Armstrong`s Wood Coating Quality Journey: Quality Improvements in

Armstrong’s Wood Coating Quality Journey:
Quality Improvements in UV Wood Finishing
Gary A. Sigel
Armstrong World Industries
Lancaster, PA
Presented at RadTech 2010, Baltimore, MD, May 24, 2010
Abstract
Finishing system requirements for wood flooring are based on Voice of the Customer (VOC) as it
relates to end user specifications including: wood species, width, stain color, gloss, coating/wood visual
and overall durability and maintenance. Because different plants have different UV finishing lines,
variability in the UV process can cause manufacturing issues. Controlling the variability has been a
major part of our quality improvement efforts.
This paper begins with a history of Armstrong’s flooring and UV/EB chemistry development
followed by Armstrong’s Wood Coatings Quality Journey. Within the quality journey, this paper will
review three primary steps: 1) Finishing Process Specifications, 2) Statistical Process Control, and 3)
Product Quality Control. A sigma process map will identify CTC (Critical to Customer attributes) and
CTQ (Critical to Quality) input variables for the Finishing Process Specifications. The associated CTQs
reviewed include: sanding, UV stains and finishing. Quality improvement in color matching, UV
finishing system requirements, e.g., coating structure/performance, and statistical process control
methodology for monitoring coating parameters and radiometry across multiple plants will be reviewed.
AWI History of Product Development
For 150 years, Armstrong has created and maintained a strong brand by manufacturing high quality
products. Beginning in 1860 with the production of cork bottle caps for juices and water, Armstrong
realized the importance of quality and ongoing process improvement as evidenced by its purchase of
cutting machines that improved product quality by reducing cork size variation and increased volume.
By 1899, Armstrong Cork had become the largest manufacture of cork. Leadership continued to drive
new product development as documented by the credo “Let the buyer have faith.”1 Nine years into the
20th century, Armstrong began taking scrap cork and producing linoleum flooring in Lancaster PA. This
marked the beginning of what would become the largest residential vinyl flooring operation (Figure 1).
Armstrong acquired wood flooring manufacturing capability in 1998 with the purchase of Triangle
Pacific. The acquisition included three brands (Bruce, Hartco and Robbins), six engineered wood
flooring plants, six solid hardwood flooring plants, adhesives and floor care manufacturing,
warehousing, an installation training facility, corporate office, and several cabinet manufacturing plants
(Figure 2). All of the plants had UV cure finish lines. Although similar in concept, the lines at the
different plants were quite different from one another. Differences included: the type and manufacturer
of equipment, line layout, capacity and type of stain system (various plants used water based, solvent
based, and 100% solids stains), and the total business was serviced by three different finish material
suppliers. The variability of the lines and finish systems and processes from plant to plant posed
problems in manufacturing the same products in different plants. Understanding and controlling the
differences between the manufacturing facilities, in a way that was transparent to our customers, marked
the beginning of the Armstrong wood floor coatings “Quality Journey.” 2
Armstrong’s Entry into UV/EB Wear Layers
Armstrong has been producing radiation curable wear layers on its products for over 35years while
continuing to develop finish systems that provide improvements in wear resistance, scratch resistance,
stain resistance, color stability and other properties that impact CTC demands (Figure 3).3 In 1976,
Armstrong introduced its first UV curable coating, purchased from W. R. Grace, and based on “thiolene” chemistry. The coating delivered “no wax” performance to a “do it yourself installation” (DIY)
market. One year later, Armstrong had developed and began producing its first UV curable coating
based on acrylate chemistry. The coating was a combination of UV and moisture cure based on a
polyester urethane acrylate. By 1979, Armstrong had eliminated the need for the moisture component
within the UV curable coating in favor of a more environmentally sustainable 100% solids UV cure
system. The new coating was based on proprietary polyester acrylates, known internally as Duracote I.
The next real breakthrough was the development of urethane acrylate chemistry based on NCO
terminated polyester prepolymers. These polymers were further reacted with hydroxyalkyl acrylates to
form an acrylated urethane oligomer. That was blended with other materials to form the final coating.
This coating became the workhorse coating for residential tile for next several years. Armstrong’s next
major breakthrough came in 1992 with the development of Sol-Gel chemistry. A patented coating was
applied as a thin microscopic coating on top of standard urethane acrylate coating to give the CTQ and
CTC attributes of excellent stain resistance and scratch resistance. In 1995, Armstrong launched its first
nitrogen inerted UV curable coating on vinyl sheet goods based on polyester acrylate coating that again
gave the CTQ attributes of stain and scratch resistance.
Elements of Armstrong’s Wood Coatings Quality Journey
Previously, we published the elements of the quality process that evolved from the Wood Coatings
Quality Journey (Figure 4). More detail regarding this process can be reviewed in the cited reference.
As highlighted in the center, the journey began with the customer. Also, as implied by the circular
format, the journey continues to loop back to the customer through the product development process as
summarized below:
1. Customer Quality Requirements are gloss, texture, color, performance and price. Each
product has a specification that is unique to the product structure and the targeted market
segment.
2. Finishing System Requirements are defined by customer requirements. This includes the
chemistry, number of layers, thickness of layers and properties of layers which collectively
provide the appearance and performance of the finish system.
3. Manufacturing Equipment Specifications are driven by capability to make the specified finish
system. Key specification elements include: type of sanding equipment; number and type of
coating stations; number, wavelength and power of UV lamps at each station; spacing between
each component; coating delivery and storage systems; VOC/waste remediation; and quality
control measurement.
4. Raw Material Purchasing Processes ensures that ingredients for manufacture are capable of
producing a product that meets customer requirements if applied at the correct thickness and
properly UV cured.
5. Finishing Process Specifications defines specific sanding machine set-up, coating machine and
UV lamp operating parameters. Good quality specifications in combination with equipment
capability will produce products that meet customer requirements. Once the finish system is
defined, the next task is defining what manufacturing process equipment is required to apply the
system which, in turn, determines which plants can manufacture the product.
6. Statistical Process Control is good manufacturing practice involving tracking key process
parameters on a periodic basis. The data is used to create upper and lower process control limits
and determine if the manufacturing process is in control.
7. Product Quality Control ensures several quality measures are in place beginning with incoming
wood to kiln drying, ripping, side matching, end matching and finishing based on statistical
process control.
8. Quality Audits are conducted at each plant to ensure that no gaps exist in our internal and
external quality control process.
9. Product Development screens new product concepts based on probability of success.
Probability of Success guidelines follows a similar pathway to that of the “Quality Journey.”
Such criteria include commercial success, manufacturing success, ease of implementation,
capital and return on investment (ROI).
Going forward, this paper will focus on steps 5-7 on the quality loop beginning with Finish Process
Specifications and ending with Product Quality Control (Figure 4).
Finishing Process Specifications
Sigma process mapping of finish lines is a method used to identify parameters that affect
performance. Finishing Process Specifications begin with sanding and end with multiple applied layers
of coating to produce the final product (Figure 5).
Finishing Process Specifications are based on the end use customer requirements. For flooring, the
most important attribute to customers is appearance. This includes a combination of UV stain color,
coating texture and gloss level. Figure 5 shows typical steps for a wood finish line. Each step in the
process represents an input variable that could result in variation. This variation is controlled by
Standard Operating Procedures (SOP), Raw Material Specifications (RMS), and Statistical Process
Control (SPC) methodology. Each step has multiple input parameters that affect the CTQ and CTC
attributes, and the objective of each manufacturing plant is to control the process.
It is instructive to consider sanding as an example (Figure 6). Key input variables4,5 are the type of
sanding equipment, the grit sequence used, the abrasive paper manufacturer, how much material must be
removed in each sanding step, and the consistency of smoothness required as the wood enters the finish
line. The last point is an important linkage. If significant variation in final product color is not
acceptable, then the sanding requirements can be adjusted accordingly.
Another key process step that can lead to product variation is staining. There are four steps in the
stain process that are important: 1) application of the stain, 2) leveling the stain, 3) removal of carrier
(water or solvent) if the stain is not a 100% solids system, and 4) UV curing the stain (Figure 7). Within
each step there are several parameters that can ultimately affect color. In the end, the final product must
meet shade, visual and performance specifications. Most flat stock manufacturers now use roll coaters
to apply stains, although some still use spray equipment. For either system, it is important to match the
applicator characteristics to the type of stain being used.
Referring to Figure 7, some typical input machine variables that affect shade appearance are shown
for a roller applicator system. These include: roll type, down pressure, stain type (100% solids vs.
solvent or water based), viscosity (temperature dependent), and evaporation rate (solvent or water base)
during the drying step. Leveling can be accomplished by one or more techniques, such as wiping,
brushing or allowing for “open time” before the curing step. Removal of the carrier can be
accomplished by air drying, but more effectively using an oven. Equipment manufacturers offer a wide
variety of options. Selection depends on the properties of the carrier, local regulations, and tradeoffs
between capital expense targets, and floor space. Finally, for UV curable systems, the drying process
for the stain also includes the UV lamps. As with the standard oven, the choice of UV lamps depends on
the product application, cost considerations, regulatory requirements and available process footprint.
Options include: medium pressure UV mercury arc lamps, microwave powered lamps, or UV LED
(light emitting diode) systems. If recommended by the stain supplier, special options such as “additive
lamps” that have small quantities of materials like gallium or iron can be used as well.
For wood flooring, the final manufacturing step of applying the finish coatings really a series of
separate manufacturing processes. In simple terms, it is analogous to applying several coats of paint. In
reality, each coating has a distinct purpose. Every coat/cure station has a set of specifications that must
be met. Figure 8 shows an example of a four station UV “flat line” finish system. Depending on the
desired finish appearance, a line such as the one shown could have additional stations, or features. For
example, the line shown has only roll type applicators. Stations could be substituted with spray
modules, pre-metered applicators like curtains or slot die, or air knife applicators. Regardless of
applicator type, there are common process control parameters including: temperature of the liquid
finish, applicator type, line speed of conveyor, substrate temperature, and the final coating weight
applied. Downstream from the applicator station are the same three steps described above for staining:
leveling the coating, removal of carrier (water or solvent) if the coating is not a 100% solids system, and
UV curing the coating. The discussion below assumes 100% solids for each of the coatings, since that
would tend to optimize space, and minimize emissions and energy requirements.
After application of each layer of the wet finish coating, that layer must be allowed to level as
described above for the stain systems. Using control charts, individual coating layers and total thickness
can be monitored to ensure SOPs are followed. Figure 9 illustrates this concept by monitoring the
thickness of individual UV coating layers for a single product at a single plant. All applied coating
thickness must lie between upper and lower process specifications. Figure 9 also illustrates how
multiple plants can ensure thickness specifications are met for a product regardless of its manufacturing
location.
The use of radiometry to monitor UV processing has been a consistent message in RadTech
publications over the years8, 9. For the example wood finish line in Figure 8, this holds true. For each
finishing line UV station a set of UV cure parameters must be defined, and periodically measured and
recorded. Key process variables include the number and type of UV lamp, the applied power, type of
reflectors; distance between the UV source and the substrate, and the temperature of the substrate.
These parameters are really the same parameters that must be tracked for any UV curing process.
Successful monitoring can be accomplished by:
x Providing each plant with modern UV radiometers and software
x Implementing procedures to measure and record UV output
x Monitoring energy UV output for each UV curing station
x Performing a preventative maintenance to avoid potential problems.
A course of action should be included in the plant SOP if the lamps are not operating within the UV
range specified. Figure 10 shows an example of what happens if two lamps are off. The effect
downstream could result in gloss being below specification.
UV lamp uniformity across machine direction or length of bulb is another CTQ parameter that must
be continuously monitored. UV output at both ends (AMD) of the web or product should fall within
specified range. Failure to meet specifications can result in poor product performance downstream, e.g.,
gloss out of specification or cycles to taber wear-through below specification. To illustrate this concept,
a plot of gloss across machine direction for a medium gloss product is illustrated in Figure 11. Although
the gloss range falls within the process specification, the gloss of product on the end lanes shows a
statistical decrease in gloss vs. end and middle lanes. A plot of UV energy density vs. inches across
machine direction for a gloss setting lamp on the final cure UV lamp oven was constructed (UVA ).
Product Quality Control
Product Quality Control for inspection of finished product can be broken down into two primary
elements: Color match and product performance.
Color match
The final test of a quality wood finish process is when product is inspected and boxed. All product
is scrutinized by the inspection and boxing teams on the line. Armstrong facilities follow industry
standard practices, mixed with proprietary systems and technology, to ensure the best possible match.
The matching process actually starts with incoming raw material COAs (certificates of analysis) and QC
to make sure that the applied stain is the correct color. Finished product is carefully inspected and
compared to standards. Appropriate measurements such as gloss and smoothness are compared to
specifications. Data from these processes are tracked using SPC and scorecard systems, and that data is
periodically compared to customer satisfaction data. This information is reviewed constantly by
manufacturing management, and presented in management reviews as a way to identify opportunities for
improvement.
Figures 12 and 13 show how matching the voice of the customer to statistical process contral can
help ensure a more consistent color. Customers may understand that wood is a natural product, and may
have intrinsic variation in color. However, as shown in the figure, differences can occur which are
visible, and objectionable to customers. In Figure 13, SPC analysis shows how finsish line operators
can track and adjust color if needed to meet customer expectations.
Product Performance
Plant quality control (QC) managers further inspect the flooring for a host of CTQs that include
finish-related items. Finish CTQs include gloss level, crosshatch adhesion, coating cure and resistance
to checking (Figure 14). Intervals for the different tests are defined by the ability of the plant to
consistently pass the QC test. For the UV cured finish, statistical process control over the coating
application weights and UV process parameters ensure that product durability, as measured by tests such
as Taber Abrasion7, Gardner Scrub and Hoffman Scrape, can be performed at low frequency.
Performing tests at the proper frequency, and documenting the results, allows plant QC managers to
focus on operational activities and process improvement. This focus is what drives continuous
improvement and increased productivity. And productivity is a key to keeping costs in line. This is
very important because price to the customer is a key CTC attribute.
Conclusions
Quality improvements in UV finishing systems begin with CTC attributes, which can be combined
with sigma mapping of manufacturing processes to identify inputs that effect CTQ attributes. Each
process in the value map will have a set of process or material variables that can ultimately affect one of
the key quality attributes. Each step in the process has input variables that must be controlled by SOPs
and work instructions to reduce variation in the final product. The elements presented in this paper can
be applied to other similar systems. One thing is for certain: the journey always begins and ends in the
same place - with the customer.
References:
1.
2.
3.
4.
5.
6.
7.
8.
9.
William A. Mehler, Jr., Let The Buyer Have Faith, Publisher: Armstrong World Industries, Lancaster, Pa. 1987
J.Ross, G. Sigel, Title: Armstrong’s Wood Coatings Quality Journey, May\June Radtech Report 2006.
J. Ross, Title: UV & EB in the Flooring Industry-Reducing Greenhouse GAS
Emissions & HAPs, July/August 2007.
G. Fitzel, Title: Sanding 101, Hardwood Floors, October/November 2008
H. Grivna, Title: Widebelt Sanding: Principles Data Source Process Optimization, 2005
Fundamentals of Color And Appearance Seminar, Gretag Macbeth Global Services.
ASTM Test D4060-01. Title: Standard Test Method for Abrasion Resistance of organic Coatings by the Taber
Abraser
J. Raymont, Radiometers, The Best of Intentions, SGIA Journal, 3rd Quarter 2002, p39
R. W. Stowe, Title: Practical aspects of irradiance and energy density, RadTech Europe 1999, November 8-10,
Berlin, Germany
Gary Sigel
May 24, 2010
Quality Improvements in UV
Wood Finishing
„
„
„
„
„
„
Historical of Armstrong Product
Development
Elements of Armstrong’s Wood Coating
Quality Journey
Finish Process Specifications
Product Quality Control
Conclusions
Acknowledgements
Quality Improvements in UV Wood Finishing
Residential Tile
Linoleum Sheet 1914
Laminate
Wood 1998
Armstrong has a Long History of Understanding CTC Attributes
Cork 1860
Figure 1: Armstrong’s History of Products
“Let the Buyer Have Faith”
„
„
„
Bruce –
Armstrong–
Robbins –
HomerWood –
Capella –
„
Beverly, WV; Center, TX; Jackson, TN; Kunshan, China ; Somerset, KY; Statesville,
NC; Titusville, PA; Vicksburg MS; West Plains, MS; Warren, AK;
Plant Locations –
„
„
„
„
„
Markets –
Brands –
Figure 2. Armstrong Entry Into Wood Markets, Brands and
Plant Locations
High End Tile
Sheet Goods:
roto type
structures; 6'
to 14' wide
Solarian Tile
Solarian Tile
Wood
1992
1995
1996
1996
1996
Wood
PE-Acrylate
Solarian Tile
1980
1998
Sol-Gel
Solarian Tile
1979
Triangle Pacific: Bruce,
Hartco, Robins brands
acquired by Armstrong
Al2O3, UV urethane
matrix
EB Adhesive
Duracote VII
Duracote IV
Duracote I
Solarian Tile
1977
Description
First UV coating
Armstrong 1st UV
coating, B1392A
Bolgiano
Application
Solarian Tile
Year
1976
Considered breakthrough coating;
wear, scratch, stain resistance
First polyester based UV Urethane
acrylate oligomer optimized, Using
modeling to design PE
UV Polyester acrylate oligomer
Superior wear and stain
designed by using predictive modeling.
resistance
Coating inerted under nitrogen.
Hybrid coating applied over Urethane
Superior properties; Improved on
Acrylate; Sol-Gel Epoxy system; cationic
scratch and stain
epoxy cure; cycloaliphatic diepoxides;
No wax, improved on scuffing,
scratching, maintenance
No Wax, Improved wear,
improved processing
First UV moisture B stage system: PE
urethane acrylate
UV Urethane acrylate oligomer;
CTC Attributes
No Wax, Improved wear
Chemistry
Thiol-ene chemistry
Triangle
PacificArmstrong
Armstrong
Multiple UV coating vendors based on
UV urethane acrylate chemistry.
EB curable urethane acrylate.
Significant improvement over
Duracote IV
Easier installation of tile,
Armstrong
EB curable adhesive on the back of tile
improved adhesion
Superior wear and scratch
Use of refractory particles to compete
resistance; S-33 Taber
Triangle Pacific
with laminate
>1000cycles, Permion wearlayer
Armstrong
Armstrong
Armstrong
Armstrong
Armstrong
Vendor
W. R. Grace
Armstrong UV/EB Coating Historical
Figure 3. Armstrong’s History of CTQ Attributes For UV/EB Wearlayers
7 Product
Quality
Control
8 Quality
Audits
6 Statistical
Process
Control
9 New
Product
Development
5 Finishing
Process
Specifications
The Quality Journey Starts
And Ends With Customer
1 Customer
Quality
Requirements
4
Raw Material
Purchasing
Process
3
Manufacturing
Equipment
Specifications
2 Finishing
System
Requirements
Figure 4. Elements of Armstrong’s Wood Quality Journey
Figure 5. Wood Finishing Value Process Map
Stain Appearance Darker With Medium Grit
- Type of equipment
- Grit sequence
- Sandpaper vendor
- Stock removal at each head
- Color varies with grit
How you control variation among
sanders:
Medium
Fine
Stock removal at each sander head:
Rough
Same grit sequence
Figure 6. Feeding & Sanding Input ‘x’s That Effect CTQ’s
Stain Roll
Coater
HMO & Stain Oven
CTQ's
Type of bulb
color visual; soft
& hard grain
Defect free fibers
Adhesion
color uniformity
Recognize Sources of Variation
Stain skips
shade appearance
CTQ's
Stain viscosity
stain prep: match
to shade COA
nip pressure
roller age
dwell time
x's UV Stain
# of bulbs
Bulb Power
air change rate
temperature
roll type
down pressure
x's HMO
x's
Figure 7. Stain Process Inputs ‘x’s That Effect CTQ ‘y’s
UV Lights
UV Lights
x's
line speed
roll type
down pressure
ctg temperature
Coating weight
Bulb type
Reflector shape
Power setting
CTQ’s
smoothness
gloss
adhesion
HA Sealer
Sealer
UV Lights
Wet-on-Wet
Topcoats
Low
CTQ’s Affected
• Adhesion
• Gloss
• Durability
High
Coating Too Brittle
UV Cure Energy
Coating Too Soft
Optimum
Cure Zone
Input ‘x’s Can Have A Major Impact On Big ‘Y’ CTQ:
UV Process Window
B-Stage Lights
Topcoat #1
Figure 8. Typical Four Station UV Finish Line
Plant 3
Each Coat/Cure Station Has A Set of Specifications That Must Be Met
Plant 1
Plant 2
Figure 9. Statistical Process Control Charts
Plant 4
UV Cure Energy
High
Coating Too Brittle
Stain
Sealer 1
Sealer 2
Topcoat
Final Topcoat
50
Gloss
Gloss
60
What If Two Lamps Are Off?
UV Measurement Drives Consistent Finish Quality
How Armstrong improved & sustains a
high quality UV finish process?
• All plants are equipped with spectral
radiometers to track UV lamp output.
• SOPs and special training for operators
• PM processes to minimize downtime and
special cause events
Low
Coating Too Soft
Optimum
Cure Zone
UV Process Window
Figure 10. Process Quality Control
18.5 21.5 24.5 27.5 30.5 33.5 36.5 39.5 42.5 45.5 48.5 51.5 54.5 57.5
Relative Position Across Lamp
UV Measurement Drives Consistent Finish Quality
80
85
90
95
100
105
Monitoring UV Lamp Uniformity AMD
mJ/cm2
What If Lamp Uniformity Off?
Figure 11. Statistical Process Control Charts For Plant Radiometry:
AMD UV Output Must Be Uniform: CTQ Gloss
Mj/cm2
Critical To Customer (CTQ) attributes for stain primarily focus on shade
match inter plant and intra plant for same products made at multiple plants.
To address variation that can exists between observers and qualitative
observations made on shade match, Armstrong utilizes an objective color
measurement system to reduce UV stain variation between plants.
Figure 12. Voice of the Customer: Shade Match
A Statistical Process Must Be Put In Place to Control Color Variation.
Figure 13. Quality Color Metrics Must Be In Place To Ensure Stain
Color Match Meets CTQ Attributes for UV stains .
Color
Gloss
Coating Adhesion
„
„
„
Durability
Radiometry
2000
1500
1000
500
0
4
3
2
1
0
Structure 1 Structure 2 Structure 3
(mils)
(mils)
(mils)
2500
5
Effect of HAS Thickness on Taber
Performance
„
„
Figure 14. Product Quality Control
HAS SEALER1
SANDING
SEALER
HAS SEALER2
1st Topcoat
2nd Topcoat
3rd Topcoat
‰The elements presented in this paper can be applied to other similar
systems. One thing is for certain: the journey always begins and ends in
the same place- with the customer.
‰Each step in the process has input variables that must be controlled by
SOPs and work instructions to reduce variation in the final product.
‰ Each process in the value map will have a set of process or material
variables that can ultimately affect one of the key attributes. The sigma
process map presented began with sanding and ended with product
quality control.
‰Quality improvements in UV finishing systems begin with sigma
attributes , which can be combined with sigma mapping of manufacturing
processes to identify inputs that effect CTQ
Conclusions