Low volatile organic component polyurethane varnish

Details Low volatile organic component polyurethane varnish Low volatile organic component polyurethane varnish

1998-07-27

2001-01-16

Mulcahy, Peter D. (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...

C524S197000

Reexamination Certificate

active

06174947

ABSTRACT:

The present invention relates to polymeric vehicles and curable coating compositions for application on surfaces. In particular this invention provides a solution to the problem of preparing such polymeric vehicles and coating compositions having a low content of volatile organic components. The resulting coatings are varnishes having excellent properties of hardness, flexibility and clarity.
BACKGROUND OF THE INVENTION
Finishes for various surfaces have been practiced widely in the field. They are based on a wide range resins, and intended for application on different surfaces.
Liquid polymers based on copolymerizing 1,3-pentadiene and 1,3-butadiene in the presence of a Friedel-Crafts catalyst were used to prepare coatings or coatings with the aid of curing agents which may be peroxides or a metal agent such as cobalt naphthenate and lead naphthenate (U.S. Pat. No. 3,942,997). The coatings are usable as paint compositions.
Curing, or crosslinking, of polymers such as oil-modified alkyd resins in the presence of oxygen is accelerated by photosensitizers such as benzil, 1-naphthil and similar compounds (U.S. Pat. No. 3,998,979). The photosensitizers replace the use of metallic driers such as cobalt naphthenate or lead naphthenate. The unsaturated oil-modified alkyd resins have incorporated into their structure moieties derived from oils such as linseed oil, tung oil, and other oils. These compositions cure in the presence of sunlight as a consequence of the incorporation of the photosensitizers. Examples provide full gloss white paints based on soya bean oil alkyd, phthalic anhydride, and pentaerythritol, using a solvent of white spirit.
A solvent-free resinous composition was developed that produces little odor or is odor free (U.S. Pat. No. 4,104,215). The composition is a varnish disclosed as having excellent electrical and mechanical properties in shaped articles. It is obtained by reacting a glycidyl ester of a fatty acid with acrylic acid or methacrylic acid at high temperatures, and combining with an acrylic-modified polybutadiene, or an unsaturated polyester resin. Curing agents such as peroxides, and accelerators such as conventional metal naphthenates or octoates optionally used in low proportions are also disclosed.
A curable resin composition disclosed in U.S. Pat. No. 4,403,073 is based on combining a polyfunctional cyanate bearing compound with a polymeric material chosen from polybutadiene, or reaction products of polybutadiene and compound selected from the group consisting of isocyanates, acrylates and unsaturated acid anyhydrides, among others. The resulting cured resin is disclosed as having heat resistance, flexural property, elasticity, adhesive force, resistance to impact, chemicals and the like. Uses for this composition include a coating for rust prevention, flame resistance and retardation, electrical insulating material, and as an adhesive.
A solventless curable urethane composition for casting compounds and encapsulating compounds for electric devices such as printed circuit boards is disclosed in U.S. Pat. No. 4,603,188. The composition is based on a polyhydroxyl component, such as an oil which can be castor oil, combined with a polybutadiene based polyol, and a polyisocyanate component. The composition can be cured at room temperature or with heating.
Sealants, coatings and binders based on polyurethanes and/or polyureas are disclosed in U.S. Pat. No. 4,721,754. A polybutadiene having terminal hydroxy groups, and/or a polybutadiene having terminal alkylamino groups, when reacted with polyisocyanates yield the corresponding products. Several diisocyanates and higher polyisocyanates are disclosed as being usable in the resin-forming composition. Optional catalysts include titanium catalysts and stannous octanoate. Elastomer sheets were formed using these compositions.
Compositions for coating concrete or steel surfaces are disclosed in U.S. Pat. No. 5,077,349. Polyisocyanates are reacted with a polyol which is a polybutadiene polyol in compositions containing in addition alkaline earth metal oxides or hydroxides. The latter may be supplied by using Portland cement or blast furnace cement. An example reports a composition that was applied to a concrete surface with a trowel.
Corrosion-resistant coatings for surfaces such as steel or plastic based on mono-substituted hydroxyl polybutadienes combined with an isocyanate curing agent are disclosed in U.S. Pat. No. 5,378,761. The monohydroxylated polybutadienes are synthesized with a living polymer reaction using lithium initiators. These are first reacted with isocyanate curing agents, and then the modified resin bearing an isocyanate capping group is blended with epoxy or acrylic resin. This blend is applied to a metal or plastic substrate, and cured for periods of time such as 1 week.
These various compositions and methods fail to address the need for a clear varnish coating for surfaces such as wood, concrete and plastic. They fail to consider the need for polyurethane-forming varnish compositions that minimize the content of volatile organic components, that provide rapid drying and curing times, and that are hard, flexible and not susceptible to loss of clarity.
SUMMARY OF THE INVENTION
An objective with polymeric vehicles and coating compositions used as varnishes on various surfaces is reduction of the content of volatile organic components. This objective is motivated by the recognition that, in the past and potentially in the future, petrochemical shortages militate against the use of organic solvent in great volumes. It is also motivated by the desire to reduce exposure of workers involved in manufacturing the compositions, and of the persons applying the resin composition and of those in the vicinity of the surface being treated, to the potentially harmful effects from the vapors of the volatile organic components (VOCs), and their unpleasant odor. This goal is further motivated by the desire to reduce adding solute vapors to the atmosphere which may contribute to air pollution such as photochemical smog, and which contain or are precursors for greenhouse substances that may contribute to warming of the Earth's atmosphere. Governments have promulgated regulations setting forth guidelines relating to VOCs which may be released to the atmosphere. The U.S. Environmental Protection Agency (EPA) has established guidelines limiting the amount of VOCs released to the atmosphere, which have been adopted or are under consideration for adoption by the various states of the United States. Thus, guidelines such as these are of particular concern to the paint and industrial coating industry which uses organic solvents that volatilize into the atmosphere.
There are several potential difficulties attendant upon reducing the content of volatile organic components in a varnish resin composition. One problem is that the composition may develop a skin at the liquid-air interface upon storage. Such a skin must be removed, for if not, and subsequently blended into the composition, it may be inadvertently applied to the surface with the liquid varnish composition leading to inhomogeneity of the applied finish. An additional concern is that unless a large amount of a volatile organic solvent is added as a thinner, the viscosity of the composition may become too high to allow for ease of application of the varnish on the surface. This relates to application methods such as those using brushes, rollers, or sprayers, for example. In addition, the curing of the resin composition may be adversely affected, leading to coatings that are not hard enough, or that do not retain a smooth surface. Furthermore, the drying time may be inappropriately short or long for the development of coatings with desired properties of hardness and gloss. An additional difficulty may be that the flexibility versus the brittleness of the varnish coating may not have desirable attributes. A still further difficulty arises from the potential for loss of clarity and discoloration of the varnish coating upon aging. In order to achieve the objec

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