Patent Application
20080058466
The weight average molecular weight of the present plasticizers is between 1,000 and 5,000 g./mol. The molecular weight of the polymers is controlled by including a total of from 11 to about 22 weight percent of at least one monofunctional carboxylic acid and/or at least one monofunctional alcohol as a chain terminator in the reaction mixture used to prepare the polymer. The chain terminator(s) can be added together with the difunctional reactants or during the polymerization reaction.
The advantages associated with the present molecular weight range and low hydroxyl number relative to higher or lower molecular weights and higher hydroxyl numbers is a combination of efficiency (less plasticizer required to achieve desired properties in a polymer/plasticizer blend), improved processability of this blend, higher surface energy exhibited by films and shaped articles, and the permanence of the plasticizer.
Outside of the present ranges for molecular weight and hydroxyl number at least one of the aforementioned properties is sacrificed. For example, lower molecular weight plasticizers are less permanent, resulting in a more rapid deterioration of the desirable properties imparted by the plasticizer. Higher molecular weight plasticizers may be more permanent than the present group of plasticizers; however this is achieved at a sacrifice of one or more of the other desirable properties that characterize the present group of plasticizers.
The polymeric plasticizers of this invention contain less than about 4 weight percent of molecules with terminal hydroxyl or carboxyl groups.
Terminal hydroxyl groups have been shown to decrease the resistance of the plasticizer to migration and/or extraction in humid environments, while terminal carboxyl groups, while providing desirable lubricity, adversely affect the heat stability of the plasticizer. A combination of terminal carboxyl and hydroxyl groups provides lubricity without sacrificing surface energy. The relative concentrations of the two types of terminal groups will be determined by the properties desired in the plasticized polymer composition.
As previously stated, the hydroxyl number of the present polyesters should preferably not exceed 10 mg. of potassium hydroxide/gram.
The non-reactive terminal groups of the present plasticizers are represented by the formulae R3C(O)— and R4O— wherein R3 and R4 are as previously defined. R3 preferably contains from 12 to 18 carbon atoms and R4 is preferably alkyl containing from 8 to 16 carbon atoms or a phenylalkyl radical such as tolyl. Particularly preferred terminal groups are derived from palmitic acid and hexadecanol. Terminal groups derived from saturated fatty acids impart excellent lubricating properties that allow reduction or elimination of additional lubricants such as stearic acid and heat stabilizers such as barium/zinc and calcium/zinc stearates.
Dihydric alcohols and monomeric glycols suitable for preparing the present plasticizers contain from 3 to 6 carbon atoms. Preferred dihydric alcohols include but are not limited to 1,3- and 1,4-butanediols, neopentyl glycol, 2-methyl-1,3-propanediol and 1,2-propanediol. This preference is based on the compatibility of the resultant plasticizer with a wide variety of organic polymers.
Dicarboxylic acids suitable for preparing the present plasticizers are represented by the formula HO(O)CR2C(O)OH wherein R2 is at least one member selected from the group consisting of linear and branched alkylene radicals containing from 1 to 10 carbon atoms and phenylene. Preferably R2 is linear alkylene and contains from 4 to 6 carbon atoms. Adipic acid is the most preferred dicarboxylic acid, based on the commercial availability of this acid and the properties of the resultant plasticizer.
The polymeric plasticizers of the present invention are prepared using known methods for preparing polyesters. Typically the difunctional and monofunctional reactants together with an esterification catalyst such as hydrated monobutyl tin oxide are combined in a suitable reactor and heated to temperatures of from about 205 to 225° C.
The water formed as a by-product of the esterification reaction is preferably removed by distillation throughout the polymerization. The progress of the polymerization can be monitored by measuring the kinematic viscosity, the hydroxyl number and/or the acid number exhibited by the reaction mixture.
When the desired viscosity, acid number and hydroxyl number have been achieved the polyester is purified. This procedure may include placing the reaction mixture under reduced pressure to remove volatile materials such as unreacted monomers and any solvents used during the polymerization reaction. Typical values for the present polyesters are a kinematic viscosity of from 75 to 80 centistokes, measured at 98.9° C., a hydroxyl number of less than 10 mg. of KOH/gram and an acid number less than 1 mg. of KOH/gram.
Additional purification procedures that can be employed include but are not limited to filtration and bleaching using hydrogen peroxide to react with high boiling colored materials in the final reaction mixture.
Depending upon their molecular weight the present plasticizers can be liquids, solids or semi-solids at 25° C.
Examples of polymers suitable for use with the plasticizers of this invention include but are not limited to homo- and copolymers of vinyl chloride, homo- and copolymers of acrylic and methacrylic acid and esters thereof, polyurethanes, epoxide polymers, and elastomers, including but not limited to neoprene and nitrile rubbers.
The plasticizer typically constitutes from 10 to 50 weight percent, preferably from 15 to 35 weight percent, of the polymer composition. The optimum concentration range will vary depending upon the intended end use application of the polymer composition. This range provides the desired softness of the polymer composition in addition to the benefits of the present class of plasticizers. As used herein, “desired softness level” refers to Shore Hardness of about 50 to about 95, preferably about 75 to about 85.
The desirable combination of properties exhibited by polymer compositions containing the present plasticizers facilitates formation of films, extruded profiles, and moldings and other shaped articles from polymer compositions and the receptivity of these articles to printed and decorative material applied using both aqueous- and organic solvent-based dyes and inks. The films exhibit improved heat stability relative to films prepared using prior art plasticizers.
The present plasticizers are particularly useful for imparting lubricity and excellent processing characteristics of polymer compositions without adversely affecting the surface energy and the receptivity of films formed from these compositions to inks.
The unique combination of properties of films formed from the plasticized polymer compositions of this invention include but are not limited to high surface energy, processability, permanence of the plasticizer, and increased humidity resistance. Some of these desirable properties are described in more detail in the following paragraphs and examples. Commercial applications of the film include but are not limited to decals, packaging, laminates, tapes for various applications, including electrical insulation, and liners for metallic and non-metallic containers of various types, including but not limited to boxes and other types of shipping containers, cans, tanks and swimming pools.
Films and other shaped articles formed from polymers containing the present plasticizers, particularly those terminated with monofunctional alcohols, exhibit higher values of surface energy than have been observed in films using structurally related plasticizers. These values are typically above 34 dynes/cm in an important aspect, about 37 to about 40 dynes/cm. High levels of surface energy facilitate printing of films and other shaped articles, particularly with water-based inks.
Plasticizers wherein at least about 40 percent of the molecules are carboxylic acid terminated are self-lubricating, allowing a reduction in amount of transitory lubricants required in polymer compositions containing these plasticizers. The presence of both acid and alcohol terminal units provides the desirable combination of lubricity with high levels of surface energy. In this aspect, levels of lubricants may be reduced up to about 50% as compared to systems using known plasticizers. Known lubricants and stabilizers used to formulate flexible vinyl compositions include: stearic acid; calcium stearate; polyethylene wax; oxidized polyethylene waxes; montan wax esters; metal soaps (heat stabilizers such as barium stearate); acrylic process aides; organic heat stabilizers; paraffin oil; and amide waxes.
Other improvements in the processability of polymer compositions that can be achieved using the present polymeric plasticizers include but are not limited to 1) an increase in line speed of calandering (an increased temperature processing range for example up to about 345° F.) and extrusion and 2) increased plasticizer efficiency, allowing for a reduction in plasticizer concentration to achieve the same level of plastization.
The following non-limiting examples describe the preparation of preferred plasticizers and the unique combination of properties imparted by these plasticizers to a polymer composition and a film prepared from this compositions. Unless other wise specified all parts and percentages in the examples are by weight and property measurements were conducted at 23° C.
This example describes the preparation of a polyester of this invention.
A 2000 mL-capacity resin kettle was equipped with a mechanical stirrer, heating means, a nitrogen inlet extending below the surface of the reaction mixture, a distillation column, and means for 1) recovering the water produced as a by-product of the esterification reaction and for 2) monitoring the temperatures of the reaction mass, refluxing liquid and vapor.
The reactor was charged with 329 grams (3.65 moles) of 1,3-butanediol, 457 grams
(3.13 moles) of adipic acid, 214 grams (0.83 mole) of palmitic acid and 0.21 grams
(0.00101 mol) of hydrated monobutyl tin oxide as the polymerization catalyst.
The contents of the reactor were heated to 120° C. to dissolve the solid reactants and the column was heated to a temperature of 90° C. Nitrogen was admitted into the reactor at a rate of approximately 70-100 mL/min and was maintained at this rate throughout the polyesterification reaction. When substantially all of the solid material had dissolved stirring of the reaction mixture was begun at a rate of 300 r.p.m. and the temperature of the reaction mixture was gradually increased to 210° C. over a five-hour period.
The amount of water removed as a by-product of the polyesterification reaction was monitored. During water removal the column temperature was slowly increased to 120° C. at a rate that was dependent upon the rate of water removal.
Five hours after heating of the reaction mixture was begun and at two-hour intervals thereafter samples of the reaction mixture were withdrawn using a syringe for determination of acid number. After 23 hours of heating the acid number had decreased to 6. At this time samples of the reaction mixture were withdrawn for determination of hydroxyl number and kinematic viscosity at 2-hour intervals.
Following a total of 32 hours of heating the polyesterification portion of the reaction was considered complete, at which time the nitrogen flow rate was increased to one liter per minute for about 7 hours. The acid number and kinematic viscosity of the reaction mixture were measured at one-hour intervals and the hydroxyl number was measured every 2 hours. At the end of this 7-hour period the reaction mixture was bleached using an aqueous solution of hydrogen peroxide and filtered. About 871 grams, equivalent to 87% yield, of a polyester was obtained. The polyester was a semi-solid at 25° C. and exhibited a kinematic viscosity of 78 centistokes at 210° F. (98.9° C.), an acid number of 0.8 mg. of KOH/gram of sample, a moisture content of 0.08 percent and an APHA color of 70.
The weight average molecular weight of the polyester, referred to hereinafter as polyester I, was about 3400 g./mole
Two commercially available polyester-type plasticizers were evaluated for comparative purposes. These will be referred to hereinafter as polyesters IIc and IIIc.
Polyester IIc was a commercially available polyester, Palamoll® 1654, manufactured by BASF Chemicals. This polyester exhibited a weight average molecular weight of 5200 g./mole and a hydroxyl number of 4 mg. KOH/gram.
Polyester IIIc was a commercially available polyester, Admex® 6985, manufactured by Velsicol Chemical Corporation. This polyester exhibited a weight average molecular weight of 7000 g./mole and a hydroxyl number greater that 15 mg. KOH/gram.
This example demonstrates the improvements in processability and film properties of three polymer compositions containing three different plasticizers of this invention prepared as described in the preceding example. The properties are compared with those exhibited by a film prepared using the same polymer but with a plasticizer that is outside the scope of the present invention.
The films were prepared by blending 30, 40 or 50 parts by weight of the polyester to be evaluated example with 100 parts by weight of a suspension grade of polyvinyl chloride using a two-roll mill operating at a temperature of 320° F. (160° C.). The milling time was 8 minutes.
The resultant milled sheet was converted to a film exhibiting a thickness of from 0.003 to 0.004 inch (0.076 to 0.1 mm.) by pressing the milled sheet for 10 minutes under a pressure of 200 p.s.i. (14.06 kg./cm2).
The properties listed in Table 1 were evaluated using the following ASTM test methods:
Preparation of Milled Flexible PVC—ASTM method: D3596
Preparation of Compression Molded Plaques—ASTM method: D4703
Plasticizer Compatibility in PVC Compounds under Humid Conditions—ASTM method: D2383-69
Oven Heat Stability of PVC Compositions—ASTM method: D2115-92
Fusion of PVC Compounds Using a Torque Rheometer—ASTM method: D2538-95
Shore Hardness—ASTM method: D2240
