Benefits of QPAC® Poly(alkylene Carbonate) Copolymer Binders for Glass Sealing Paste Applications

In this ‘Insight from Industry,’ Nick Gilbert from talks to Peter Ferraro, Director of Business Development at Empower Materials, about the benefits of QPAC® Poly(alkylene Carbonate) Copolymer Binders for Glass Sealing Paste Applications.

Empower Materials is at the forefront of the development of cleaner, more environmentally friendly binders. Can you tell us more about the QPAC® range and the main benefits of CO2-based polymers for binding and sealing applications?
Empower Materials manufactures a family of Polyalkylene carbonates. Our main product is QPAC® 40 Polypropylene Carbonate. This material is manufactured with a range of molecular weights ranging from as low as 50,000 to 350,000 +. Our new catalyst technology developed over the last several years has allowed us to make higher molecular weight QPAC® 40 which has opened up new binder opportunities.

We also make QPAC® 25 Polyethylene Carbonate with a molecular weight range from 100,000 to 230,000+. Again our new catalyst technology has allowed us to make this product with a higher molecular weight. We are also able for the first time to commercially offer both QPAC®100 Polypropylene/Polycyclohexene Carbonate and QPAC® 130 Polycyclohexene Carbonate.

The main benefit of this family of polymers is the ability to completely decompose the binders at low temperatures, lower than most any other binder in the marketplace in not only air but in non-oxidizing environments. Additionally, after debind there is very little residual contaminants remaining after the binder is decomposed.

These two qualities are highly important to our customers who are working with sensitive materials in high-tech applications. At the same time, the adhesion and green strength of the polyalkylene carbonates are excellent. Therefore mechanical and sealing properties can be improved along with the benefits of an improved binder decomposition process.

What makes the QPAC Poly(Alkylene Carbonate) systems greener?
QPAC® Polyalkylene Carbonates are synthesized from carbon dioxide and require approximately 50% less petrochemicals than traditional petroleum-based polymers. They also exhibit some biodegradable properties. Both of these features make QPAC® a green material,

QPAC® Poly(Alkylene Carbonate) copolymer binding systems are used for a number of different applications. Can you tell us a little bit more about the vast range of industries that use the empower range?
Yes, QPAC® Polyalkylene Carbonates binders / sacrificial materials are used in a wide range of industries. This includes binder applications in dielectric tapes and pressed parts in passive electronic components, conductive pastes for electronic, solar, and other applications, brazing binder in flux pastes, and as sacrificial channel formers for MEMS and other electronic components. One of the most promising areas of growth using the binder is in glass systems such as thick films, sealing pastes, and glass preforms. Applications include glass packaging, displays, LEDs, OLEDs, and hermetic glass gaskets.

Glass sealing pastes require some specific properties, how do the Empower QPAC Poly(Alkylene Carbonate) copolymer binding systems meet these requirements?
As in the name, glass sealing pastes need to create a good seal. Therefore the paste should be dense with few voids and have good adhesion. Additionally, any contamination in the seal after the glass is sintered will negatively affect the seal and create the opportunity for leaks. The decomposition properties of QPAC® 40 Polypropylene Carbonate results in a higher density seal with few voids. The binder also has very high adhesion properties with glass frit.

Glass sealing pastes also require unique rheology. QPAC® 40 Polypropylene Carbonate is shear thinning which is an important feature for dispensing/ printing glass pastes. Additionally, the polymer can be modified to offer a range of viscosities.

In particular, the system offers complete decomposition at low temperatures, why is this so important?
Many glass sealing applications require a low-temperature melt glass powder or frit. Advancements are continually being made to lower the melt temperature of the glass by the glass frit manufacturers. A lower binder decomposition temperature is required for these types of glass powders. The binder must be decomposed before the glass starts to melt. Otherwise, the binder and its gases will get trapped within the glass structure. This will result in voids, and hence lower density.

QPAC®40 Polypropylene Carbonate can be fully decomposed before the glass melts. This has been proven in several glass sealing paste applications where other binders could not work because of their high decomposition temperature.

Leaving behind low residuals and ash content after decomposition are also benefits, how does the QPAC solution ensure minimal residuals?
Trapped contaminants such as ash and carbon that are left behind after the binder decomposes also create problems with sealing of the substrates. A compromised seal caused by contaminants will negatively affect the reliability of the final product. Since QPAC® does not leave behind carbon or other contaminants, this eliminates the problem of having particulates left behind to adversely affect the seal.

Other binders such as ethyl cellulose inherently contain higher amounts of ash and carbon. These levels of contaminants are further amplified because the glass melts before the binder can fully decompose.

QPAC system offers a more environmentally friendly manufacturing environment. Can you tell us a little bit more about how this can benefit your customers?
QPAC Polyalkylene Carbonates decompose to water and carbon dioxide. Therefore venting of toxic byproducts from the decomposition process is not needed. Other binders result in harmful fumes and soot that cause environmental and equipment issues. Since the byproducts are clean, the furnaces stay cleaner and require less downtime for maintenance. Additionally the work environment is improved.

What’s next for Empower Materials? What can we expect to see in the future?
Empower Materials continues to expand the range of different types of Polyalkylene Carbonates. This is mostly driven by the need placed on us by our customers. We are also working with our customers in different applications such as glass sealing pastes, to help optimize their formulations for maximum performance. Interest in our products continues to grow as the need increases for cleaner binders that decompose at lower temperatures. QPAC® Polyalkylene Carbonates addresses these needs.

QPAC® 40 offers excellent performance as a binder in solar pastes

A great deal of effort has been afforded over the last 20 years improving photovoltaic (PV) efficiencies, reliability, and manufacturability. Much of this work has been focused on the front-side construction of PV, including metallization and contact formation with glasses. In general, the front-side contact pastes are silver pastes which are heterogeneous mixtures containing metallic silver powder or flakes, glass frit(s), organic binders, and other additives (solvents, plasticizers, dispersant/surfactants, inorganic additives, etc.). The role of the organic binder is critical in the formulation but is many times overlooked.

In this study, the clean-burning QPAC®40 polypropylene carbonate binder was used to formulate a front-side solar cell thick film paste sample. The paste characteristics were compared to commercially available pastes and found to exhibit nearly identical characteristics, such as solids loading, rheology, and fineness of grind. Thermal analysis of the paste sample compared to available commercial systems showed the QPAC®40 based paste to provide complete organic phase burn-out by 300°C in air, whereas the commercial systems exhibited a broad decomposition range and residual carbonaceous material presence as high as 630°C. The final cosmetic and microstructure features of the printed and fired structures on the front-side of solar cells were also compared. The QPAC®40 based paste showed higher retention of imparted geometry from the screen printing process through narrower and higher finger lines as well as better conductive architecture density through reduction of pore/void features as compared to the commercial paste samples A and B.

To read full report: Using Polyalkylene Carbonates (QPAC) as a Binder in Solar Pastes

QPAC® performance in ultra low-temperature co-fired ceramics (ULTCC)

This paper reports the first ultra-low sintering temperature (450 °C) cofired multifunctional ceramic substrate based on a commercial lead zirconium titanate (PZ29)−glass composite, which is fabricated by tape casting, isostatic lamination, and sintering. This substrate was prepared from a novel tape casting slurry composition suitable for cofiring at low temperatures with commercial Ag electrodes at 450 °C. The green cast tape and sintered substrate showed a surface roughness of 146 and 355 nm, respectively, suitable for device-level fabrication by postprocessing. Additionally, the ferroelectric and piezoelectric studies disclosed low remnant polarization due to the dielectric glass matrix with average values of piezoelectric coefficient (+d33) and voltage coefficient (+g33) of 17 pC/N and 30 mV/N, respectively. The dielectric permittivity and loss value of the sintered substrates were 57.8 and 0.05 respectively, at 2.4 GHz. The variation of relative permittivity on temperature dependence in the range of −40 to 80 °C was about 23%, while the average linear coefficient of thermal expansion was 6.9 ppm/°C in the measured temperature range of 100−300 °C. Moreover, the shelf life of the tape over 28 months was studied through the measurement of the stability of the dielectric properties over time. The obtained results open up a new strategy for the fabrication of next-generation low-cost functional ceramic devices prepared at an ultralow temperature in comparison to the high-temperature cofired ceramic and low-temperature cofired ceramic technologies.

QPAC® 40 was used as a binder with a solvent and glass composite powder in a tape casting process.

Read the full article: Multilayer Functional Tapes Cofired at 450 °C: Beyond HTCC and LTCC Technologies

Penn State University Research shows the benefits of QPAC® Polypropylene Carbonate as a binder in the Cold Sintering Process

The Cold Sintering process has been developed by Penn State University at the Material Research Institute. It allows for combining different material classes for a wide variety of applications. The lower temperature sintering process allows for the fabrication of inorganic compounds that could otherwise not be combined at high densities. This process has opened up many new opportunities in the electronic device industry, including multilayer electroceramic devices. Fabrication of multilayer devices involves both tape casting and screen printing of pastes. Both of these processes use binders for temporary strength. The binder for these applications needs to be clean burning. Additionally, for the cold sintering process, the binder needs to be removed at temperatures as low as 150℃ because of the lower sintering temperatures. QPAC® polyalkylene carbonate, specifically QPAC®40 Polypropylene carbonate, meets both the clean-burning and low-temperature requirements.

Penn State’s research shows that the QPAC®40 is an effective binder for the cold sintering process. It can be removed completely from the formed parts at temperatures low enough to avoid oxidation and/or not affect low-temperature stability materials such as polymers. The research conducted also showed that the QPAC®40 binder can be completely removed as low as 125°C. This enables the use of materials that offer unique properties of electrical conductivity, thermal conductivity, and heat capacity to name a few.

Using QPAC® Polyalkylene Carbonate as a solid state electrolyte for flexible solid lithium batteries

Numerous organizations have investigated the use of QPAC®25 polyethylene carbonate (PEC) and QPAC®40 polypropylene carbonate (PPC) in solid lithium ion battery applications. Research has been ongoing for many years to find an alternative to liquid electrolyte batteries because of their inherent safety issues mainly due to the volatility and combustion of the liquid carbonate organic electrolyte. Solid polymer electrolytes can also offer enhanced flexibility and processability. The challenge with the past solid polymer electrolyte has been low ionic conductivity. There has been a lot of work to overcome this past issue so that the solid lithium batteries perform as well as the liquid polymer batteries.

QPAC®25 polyethylene carbonate and QPAC®40 polypropylene carbonate are both polymer candidates for electrolytes. Carbonate-based solvents are usually used as the electrolyte solution in Li-ion batteries because of their high dielectric constant. Therefore, the carbonate groups of QPAC®25 and QPAC®40 provide a good structure for the polymer framework. The work shows that the PEC can form a high-performing polymer matrix for the electrolyte and shows very good ion-conductive properties. Additional work by other groups focused on PPC for the polymer matrix. This work also showed favorable battery performance results.

Overall, the use of both QPAC®25 polyethylene carbonate and QPAC®40 polypropylene carbonate exhibited high conductivity and high ionic transference number along with good mechanical strength. The results show comparable performance to liquid electrolyte battery technology. Therefore, the safety issues and flexibility constraints of liquid polymer batteries can be eliminated without sacrificing performance by using these polyalkylene carbonate polymers in the electrolyte formulation.

The benefits of QPAC®25 Polyethylene Carbonate in Controlled Drug Delivery Applications

QPAC®25 Polyethylene Carbonate has been studied as a biomaterial for controlled drug delivery applications. The QPAC®25 PEC offers biodegradable properties that make it attractive for this application. Films prepared from PEC have been made with various drugs to study the characteristics and performance of PEC as a potential carrier for controlled drug delivery. Studies have shown that QPAC degrades linearly via enzyme breakdown. There was also a correlation between PEC molecular weight and degradation time. Overall, the studies show that QPAC®25 can be used in controlled drug release applications. Note that QPAC®25 is not FDA registered.

A Binding Matter

Ceramic Industry Magazine article 

Poly(alkylene carbonate) binders have been shown to burn out cleanly and uniformly, while providing high green strength to refractory products.

It is widely understood that the use of additives and processing aids is critical in the forming stage for ceramic materials. These additives include binders, plasticizers, dispersants, surfactants, and lubricants. Each has their own specific use in the ceramic system, but all are a potential source of contamination and therefore can affect the production cycle, rejection rates, properties of the finished product, and ultimately the overall manufacturing cost.

Binders have been called the most important processing additive of the ceramic sintering process, and along with plasticizers, account for the bulk of all additives used in the ceramic processing industry. An effective binder will hold dry powders or aggregate together during sintering, burning out cleanly and uniformly while providing exceptional green strength to the sintered parts.

Poly(alkylene carbonates) are a family of organic polymers that possess a number of unique characteristics which make them ideal for use as binders for ceramic powders, especially alumina and silicon carbide, two well-known refractory grade ceramic materials commonly formed by way of various pressing, extrusion, slip casting (tape casting) and powder injection molding (PIM) operations.

Properties of Poly(Alkylene Carbonate) Binders

The poly(alkylene carbonate) binders are synthesized through the reaction of carbon dioxide and epoxides. Two polymers are readily available as binders–poly(propylene carbonate) and poly(ethylene carbonate). Both have properties that translate into superior performance for advance ceramics. Decomposition of poly(alkylene carbonate) binders is complete through three phases–solid, liquid and vapor.

Poly(alkylene carbonate) binders decompose completely in air below 300°C, at temperatures at least 100°C less than conventional binders. Complete burnout in nitrogen and argon and reducing atmospheres that contain hydrogen is possible at temperatures as low as 360°C, and under vacuum, poly(alkylene carbonate) burnout temperatures are even lower.

Poly(alkylene carbonate) binders burn out completely, as the products of their combustion are carbon dioxide and water vapor are non toxic, non flammable and environmentally safe. Many refractory type ceramis find end uses in applications in the electronics industry as capacitors, piezo-electrics, insulators, and sensors, all requiring high purity. Poly(alkylene carbonate) binders have been shown to yield strong green sintered parts that are virtually contaminate free. Ash residues are typically less than 50 parts per million (ppm) for the pure binder. Based on 3% binder use (a typical amount), residual ash and finished parts is well under 2 ppm, suitable for applications where purity is essential.

The low sodium levels of the binders are also encouraging for those producing dielectric materials, which have critical purity requirements. Based on 3% binder levels, poly(alkylene carbonate) binders exhibit less than 0.3 ppm residual sodium.

Unlike other binders, poly(alkylene carbonate) binders are also unique in that they burn out mildly, without violent gas formation. Therefore, fewer rejects due to cracking and variations in thermal expansion can be expected. Decomposition can be easily predicted, allowing for more reliable control.

Poly(alkylene carbonate) binders are amorphous with an easily reached class transition temperature (Tg) of 40°C. Poly(ethylene carbonate) binders are also amorphous but with a Tg of 25°C. The Tg can be further lowered with the addition of propylene carbonate, a monomer co-produced during the polymerization process of poly(propylene carbonate).

Poly(alkylene carbonate) binders are soluble in a wide range of polar organic solvents, including:

  • Acetone
  • Methylene chloride
  • Methyl ethyl ketone
  • Ethyl acetate
  • Chlorinated hydrocarbons

The binders are insoluble in alcohol, ethylene glycol, and aliphatic hydrocarbons. Although they are also insoluble in water, stable aqueous emulsions are available on a custom basis for using the water-based processes.

The poly(propylene carbonate) form of poly(alkylene carbonate) binders performed well in tests with numerous ceramic powders including the following:

  • Alcoa alumina (A-12, A-14, A-16, SG)
  • Coors ADA-90 alumina
  • Reynolds RC-HP-DBM alumina with MgO
  • Herman Stark B-10 silicon carbide

Binder Comparison

The poly(propylene carbonate) form of poly(alkylene carbonate) has shown significant benefits in ceramic applications. The use of poly(propylene carbonate) over conventional binders, such as polyvinyl alcohol (PVOH) and methylcellulose is pressing, extrusion, tape casting, and PIM operations has been successfully demonstrated.

During the pressing operation, samples coated with poly(propylene carbonate) had higher green densities relative to theoretical densities than those samples coated with no binder, with PVOH, and with Methylcellulose.

By using a binder that decomposes cleanly and completely in inert atmospheres, the volume of gas products produced was dramatically reduced during sintering relative to combustion in air. Reducing the gas volume produced during sintering in this manner decreases the likelihood of flaw generation during sintering thereby increasing the likelihood of crack-free ceramic parts being produced, and allows for thicker ceramic parts to be manufactured.

Tape Casting and Injection Molding

The tape casting process is often used to form thin flat ceramic parts, but this process requires that the chosen binder remain flexible, even after drying. One of the unique characteristics of poly(propylene carbonate) is its ability to be plasticized by its own monomer, propylene carbonate. Poly(propylene carbonate) binders also have excellent film forming and coating capabilities, making them an excellent choice for the tape casting process. Extensive work has ben done to develop optimal formulations for binding alumina, using poly(propylene carbonate) as a binder in MEK and MEK/toluene solvent mixtures. These formulation offer high green strength and density, efficient binder burn-off, and good ability for lamination. Tapes significantly thinner than 1 mil (.001″) and as thick as 50 mils (.050″) have been produced using poly(propylene carbonate).

Studies have been carried out comparing a poly(propylene carbonate) based alumina composition with a wax-based (based on paraffins and microcrystalline waxes) alumina composition in ceramic injection molding trials. Results from these trials suggest dramatic improvement in mean failure stress, from about 230 to over 300 MPa when going from the wax mix to the poly(propylene carbonate) mix. Overall, there were fewer flaws in the poly(propylene carbonate) bars than in the bars made from wax mix composition. In the poly(propylene carbonate) bars, the flaws were limited to the contours of the molding defects that were knit lines in the thick sections. In the wax-mix bars, flaws were evenly distributed and more spherical in nature.

Expanding Applications

Poly(propylene carbonate) binders have demonstrated their value commercially over a wide range of critical ceramic powder forming operations for over a decade. Their unique and valuable properties provide advantages for certain refractory grade ceramics in pressing, extrusion, tape casting, and injection molding processes. As novel and demanding applications involving refractory type powders increase, the use of binders such as poly(alkylene carbonate) will become even more critical.