Patent Application
20080021141
The present inventors discovered that replacing butylbenzyl phthalate (BBP) with the dibenzoates of diethylene glycol and dipropylene glycol in a specific plastisol formulation resulted in a 25-fold increase in plastisol viscosity. The resultant plastisol was too viscous for processing using conventional equipment. This viscosity could not be reduced to a processable level using a liquid hydrocarbon mixture traditionally used with plastisols containing BBP as the plasticizer. The hydrocarbon mixture evaluated in both plastisols contained 63 weight percent of aromatic hydrocarbons, 15 percent of mixed aliphatic hydrocarbons and 22 percent of normal paraffinic hydrocarbons.
While exploring possible explanations for the aforementioned unexpectedly large increase in viscosity that occurred when BBP was replaced with a benzoate ester the present inventors discovered that the viscosity of a plastisol comprising a dispersed polymer, a plasticizer and a solvent is directly related to a hitherto undisclosed mathematical relationship between a) the Hildebrand solubility parameter of the polymer and b) the weight average of the Hildebrand solubility parameters of the organic diluent(s), plasticizer and any other liquid ingredients present in the plastisol. It was determined that the difference between a) and b) must be within specified limits to avoid, on the one hand, too high a plastisol viscosity or, on the other hand, the possibility of exudation of liquids from articles formed from the plastisol.
The solubility parameters of many plasticizers, polymers, and liquid organic compounds suitable as diluents for the present plastisols are available in publications or can be calculated from experimental data such as surface tension values using mathematical formulae such as the one developed by Small (Journal of Applied Chemistry, 3, 76-80 (1953)), which is incorporated herein by reference.
The term “about” appears in the definition of the ranges for solubility parameter values in the foregoing description of the present invention because 1) measurements of the physical properties, including surface tension among others, that are used to calculate the solubility parameter values exhibited by the polymer, diluent(s) and other liquid ingredients of the plastisol can vary by as much as ±5 percent or more due to the experimental conditions under which they are measured and 2) the Small's constants used to calculate the solubility parameter values reported herein are only approximations and will vary depending upon the environment of the functional groups on which they are based. Even though the limits that define the present operable ranges of weighted average solubility parameter values of the liquid phase may be approximate, selecting a value within these ranges will enable one skilled in plastisol formulation to prepare of low viscosity plastisols with a minimum of experimentation.
As used herein. the term “plastisol” refers to liquid polymer compositions comprising a particulate form of at least one organic polymer suspended in a liquid medium that includes at least one plasticizer for the polymer and at least one liquid organic compound that functions as a diluent. Plastisols containing a total of more that about five weight percent of one or more of these liquid diluents in addition to the required plasticizers are also referred to as “organosols”.
As used herein, “coating binder” means the polymeric part of the film of the coating after solvent has evaporated.
As used herein, the term “miscible” means a liquid which is dissolved or is soluble in a liquid. “Dissolved” means that the material which is dissolved does not exist in a liquid in particulate form having at least about 5 weight percent particles having diameters greater than about 30 nM which are as measured by dynamic light scattering. “Soluble” means a liquid dissolved in a liquid or a solid dissolved in a liquid.
In addition to imparting a low viscosity to the plastisol, the combinations of liquid ingredients in the present plastisols are sufficiently compatible with the polymer that these liquids will not exude from articles formed from the plastisol.
Any of the known polymers that can be formulated into a plastisol can be used to prepare low viscosity plastisols in accordance with the present invention. The polymers constituting the dispersed phase of the present plastisols include polymers of ethylenically unsaturated organic monomers and mixtures of these monomers that can be prepared by a free radical-initiated emulsion polymerization. Suitable monomers include but are not limited to 1) ethylenically unsaturated halocarbons such as vinyl chloride, 2) ethylenically unsaturated acids such as acrylic and methacrylic acids and esters thereof with alcohols containing up to eight or more carbon atoms, and 3) copolymers of vinyl alcohol with olefins such as ethylene.
Homopolymers and copolymers of vinyl chloride and the homo- and copolymers of esters of acrylic and methacrylic acid are preferred based on their wide range of commercial applicability in plastisols containing esters of benzoic acid as the plasticizer. Vinyl chloride polymers suitable for preparing the present plastisols are classified according to particle size. Dispersion grade resins typically exhibit particle sizes of from 0.5 to about 5 microns, and blending grade resins from about 20 to about 55 microns.
Any of the known organic plasticizers that are liquids at about 25° C. can be used to prepare low viscosity plastisols in accordance with the present invention. Many of these plasticizers are esters of mono- and dicarboxylic acids. A detailed discussion of suitable plasticizers can be found in The Technology of Plasticizers, Edited by J. Kern Sears and Joseph R. Darby, published by John Wiley and Sons (1982), which is incorporated herein by reference.
Plasticizers preferred for use in preparing the low viscosity plastisols of the present invention include but are not limited to:
Monohydric alcohols suitable for preparing esters of phthalic acid contain from 1 to 8 or more carbon atoms in a linear or branched configuration and include but are not limited to methyl, ethyl, propyl, isopropyl, 2-ethylhexyl, isononyl and benzyl alcohols. Dihydric alcohols suitable for preparing esters of benzoic acid include but are not limited to propylene glycol and oligomeric ether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol and 1,3-butanediol.
The benzoate and phthalate plasticizers can be used individually or in mixtures. Suitable mixtures include combinations of ethylene glycol and propylene glycol esters of benzoic acid that form eutectic mixtures with melting points below 25° C. Mixtures of benzoic acid esters derived from the dimeric and/or trimeric glycol ethers of ethylene and propylene glycols are particularly preferred plasticizers for the present plastisol compositions. The solubility parameter values for the preferred benzoic acid plasticizers are typically greater than 10. The solubility parameters of preferred phthalate ester plasticizers such as butyl benzyl phthalate are typically less than 10.
In addition to the plasticizers listed in the preceding section, which can also be referred to as primary plasticizers, the present plastisols can optionally include one or more auxiliary plasticizers which, while not effective plasticizers when used alone, act in combination with primary plasticizers to adjust the viscosity of the plastisol to the desired level. Preferred secondary plasticizers are 1) liquid monobenzoates derived from benzoic acid and a monohydric alcohol such as 2-ethylhexanol, isooctanol or isononanol and 2) liquid monobenzoates of diols, glycols and ethers of glycols containing from 2 to 8 or more carbon atoms, and 3) commercially available esters of diols, such as the mono- and diisobutyrates of 2,2,4-trimethyl-1,3-pentanediol.
The third required component of the present plastisols is at least one organic diluent that is not a solvent for the polymer at the required concentration level. Preferred diluents include hydrocarbons and ketones that are liquids at 25° C. Liquid hydrocarbons are typically supplied as mixtures of aromatic and/or aliphatic hydrocarbons boiling within a specified temperature range.
Mixtures of cycloaliphatic hydrocarbons alone or in combination with linear and branched aliphatic hydrocarbons are suitable diluents for plastisols containing vinyl chloride and at least one glycol ester of benzoic acid as the primary plasticizer. The total concentration of all diluents is typically from about 2 to about 55 percent, preferably from about 10 to 50 percent, based on the total weight of the plasticizer and any other liquid ingredients present in the plastisol.
When present at the desired concentration level the diluent portion of the plastisol contributes to a weight averaged value for the solubility parameters of all liquid ingredients that is within the present ranges of from 0.6 to 1 on either side of the Hildebrand solubility parameter of the polymer, which is 9.6 for PVC.
When the plasticizer is a diester of phthalic acid such as butyl benzyl phthalate, a high solvating plasticizer for vinyl chloride polymers, preferred diluents are mixtures of aromatic hydrocarbons together with straight chain and branched chain alkanes. The Hildebrand solubility parameters for commercially available hydrocarbon mixtures are 8.4 for alkybenzenes and 7.2 for normal paraffinic hydrocarbons.
It should be apparent from the foregoing discussion that the choice of a particular organic liquid or mixture of these liquids as a diluent is based not on the numerical value of the solubility parameter of the diluent alone, but rather on the numerical value of its contribution to the weight averaged Hildebrand solubility parameter exhibited by the combination of liquid ingredients present in the plastisol. This contribution is calculated by multiplying the value of the solubility parameter of the ingredient by its concentration by weight in the mixture.
In addition to the polymer, plasticizer and liquid diluent(s) plastisols may contain additional solid and/or liquid ingredients including but not limited to
Fillers such as calcium carbonate;
Heat stabilizers such as the calcium and barium salts of fatty acids;
Esters of phosphoric acid;
Foaming agents such as azodicarbonamides;
Foaming catalysts such as zinc oxide;
Flame retarding agents;
Surfactants;
UV absorbers; and
Pigments such as titanium dioxide.
The solubility parameters of all liquid ingredients of the plastisol must be determined and these values included in the calculation of the weighted average solubility parameter value for the liquid phase.
The plastisols of the present invention are useful in end-use applications requiring rapid application of a low viscosity plastisol. These applications include but are not limited to 1) coatings that are applied onto metallic or non-metallic surfaces by dipping, spraying or the use of coating rollers and 2) as molding materials. The plastisols are particularly useful for coating on to layers of fabric, particularly those used in the construction of resilient floor coverings and wall coverings, and as spray coatings for metal surfaces. Molding applications include but are not limited to fabrication of shaped articles by techniques referred to as “slush molding”, rotation molding and the use of both closed and open molds.
The following example describes two preferred embodiments of the present plastisol compositions and should not be interpreted as limiting the scope of the invention described in this specification and the accompanying claims. In the accompanying tables the parts of the two polyvinyl chloride resins are by weight. The amounts of all other ingredients of the plastisol are expressed as weights of these ingredients per 100 parts of the combined resins (PHR). Viscosity measurements were performed at 23° C. using 1) a Brookfield model RVT viscometer equipped with a spindle suitable for the viscosity range and rotating at a speed of 20 RPM and 2) an extrusion type rheometer available as model A-120 from Burrell-Severs.
Plastisol compositions with liquid phases exhibiting weight averaged solubility parameters relative to polyvinyl chloride that were within and outside the limits that characterize the compositions of the present invention were prepared by blending to homogeneity the following ingredients:
60 parts of a dispersion grade polyvinyl chloride resin exhibiting an average particle size of from 0.5 to 5 microns. A suitable resin is available as one of the Geon® 170 series from Polyone;
40 parts of a blending grade polyvinyl chloride resin exhibiting an average particle size of from 20 to 55 microns and available as the Geon® 210 series from Polyone.
30 parts of a plasticizer consisting essentially of either butylbenzyl phthalate or a mixture containing 65 weight percent of diethylene glycol dibenzoate and 35 weight percent of dipropylene glycol dibenzoate
10 parts of 2,2,4-trimethyl-1,3-pentanedioldiisobutyrate as an auxiliary diluent and
30 parts of calcium carbonate as a filler.
The diluent for both 1) the plastisol containing BBP as the plasticizer, identified as formulation 1 in the accompanying tables, and 2) the plastisol containing the aforementioned mixture of benzoic acid esters and identified as control formulation A consisted of
18.0 parts of a mixture containing 14.4 parts of alkyl benzenes exhibiting a boiling temperature range of 282 to 301° C. and 3.6 parts of a mixture of normal paraffinic hydrocarbons, exhibiting a typical boiling temperature range of from 222 to 242° C.; and
5 parts of a mixture of aliphatic hydrocarbons exhibiting a typical boiling range of from 249 to 269° C.
The diluent for the plastisol identified as Formulation 2 that contained the same mixture of benzoic acid esters as control formulation A consisted of
a combination of 7.2 parts of mixed cycloaliphatic hydrocarbons and 10.8 parts of a mixed paraffinic hydrocarbons, wherein the mixture exhibits a typical boiling range of from 214 to 230° C.; and
5 parts of a mixture alkanes and cycloalkanes exhibiting a typical boiling range of from 249 to 266° C.
Control formulation A contained the same types and amounts of ingredients as formulation 1 of the present invention, with the exception that mixture of benzoic acid esters of formulation 2 replaced BBP on an equal weight basis.
The viscosities of the three formulations are summarized in Table 2.
The calculated Hildebrand solubility parameters for the individual ingredients and the difference between the weighted average values of the solubility parameters for the liquid phases appear in Table 3.
The data in Table 3 demonstrate that when the difference between a) the weight averaged values of the Hildebrand solubility parameters for all of the liquid ingredients, which included the liquid hydrocarbons, diisobutyrate, and plasticizer and b) the solubility parameter of the polyvinyl chloride are within the present range of 0.6 to 1, as in formulations 1 and 2, the viscosity of the plastisol was in a useful range.
For Control A the difference of 0.54 between the solubility parameter (SP) of PVC and the weighted average of the SP values of the liquids was below the present range, indicating that the combination of liquid ingredients is too compatible with polyvinyl chloride. It appears that the observed substantial increase in plastisol viscosity resulted from swelling of the polymer particles due to this increase in compatibility between polymer and liquid ingredients.
