Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2000-03-02
2002-03-19
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyester
Reexamination Certificate
active
06358620
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to chemically resistant thermosetting resin having very low contents of volatile organic components. More particularly, this invention relates to improved unsaturated polyester resins, particularly unsaturated isophthalate polyester resin compositions, which are suitable components for products having low contents of ethylenically unsaturated reactive solvent-monomer. Thermosetting resins of the invention with reduced content of styrene monomer and the improved unsaturated polyesters have demonstrated excellent physical properties and retention of strength and hardness in corrosive environments.
BACKGROUND OF THE INVENTION
A versatile family of thermosetting materials known as unsaturated polyester resins comprise low molecular weight polyester polymers derived from unsaturated dibasic acids and/or anhydrides dissolved in unsaturated vinyl monomers. While dominant uses of unsaturated polyester resins are in conjunction with glass fiber or carbon fiber reinforcement to form laminar composites, unsaturated polyester resins are also used in casting processes, which usually contain high loadings of fillers or mineral aggregate.
Properties of thermosetting materials formed by the step growth esterification of glycols and dibasic acids can be manipulated widely by the choice of coreactant raw materials. Reactivity fundamental to the majority of commercial resins is derived from maleic anhydride as the unsaturated component in the unsaturated polyester, and styrene as dilutent and coreactant monomer. Propylene glycol is the principal glycol used in most compositions, and ortho-phthalic anhydride is the principal dibasic acid incorporated to moderate the reactivity and performance of the final resins. Although phthalic resins find wide application in ambient fabrication processes, isophthalic resins are more widely used in products employing high temperature forming processes.
Substitution of isophthalic acid for phthalic anhydride provides enhanced mechanical and thermal performance and improved resistance to corrosive environments, which are significant properties for a variety of products including underground gasoline storage tanks and large diameter sewer and water pipe.
However, the melting point of the higher molecular weight isophthalic polymer is much higher than ortho-phthalic resins, and blending temperatures in styrene must be increased to avoid freezing the polymer out. Due to the high molecular weight and high viscosity of these isopolyester resins in styrene, larger amounts of styrene are necessary to control viscosity of the blend.
Increasingly stringent policies and regulations for protection of the environment have increased need for thermosetting materials, particularly unsaturated polyester resins, having very low contents of volatile organic components, that is, having very low VOCs (“volatile organic contents”). For example, unsaturated isopolyester resins are desired in laminar composites with glass fiber reinforcement to enhance thermal endurance as well as to produce stronger, more resilient cross-linked plastics that demonstrate improved resistance to chemical attack. Since unsaturated isopolyester resin often makes up a substantial part of the composition as a whole, resin having very low contents of volatile organic components is quite important to achieving very low VOC for the composition as a whole.
However, it has been difficult to achieve desired low VOC in cross-linked plastics employing unsaturated polyester resins, particularly in systems employing a combination of unsaturated isopolyester with styrene as dilutent and coreactant monomer. Removal of styrene from compositions containing isopolyester resins in attempting to achieve a low VOC generally is accompanied by significant drawbacks that include causing viscosity of the resin compositions to increase to a undesirable extent, and/or loss of required physical and corrosion resistant properties.
There is, therefore, a present need for thermosetting resin compositions having low contents of volatile organic components.
It is desirable that improved unsaturated polyester resins, particularly unsaturated isophthalate polyester resin, should be suitable components for products having low contents of ethylenically unsaturated reactive solvent-monomer. For example, unsaturated isopolyester resins, which are desired in laminar composites with glass fiber reinforcement to enhance thermal endurance, should, as well, produce stronger, more resilient cross-linked plastics that demonstrate improved resistance to chemical attack.
Advantageously, such improvements shall be combined in a thermosetting resin with reduced content of styrene monomer which improved composition can demonstrate excellent physical properties, retention of strength, and hardness in corrosive environments
SUMMARY OF THE INVENTION
This invention is directed to overcoming the problems set forth above in order to provide thermosetting resin having low contents of volatile organic components. It is desirable to have an unsaturated polyester resin, particularly unsaturated isophthalate polyester resin composition, which is a suitable component for thermosetting products having low contents of ethylenically unsaturated reactive solvent-monomer, yet has excellent physical properties and retention of strength and hardness in corrosive environments.
Preferably, thermosetting resins of this invention have a Brookfield viscosity of less than about 1500 cps at 25° C., more preferably less than about 1200 cps, and most preferably less than about 1000 cps.
Aspects of this invention include chemically resistant thermosetting resins having low contents of volatile organic components comprising (i) a minor amount by weight of ethylenically unsaturated reactive solvent, (ii) a major amount by weight of unsaturated polyester.
Unsaturated polyester of the invention is produced by a process which comprises (a) condensing dihydric alcohol with at least one dicarboxylic acid and/or anhydride of dicarboxylic acid to form a polymer of esterification having an acid number in a range upward from about 5 mg KOH/g polymer, and (b) reacting the polymer of esterification with an amount of glycidyl methacrylate to form unsaturated polyester having an acid number in a range downward from about 15 mg KOH/g unsaturated polyester. Preferably, the unsaturated polyester has an acid number which is in a range from about 1 to about 15 mg KOH/g of unsaturated polyester, more preferably acid number is in a range from about 1 to about 10, and most preferably acid number of the unsaturated polyester is in a range from about 1 to about 5 mg KOH/g of unsaturated polyester.
Weight ratios of glycidyl methacrylate to the polymer of esterification generally are in a range downward from about 0.005 AN, i.e., the product of 0.005 and the acid number of the polymer of esterification. Preferably, the weight ratio of glycidyl methacrylate to the polymer of esterification is in a range of from about 0.001 AN to about 0.005 AN. More preferably, the weight ratio of glycidyl methacrylate to the polymer of esterification is in a range of from about 0.001 AN to about 0.004 AN, and most preferably, from about 0.001 AN to about 0.003 AN.
Preferably, the polymer of esterification is formed by a process which comprises initially condensing a dihydric alcohol containing from 2 to 10 carbon atoms and an aromatic dicarboxylic acid while distilling off water of condensation to form a melt of polymer having an acid number in a range from about 5 to about 15 mg KOH/g of polymer, and then condensing the polymer with unsaturated dicarboxylic acid and/or anhydride of unsaturated dicarboxylic acid and or anhydride while distilling off water of condensation to form the polymer of esterification having an acid number, AN, in a range upward from about 10 mg KOH/g polymer.
One aspect of this invention is a chemically resistant thermosetting resin, having low contents of volatile organic components comprising (i) about 35 to about 45 parts by weight of ethylenically uns
Fleet James Van
Medema Karen E.
Yokelson Howard B.
Acquah Samuel A.
BP Corporation North America Inc.
Henes James R.
Jerome Frederick S.
Kanady Mary Jo
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