Plasticizers, as polymer additives, have been known for more than a century. Most high volume plasticizers have been developed in the last seventy years, primarily for use with vinyl and other polymeric substances. Plasticizers are used more than any other type of polymer additives, particularly in polyvinyl chloride (PVC) applications, such as plastisols; however, a wide variety of applications for plasticizer use are well known. Hundreds of plasticizers have been produced, but only a few remain having acceptable performance properties when combined with vinyl or other polymeric materials.
General purpose phthalates dominate the volume of plasticizers purchased every year and are most often selected for compounding flexible vinyl.
A typical plasticizer is defined as an organic liquid that will soften a polymer and make it more workable, as long as the polymer and plasticizer are at least partially compatible. Generally, plasticizers are used to adjust hardness (or softness) of a polymer, alter tensile properties (such as strength, elongation or flexibility) and to facilitate processability, as required, for a multitude of applications, including without limitation flexible vinyl applications.
Plasticizers serve as a vehicle for the dispersion of resin (polymer) particles, such as PVC in a plastisol. The dispersion is initially a two-phase, heterogeneous system. Plasticizers promote the formation of homogeneous systems and polymer fusion occurs upon heating. The higher the solvating power, the lower the temperature at which the system is fused, which, in turn, decreases the residence time and increases the speed at which polymeric compositions can be processed into an end product, resulting in a faster, more efficient and economical process.
In adhesives, plasticizers are used as additives to modify physical properties of the adhesive and the polymer film formed by the dried adhesive. Plasticizers facilitate the formation of an adhesive bond and prevent failure of the bond after aging. Plasticizers soften the polymer and add flexibility to the adhesive bond, without adversely affecting the degree of adhesion, lower the glass transition temperature (Tg) of the adhesive film making the polymer more flexible and the glue more efficient, and enhance film formation by lowering the minimum film formation temperature (MFFT).
In all applications, a plasticizer must be at least partially compatible with the base polymer. Compatibility is an important requirement for the selection of a plasticizer. Plasticizers should also possess chemical stability, low toxicity and low volatility. Finally, plasticizers should also be economically feasible.
Plasticizers are available in a wide variety of alternative chemistries and include: 1) general purpose, 2) specialty types and 3) secondary and diluent types, more fully described herein. Plasticizers are also distinguished based on their ability to solvate dispersed solid polymers and/or their gelation and fusion temperatures in plastisols. Gelation and fusion temperatures dictate the speed of production and are influenced by the solvating power of the plasticizer. By way of example only, the gelation and fusion temperatures of a plastisol containing a dibenzoate plasticizer will be lower than a plastisol containing a general purpose phthalate, thus enabling speed of processing in that particular application.
General purpose plasticizers provide an excellent compromise between performance characteristics and economy for most applications. Some examples include: bis (2-ethylhexyl phthalate) (DEHP or DOP), diisononyl phthalate (DINP), dioctyl phthalate (DnOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT), and diisononyl-1, 2 cyclohexane dicarboxylate (DIDC, BASF's Hexamoll® DINCH®).
Environmental scrutiny has led to the development of “next generation” general purpose non-phthalate plasticizers, such as DOTP and DIDC. Even though DOTP, chemically, is a phthalate, it is not an orthophthalate, the use of which is subject to increasing regulatory pressure. These “next generation” phthalate alternatives are viable; however, they do not always give the performance desired in vinyl compositions, particularly in plastisols (i.e., they have poorer compatibility resulting in slower speed, higher gel temperatures, lower gel strength). Blends of plasticizers can be used to adjust performance, although there may be some limits to this approach.
Some applications, however, require performance that cannot be achieved by use of a general purpose plasticizer alone. Applications that require better resistance to oils and solvents are one such example. General purpose phthalates are easily extracted by nonpolar solvents such as hexanes, such that alternative plasticizers would be a much better choice. There is also a need for plasticizers that are higher solvators for PVC and other polymer applications. These high solvators should also have a favorable rheology profile.
Specialty type plasticizers were developed, in part, to fulfill the need for high solvators, the most popular being lower molecular weight phthalates. An example of such a plasticizer is butyl benzyl phthalate (BBP), which is often employed as a high solvating plasticizer. Di-n-butyl phthalate (DBP) and diisobutyl phthalate (DIBP) are also useful high solvator, specialty type plasticizers. Examples of non-phthalate, high solvating plasticizers include dibenzoate esters, some citric acid esters, alkyl sulfonic acid esters, and certain phosphates. Dibutyl terephthalate (DBTP) and N-alkyl pyrrolidones have also been proposed as specialty type, high solvator plasticizers. Most high solvating plasticizers are limited in their usefulness due to high viscosity or poor rheology characteristics. An ideal plasticizer possesses a good balance between solvation and rheology characteristics.
Benzoate plasticizers include dibenzoates and monobenzoates, such as diethylene glycol dibenzoate (DEGDB) and dipropylene glycol dibenzoate (DPGDB) esters that have been used in a wide variety of polymer applications, including in the vinyl industry. DEGDB is an excellent plasticizer, but due to its high freeze point, blends with DPGDB were also developed to capitalize on the utility of DEGDB. Several years ago a blend of DEGDB, DPGDB and triethylene glycol dibenzoates (TEGDB) was introduced as a high solvating dibenzoate blend. More recently, a new dibenzoate triblend was introduced as a plasticizer/coalescent for use in plastisols, adhesives, architectural paint and coatings, and polishes, among other applications. This triblend, comprising DEGDB, DPGDB and 1, 2-propylene glycol dibenzoate (PGDB) in various ratios and sold as K-FLEX® 975P, has been found to be very versatile for a variety of applications, based on its broad range of compatibilities with polymers. The triblend possesses good solvating properties for polyvinyl chloride applications. Its performance properties compare favorably to traditional high solvating phthalate plasticizers as well as traditional benzoate ester plasticizers. Suitable applications include: plastisols, including without limitation PVC and acrylic-based plastisols; adhesives, including without limitation polyvinyl acetate and vinyl acetate ethylene; caulks and sealants, including without limitation polysulfides); and coatings, including without limitation vinyl acrylic, acrylic and styrene acrylic types.
Monobenzoate esters known to be useful as plasticizers include: isodecyl benzoate, isononyl benzoate, and 2-ethylhexyl benzoate. For example, isodecyl benzoate has been described as a useful coalescent for paint compositions and for use in the preparation of plastisols in U.S. Pat. No. 5,236,987 to Arendt. The use of isodecyl benzoate has also been described in U.S. Pat. No. 7,629,413 to Godwin et al. as a useful secondary plasticizer in combination with phthalate plasticizers to provide lower viscosity and lower volatility in PVC plastisols. The use of 2-ethylhexyl benzoate in a blend with DEGDB and diethylene glycol monobenzoate is described in U.S. Pat. No. 6,689,830 to Arendt et al. The use of isononyl esters of benzoic acid as film-forming agents in compositions such as emulsion paints, mortars, plasters, adhesives, and varnishes is described in U.S. Pat. No. 7,638,568 to Grass et al. More recently, as described in WO 2013/123127, WO 2013/123149, and WO 2013/123188, it has been discovered that the monobenzoate, 3-phenylpropyl benzoate (3-PPB), which had not heretofore been used in polymeric applications of the type discussed herein, is a surprisingly effective plasticizer alone or in blends for polymeric applications.
“Half ester” monobenzoates include dipropylene glycol monobenzoate and diethylene glycol monobenzoate, which are byproducts of the production of dibenzoates, but which, most of the time, are not objects of production. Half esters are not known for being high solvators, although they may be used in conjunction therewith. Half esters are also not as useful in PVC as dibenzoate plasticizers, because they are less compatible than the corresponding dibenzoate with PVC. However, the half esters are compatible with emulsions polymers, such as acrylic and/or vinyl ester polymers.
Examples of secondary and diluent type plasticizers, used primarily to reduce plastisol viscosity, include those based on castor oil and soybean oil. Isodecyl benzoate, a monobenzoate, is also a useful diluent type plasticizer.
All of the high solvator plasticizers (regardless of type) add value to vinyl compositions that traditional general purpose plasticizers cannot. Traditional general purpose plasticizers have good rheology profiles and are compatible with many polymers, but have poor solvating ability. Moreover, many of the high solvator plasticizers are phthalates, for which safer alternatives are being sought.
There remains a need for non-phthalate, low VOC plasticizers for use in polymeric applications, such as plastisols, adhesives, paints and other coatings, as alternatives to traditional primary and secondary diluent plasticizers. These alternatives should be compatible with a wide variety of polymers and have lower VOC content and comparable or better performance properties, when used in polymer applications, such as vinyl, traditionally requiring plasticizers. Non-phthalate, low VOC alternatives are particularly desirable in view of environmental, health and safety issues associated with many of the traditional diluent type plasticizers.
It has been discovered that certain analogs of 3-PPB are surprisingly effective plasticizer alternatives for use in polymeric applications, including but not limited to plastisols, paints and other coatings, adhesives, OPV's and inks, and provide improved performance over 3-PPB alone. These analogs are derived from alcohols not traditionally used in industrial applications, but rather in the flavor and fragrance field. Advantages of these monobenzoate analogs versus conventional plasticizers are their performance and handling properties, which are better than most dibenzoates and monobenzoates previously used, including comparable or better viscosity, rheology and solvating properties, improved viscosity stability over time and lower cost. A significant, unexpected advantage is gained in viscosity control, with no sacrifice of solvating properties, as compared to traditional plasticizers, including the benzoates.
The monobenzoate analogs of the invention include compounds that are structurally similar to 3-PPB. One of the inventive monobenzoate analogs, 2-methyl-3-phenylpropyl benzoate (HMCA benzoate) is not commercially available and has not been used in polymeric applications of the type discussed herein. Other inventive analogs include 2-phenylethyl 2-phenylacetate, commonly used in the fragrance industry, benzyl 3-phenylpropanoate, and benzyl 2-methyl-3-phenylpropanoate. None of these analogs have been used in polymeric applications of the type herein described.
While this invention is focused on the use of the inventive analogs as plasticizers in plastisol compositions and adhesives, other applications include a variety of coatings, including without limitation overprint varnishes, polishes, inks, paints, sealants, and caulk. In addition, the inventive analogs are useful as secondary plasticizers or diluents when blended with other traditional plasticizers.
It is an object of the invention to provide plasticizers having excellent compatibility with a wide variety of polymers and other plasticizers, lower VOC content than traditional diluent type plasticizers used to control plastisol viscosities, and improved viscosity stability, for use alone or in blends with other plasticizers, in plastisols and other polymeric applications where plasticizers are traditionally required and used.
It is a further object of the invention to provide non-phthalate alternative plasticizers for use as a primary or secondary plasticizer in PVC applications.
It is also an object of the invention to provide alternative, non-phthalate plasticizers having excellent compatibility with a wide variety of polymers, with improved handling and a superior toxicological profile over traditional plasticizers, for use alone or in combination with other plasticizers in adhesive applications.
Another object of the invention is to provide alternative, non-phthalate plasticizers for use in adhesives, which achieve comparable or better performance properties over traditional plasticizers, including but not limited to viscosity response, Tg suppression, set time, and open times, minimum film formation temperature (MFFT), among other properties.
Still another object of the invention is to provide plastisols, waterborne or non-aqueous adhesive compositions, and other polymeric compositions comprising the inventive monobenzoate analogs, which have comparable or better properties than compositions utilizing traditional plasticizers.
Yet another object of the invention is to provide non-phthalate plasticizers that have high solvating properties and/or good rheology profiles, which are useful as specialty blending plasticizers to improve the compatibility and processability of poor solvating plasticizers, while minimizing the attendant disadvantages of high viscosity and poor rheology associated with the use of traditional high solvating plasticizers.
Still a further object of the invention is to provide plasticizer blends comprising the inventive monobenzoate analogs of the invention.
Finally, another object of the invention is to provide a plastisol formulation utilizing the inventive non-phthalate plasticizers, which allows faster processing and economic efficiencies to be achieved and provides comparable or better tensile strength properties over traditional diluent type plasticizers.
Other objects of the invention will be apparent from the description herein.