two heat stabilizers. The formulations (in pph, parts-per-hundred) were preblended prior to compounding the 40-mm twin screw Werner & Pfleiderer extruder without venting. After compounding, the resins were pelletized, and then dried for 3 hours at 250°F. The dried resins were extruded in the same extruder with vacuum using only 80% of available total vacuum (20-in Hg). The vent port that was devised with an air leakage was connected to a glass trap with a short Teflon (D tubing. The trap was cooled with ice/water mixture to capture evaporating products. For this plateout evaluation, approximately 100 pounds of resin was extruded with an extruder temperature profile of (480-570-610-630-580F) at 500 rpm and a feed rate, which yields 80% of maximum torque.

Table I lists polycarbonate formulations and plateout collected in the trap. The additive of the invention was bis (2,4-dicumyl-phenyl) pentaerythritol diphosphite as shown in Formula II. The prior art additive was tris (2,4-di-t-butylphenyl) phosphite.

Table I Component (pph)#1 #2 #3 #4 #5 #6 #7 Can@100 100 100 100 100 100 100 100 Diphosphite of 0.03 0.06 0.09 theInvention Prior Art 0.03 0.06 0.09 Phosphite Plateout 7.2 6.0 13.0 16.2 13.6 16.2 23.2 collected(ppm) The resin compositions containing bis (2,4-dicumyl-phenyl) pentaerythritol diphosphite generate less plateout during extrusion. For both stabilizers, increase of a stabilizer content in the resin increase the amount of plateout during extrusion. Note the surprising and unexpected result in formulation #2, where the amount of plateout is reduced in comparison to formulation #1, where no additive is used at all.

Example 2: In order to quantify components of the evaporated products, the plateout was extracted with 25 ml of methylene chloride. The extracted solution was then diluted with methylene chloride and analyzed by high temperature GC-MS. The major compounds detected are listed in the following tables : Table II. Major contribution from polycarbonate resin. ldentified compound #1 #2 #3 #4 #5 #6 #7 Paracumyl phenol 0. 41 0.67 0.85 1. 83 0. 23 0. 58 0.79 BPA 0. 19 0.05 0. 03 0. 03 0. 01 0. 05 0. 05 paracumyl phenyl carbonate, 0.12 0.02 0.05 0. 13 0. 01 0. 05 0.05 PCPC diparacumyl phenyl carbonate 6.16 4.88 4.45 3. 79 11. 87 6. 32 4.73 Total plateout (ppm) 6.88 5.62 5.38 5. 78 12. 12 7. 00 5. 62 While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.