Polymer coating for dipped goods
Dear Linked in Members I could catch up with some interesting technical papers published by some leading Rubber Technologists across the World.
Here they are edited for yr ready ref. Developments in Polymer Coatings for Dipped Goods
By Bill Howe
President, PolyTech Synergies LLC
Canal Fulton, Ohio USA
Published on: Mar 4, 2016
Transcripts - Polymer coating for dipped goods
Dear Linked in Members
I could catch up with some interesting technical papers published by
some leading Rubber Technologists across the World.
Here they are edited for yr ready ref.
Developments in Polymer Coatings for Dipped Goods
President, PolyTech Synergies LLC
Canal Fulton, Ohio USA
(Latex glove donning requires lubricious surfaces other than powders.)
(Polymer coatings are applied on-line in properly designed dip tanks)
(The catheter industry has routinely used silicone lubricious coatings for
The use of corn starch, calcium carbonate, and talc as slip agents for
dipped products has seen better days for those manufacturing these
processing products. Historically, these products of choice dominated
latex processing as an anti-tack and donning application agent. The
manufacturing of products using powders was generally quite simple to
control, and easy to apply during the manufacturing process. A simple
controlled dosage of powder in a water or alcohol slurry tank normally
produced acceptable results, followed by de-powdering through a
tumbling process. Products such as gloves, condoms, finger cots,
breathing bags, medical balloons, probe covers, and toy balloons all use
this approach routinely during the manufacturing process.
However, with the advent of heightened alerts of latex allergies in the
1990’s, it was determined that proteins could be spread by residual
airborne powder from using latex gloves, which in turn jeopardized latex
sensitized personnel who could potentially react to latex allergens. This
led to the growth of powderfree latex products, which was primarily
achieved through chlorination of the finished product. Powders were
still employed in the manufacturing process for purposes of anti-tack of
work-in-process inventory. The finished latex products were then
transferred to a chlorination room where separate processing equipment
enabled the product to be subjected to chlorine, which in turn removed
the processing powders, and altered the surface of the film, allowing for
improved donnability and/or lubricity of the product.
However, there were many disadvantages to chlorination as a choice to
achieve the feature of powderfree donnable products, such as:
• Controlling levels of chlorination during batch processing proved
challenging, yielding batches with different donnability
characteristics, frustrating manufacturers and end users.
• Thin film products such as medical gloves and finger cots,
required extensive downstream handling, adding to
manufacturing cost. These products required a two cycle
chlorination process – one for each side of the product, with a
manual turning operation in between. This was necessary
because the thin film characteristics did not allow the chorine
batch to penetrate the inside of the product successfully.
Exceptions to this problem are household gloves, and other
thicker film products which allowed the chlorine batch to properly
penetrate the inner layer using one cycle only.
• Chlorination tends to degrade and weaken latex film properties. At
times, the chlorination-associated glove degradation results in
poor glove donning. Also, chlorinated gloves tend to adhere to
each other as part of the packaging process, especially exam
gloves and finger cots, which are packed in bulk boxes or poly-
• Those attempting to reduce downstream manufacturing handling
cost by applying the chlorine on-line during the dipping process
were introduced to other challenges of harrowing proportions. It
was often difficult to find space within existing dip lines to achieve
this process. Furthermore, without absolutely impeccable
ventilation control of chlorine fumes from the on line tanks, dip
lines were subjected to extensive corrosiveness from the process.
Those companies attempting to maintain a clean process found
the exercise futile, as particles were generated from damaged
machine structure and form carrier components.
• The buying marketplace generally did not warm up to the yellow
appearance of the dipped product, especially for surgical gloves.
The color “white” was king and perceived to be a more pristine,
In the 1980’s, a patent was issued for Biogel, a hydrogel product that
continues in use today. This coating was developed by then London
International Group, primarily for surgical gloves. This ingenious
product led to what today is a wave of choices for powderfree dipped
products through slip coatings. Enough history – let’s get on to today’s
choices for anti-tack and donning coatings.
Key RequirementsKey RequirementsKey RequirementsKey Requirements to Considerto Considerto Considerto Consider
Allegiance Healthcare (Cardinal Health), in its informative on-line
bulletin on “Powder Coatings for Powderfree Medical Gloves”, offers
some basic advice on preparing for the use of coating technologies for
latex products. The polymer design must consider the following
1. It must adhere to the underlying rubber latex substrate and offer
durability and good donning characteristics.
2. It must be resistant to chlorination and the vigorous post-forming
processing steps that can include rinsing, extraction, and drying.
3. It should not degrade after sterilization.
In Bill Williams’ (Research and Development Manager – Best
Manufacturing Co.) article from an earlier Rubber Asia article on “The
Science of Donning Coatings”, he states that donning coatings actually
serve two purposes. In addition to the obvious use discussed, which is
as a slip coating for donning latex products, he suggests that a second
purpose is to provide additional barrier properties. A properly applied
barrier film in some cases may reduce the affects of type 1 and type 4
allergic reactions. Agents such as anti-microbial agents, Aloe Vera and
vitamin E can be incorporated into the coating for improved benefit to
the end user. This is an excellent example of how differentiated the latex
glove business has become since the turn of the millennium.
In today’s highly differentiated product world of latex medical and
industrial products, the development of donning coatings can in be
applied to many substrate materials including natural rubber, nitrile,
polychloroprene, polybutadiene, polyvinylchloride, polyurethane,
polyisoprene, styrene diblock and triblock copolymers, and other
The application of donning or slip coatings on latex dipped goods is
primarily for one time or disposable use. Most coatings tend to be
hydrophilic, which reacts with the human skin, and degrades with
repeated use. Therefore the use of donning coatings with products that
are worn repeatedly, such as industrial gloves, is not a normal
Polymer Coating ChoicesPolymer Coating ChoicesPolymer Coating ChoicesPolymer Coating Choices
The development of polymer coatings for latex products continues to
expand. Listed below are those most commonly employed as of this
This type of polymer coating continues to be the most popular choice for
donning coatings on latex products. They have excellent
biocompatibility. They are normally applied to the latex layer as part of
the on-line dipping process. The adhesion of the polyurethane to the
glove substrate has of late been enhanced by the formulation’s ability to
be applied to the wet gel state of the latex during processing. During the
most recent International Latex Conference, Mr. Fung Bor Chen of
Medline Industries reported in his presentation and paper that this
capability of cross linking is achieved through inclusion of hydroxyl and
carboxyl functionalities in the polymer composition.2
improves blocking and increases stain resistance. He reports that a
system pH of 9 – 10 and a concentration of 0.1 to 1.0 phr of cross-linking
agent will enhance results.
Some recent advances have combined polyurethane with other
materials to achieve desired results. One PU dispersion is a linear
dihydroxy polyester reacting with diisocyanatetodiphynylmethane. This
emulsion is a copolymer of ethoxy ethyl methacrylate and methoxyl
methacrylate. A blend of 70 parts of PU dispersion with 30 parts of the
acrylate emulsion is used to coat the glove. Polyurethane dispersions
are typically diluted with water to 5-10% solids and applied to the
surface of the glove by dipping.
Another recent innovation, patented by Tony Yeh of Allegiance
Healthcare in March, 2002, suggests the achievement of powderfree
gloves with a silicone impregnated cross-linked polyurethane inner
This formulation suggests the aqueous coating composition
employ the following general recipe: 100 parts PU; 11.1 parts silicone;
1.0 parts surfactant; 2.2 parts cross-linking agent. Surfactants are added
to give stability to the compound and improve the wetting of the film. It
is critically important not to use an inordinate amount of surfactant, as
too much leads to oven efficiency issues and can cause excessive
foaming in the dip tank.
In his patent, Mr. Yeh suggests the following process for making a
powder-free elastomeric article having a coating comprised of a
crosslinked polyurethane impregnated with silicone on an internal
surface of the article. The steps include: (a) dipping a former into a
coagulant dispersion to deposit a coagulant layer onto the former; (b)
drying the former with the deposited coagulant layer; (c) dipping the
former with the deposited coagulant layer into an elastomer to produce
a second layer comprising coagulated elastomer thereon; (d) dipping the
second layer of coagulated elastomer into a powder-free dispersion
comprised of polyurethane dispersion, wetting agent, silicone emulsion,
crosslinker, stablizers and water to form a coating on the second layer;
(e) curing the layers and the coating on the former; (f) stripping the article
from the former; (g) treating the article to remove powder; and (h) drying
the article. 4
Thermoplastic or cross-linkable acrylics are employed as a powderfree
solution for latex dipped goods. It is reported that the capability of
cross-linking is achieved through inclusion of hydroxyl and carboxyl. A
hydroxyl is cross-linked using amino resins and isocyanates, whereas a
carboxyl is cross-linked through carbodiimides, azridines, and epoxies.
Acrylic coatings are based on acrylate polymers with elastic properties.
Their tensile strength and elongation are comparatively low to that of
natural rubber. This differentiation in properties may cause the acrylic
coating to crack and possibly delaminate or separate from the natural or
synthetic rubber. From a manufacturing viewpoint, some acrylic coated
devices are difficult to strip from the mould when hot, which may
produce challenges for processes being retrofitted from earlier latex
The initial hydrogel employed in actual production was Biogel, which
was a coating applied to surgical gloves. This coating dominated the slip
coating industry in the 1980’s and early 1990’s. Hydgrogel coatings are
used routinely on other medical products such as heart balloons,
contact lenses, and catheters. The absorbed water in the hydrogel
coating forms a water film on the substrate surface.
The key challenge is to achieve high reliability of bond of the hydrogel to
the substrate surface. It is reported that some treat the substrate layer of
rubber with acid or other adhesive before applying the hydrogel to the
product. This has obvious disadvantages by making the manufacturing
process complex and inconsistent. In many cases, if an adhesion is
poor, then the hydrogel coating will delaminate and flake, generating
harmful particulate during use.
Past practice in latex processing has led to the application of silicone to
finished dry film products. For many years, latex breathing bags were
treated with silicone in downstream tumble dryers, which in turn
provided a sheen or appealing cosmetic appearance to the end product.
For other medical devices, such as Foley catheters, silicone coatings
have been routinely used to improve the surface lubricity and patient
comfort during use. Using silicone coatings for catheters rather than
chlorination, again produces a more pristine looking product, given its
white appearance as opposed to the less attractive yellowed chlorinated
Some gloves today are treated with silicone as a donning agent, but in
general are not as popular as other donning polymers in that they
typically fail to provide adequate damp and wet donning capability.
The newest innovation in donning coatings, especially in use with
natural rubber products, is nitrile latex. Nitrile is a synthetic latex
comprised of acrylonitrile, butadiene, and carboxylic acid. An
advanatage of using nitrile is that it has excellent chemical resistant
properties. Its benefits include good tensile strength, adequate elasticity,
and adequate adhesion to natural rubber during the manufacturing
process. Cardinal Health introduced this concept with their Protegrity®
surgical glove, a triple dipped product. The outer layer is natural rubber
latex. The inner layer is reportedly a blend of natural rubber latex and
nitrile, with the donning side comprised of 100% nitrile polymer.
Cardinal’s product literature makes performance claims of tensile
strength range from 3919 to 4064 psi and ultimate elongation in excess
Coating CharacteristicsCoating CharacteristicsCoating CharacteristicsCoating Characteristics
The following table offers some general guidelines to the use and
performance of slip coatings.
HydrogelHydrogelHydrogelHydrogel PUPUPUPU AcrylicAcrylicAcrylicAcrylic SilicSilicSilicSiliconeoneoneone NitrileNitrileNitrileNitrile
Low Low High
Adhesion toAdhesion toAdhesion toAdhesion to
Low Medium Medium Low Medium
ElongationElongationElongationElongation Low High Low Medium High
LubricityLubricityLubricityLubricity High Medium Medium High High
Medium Low High
Low Medium Medium Low Medium
Oil resistanceOil resistanceOil resistanceOil resistance Medium High High Low High
(lower is(lower is(lower is(lower is
High Medium Low Low Low
Integrity afterIntegrity afterIntegrity afterIntegrity after
Low Low High
(Table made courtesy of Cardinal Health; Billmeyer, 1984; Pauly, 1989)
Manufacturing ConsiderationsManufacturing ConsiderationsManufacturing ConsiderationsManufacturing Considerations
It is imperative that polymer coatings be applied uniformly on the latex
substrate surface for optimal performance. Since a polymer coating is a
mixture of water and polymer, it has a higher surface energy than dry
latex films. Therefore, coatings tend to perform better when applied to a
latex substrate in wet gel state, and especially when the latex substrate is
dipped using lower solids content. The higher water content tends to
benefit the application of polymer coating when in a wet gel.
The quality of water employed in the slip coating solution contributes to
performance as well. Water with high iron content and rich in calcium
can lead to an instable polymer. Deionized water may be helpful to
performance, but one must be careful as bacteria can breed more easily,
and typically is lower in pH. Careful use of FDA approved bactericides
can overcome these issues.
The application of the water based polymer is performed as part of the
on line dip system. The latex substrate should be leached as a wet gel
prior to applying the coating. Leaching time should not be less than 1.5
minutes, and preferably more. After drying the film to remove surface
water resultant from the leach system, the coating application can then
ensue. One should allow the polymer to drip for a short time (12
seconds), before camming to help distribute the polymer coating for
uniformity purposes. The product is then ready for final vulcanization.
On-line, post oven leaching follows the final cure process.
For the coagulant bath, some continue to use calcium carbonate
powders to achieve proper release from the mold. For example, Mr. Yeh
reports in his patent for PU and silicone coating, that the coag bath is
comprised of calcium nitrate, calcium carbonate powders, wetting
agents and water (or alcohol for alcohol based coagulant dispersion).
However, others have made successful strides to eliminate calcium
carbonate from coag solutions to achieve a true powderfree product.
Products such as Coag Plus Hydrogel and Coag Plus Dispersion, by
Crusader Chemical in the USA, are employed with water or alcohol
accompanied by calcium nitrate. No calcium carbonate is employed
using this process. The Coag Plus products have been prepared with
proper defoamers and surfactants, to enable the manufacturer to simply
add Coag Plus to warm water, followed by the addition of calcium
nitrate. Products such as this have been designed to promote leveling,
wetting, and latex pick up, as well.
Unicote® is a product offering of National Starch and Chemical which
also claims to offer solutions for both coagulant and polymer coating
Simple Tests of Coating EffectivenessSimple Tests of Coating EffectivenessSimple Tests of Coating EffectivenessSimple Tests of Coating Effectiveness
At the International Latex Conference in 2004, Mr. Fung presented a
basic method for screen testing of polymer coated films, as follows:
1. Cytotoxicity – take a cup of water, placing the glove in the cup
with water about ¾ full. Rub the glove under water for 2 minutes.
Remove the glove and observe bubbles formed. The more bubbles
that are formed, the more likelihood that the glove will cause an
allergic reaction to those sensitized.
2. Dry Donning – Hold glove in one hand at the cuff area. With the
other hand, twist the glove with two fingers, feeling for the ease of
movement for one surface with the other.
3. Wet Donning - Fill the glove with water, and allow to set for a few
seconds. Pour out the water. Hold the glove in one hand at the
cuff area. With the other hand, twist the glove with two fingers,
feeling for the ease of movement for one surface with the other.
4. Adhesion – Stretch the glove while rubbing the coating repeatedly
with thumb. Observe the degree of coating that flakes off the glove
to the thumb.
5. Block – Press two gloves together. Evaluate adhesion by observing
the ease of separation between the two when pulled apart.
With many choices available today for polymer coatings, it is apparent
that the dipped goods industry has been rewarded because of its due
diligence towards reducing latex protein exposure, and providing
improved product offerings.
About the Author
Bill Howe is President of PolyTech Synergies, a firm specializing in
engineering and marketing services for dip molded and dip coated
polymer products. Contact Mr. Howe at firstname.lastname@example.org or
“Research & Technology Supporting Your
Fung Bor Chen, “Overview of Powder-Free Technology and Materials”,
2004 International Latex Conference – Akron, Ohio.
Y.S.T. Yeh, “Powder-free gloves with a silicone impregnated cross-linked
polyurethane inner coating and method of making same, “US Patent
Application No. 20020029402, March 14, 2002.
Y.S.T. Yeh, “Powder-free gloves with a silicone impregnated cross-linked
polyurethane inner coating and method of making same, “US Patent
Application No. 20020029402, March 14, 2002.
mportant Facts about Latex and Latex Gloves
Natural Rubber Latex Gloves - Made from a Renewable Resource Natural rubber (NR) late
gloves are natural products. They are derived from NR latex obtained from the Hevea
Brasiliensis tree when the bark is tapped (Figure 1). This is unlike all synthetic gloves, wh
are made from petrol chemicals.
Figure 1. Natural rubber latex collected in a cup after skillful tapping of the bark o
Hevea Brasiliensis tree.
Raw NR Latex
This is a milky fluid comprising 25%-40% of rubber hydrocarbon in the form of particles
suspended in an aqueous serum together with a few percent of other non-rubber substa
such as proteins, lipids, carbohydrates, sugars, some metals, fatty acids, and other substa
known as the non-rubber fraction. The remaining major component is water.
NR Latex Concentrate
Latex collected from the tree after tapping is concentrated generally by centrifugation, to
remove much of the aqueous components. The concentrated latex with about 60% dry ru
content (or drc) is then usually preserved with ammonia to combat bacterial growth. The
resulting latex concentrate becomes the starting material for all natural rubber latex prod
whether by dipping (for gloves, balloons, condoms, catheters, baby soothers, rubber tubi
toys and dental dams) or other processes such as foaming (for latex foam to sponge), or
extrusion (for latex thread, more commonly known as "elastic").
Steps in the Manufacturing Process
The manufacture of most NR latex gloves follow roughly the same sequence. However, m
manufacturers include processing steps that reduce the level of protein in their gloves. Th
typical glove manufacturing process is as follows:
The salient features of the above manufacturing processes include the following:
Dipping: Liquid latex concentrate is mixed with various compounding chemicals and is
introduced into one of the tanks in the processing line. Clean, dry formers in the shape o
hands are immersed first in a coagulant and then in the latex mix for appropriate dwell
to give the desired latex film thickness. The coagulant is applied to facilitate the depositio
layer of latex on the formers.
Wet-gel leaching and beading: The thin latex film on each former is partially dried and
leached briefly in clean water to remove the water-soluble materials. Beading also is
introduced at this stage to give each glove a rolled bead or rim at the open end.
Drying and curing: The gloves are then dried and vulcanized. Drying and vulcanization o
curing of the gloves are usually done in hot-air ovens, initially at lower temperatures of 8
C, and then at higher temperatures of 100º-140º C where necessary.
Post-cure leaching or dry-film leaching: The cured gloves are immersed in clean water ta
remove more water-soluble substances, particularly proteins on the surface of the gloves
Powdered gloves: The leached gloves are dipped into cornstarch powder slurry to pick up
coat of lubricant that makes them easier to don. They are then further dried.
Glove stripping: This is the final operation on the production line - removal of gloves from
formers. This is often carried out manually, frequently with the assistance of compressed
but an automatic stripping system is becoming more common.
Powder-free gloves: Latex gloves with very little or no powder lubricant can be prepared
either (i) chlorination or (ii) polymer coating. While chlorination oxidizes the outer rubbe
surface to eliminate tackiness and reduce the residual soluble protein content, polymer
coating involves replacing powder with a suitable lubricating coat on the glove surface. B
processes can be carried out on-line, without the powder-coating step, or off-line by was
first the finished powdered gloves, then subjecting them to the chlorination or polymer-c
Removing Glove Proteins
Protein Status in Latex
When subjected to ultracentrifugation at approximately 59,000 gmax, latex can be separ
into three main fractions: (i) top rubber hydrocarbon fraction, (ii) the ambient serum (kno
C-serum) in which all rubber particles are suspended, and (iii) the denser bottom non-ru
particle fraction, particularly lutoids, which contain yet another serum (known as B-serum
• Yip E. & Cacioli P, The manufacture of gloves from natural rubber latex, J. Allergy C
Immunol., 2002; 110: S3-14
Like all plant materials, Hevea latex contains proteins. Of the approximately 1% of total
proteins present in the latex system, about one-quarter are found on rubber particle surf
(i), the remaining three-quarters are in the non-rubber phase [fractions (ii) and (iii)] of the
and they are mostly water soluble (Figure 3).
Figure 3. Freshly collected Hevea Brasiliensis latex separated into its three main fractions
ultra centrifugation at 59,000 gmax.
When processed into latex concentrate, considerable amounts of the soluble proteins are
removed. Further conversion of the latex concentrate into gloves removes more of these
proteins through the leaching and washing steps. Therefore, the remaining levels of solub
proteins - or the residual extractable proteins implicated in allergic reactions - are marke
low. Depending on which manufacturing process is used, the level of residual extractabl
protein can vary widely.
• Dalrymple S.J. and Audley G.B. "Allergenic proteins in dipped products: Factors
influencing extractable protein levels," Rubber Developments, 1992; 45(2/3):51
• Yunginger J.W., Jones R.T., Fransway A.F., et al. "Extractable proteins in disposable
medical gloves and other rubber products," J. Allergy Clin. Immunol. 1994; 93: 836
• Ng K.P, Yip E., Mok K.L. "Production of Natural Rubber Latex Gloves with Low Extra
Protein Content: Some Practical Recommendations," J. nat. Rubber Research, 1994;
Not all proteins in the residual extractable fraction cause the allergic reaction. Although t
13 proteins (mostly soluble) in raw Hevea latex have been reported to be possible allerge
defined by their display of IgE antibody binding activities, it is unlikely that all of them w
be present in the finished products after processing.
• Alenius H., Turjanmaa K. and Palosuo T. "Natural rubber latex allergy," Occup. Envi
Med, 2002; 59: 419-424;
• Yeang H.Y. "Natural rubber latex allergens: New developments," Curr Opin Allergy C
Immunol. 2004; 4: 99-104),
“Close structural similarities between any two allergens from divergent sources can prod
similar allergic reactions in sensitive patients, and is termed cross-reactivity or
cross-sensitization. Ingestion of some foods could produce allergic symptoms in patients
sensitive to latex proteins due to the presence of these common or cross-reactive protein
allergens, such as in the case of avocado, banana, chestnut and kiwi. However, it is impo
to note that not all food-allergic individuals are sensitive to latex, and not all patients wit
allergies will have problems with these foods.
A study of binding patterns of IgE antibodies from the blood sera of individuals, who wer
latex allergic but who had reactions to fruits, supported this. The study findings also show
that multiple bindings could occur between latex serum proteins and IgE from many wh
reacted to extracts of fruits but not to latex gloves. On the other hand, more specific and f
bindings to latex protein were observed by those who were skin tested positive to latex g
• Hasma H., Shahnaz M., Yip E., Azizsah M., Mok K.L. and Nasuruddin B.A. "Binding
Patterns of IgE Antibodies in Sera of Rubber Tappers to Fresh Hevea Latex Serum
Proteins," J. Rubber Research, 1998; 1(3): 146-153
Allergenicity of Latex Gloves
The allergenic potential of latex gloves can be measured in-vivo by skin-prick testing (SPT
latex-allergic subjects, or in-vitro by specific IgE antibody-inhibition immunoassays. The
method is known to be more specific and more sensitive than the IgE binding technique
However, all of these methods are relatively sophisticated, and require further improvem
and they are also expensive to perform.
The presently preferred method is the quantification of total proteins using the modified
micro-assay, which is technically easy and possible to standardize as well as cost effectiv
However, the test is not allergen specific. Nevertheless, significant correlations between
residual total extractable protein content and the allergen levels of extracts of NR latex gl
based on both serological IgE specific inhibition immunoassays, and the SPT testing, hav
been established. Latex gloves with high residual extractable protein contents are associa
with positive SPT or high allergen contents. Latex gloves with very low residual extractab
proteins, on the other hand, tend to have very low or negligible SPT reactions by latex sen
Figure 4. Total extractable protein content (as measured by modified Lowry assay) of la
gloves and percentage negative skin prick test response shown by latex sensitive subject
Yip E., Turjanmaa K., Ng K.P. and Mok K.L. "Residual extractable proteins and allergenic
natural rubber products," J. nat. Rubber Research, 1994; 9: 79-86;)
Figure 5. Total extractable protein content and allergen level of 46 lots of latex gloves
determined by modified Lowry test and IgE latex specific ELISA-inhibition respectively
Yip E., Palosuo T., Alenius H., and Turjanmaa K. "Correlations between total extractable pr
and allergen levels of natural rubber latex gloves," J. nat. Rubber Research, 1997; 12: 120
This method, although non-allergen specific, offers a technically easy and standardizable
method that is very helpful in product developments and improvements.
• Yip E., Turjanmaa K., Ng K.P. and Mok K.L. "Allergic Responses and Levels of Extractab
Proteins in NR Latex Gloves and Dry Rubber Products," J. nat. Rubber Research, 1994;
• Yip E., Palosuo T., Alenius H., and Turjanmaa K. "Correlation Between Total Extractable
Proteins and Allergen Levels of Natural Rubber Latex Gloves," J. nat. Rubber Research,
• Palosuo T., Makinen-Kiljunen S., Alenius H., Reunala T., Yip E. and Turjanmaa K.
"Measurement of natural rubber latex allergen levels in medical gloves by allergen-sp
IgE-ELISA-inhibition, RAST inhibition, and skin prick test," Allergy, 1998; 53: 59-67;
• Beezhold D., Pugh B., Liss G. and Sussman G. "Correlation of protein levels with skin p
test reactions in patients allergic to latex," J. Allergy Clin. Immunol., 1998; 98: 1097-11
• Yip E. and Sussman G. L. "Allergenicity of latex gloves with reference to protein sensiti
individuals in a Canadian population," J. nat. Rubber Research, 2000; 3: 129-141.
Protein Reduction - Product Improvement
Residual extractable protein content of gloves can now be reduced from as high as 1,000
µg/g of gloves to a low of less than 50 µg/g using improved manufacturing technologies,
o Use of low-protein latex concentrates
o Proper leaching protocols
o Chemical or enzymatic deproteinization
AUTOMATIC STRIPPING OF GLOVES
IN A HIGH VOLUME PRODUCTION ENVIRONMENT
- A TECHNICAL PRESENTATION AT MARGMA
GLOVE CONFERENCE; K-L, MALAYSIA; 1999 –
By: William L. Howe
PolyTech Synergies LLC
8751 Mardel Ave. NW
Canal Fulton, OH 44614 USA
(P) 330 854 6715
Probably no innovation in the 1990's for automation in the glove
manufacturing sector has impacted productivity of manufacturing
plants like that of technology for automatic stripping of gloves. The
purpose of this paper is to inform and prepare the reader for the
1. Identification of the critical evaluation factors before investing in
technology for automatic stripping.
2. he general techniques employed today for successful automatic
stripping of gloves.
3. ealistic expectations for commissioning and performance of the
4. To spur creative thinking and planning for related downstream
automation, connected to production machine auto strip devices.
In general, this paper will address techniques for unsupported thin
gauge gloves, with brief mention of techniques for household gloves and
supported industrial work gloves.
The writer and his company have identified and/or designed for five (5)
different techniques for automatic stripping. These techniques can also
be considered for dipped products other than gloves, such as bags,
condoms, catheters, balloons, etc. Selection technique for each
application will depend upon many factors, which will be identified and
briefly described in Section 3.0 of this presentation.
2.1 Pressure Pad / Rotating Brushes
This technique is used primarily for a "straight-off " stripping of a dipped
product. For the glove industry, one will find this technique utilized for
stripping of supported industrial work gloves.
Typically, a pair of cushioned pads (to protect ceramic formers) would
encase the glove former as it passes, using a two axis motion (squeeze
and drop), which through pressure, will enable the glove to loosen and
free from the mold, for deposition onto a conveyor or tote bin.
A similar technique uses a pair of rotating brushes, which encase the
former. The brush technique typically involves the use of one axis
motion only (brush rotation) to accomplish the strip. However, a second
axis can be added to accommodate different size formers entering the
same brush system. This second axis is often accomplished with the use
of compressed air or mechanical spring, to enable the brush to adjust to
the differing former diameters.
The rotating brush technique is seldom employed with glove stripping,
and is more conducive to " straight-off " stripping of symmetrical dipped
products, such as condoms and toy balloons (See Figure 2. 1. 1).
2.2 Water Jet
Though not a popular choice for glove stripping, the use of water jets can
enable gloves to be automatically removed from molds, if the "straight-
off" method is desired. The primary disadvantage of this approach is that
the glove becomes wet, which necessitates more attention to glove
collection and downstream drying.
The writer has specified the use of water jet systems for back-up
stripping, when requested. In this format, the actual automatic stripping
is first conducted by "dry" means in the main stripping station. If gloves
are missed (which is a normal occurrence), the water jet(s), located in the
former washing station, would eject gloves from the mold onto a screen
inside a containment tank. Normally, the gloves removed using this back
up technique, are considered as Scrap.
The use of water stripping is more common for use with symmetrical
products such as condoms and toy balloons.
2.3 100% Compressed Air
If removing unsupported gloves via a "straight-off" technique, the most
reliable method is by compressed air, which typically requires
significant volume and pressure to accomplish the strip. If the
manufacturer is chlorinating both glove sides downstream, this method
can be employed successfully. Otherwise, the texture of the mold is
transferred over to the inside of the glove, which is typically not the
preferred result. Furthermore, the outside of the glove when used, would
represent the side of the glove having seen most effects of the protein
wash station. This means that the inside of the glove, which is next to the
user's skin, would be the side not seeing the effects of the protein wash.
The use of "straight-off" technique via air has the advantage of being a
low cost in capital investment. However, operational costs are typically
considered as high.
2.4 Combination Air/Mechanical
The technique patented by the writer's company, combines the use of
compressed air and mechanical grasp, which has been designed for
reversing the glove during the pick to minimize downstream product
An artist rendering of the concept can be seen in Figure 2.4. 1. The
technique is most commonly employed with continuous chain lines. A
key consideration is that of line speed and the ability to synchronize the
apparatus with the movement of the line. The system shown
accomplishes that with mechanical gearing in conjunction with the
conveyor chain. A second method for synchronization would be to
accomplish this electronically by communicating pulses to the conveyor
This technique (first proven in production in the late 1980's), uses a three
(3) step approach as follows;
• First, engage a set of fingers to "hold" the glove at the middle finger
area of the former.
• During the engagement of the mechanical finger, a blast of air is
enacted at the cuff area (effective for both beaded and non-beaded
gloves) so that the film begins to move down the mold. The
"holding" device prevents the fingers from inflating, which in
conjunction with the air blast, allows the cuff area to reverse on
itself, with the cuff area surrounding the mechanical fingers.
• Thirdly, the mechanical "grasp" fingers cam away from the former,
leaving the glove cuff free to be removed with a final set of rotating
brushes into a vacuum delivery system or moving conveyor. This
effectively fully reverses the glove.
This technique has been considered an effective approach in stripping
natural rubber latex gloves. I believe it fair and accurate to say that this
specific technology has had limited success in conjunction with other
polymers, such as nitrile and neoprene.
Investment capital cost and operational cost for this technology are
considered in the moderate range.
2.5 Full Mechanical Pick Technique
Common sense would inform us that the best motion to simulate for
automatic stripping would be that of the human motion. This technique
involves the automation simulation of that thought. An example of such
a technique can be seen in Figures 2.5. 1. The device normally employs
the use of 3 axes for both batch machine and chain machine
The key to its success is that of accurately engaging the "finger grasp
mechanism" to the bead on the glove or inside the cuff of the glove. This
accuracy is often accomplished by a roll down brush followed by
mechanical finger engagement in the cuff area, followed by a roll up
brush back over the fingers. The two mechanical fingers are now
positioned between the glove film and the former. After this first step is
accomplished, the mechanism can be moved vertically in a downward
stroke, to effectively reverse the glove and remove it from the mold.
This technique has more universal appeal to different types of polymers,
including natural rubber latex, nitrile, neoprene, and PVC.
However, the primary disadvantage to this technology is that capital
acquisition cost is typically high. Furthermore, on going maintenance
costs make for moderate to high operational cost as well.
This technique is adaptable to both batch dipping systems or chain
3.0 CRITICAL FACTORS FOR SUCCESS
The following factors must be evaluated before advancing into the
design and implementation phase of automatic stripping. A brief
commentary on each factor will assist the reader in evaluation of his or
her own factory situation.
3.1 Type of Machine
Two primary types of dipping units are employed in production
manufacturing - batch and continuous chain. The technique used for
automatic stripping will differ in accordance with the general overall
type or machine employed. General access into tile former rack or
individual former is a consideration and must be evaluated.
A batch machine often employs the use of pallets measuring 1.5 by 3.0
meters, containing a dense former pack. The key to consider automatic
stripping in this environment is accessibility to all formers. The best
condition for batch machines are those whereby individual former
"strips" (containing several formers) separate from the pallet, which
enables free and clear access for the automation.
The key consideration for chain lines is that of former orientation and
chain speed. For nonrotating former chain lines, orientation of the molds
are already accomplished, making for an ideal auto stripping condition.
However, rotating former lines, which are the most common type used
in Asian factories, require the adaptation of a former orientation system
when entering into .the automatic device. This can be accomplished
with a "carrier spoke" or "D" cam device (machined flat surface on a
round bar), both of which contact and slide across a frictionless surface
to stabilize the mold.
3.2 Type of Glove and Sizing
In general, supported gloves utilize the "straight-off" techniques and
unsupported gloves necessitate the "glove reversal" techniques available.
However, there are some exceptions to unsupported gloves, which can
mandate "straight-off" approach.
In general, ambidextrous gloves are easier to strip than hand specific
ones, considering the reversal technique. The protruding thumb on a
surgical glove former can make for a stubborn strip, unless employing
the proper technique. Another consideration for hand specific gloves is
that of straight finger versus curved finger design. The most challenging
combination would be that of a curved finger surgical-mold, produced
on a continuous chain conveyor. It can be accomplished but generally
by using the full mechanical pick technique described in Section 2.5,
which can involve a sizable investment in capital.
3.3 Type of Polymer
The type of polymer employed will also greatly sway the selection
technique. A general order of automatic stripping complexity by glove
polymer list for unsupported gloves, in the opinion of the writer, is as
follows, listed from easiest to hardest;
Easiest 1 Natural rubber latex
5 Styrene butadeine
Hardest 7 Polyurethane
3.4 Former Shape and Texture
Mention has already been made for the consideration of ambidextrous
gloves (formers) versus hand specific gloves (formers). However, another
key to auto stripping successfully, lies in the former shape and texture.
For natural rubber exam gloves, a more "tapered" mold shank from cuff
to wrist area, functions better for certain strip techniques, particularly
the combination air and mechanical approach. The other key area of the
mold is that of the thumb orientation or protrusion. A more gradual 1,
sloping" thumb allows the glove to work its way over the mold more
easily, versus a sharp bend at this area.
A lesser consideration, at least for natural rubber products, is that of
glove texture. In general, all former surfaces can adapt well for
unsupported natural rubber glove former textures employed, including
unglazed, spray bisque, and glazed. However, for synthetic polymers
such as silicone and polyurethane, a glazed former surface will perform
more consistently for removal techniques, both manual and automatic.
3.5 Glove Sizing Management
This factor may not affect many of the participants of this conference. In
general, most current chain lines in Asia are dedicated to one glove size
only. This is the most simplistic condition under which to address
automatic glove stripping. Some of these machines (rotating form - over
and under chain), may employ one size former on one line side, with
another size former on the other machine side. This also represents a
However, larger volume machines (the writer's company has designed
machines with volumes up to 60,000 pieces per hour) typically contain
several gloves sizes on the same system. Therefore, two further
considerations must be given to this condition;
1. The technique employed must be able to adapt to different former
sizes coming through the system.
2. After, the automatic strip is. accomplished, size sortation must be
considered, which can be accomplished manually by a single
operator, or by additional automatic means.
3.6 Polymer Formulation
One word of caution to anyone considering implementation of
automatic stripping technology to their plant - be prepared to aller your
latex and coag formulations, if necessary. The writer is not qualified to
comment on specifies of formulation adjustment. However, we have
more often than not, seen our customer base require some modification
to their formulation to avoid glove tearing (if using compressed air
source as part of the technique) and ease of release from the mold. The
amount of mold release in the coag may require adjustment.
3.7 Current Level of Formulation Reliability and Equipment Reliability
This is key - key - key. The writer cannot emphasize enough the
importance of consistent glove production in a manual stripping
environment, before investing in automatic technology. Inconsistent
formulation management in film properties from day to day, machine to
machine, etc. can allow the auto strip technology to work some days,
and falter on other days. For example, if the level of calcium carbonate
in the coag fluctuates, auto strip effectiveness can plummet.
On the machine side, one important performance statistic is that of
"good beads (rolled cuffs)". If the bead roller unit on the machine misses
beads from time to time, you can expect the auto strip device to do the
same. If the system oven performance fluctuates thus causing the
general state of curing to decrease, auto stripping performance will
suffer. In general, auto stripping works best with a more highly cured
You should consider yourself a candidate for automatic stripping
technology only if your day to day machine and formulation
performance is consistent and reliable.
4.0 IMPLEMENTATION OF TECHNOLOGY
The candidate for automatic stripping technology, after determining that
they meet all prerequisites for institution of the automation, must be
prepared to exercise patience during implementation.
Initially, the first phase of the evaluation, which is proper identification
of technology, should occur by an on site study on the part of the
automation provider. After thorough assessment of the application and
other factors, expect a design phase to ensue, even in the event the
automation provider has already supplied technology to other firms. As
insinuated throughout this paper, every plant can differ in machine
conveyance, type, speed, and especially formulation. The state of glove
cure at the strip station is crucial for reliable performance.
After this phase, the automation equipment is fabricated and assembled
for installation at the user's plant. Installation of the technology normally
would require from 3 to 7 days to complete.
The commissioning phase of the technology is the area whereby the user
needs to exercise patience. Several adjustments to the technology are
typically necessary. As previously mentioned, it may by imperative for
the formulation to change to assist reliable take off of the glove.
Itemized below for the reader's review is a representation of a typical
schedule for an automation program;
Phase One Technology Identification 2 to 6 weeks
Phase Two Engineering Design 3 to 9 weeks
Phase Three Build Equipment 8 to 10 weeks
Phase Four Install Equipment 2 to 3 weeks
Phase Five Commission and Debug to 12 weeks
TOTAL PROGRAM 20 to 40 weeks
5.0 I A CHALLENGE FROM THE AUTHOR
The writer encourages the reader to not limit the prospects of their plant
to automatic stripping alone. Without question, the implementation of
auto strip technology will make for significant productivity
improvements in your operation.
However, my challenging question to the reader is this - why limit your
thinking to that of glove removal only? Today, in the USA, few glove
manufacturing plants remain due to many reasons, the primary one
being competitive forces and productivity improvements over the last 15
years in Asian operations.
The plants that remain active and successful in the USA, in general, are
successful for one reason - they have nearly removed all plant labor
from the manufacturing process. This means they not only strip gloves
automatically in a reliable fashion, but after stripping automatically sort
gloves, and automatically convey them to the packing room,
automatically moving them through any tumble drying necessary, and
automatically counting and orienting the gloves, into an automatic
The writer has not only seen the advent of this technology, but has been
intimate with it in concept and design. My challenge to you is to have
this vision for your factory. This is not"drawing board fluff" -it is reality for
the 20th century and beyond.