Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-12-31
2004-11-16
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S247000, C524S251000, C524S322000, C524S816000
Reexamination Certificate
active
06818698
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention relates generally to the aqueous emulsification of high molecular weight polyolefins using a direct pressure process. In particular, the present invention relates to the aqueous emulsification of functionalized or chemically modified polyolefins that have a molecular weight greater than 10,000 in a one-step direct pressure process. The present invention also relates to the direct application of these high molecular weight functionalized polyolefin emulsions onto glass fibers, either during the glass fiber manufacturing process or at a later stage, to obtain reinforced polypropylene composites with a high mechanical performance.
BACKGROUND OF THE INVENTION
It is known in the art that glass fiber reinforced polymer composites possess higher mechanical properties compared to unreinforced polymer composites, provided that the reinforcement fiber surface is suitably modified by size chemical formulation. Thus, better dimensional stability, tensile strength and modulus, flexural strength and modulus, and impact resistance and creep resistance can be achieved with glass fiber reinforced composites.
Glass fiber reinforced polypropylene (PP) composites have widespread applications in various market sectors such as automotive, household, and other electrical appliances, that require a combination of specific short- and long term mechanical, physical, chemical, aging, and aesthetic properties. These properties play an important role in designing the final composite part. For example, stronger polypropylene composites permit the formation of parts with thinner walls, which helps to improve productivity with reduced cycle time, to reduce the weight of the part, to reduce the materials used to make the part, and to reduce the cost of the part. Improving the strength of composites also helps extend the life of the final part. In view of emerging application demands, the polypropylene composite industry is constantly looking for ways to develop stronger “next generation” polypropylene composites for new market applications and for replacements of other more expensive engineering plastics currently in use.
It is also known in the art that fiber-matrix interface interactions influence many bulk mechanical properties of reinforced composites. Thus, to effectively transfer the applied load from a weaker matrix resin to stronger fibers, it is necessary to improve fiber-matrix interactions, especially in glass fiber reinforced thermoplastic composites. Fiber surface treatment by applying chemical sizing formulations during glass fiber manufacturing to modify the fiber surface and improve fiber-matrix interactions, adhesion, and compatibility in composites has been practiced in the industry.
Various aqueous sizing formulations have been used in the glass fiber industry to maximize the fiber-matrix interactions for polypropylene composites. These sizing formulations include ingredients that collectively form an interphase between glass fibers and the matrix resin. Typically, the sizing formulation includes ingredients such as a film forming resin, a silane, a lubricant, an antistatic agent, and other chemical ingredients. Sizing formulations that include an aqueous emulsion of chemically modified or functionalized polyolefins, such as maleic anhydride grafted polypropylene, have been found to be beneficial.
The maleic anhydride grafted polypropylene ingredient included in most conventional sizing formulations in the form of an aqueous emulsion possesses a very low molecular weight (i.e., a molecular weight 6,000-9,000) and high grafting functionality levels (i.e., 5-10% by weight). The lower molecular weight (i.e., a molecular weight less than 10,000), the lower melt viscosities, and the higher maleic anhydride functionalization of these grafted polypropylenes have enabled their emulsification, such as by “indirect pressure” or “direct pressure” methods, without much difficulty. For example, a low molecular weight polyolefin is typically melted together and mixed with suitable emulsifying agents. An emulsion is then obtained by adding the necessary amount of water.
One example of a low molecular weight grafted polypropylene that is readily available is Epolene E43, a homopolypropylene grafted with maleic anhydride having a weight average molecular weight of approximately 9100. An aqueous emulsion from this grafted polypropylene has been useful in glass fiber sizing applications when it is a major ingredient. However, it is believed that because of the low molecular weight of the grafted polypropylenes, the composites reinforced with glass fibers sized with such low molecular weight grafted polypropylene formulations are not strong enough to meet current application needs. To enhance the lower end properties of such polypropylene composites, it has become common practice to add a high molecular weight functionalized polypropylene in solid form during the compounding stage of the manufacturing process. However, high quantities in solid form must be added to compensate for these lower end properties (e.g., between 2-15% by weight of the matrix resin must be added). Moreover, during the compounding stage, the added high molecular weight grafted polypropylene is dispersed throughout the composite part and is only partially directed towards the fiber surface, which results in a non-optimal use of this generally more expensive grafted solid polypropylene additive.
The aqueous emulsification of such high molecular weight grafted polypropylenes is difficult due to their higher molecular weight, higher melt viscosity, lower melt flow rate (MFR) or melt flow index (MFI), higher hydrophobicity, and relatively lower polarity. The emulsification of isotactic, high molecular weight grafted polypropylene becomes even more difficult due to their higher tendency to crystallize. Thus, it is extremely difficult to derive formulations to successfully achieve an aqueous emulsification of high molecular weight grafted polypropylene.
Various techniques have been disclosed to emulsify high molecular weight functionalized polyolefins. For example, French Patent No. 2,588,263 describes a technique for emulsifying isotactic polyolefins of high molecular weight by dissolving the polymer with heat in an organic solvent that is immiscible in water. Water is then added to dilute the mixture. This process requires the subsequent elimination of the solvent by extraction or by washing and drying. In addition to the burden of having additional steps, the use of organic hydrocarbon solvents creates safety concerns for the chemist emulsifying the polyolefins.
U.S. Pat. No. 4,240,944 describes the co-emulsification of a mixture of a high molecular weight isotactic grafted polypropylene together with a lower molecular weight amorphous grafted polypropylene in a ratio of 1:1 to 1:4 parts by weight along with the base and surfactant and subsequent addition of water to obtain an emulsion. However, in this method, not more than 50% of the isotactic high molecular weight grafted polypropylene can be incorporated into the emulsion. Further, it is believed that fairly large concentrations of lower molecular weight amorphous grafted polypropylene may ultimately be detrimental for composite properties at room temperature and, particularly, at elevated temperature applications.
U.S. Pat. Nos. 5,242,969 and 5,389,440 describe a two-step method of forming a high molecular weight polypropylene aqueous emulsion. In the first step, fluidization, melt mixing, and melt blending of a high molecular weight grafted polypropylene with a sufficient quantity of fatty acid is accomplished in an extruder at high shear and high temperature. The mixture is then cooled and ground. In the second step, the mixture is combined with a base and other ingredients in a pressure reactor. This method is disadvantageous in that it requires two steps, is expensive, and causes the polypropylene resin to experience two thermal cycles, which leads to excessive degradation and deterioration of the
Eckert Inger H.
Egwim Kelechi C.
Gasaway Maria C.
Owens Corning Composites SPRL
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