Vinylite Resins, New Plastic Molding Materials' L K. MERRILL
Vinylite
Dvision, NationalCarbonCo., Inc., Cleveland, Ohio
"VINTLITE" in a registered trade name identifying synthetic thermoplastic resin products of the Carbide and Carbon Chemicals Corp. These products are represented by the conjoint and coporymerisation of vinyl chloride and vinyl acetate produced from basic raw materials of natural gas, salty water, coal, and air. These sources are not subject to violentfluctuationsin either price or availability—points to be considered particularly in these times.
cylinder which combines streamlining of the entire internal construction with balance of cross sectional areas so that the linear velocity of the plasticiied mass is constantly increasing from the point of softening to emission from the nozzle. By means of integral construction the resin mass is heated from two sides at once, eliminating the necessity for superheat. Equally important is the use of chromium plate on the entire internal surface of the
The resins, as a series, range in molecular weight from 6,000 to about 25,000. Those in the lower molecular weight range are softer and of greater plasticity at any given elevated temperature, while the higher molecular weight materials are stiff, hard, and lower in plasticity andflowbehavior. Therefore, a controlled mixture of these different molecular weights permits compounds essentially self-plastidsed and removes the necessity of addition agents to obtain variations inflowbehavior. One of the first obstacles encountered in the injection molding of copolymer vinyl resin was its seeming inherent sensitivity to thermal abuse in any fabricating process. Prolonged exposure to temperatures above 225° F. tended to cause a definite color change in the compound, the end point being definite heat decomposition. By heat stabilisers the heat stability of the resins, as measured on a standardised test of time of immersion in an oil bath at elevated temperatures to the beginning of color change, has been raised from about 180 minutes to around 300. Turning to the heating cylinder itself, we have built heaters of all conventional types and finally developed a heating
hot nones of the cylinder on the basis of the proved fact that certain metals, of which iron is one, tend to catalyse the heat decomposition behavior of copolymer vinyl resin, whereas chromium does not.
1 Abstract of a paper presented at a meeting on New Developments in Molded Plastic* in the Lecture Hall of the Franklin Institute. HtUsdtftphia, Penna.. February 13.
One of many applications of Vinylite resin in the injection molding field. 496
Vinyl resin is unaffected by practically all strengths of all mineral acids including hydrofluoric; sodium and potassium hydroxide; iodine, chlorine, and bromine waters or tinctures; potassium permanganate and dichromate; silver nitrate; hydrogen peroxide; alcohols and polyalcohols; aliphatic hydrocarbons, but not the aromatics; oils, fats, and waxes whether animal, mineral, or vegetable. The resin's other chemical aspect of low moisture absorption means two practical things to the molder. The granular compound's operating behavior is not sensitive to material storage conditions prior to or during use, and the finished parts are not subject to shrinkage, warpage, or distortion by high humidity atmospheric exposure or direct immersion in water. The material is nonflammable because its products of heat decomposition will not support combustion, eliminating usage or storage hasard. Along with good electrical properties common to several thermoplastics, copolymer vinyl resin exhibits the characteristic of extreme rigidity per unit of cross section, as well as high tensile strength. Data in the literature imply a relatively low order of impact strength, and to some extent this is true, especially at high rates of application of the energy of impact. The unplasticised variety exhibits an elongation under strain of less than 2 per cent. Its actual tensile is comparable with the highest of other materials, but it will not deform appreciably below its rupture point. Consequently, when struck at high impact velocities the energy is concentrated, rather than distributed over a larger area as in more elastic materials, and rupture can occur. The magnitude of differences between test results obtained from notched and unnotched specimens illustrates this relative impact strength feature. The shrinkage factor for copolymer vinyl resin between its plastic and its solid phase is about 0.001 inch or less per inch, which may mean that castings which have ejected satisfactorily with high shrinkage material will tend to stick. This condition can be readily compensated for in mold design and the result is a mors accurate reproduction of the mold cavity. With this low shrinkage feature it Is possible to produce injection molded cartings of thicker section without the hazard of shrink andflowmarks. We have already successfully produced solid homogeneous sections up to 0.6875 inch thick. These are some of the reasons for believing this material has a legitimate place in the injection molding field. Practical experience bears this out where some one or more of the distinctive properties have placed the material actually in production in thefieldsof toothbrush handles, combs, novelties, beer scrapers, hair ornaments, etc. In every case there has been some technological justification in the way of chemical resistance,freedomfrom warpage or distortion, rigidity and strength, ae-
NEWS
June 10,1940
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RELATIVE WELD STRENGTH -*
W. F.
WELD SECTION STPENSTH CONTINUOUS SECTION STRENGTH
49 Academy St. Nework, N. J.
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Economic Significance", at ike otdfteation of the new ehwnirnl unejiilining boildiaf for unit operates*. In tne faculty nnd atudeat» on "Rw*irrh« in tlttOi Industry".
