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Award winning CintoTM stackable chair improves comfort by conforming to the body
Case Study:
Humanscale® Cinto
Stackable Chair
Objective:
To produce a stackable chair that is comfortable
Designer:
Humanscale Corporation
Material Used:
Santoprene™ TPV 221-73 M100
Manufacturing Process:
Injection overmolding
Color:
Colorable with four options
PROBLEM
Can stackable chairs be comfortable? That was the problem that Humanscale Corporation, acknowledged as a leader in ergonomic office products, wanted to solve.
Founded in 1982 in the heart of Manhattan, Humanscale’s mission is to design and manufacture products that create a healthier, more comfortable and more productive work environment. It strives to design products that combine uncompromising function and honest aesthetics with ultimate ease-of-use. In fact, such is the company’s reputation for design excellence that in 2004, I.D. Magazine recognized Humanscale as one of the ten “Best Companies” worldwide that help push design forward.
But how would the Humanscale Design Studio craft a stackable chair strong enough to withstand the rigors of everyday use and still be comfortable?
SOLUTION
Knowing that a truly ergonomic chair could make more of a difference to user well being than almost any other product, Humanscale first entered the task seating market in 1999. As part of a product portfolio extension, the company then turned its attention to stackable chairs, having already produced a number of award winning office chairs.
Because stackable chairs need to be strong, they are often made of steel or from a hard, strong plastic, such as nylon or glass-filled polypropylene (PP). Then, to provide a level of comfort, these materials are sometimes combined with vinyl or fabric.
Because the materials generally used in the manufacture of stackable chairs allow little or no movement, the person using such a chair becomes stiff and tired very easily.
“One of the most important aspects of designing a comfortable chair is to ensure there is adequate support and flex for the lower back. Combining the required strength with a high level of comfort in a stackable chair can be a problem because flexible materials often aren’t strong enough,” said Mr. Lachezar Tsvetanov, Senior Designer, Humanscale.
Humanscale’s conceptual objective was to produce an attractive, ergonomic design with a breathable, flexible back for comfort. It included a wide belt attached to the lower back of the chair to support the lumbar region.
Humanscale sent its designs to processor L&P Plastics of Carlyle, Illinois suggesting PP for the back and seat of the chair, and an elastomer for the lower-back support belt. Together, L&P Plastics and Humanscale designers worked to develop a chair that met both the physical and aesthetic requirements.
From a performance perspective, the chair had to pass the Business and Institutional Furniture Manufacturers Association (BIFMA) testing and CAL133 flame retardant tests. The material used for the support belt needed to withstand up to 200 pounds weight, be UV resistant, offer good creep resistance and adhere to the structural PP. From an aesthetic viewpoint, the surface of the chair had to look good. The ability to color the chairs to suit office environments was important, as was being able to incorporate the Humanscale logo.
“While Santoprene™ brand TPVs were high on the list of elastomers considered, their ability to bond tightly with PP, plus the technical support and depth of resource available from ExxonMobil Chemical convinced us we could rely on them,” said Jason Peters, Program Manager, L&P Plastics.
Crucial to the successful development of the chair were consultative meetings involving Humanscale, L&P and ExxonMobil Chemical at the very outset of the project.
Following these meetings, ExxonMobil Chemical’s specialty elastomer technical support team reviewed the concepts and provided part design suggestions and product “watch outs.” In particular, the team provided advice regarding belt thickness and also recommended a reduction in the side post attachment areas to alleviate sink marks.
ExxonMobil Chemical undertook mold flow analysis to confirm that Santoprene thermoplastic vulcanizate (TPV) would flow well enough to fill the part. Finite element analysis (FEA) tests were done to identify areas of stress concentration.
Sample materials were then provided for prototype testing at the L&P facility in Brownsville, TX. On reviewing the results, ExxonMobil Chemical undertook further FEA analysis which resulted in a slight, but important, change in the elastomer’s durometer. With additional processing advice from ExxonMobil Chemical, the prototypes successfully passed the BIFMA tests.
ExxonMobil Chemical also provided L&P with connections to suppliers of compatible colorant materials to meet the requirements of the application. With long flow lengths, non-uniform thicknesses and the complexity of the part, there were many opportunities for halos and flow marks. Texturing was promoted, and sample parts and test plaques were shared with Humanscale to demonstrate the potential for aesthetic improvement.
“The samples provided by ExxonMobil Chemical along with their overall awareness and knowledge of the capabilities of Santoprene TPV have been a significant factor in the successful development of this chair,” said Peters.
The lower back support belt, weighing about 0.66 lbs (.3 kg) and measuring 20 inches (508 mm) long by 4.5 inches (14 mm) wide by up to one inch (25 mm) thick, is manufactured by injection overmolding Santoprene TPV onto the PP chair back. In the overmolding process the Santoprene TPV and PP chemically adhere to create a very strong cohesive bond.
“Santoprene TPV provided the mechanical advantage that we were looking for. It enabled us to design a comfortable stackable chair by providing lower back support that could flex while retaining its structural integrity,” said Tsvetanov.
RESULTS
Humanscale’s international design team has continued the company’s history of innovation with the multi-award winning Cinto™ stacking chair. Designed to move with the body, the Cinto chair offers unprecedented comfort and ergonomic features for a chair in its class. It is currently available in ten colors, and the logo is tastefully molded into the back of the lower belt.
“We have had a great reaction from the industry. I honestly believe people are genuinely surprised at just how comfortable it is,” said Mike
Buhmann, National Director of Seating and Training, Humanscale.
Made of steel, polypropylene and Santoprene TPV, the chair is also fully recyclable – an important consideration for Humanscale.
“Humanscale has always been committed to environmental sustainability, continually striving to design, engineer and manufacture products that consume less of the Earth’s resources,” said Buhmann. “By creating products that use less material, that have fewer assembly processes, and which contain a high percentage of recyclable or recycled content help us to accomplish this goal.”
Cinto Chair Awards
First Prize, Interior Furniture
2007 International Design Awards First Category Winner
2007 International Design Awards Product Design of the Year
2007 International Design Awards
2007 Good Design Award (Japan)
I.D. Magazine’s 2007 Annual Design Review
2007 Chicago Athenaeum Museum of Architecture and Design
GOOD Design 2006 Best of IIDEX/NeoCon Canada 2006, Silver
