The process of producing a quality floor
coating that shines brilliantly, or stands
up to the most rigorous traffic, is an
interesting event. To give you an idea
of the complexities of producing a high
quality polymer formulation and how it
works is described in the "White Paper" below.
The Birth Of A Floor Polish Film
It's a product that is by and large taken completely for granted by the thousands of people who walk on it, track dirt on it, scuff it with every imaginable type of heel and wheel, and occasionally admire it, perhaps subconsciously, for its crisp, clear shine.
And yet, to the handful of "insiders" involved in its manufacture and sale who know first hand the ever-broadening spectrum of performance requirements it is expected to meet, the product represents a Herculean achievement in the fields of chemistry and engineering.
The actions and reactions that take place from the moment a coat of polish is applied, to the point at which it becomes a film no thicker than two-tenths of a millimeter, are to us as intriguing as they are challenging. Moreover, they are important and well worth understanding by anyone charged with the responsibility of making or selling this singular product.
As shown in Table I, water is by far the most common component in a floor polish formulation, amounting to approximately 80% of the total weight of a floor polish as it is manufactured. Water, then is the continuous medium that allows all the active components to form a stable mixture until the wet polish is applied to a floor and the complex process of drying occurs. Simply put, the drying process is the evaporation of water and other volatile components and the formation of a film. When the drying process is studied on a microscopic scale, it is recognized that the birth of the floor polish film is not only very complex, but also a most important event in the life of the polish. If improperly born, the polish film cannot be expected to perform effectively.
The Influence of Materials
Figure IIA shows the wet polish film that has just been applied to a flooring substrate. The wet film is approximately 1 mm thick and contains all the various components listed in Table 1.
The polymer, which is the predominant active component, accounts for 60-80% of the material in the dry film. Therefore its effect on the performance of the polish is very important. Referring to Figure IIA, the polymer in the wet polish consists of spherical emulsion particles ranging in size from 0.1 to 0.5 microns. These are depicted as orange spheres. The emulsion particles are stabilized with anionic and nonionic surfactants shown as short bristles surrounding the particle (see Figure IIB). Inside the particles are the polymer molecules composed of acrylate, methacrylate, and styrene monomers that have been polymerized to a molecular weight that in some cases exceed over 1 million. The particles may also contain some low molecular weight material, sometimes called oligomers. A model of a polymer chain segment comprised of about five methacrylate molecules is shown in Figure I. The molecular structure of these polymers is very random or amorphous and resembles several strands of rigid fibers formed into a ball. Associated with most polymer emulsions are multivalent metal complexes that serve to crosslink the polymer during the final stages of the drying process by reacting with pendant carboxylic acid groups that are part of the polymer molecule. These metal complexes are represented by the x's in Figure IIA.
The polyethylene or wax emulsion particles are another important component of a floor polish. These are depicted as black spheres (see Figure IIA and IIC) that contain some parallel lines denoting crystallinity or a certain order in how the individual molecules associate. A wide variety of synthetic and natural waxes have been used in floor polish; however, the most popular types are oxidized polyethylenes and polyethylene copolymers. These generally have a molecular weight of 1000 to 5000 and varying degrees of crystallinity. Due to their physical properties these tiny black spheres impart the important characteristics of buffability and scuff resistance to a floor polish.
The next material appearing on Table I is the alkali-soluble resin (ASR). ASR's (gold strands in Figure IIA) have generally low molecular weight of about 500 to 2000 and sufficiently high acid numbers of 150 to 250 to permit solubility in water and ammonia or other alkalis. Resins are used to enhance gloss, leveling and, by virtue of their alkali-solubility, removability. As Table I indicates, an ASR is not a necessary component, although most floor polishes contain some ASR to finely tune a formulation. Generally, there are three types of ASR's used in floor polish: rosin adducts, acrylic resins, and styrene/maleic anhydride resins. More information on these materials is readily available from other sources.
Minor Components Play Major Role
Before discussing plasticizers in detail, we will examine the respective functions of the minor components of the floor polish: defoamers, wetting agents, stabilizers, and biocides. The designation "minor components" may be a little misleading because, albeit small in quantity, these materials can be very important to the proper functioning of a polish.
A silicone emulsion defoamer may be added to a polish at a rate of 0.004%, and is absolutely necessary if a polish is to be applied to the floor without the retention of foam bubbles and an unsightly appearance. Wetting agents, also used in very small quantities, act to reduce surface tension of a polish to 30 dynes/cm or less, and thereby assure improved flow and leveling characteristics. A number of commercially available fluorocarbon surfactants are the most popular wetting and leveling agents used by the floor polish industry. Stabilizers protect the polish during shipping and storage from increases in viscosity or destabilization caused by high temperatures or freezing, thereby enhancing the shelf life stability. This means that polishes stored in hot warehouses or frozen in winter transport do not deteriorate and, when brought back to normal temperatures, can be used without impairment of quality. The use of effective biocides in floor polishes is critical in protecting against the growth of bacteria, fungi, and yeasts. Needless to say, once biocontamination strikes, the effects are most unpleasant as evidenced by the formation of malodors, slime, and coagulation in a polish. Spoiled polishes frequently cannot be salvaged and result in a complete loss.
The Importance of Plasticizers
Plasticizers play a major role in the film formation process of a floor polish. Anyone familiar with compounding of floor polishes knows that, if you try to evaluate a formulation in which the plasticizers have been omitted, you will be very disappointed. A polish without plasticizers may dry to a powder and become a totally useless product. Therefore, the amounts and types of the various plasticizers required to produce an optimized floor polish film are of critical importance. Of course, other factors also affect the film formation process, such as temperature, humidity and nature of the substrate.
Dealing with typical field application requirements, it is often necessary to lay down several coats of polish with no more than 30 minutes drying time between coats. The environmental conditions under which these applications occur may vary widely as follows:
Under extreme conditions of humidity and temperature, the evaporation rate of volatiles can be accelerated or retarded so that optimum film formation will not take place. Likewise a porous substrate may absorb certain components from a coat of wet polish and adversely affect film formation. Fortunately, most field applications are performed under moderate conditions which we will assume is the case in this presentation.
The reason a polish without plasticizers dries to a powder has to do with the chemical composition of the polymer. Polymers used in floor polishes are designed to have Glass Transition Temperatures (Tg) in the range of 50° to 75°C. At its Tg the properties of a polymer change from glass-like and brittle to a flexible and rubbery consistency. Therefore, an emulsion containing a polymer with a Tg of 65°C cannot be expected to form a film at a room temperature of 22°C. A related concept is Minimum Film Formation Temperature (MFT), which is defined as the lowest temperature at which an emulsion polymer or a floor polish will produce a continuous film upon drying. In short, at the MFT and above there is film formation, below the MFT there is discontinuity and powder.
To obtain a better understanding of the concepts of Tg and MFT, let us look briefly at a polymer particle as depicted in Figure IIB. The cutaway of a polymer particle shows several closely packed polymer molecules that are high in molecular weight. Below the Tg, the polymer molecules are so rigid and tightly associated that there is very limited space for molecular movement. However, at their Tg and above, the polymer molecules acquire more kinetic energy creating more free space into which the polymer molecules expand and gain more freedom of movement. This phenomenon can be observed by using a dilatometer to measure the small increase in polymer volume and a corresponding change in the specific gravity. The transition to new physical properties that polymers acquire at and above their Tg allows for the deformation of polymer particles in the drying process and formation of continuous films at the MFT (see Figures IID, IIE, and IIF). Of course, floor polishes are not applied at the Tg (65°C) of a typical polymer, therefore we need plasticizers to promote film formation at room temperature.
Plasticizers - Some Flee, Some Stay
Specifically, plasticizers reduce the MFT of a floor polish, permitting it to be transformed into a tough, durable film while drying at room temperature. There are two types of plasticizers: permanent and fugitive. The fugitive plasticizers are also referred to as coalescents. Both types of plasticizers are required in a balanced floor polish and have a significant effect on the performance of a polish film. Permanent plasticizers (small green and yellow spheres in Figure II) are absorbed completely by the polymer and other solid components upon drying and remain in the film to provide continuing plasticization. Coalescents (red spheres), which volatilize during the drying process, are used to temporarily lower the MFT of a polish during the drying phase. The evaporation rate of the fugitive plasticizers or coalescents must be carefully evaluated, so that proper film formation will be accomplished before the polish has completely dried. If the evaporation rate of the coalescents is too slow, the polish film will remain soft and even tacky after drying.
This will result in recoat problems and dirt pick-up when the floor is exposed to traffic. The most effective coalescents have vapor pressures that fall in the range of 0.1 to 1.0 mm Hg at room temperature.
A permanent plasticizer of special significance in floor polish is tributoxyethyl phosphate (TBEP), represented by the green spheres in Figure II. As a result of its hydrophobicity (solubility in water is 0.2%), TBEP resides on or inside the polymer particles in a wet polish. With a solubility parameter of 8.7 (see Table II), TBEP is predictably a good solvent for acrylate-styrene copolymers, however, it also acts as an effective leveling agent. Speculation is that the leveling activity of TBEP is the result of its molecular structure, which may lead to a specific orientation on the polymer particle surface.
Solubility and Stability
The degree of oil and water solubility (hydrophobic-hydrophilic balance) of a plasticizer system is important, because it can have a significant effect on the stability of a polish in the wet state. Assuming that we have chosen a system with the proper solubility parameters, then we can expect the plasticizers to be readily soluble in the polymer particles. If the plasticizers are mostly hydrophobic, they will quickly solvate and swell the polymer particles, which can lead to agglomeration and coagulation of a polish in the container. The distribution of the plasticizers in the wet polish is difficult to predict theoretically, so stability studies at elevated temperatures are an important part of designing a new polish. One method to improve the wet stability of a polish, is to shift the plasticizer blend towards the hydrophilic side.
The Drying Process
Having discussed the various roles of the components in an industrial floor polish, let us take another look at Figure II and carefully follow the drying and film formation process. The section of vinyl composition tile (Figure IIA) at the bottom has just been coated with a typical polish at a rate of 2000 square feet per gallon. The wet coat is approximately 1 mm thick and contains all the components listed in Table I. Assuming that normal indoor conditions exist, the drying process begins immediately at the proper rate. This is indicated by the blue arrows and the red spheres denoting water and some fugitive plasticizer molecules escaping. However, the water volatilizes much faster than the fugitive plasticizer and after approximately five minutes sufficient water has left the wet film for the polish to begin to solidify. Of course, before solidification sets in, we hope the polish has leveled smoothly and the defoamer (not depicted) has performed its function by eliminating any entrapped air bubbles that might have formed during application.
At this point, the permanent and remaining plasticizer molecules that have resided in the water phase begin to solvate the polymer particles and the other non-volatile materials. If plasticizers with the appropriate solubility parameters have been selected, they will now perform their intended function with ease and render the polymer particles soft and pliable. On the molecular level, the plasticizer molecules have loosened the cohesive forces that were holding the polymer molecules rigidly together. The newly gained mobility of the polymer molecules combined with the enormous capillary pressure deform the polymer particles to assume the conventional hexagonal configuration of close-packing (See Figures IID, IIE and IIF). The polyethylene particles (black), which have a natural Tg below room temperature, have also absorbed some plasticizer and deform with little effort to occupy any available space between the polymer particles.
As the polymer particles come in intimate contact with each other, a certain amount of molecular entanglement will occur depending on the degree of plasticization and molecular weight of the polymer. The lower the molecular weight, the more freely polymer molecules will entangle.
When more water and volatile plasticizers have escaped the film, the metal complexes dissociate and the free multivalent metal ions begin to associate and crosslink with the available acid groups on the polymer and other components. In about 20 minutes, the polish film is dry to the touch and most of the complex process of film formation has taken place.
A small amount of fugitive plasticizers and trapped water still remains in the film, but this does not usually interfere with the application of the next coat in 30 minutes. However, if too many coats of finish are applied in 30-minute intervals, the amount of retained fugitive plasticizer and water may increase so much that trouble-free recoating will not be possible.
A typical floor polish film after complete drying is shown in Figure IIF. The polymer particles have deformed and some molecular entanglement has taken place. The TBEP (green spheres) and the other permanent plasticizers (yellow spheres) are dispersed throughout the film. The polyethylenes and waxes are presented as deformed but distinct black particles and will provide an important degree of lubricity to the polish under foot traffic and buffing maintenance. The multivalent metal ions have tightly crosslinked the film for durability and later will allow removability when the floor is stripped by releasing their hold on the acid groups. The ASR (gold) is randomly distributed throughout the film. In many cases, the resin has helped in the leveling process and now is filling small voids in the polish film resulting in higher gloss.
A thorough knowledge of the intricacies of the film formation process is necessary to produce the very best floor polish formulation, one that is truly "strong to the finish."
COMMON PROBLEMS WHEN USING FLOOR POLISHES
While there is always the possibility of a misformulated batch of polish reaching the end user, improved quality management techniques have greatly reduced the number of errors in production. Experience shows that most problems with floor polish break down into two areas: A) Application, the process of getting the polish onto the floor, and B) Maintenance, the results that occur when inappropriate procedures damage an initially excellent looking floor. These areas will be the focus of our attention.
In this section we refer to conditions that may be observed upon application of polish to a new floor or an existing floor which has been stripped or otherwise prepared for the application of one or more coats of polish.
The most common cause of low initial gloss is improper floor preparation. Inadequate stripping and/or rinsing will leave residue that interferes with the film formation process of the polish, resulting in reduced gloss. The practice of using floor "neutralizers" can leave the floor coated with residual acid, which reacts with the alkaline components in the polish, causing instability and improper film formation. Neutralizers are not recommended with today's products. In fact, a small amount of residual alkali is less harmful than residual acid. A "floor pH" of 9.5 will not interfere with the application of a well-formulated polish, but a pH of 4.5 most likely will.
Occasionally low gloss is the result of a very porous substrate. Additional polish coats, or the use of an effective sealer will be helpful in this situation. A well-formulated sealer is designed to have superior "hold out" over porous substrates. Its use as a base coat will assist in building gloss.
Poor recoat can also interfere with the gloss development of a floor polish. When investigating complaints of low gloss, one should try to differentiate between a recoat problem and other possible causes. Recoat problems can result from inadequate drying conditions or an interaction with the substrate.
The development of a haze on the polish film is a complex problem, which can usually be traced to the environmental conditions during application. All polish formulations have a "window of use", based on temperature and relative humidity. Some formulations may look great at 70°F (21°C) / 50% RH, but will not function well at 80°F (27°C) / 80% RH. As was discussed in "The Birth of a Floor Polish Film", the volatile components, namely: water, coalescents, and ammonia from the zinc complex are designed to evaporate in a certain order and at specific rates to optimize film formation. Extremes in temperature and humidity will change the rate and order of evaporation of these components. In high humidity conditions the slow rate of water evaporation will leave an insufficient amount of coalescent available to form a properly fused film.
Several different types of "haze" can develop upon application. One type could be described as a "light ghosting" on the floor surface. This type of haze is usually caused by low molecular weight material, such as surfactants, that have migrated to the surface. Generally this material is easily removed by buffing, and does not permanently damage the film. Another haze problem that can occur is a graying or dulling of the film. This type of haze is not removable with buffing and is evidence that the underlying film has been damaged by recoating too quickly for the ambient environmental conditions. Under unfavorable drying conditions more time is needed between coats. As the number of coats increases, the greater film thickness will retain more moisture leading to surface irregularities and unsightly haze. Under high humidity conditions more drying time should be allowed between coats as the number of applications increases.
Applying polish successfully in high humidity can be difficult due to the complex nature of the drying process. Even under apparently similar temperature and humidity conditions, differences in air movement and floor surface temperature will affect the rate of evaporation of the various components, and the final appearance of the polish on the floor.
Occasionally a haze can develop in a polish under the best of drying conditions. This is usually the result of an incompatibility between the polish and the substrate, or a contaminant on the floor. For instance, the floor may be coated with residue from ice melt, which is incompatible with most polishes and results in a dull film. In addition, not all sealer/finish combinations are compatible. Care should be taken to select the right companion product.
Poor leveling is typically due to a residue on the floor. Any oily material left on the floor will inhibit the polish from leveling properly. Culprits such as commonly used furniture polish or dust mop treatments can negatively affect leveling. The surface energy of a given substrate will also have an effect on the leveling properties of a product. Certain substrates must be investigated carefully to assure that the floor polish will level properly.
Short term tackiness is usually due to inadequate drying conditions, which can generally be improved by longer dry times and better air movement. Care should be taken to ensure that the polish is completely dry before returning furniture, particularly in closed areas such as classrooms. As mentioned in the section on hazing, the time required for the drying process escalates exponentially with increasing coats rather than linearly, because more water is entrapped by the underlying coats.
Adhesion can be a serious problem, particularly on mineral surfaces and specialty substrates, such as urethane and polypropylene. To remedy these situations, specialty sealers are available that are designed to adhere to difficult substrates. When coating mineral floors, the application of one or two coats of sealer followed by several coats of polish will usually result in an attractive and serviceable floor. Here again, care should be taken to allow adequate dry time between coats.
Properly formulated polishes should not have a problem on most standard resilient tile floors. However, there are a few situations that can cause problems. New tile has usually been coated with a factory finish, which is designed to keep the individual tiles from sticking together in the shipping boxes. Unfortunately this anti-block coating also keeps the polish from adhering to the tile. The factory finish must be removed from the tile before the polish is applied. If the polish is having difficulty adhering to an older floor, it is most likely that something has been spilled on the floor prior to the application of the polish. As always, removal of any foreign material on the floor is essential before applying polish.
In some instances the problem may not be adhesion, but rather film deterioration due to plasticizer absorption by the substrate. Specific questions about the substrate and its preparation should be the first step in determining the nature of the problem.
While this problem is usually considered in the maintenance category, excessive powdering can also indicate improper film formation and may be described in different ways. Comments may be that the product is "walking off the floor", or has poor durability. In some cases the product will generate excessive "grinding dust" while buffing. These are all descriptive of poor film fusion.
A major impediment to good film formation is low temperature during application of the polish. The emulsion polymers used in formulating floor polishes have minimum film formation temperatures (MFT) well above room temperature. As discussed earlier, plasticizers and coalescents are used to reduce the MFT of the polish so that film formation will occur at floor surface temperatures as low as 50°F (10°C). If for some reason the temperature of the floor falls below the MFT of the polish, a properly fused film will not form. The temperature of the floor can be affected by a number of conditions. A concrete slab floor on grade will conduct the heat away quickly, leaving the surface of the floor at a much lower temperature than the air at eye level. There have been many cases where a product performed well on the upper floors of a building, but the ground floor showed a powdering problem. The phenomenon known as evaporative cooling will also reduce the temperature of the floor as the polish dries. If fans are used to accelerate the drying process, proper film formation can be inhibited by evaporative cooling.
The substrate can also have a negative effect on the film formation of the system. Resilient tile with a high filler content, or older linoleum can absorb some of the coalescents and plasticizers from the polish, thus reducing the amount available for film formation. As a result of this coalescent/plasticizer depletion, the MFT of the system will rise and possibly reach a point above the temperature of the floor. In such circumstance the polish will develop a severe case of powdering. The use of a properly formulated sealer before applying polish is generally effective in remedying this condition.
It is important to remember that the MFT of a polish is not an exact temperature. There can be a 3° to 6°F (2° to 3°C) range where a finish will start to lose optimum film formation characteristics. When coating a floor with a surface temperature near the MFT of a polish, a glossy film may form. This film, however, will not be strong enough to withstand heavy traffic or maintenance operations such as high speed buffing. In a matter of days a complaint will be received that "the polish is blowing off the floor".
Premature Loss of Gloss
At times a product will exhibit a sudden and significant drop in gloss after having been down for a week or two. This is usually an indication that some foreign material has contaminated the floor. Such materials include furniture polish, dust mop treatments, ice melt chemicals and the overuse of cleaners, maintainers or spray buffs. Reduction in gloss can also be the result of an adverse response to buffing. Generally this is a uniform dulling of the floor as a result of micro scratching, which appears as unsightly swirl marks.
Swirling is a condition traditionally associated with the response of a polish to buffing. Polishes are designed to respond to a specific pad, pad speed and pad pressure combination. The polish supplier will usually recommend the buffing combination needed to achieve the best results. Buffing a polish with the wrong combination will fail to produce the desired appearance.
When buffing or burnishing a floor the polish surface is abraded and heat is generated. The relative amount of each is determined by the pad and the equipment used. Coarse pads are very open and primarily abrade the polish, while softer pads will have more surface area and will generate more heat. This heat will cause some movement of the thermoplastic components of the finish. The polish formulation will determine which type of pad and buffing equipment produce the best results.
Buffing with an overly aggressive pad can result in "micro scratches", usually in a semicircular pattern. The end-user should evaluate a softer pad, and/or a lighter pressure setting on the machine. Conversely, a softer pad will have more contact with the floor, which generates more heat, potentially damaging the film. As can be seen, instructions regarding the proper use of a polish are very critical and must be clearly communicated to the end user.
Occasionally a polish will develop a buffing problem over time. This can be due to excessive use of a maintainer/spray-buff, or an aggressive detergent cleaner which alters the surface of the finish. Proper maintenance procedures which include following the manufacturer's instructions will avoid this type of problem.
Dirt pick-up problems are usually described as a darkening or yellowing of the floor. This discoloration can be uniform in a given area, or be seen as "splotchy" dark spots. Such problems occur for several reasons, but are generally associated with inappropriate maintenance procedures. Softer polishes that are designed to be UHS burnished frequently may have dirt pick-up problems, if used in areas that are not cleaned regularly.
The misuse of maintainers can lead to dirt pick-up problems. Polymer containing maintainers can be excellent for restoring a trafficked floor. However, if the floor is not properly cleaned before application, trapped dirt can leave the floor looking darker. Maintainers containing permanent plasticizers will soften the polish if overused. This practice will lead to discoloration as the softened polish can no longer effectively repel dirt. Tackiness and soiling of the polish surface can also develop over time due to plasticizer migration from a highly plasticized substrate. Any material that softens the polish film will potentially lead to a dirt pick-up problem.
Today's modern floor polish formulations are complex mixtures of polymers, waxes, surfactants and other additives that are designed to work together under a wide variety of conditions. But even the very best formulations can develop problems depending upon application conditions and the practices employed to maintain the polished flooring.
We certainly hope this provides you with a solid foundation for understanding the complexities of one of today's most under-appreciated products. As the leading supplier of specialty polymers to the Floor Polish Industry for over thirty-six years, Interpolymer takes special pride in providing this information to you and looks forward to meeting your specific needs in the future.