Adhesive Consisting Essentially of an Isocyanate Terminated Ricinoleate Prepolymer and a Chlorinated Polyvinyl Chloride

Ricinoleate derived urethane adhesives that cure by reaction of the isocyanate groups with compositions having reactive hydrogens such as water, amines, urethanes, ureas, polyols and the like are well-known in the art. While these adhesives exhibit excellent adhesion, water resistance and flexibility after curing, they are deficient in green strength before curing for many applications. "Green strength" as used herein means the ability to hold two surfaces together when first contacted and before the adhesive develops its ultimate bonding properties when fully cured.

The degree of green strength exhibited by an adhesive is vital to many applications. High green strength tends to prevent wrinkling and slippage of films during laminations. In panel assembly and packaging it permits faster handling and wrapping. When adhesive is applied to a vertical surface, a sufficiently high green strength prevents a mechanically unsupported, bonded member from slipping under the influence of gravity. When employed for flocking, high green strength holds the fibers in place while the adhesive cures and in the laying of carpet or synthetic flooring, it resists curling due to the shape memory thereof acquired when stored in a roll.

Attempts to increase the green strength of isocyanate terminated ricinoleate prepolymers by adding other high polymers such as polyvinyl acetate, cellulose acetate butyrate, acrylics, polyketones, phenoxy and polyvinylchloride-vinyl acetate copolymers have proven unsuccessful.

Chlorinated polyvinyl chloride (CPVC) is known for its excellent adhesion to rigid polyvinyl chloride and other rigid plastics, high tensile strength and inherent flexibility but not as a product known to impart green strength in adhesives as claimed in the present invention.

In accordance with the present invention, the use of chlorinated polyvinyl chloride with an isocyanate terminated ricinoleate prepolymer produces new and unexpected results including coverting the prepolymer from one that has little tack to one that is tenacious. Since the tenacity occurs before the composition cures, it is referred to as green strength. Additionally, the aforesaid prepolymers with chlorinated polyvinyl chloride exhibit the quick grab properties of contact type adhesives when applied to only one substrate instead of both, improved adhesion to certain substrates, improved water resistance and hydrolytic stability and improved film forming properties.

The aforesaid advantages are achieved only with a ricinoleate derived prepolymer, the increase in green strength not being noted when using prepolymers not derived from ricinoleate polyols. Such non-ricinoleate derived prepolymers are either incompatible with chlorinated polyvinyl chloride or, when compatible, exhibit quicker tack-free dry without improved green strength.

While high green strength makes the compositions of this invention particularly well suited for adhesives, the compositions also have utility as a coating. Isocyanate terminated urethanes that cure are often used interchangeably as both coatings and adhesives. A coating can be looked upon as a one-substrate adhesive and an adhesive as a two-sided coating. The preferred type of urethane sealers, primers and topcoats for floors are those which develop sufficient hardness quickly so that they can accept traffic. This minimizes shutdown time whether it be a new construction site or an operating office, factory and other site. As used herein, the term "adhesive" is intended to include such coatings or other uses to which the claimed compositions may be put.

A curable adhesive composition consisting essentially of an isocyanate terminated ricinoleate prepolymer with an available isocyanate content, exclusive of solvent and expressed as 100% solids, at least as high as 2% by weight, and a chlorinated polyvinyl chloride appearing in quantities no more than approximately 90% by weight of the mixture of the chlorinated polyvinyl chloride and said prepolymer.

The aforesaid objects and advantages may be achieved from a mixture of a chlorinated polyvinyl chloride and an isocyanate terminated ricinoleate prepolymer. The isocyanate groups are free to react with water, polyols, amines, urethanes, ureas and the like to form a cured adhesive.

The chlorinated polyvinyl chloride may be made by post chlorinating polyvinyl chloride resin. Merely by way of example, the following chlorinated polyvinyl chlorides may be employed in this invention: GENCLOR S, GENCLOR T manufactured by Imperial Chemical Industries Ltd, London, England and marketed in the USA by ICI United States, Inc., Wilmington, Del. and GEON 625X560, GEON 623X560 manufactured by B. F. Goodrich Chemical Group, Cleveland, Ohio.

The chlorinated polyvinyl chloride content by weight should be not more than approximately 90% of the chlorinated polyvinyl chloride and ricinoleate prepolymer combined. This percentage excludes changes which result from adding reactive and non-reactive modifiers such as plasticizers, solvents, fillers, etc.

The isocyanate terminated ricinoleate prepolymer of this invention is made by reacting an isocyanate having an average functionality of 2 or greater with a ricinoleate polyol having an average hydroxyl functionality of 2 or greater. The polyol is reacted with an excess of isocyanate so that the available or residual isocyanate content of the finished prepolymer, excluding solvent and expressed as 100% solids, should be at least approximately 2% by weight.

Both aromatic and aliphatic polyisocyanates can be used to react with the ricinoleate polyol when making the isocyanate terminated ricinoleate prepolymer of this invention. The preferred polyisocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Illustrative of other suitable polyisocyanates are the following: isophorone diisocyanate (IPDI), 4,4',4" triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, m-phenylene, 1-chlorophenylene 2,4 diisocyanates, methylene-bis (4-cyclohexylisocyanate), or an equivalent. The methods of preparation of the above prepolymers are well known in the art and need no further explanation.

The ricinoleate polyols that can be used to react with the polyisocyanates to make the prepolymers of this invention are diol, triol, or higher polyhydric alcohol esters of ricinoleic acid. The preferred ricinoleate polyol is castor oil which is composed mostly of the triglyceride of ricinoleic acid. Illustrative of other ricinoleate (castor oil) derived polyols which may be used to obtain the ricinoleate urethane prepolymer are the following: glycerol monoricinoleate, glycerol diricinoleate, propylene glycol monoricinoleate, dipropylene glycol monoricinoleate, ethyleneglycol monoricinoleate, polyethyleneglycol monoricinoleate, pentaerythritol monoricinoleate or an equivalent. The methods of preparation of the above polyols are well known in the art and need no further explanation.

The chlorinated polyvinyl chloride may be combined with the isocyanate terminated ricinoleate prepolymer by several methods. Merely by way of illustration and without limiting the scope of the claims hereof, some of the methods are: (a) The chlorinated polyvinyl chloride is dissolved in components used in the prepolymer manufacturing prior to or during the reaction process; (b) the chlorinated polyvinyl chloride is dissolved in the finished prepolymer; (c) the chlorinated polyvinyl chloride is added to the prepolymer as a solution of the chlorinated polyvinyl chloride dissolved in solvent, or dissolved in a non-reactive resin or in non-reactive plasticizer or combination of the same; (d) the chlorinated polyvinyl chloride could be added to the prepolymer dissolved in reactive materials such as polyols, amines or other solutions that react with isocyanate terminated ricinoleate prepolymers.

When combining by methods (a), (b) and (c) above, the composition of the isocyanate terminated ricinoleate prepolymer/chlorinated polyvinyl chloride mixture could be used as either a one package moisture cured urethane or as the isocyanate part of a two package urethane in which the other part is a reactive polyol, amine, or other material that reacts with isocyanate terminated ricinoleate prepolymers. In (d) the chlorinated polyvinyl chloride would be the part of a two package urethane that reacts with the other part which is the isocyanate terminated ricinoleate prepolymer.

The following examples are illustrative of the adhesives and coatings claimed herein.

This example discloses the formulation, properties, performance, and testing of an adhesive in accordance with the invention claimed herein. The adhesive cures by the reaction of the isocyanate groups on the ricinoleate terminated prepolymer with water from the atmosphere. The mixture is stable for several months and is therefore considered to be a one-package, moisture cured, urethane adhesive.

The prepolymer and chlorinated polyvinyl chloride solution are mixed at the weight ratio shown. Viscosity was determined using a Brookfield Viscometer. The percent solids was determined by calculation.

Performance

The data in Table I illustrates the improvement in green strength between the control and the adhesive of this example.

Test Procedure

The data set forth in Table 1 was determined in the following manner:

(A) Finger Tack--An 8 mil. wet film was cast on glass using a draw down blade. The film was given approximately a five minute open-time to allow the solvent to evaporate. An index finger was pressed into the adhesive; withdrawn slowly; and based on its "feel" was rated as oily or tacky. In the latter case, a material rated as tacky not only had tack but also had a high green strength, legs and grab.

(B) Green Strength (Finger Test)--An 8 mil. wet film was cast on glass using a draw down blade. The film was given approximately five minutes open time in order to allow the solvent to evaporate. The relative green strength was determined subjectively by pressing an index finger into the adhesive and removing it slowly. A green strength rating of 1 or "poor" indicates that little force was necessary to remove one's finger and a rating of 10 or "excellent" means that a very high force was required to pull away from the glass.

(C) Green Strength (Scott Pendulum Type Tensile Tester)--A 5 mil. wet film, 1" wide and 3" long, was cast on an aluminum panel using a draw down blade. After five minutes open time to allow the solvent to evaporate, a piece of natural cotton fabric was pressed in the adhesive and rolled using a 2 lb. weight. The relative green strength of this lamination was determined by immediately placing it in the Scott Pendulum Type Tensile Tester and pulling the aluminum and fabric in opposite directions at the rate of two inches per minute (shear adhesion). The numbers recorded were direct readings from the tester with the lowest numbers being the poorest green strength and the highest numbers being the strongest.

(D) Bond Strength--The solution was applied to two pieces of 1" wide natural cotton fabric using a paint brush. After a five minute open-time to allow the solvent to evaporate, the two coated pieces of fabric were then pressed together like contact cement. After curing, the samples were subjected to a 90.degree. Peel Strength Test using the Scott Pendulum Type Tensile Tester by pulling apart at a rate of about 2 inches/minute. The numbers shown are the direct readings from the tester with the lowest number being the weakest bond and the highest number being the strongest peel strength.

The principal difference between the adhesive formulation of this example and that of Example I is that the isocyanate terminated ricinoleate prepolymer in this example is made by reacting castor oil and toluene diisocyanate whereas the ricinoleate prepolymer in Example I was made from reacting castor oil and diphenylmethane diisocyanate. The test procedures were the same as employed in Example I.

Performance

The data in Table II shows the improvement in green strength between the control and the adhesive of this example.

The principal difference between the formulation of this example and that of Example I is that this example illustrates a two package coating in which the chlorinated polyvinyl chloride is first combined with the polyol whereas Example I illustrates a one package adhesive.

Performance

The data in Table III illustrates the rapid development of hardness and toughness between the control and the coating of this example.

The principal difference between the coating of this example and that of Example III is that this illustrates a one package, moisture-cure urethane whereas Example III illustrates a two package urethane which cures by the reaction of hydroxyl groups on the polyol with isocyanate groups on the ricinoleate prepolymer.

Performance

The data in Table IV shows the rapid development of hardness for the coating of this invention as compared to the control.

The principal difference between the coating of this example and that of Example IV is the isocyanate terminated ricinoleate prepolymer which is aliphatic and prepared from glycerol monoricinoleate whereas in Example IV the prepolymer is aromatic and prepared from castor oil.

Performance

The data in Table V illustrates the difference in hardness and toughness between the coating of the control and that of this example.

The principal difference between the two package system of this example and that of Example III is that the chlorinated polyvinyl chloride in this example is included with the prepolymer whereas in Example III it is mixed with the polyol.

Performance

The data in Table VI illustrates the improvement in green strength between the control and the adhesive of this example.

The principal difference between the coatings of this example and that of Example IV is that the chlorinated polyvinyl chlorides of this example are from another manufacturer.

Performance

The data in Table VII shows the rapid development of hardness for the coating of this invention as compared to the control.

It will be understood by those skilled in the art that many modifications and variations of the present invention may be made without departing from the spirit and the scope thereof.