1 2
processing aid. Commercial polyvinyl chloride (PVC)
IMPACT MODIFIED POLYMER COMPOSITION is conventionally milled with a processing aid, though it
can be melt-blended without one; but commercially
BACKGROUND OF THE INVENTION chlorinated polyvinyl chloride (CPVC) has a high melt
It is well known that a chlorinated vinyl polymer 5 elasticity and therefore requires a processing aid or it
referred to as chlorinated polyvinyl chloride (CPVC) cannot be acceptably melt-blended. By "acceptably
has excellent high temperature performance character- melt-blended" I refer to the requirement that CPVC
istics, among other desirable physical properties. CPVC must be melt-blended within a relatively short time,
resin is commercially available as a mixed polymeric usually no more than 2 or 3 minutes, and desirably less
structure of vinyl chloride, vinylidene chloride and 10 than 2 mins. Since the fusion temperature of CPVC is
1,2-dichloroethylene. Typically, commercial CPVC has relatively high, even long mixing at about 190° C. can
in excess of about 60 percent by weight (% by weight) cause evolution of HC1 and consequent degradation of
bound chlorine, and is most conveniently prepared by the resin. Of course, degradation can be postponed by
the chlorination of polyvinyl chloride as described in adding more stabilizer, usually a liquid compound con
U.S. Pat. Nos. 2,996,489; 3,100,762; 3,334,077; 15 taining tin, or more processing aid, both of which are
3,334,078; 3,506,637; and 3,534,013 inter alia. The term expensive. However, this is not a practical solution
CPVC is used herein to define a chlorinated vinyl chlo- because it increases the cost of the blend and decreases
ride polymer having in excess of about 60% by weight the heat distortion temperature owing to the plasticiz
bound chlorine. ing effect of the stabilizer or processing aid. Processing
A well-known undesirable characteristic of CPVC 20 at higher temperatures than would be required with the resin is that it has inherently low impact properties, a use 0f a processing aid accelerates HC1 evolution, discharacteristic which is common to vinyl chloride ho- colors the resin and results in a low quality end product, mopolymers. The burgeoning demand for CPVC pipe, Thus, from a practical point of view, a processing aid is vessels, valve bodies and fittings of all kinds, and the essential to melt-blend CPVC. Since the end use prodfact that an impact-deficient CPVC matrix may be im- 25 uct must haye desirable strength, from a practiproved by compounding it with impact modifiers, has cal point of view> m impact modifier is also essential in instigated concerted efforts to develop better impact a cpyc composition
modified CPVC compositions. Most of these efforts To k^^dge, until this invention, CPE was
have been channeled towards rigid CPVC applications uni m ^ jt functioned ^ a duai function additive
where acceptable impact strength is critical. Such apph- 30 of mo functionin both as a processing aid and as
cations include the manufacture of exterior struc ural mo * a
products, rigid panels, pipe and conduit, injection- „ .>■*•» m. c A J •
u J j it. ■ c I- J *-i r pro-modifier . The reasons for this unique and desir
molded and thermoformed industrial parts, appliance 5, , , , , ^ _, T> •
. j • ^ r J able behavior of CPE are not clean v understood. Desir
housings, and various types of containers both large and "7. '\ 3"
small 35 a"*e 38 tms behavior ls>11 ls known that CPE is a more
Impact modifiers when used in CPVC reduce the eiSefve Pressing aid than impact modifier. Thus, for tensile strength and heat distortion temperature (HDT) applications where prrcessabihty is essential and some of the resin, and many reduce the processing heat stabil- mPact stTen&h » desirable, CPE alone is used as an ity. There are very few modifiers which yield a signifi- mPact modifier, but where optimum impact is essential, cant increase in impact strength or improvement in 40 CPE is generally used m combmation with one or more processability of the CPVC resin without vitiating the of the above-mentioned conventional impact modifiers, quality of the resin. Most elastomeric additives such as Similarly, where processability is a predominant conconjugated diene homo and copolymers or acrylic poly- cem> ABS resins> Cycolac (Registered U.S. Trademers which reduce the brittle temperature of vinyl mark) L m particular, provide improved processability chloride polymers, are ineffective when present in an 45 although from about 10 to about 15 parts per hundred amount less than about 10% by weight, and if used in a parts CPVC resin (phr) are required. PVC, vinyl chlogreater amount than 10% adversely affect the high ride, vinyl chloride-vinylidene chloride copolymers and temperature stiffness of the resin. Elastomer additives other vinyl or vinylidene chloride based polymers do commonly used as conventional impact modifiers are not produce enough improvement in processability to graft copolymers containing butadiene, and other co- 50 offset the loss of other physical properties, particularly polymers including chlorinated polyethylene (CPE), HDT. Acrylates such as polymethylmethacrylate ethylene-vinyl acetate copolymers (EVA), acrylate- (PMMA) improve processability but do not contribute methacrylate (all acrylic) polymers, grafted elastomers an appreciable improvement in impact strength, based on vinyl chloride (VCG), nitrile rubbers (BR), Of course, because conventional impact modifiers are styrene-butadiene rubbers, and the like. These conven- 55 rubbery polymers, it is evident that relatively large tional impact modifiers are generally used in a substan- amounts of an impact modifier, greater than about 10% tial amount, that is, an amount sufficient to provide at by wt of the total resinous components in the composileast a 20% increase in Izod impact strength over a tion, will have a beneficial effect upon the processability non-impact modified CPVC matrix. When any of the of CPVC which, by itself, is so difficult to process. At foregoing conventional impact moifiers, with the excep- 60 levels lower than about 10% by wt, conventional imtion of CPE, is used, it is essential that a processing aid pact modifiers exhibit little, if any, improvement in be blended into the CPVC composition. processability, and sometimes even increase the melt
A processing aid is used in melt blending a resin com- elasticity. Some like ethylene-propylene rubber (EPR),
position to hasten fusion, to smooth out the otherwise show incompatibility with CPVC at levels below 10%
rough texture of the composition and to soften the resin 65 by wt.
so that it is uniformly melt-blended within an accept- It is reasonable to expect that a desirable pro-modifier
ably short time. Easily melt-blended materials such as should have certain solubility characteristics compati
acrylonitrile-butadiene-styrene resins do not require a bly matched to CPVC. Having decided upon the solu
