ASTM D5946-99

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Designation: D 5946 – 99
Standard Test Method for
Corona-Treated Polymer Films Using Water Contact Angle
Measurements
This standard is issued under the fixed designation D 5946; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope * contact angle; or (3) from the dimensions of the droplet’s
image, as follows (Test Method D 724):
1.1 This test method covers measurement of the contact
angle of water droplets on corona-treated polymer film sur- u5 2 3 arc tan H/R (1)
~ !
faces.
where:
NOTE 1—There is no similar or equivalent ISO standard.
H 5 height of a droplet’s image, and
R 5 half its width.
1.2 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information
Method (1) is biased due to the subjective nature of finding a tangent
only.
to the droplet image at the three-phase point; if Method (1)istobe
1.3 This standard does not purport to address all of the
used, the bias of each operator’s measurements must be determined;
Methods (2) and (3) are generally free of bias.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety and health practices and determine the applica-
4.1 In this test method, drops of water are placed on the
bility of regulatory limitations prior to use.
surface of a film sample, and the contact angle values are
2. Referenced Documents
measured and then averaged.
2.1 ASTM Standards:
5. Significance and Use
D 618 Practice for Conditioning Plastics and Electrical
5.1 The ability of polymer films to retain inks, coatings,
Insulating Materials for Testing
adhesives, etc. is primarily dependent on the character of their
D 724 Test Method for Surface Wettability of Paper (Angle-
surfaces and can be improved by one of several surface-
of-Contact Method)
treating techniques. The electrical discharge treatment, such as
E 691 Practice for Conducting an Interlaboratory Study to
corona treatment, has been found to increase the wetting
Determine the Precision of a Test Method
tension of a polymer film. The stronger the treatment, the more
3. Terminology
actively the surface reacts with different polar interfaces. It is
therefore possible to relate the contact angle of a polymer film
3.1 Definitions of Terms Specific to This Standard:
surface to its ability to accept and retain inks, coatings,
3.1.1 static contact angle, u (degrees), n—the angle be-
adhesives, etc., if the ink, coating, or adhesive contains the
tween the substrate surface and the tangent line drawn to the
polar functionalities. Contact angle in itself is not a completely
droplet surface at the three-phase point, when a liquid drop is
acceptable measure of ink, coating, or adhesive adhesion.
resting on a plane solid surface.
5.2 The wetting tension of a polymer film belongs to a
3.1.1.1 Discussion—Contact angle values can be deter-
group of physical parameters for which no standard of accu-
mined as follows: (1) by measuring the contact angle directly
racy exists. The wetting tension of a polymer cannot be
with a protractor by using tangential alignment of a cursor line;
measured directly because solids do not change shape measur-
(2) by measuring the angle between the substrate surface and
ably in reaction to surface energy. Many indirect methods have
the line from the three-phase point to the apex of the droplet,
been proposed. Different test methods tend to produce differ-
and then multiplying the obtained number by 2 to calculate the
ent results on identical samples. Practical determination of a
solid’s surface energy uses this interaction of the solid with test
liquids.
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
5.3 Although the level of surface treatment of polymer films
and is the direct responsibility of Subcommittee D20.19 on Film and Sheeting.
Current edition approved Dec. 10, 1999. Published March 2000. Originally
has been traditionally defined in the industry in terms of
published as D 5946 – 96. Last previous edition D 5946 – 96.
Annual Book of ASTM Standards, Vol 08.01.
3 5
Annual Book of ASTM Standards, Vol 15.09. U.S. Patent No. 5 268 733.
4 6
Annual Book of ASTM Standards, Vol 14.02. Wu, S., Polymer Interface and Adhesion, Marcel Dekker, Inc., New York, NY,
1982.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 5946
dynes/cm (mN/m), these values are derived from a subjective 6.6 The contact angle measuring method using tangential
interpretation of the observed test liquid behavior. alignment of the cursor line of a protractor, as described in
3.1.2.1 (1), is biased due to the subjective nature of finding a
5.4 The following ranges of water contact angle values can
be used as a guide for defining the level of surface treatment of tangent to the droplet image at the three-phase point. The
smaller the measured contact angle, the larger the error. The
polyolefins and many other polymer films with initial low
surface energies: bias of each operator’s measurements must be determined if
this method is to be used.
Marginal or no treatment >90°
Low treatment 85 to 90°
Medium treatment 78 to 84°
7. Apparatus
High treatment 71 to 77°
7.1 Contact Angle Meter, or Goniometer—The apparatus
Very high treatment <71°
for measuring contact angles must contain the following: (1)a
5.4.1 The suitability of the test for specification acceptance,
liquid dispenser capable of suspending a precise droplet of the
manufacturing control, and end use of polymer films will have
specified volume from the tip of the dispenser, (2) a sample
to be established through capability studies for each particular
holder that can stretch a film sample flat without wrinkles and
film and treatment.
distortions, (3) provisions for bringing the sample toward the
5.5 Almost all materials have variations in contact angle as
suspended droplet in a controlled manner to accomplish droplet
one moves from point to point. Non-uniform treatment of film
transfer onto the measured surface, and (4) means for project-
with corona treaters may also add variability to the results.
ing a “silhouette” image of the drop with minimal distortions.
Therefore, multiple measurements are necessary to reflect
The apparatus must have means for direct angle measurements,
variation in treatment and surface roughness.
such as a protractor, or direct measurements of the droplet’s
dimensions, such as a grid or scale, or both, or a suitable charge
6. Interferences
coupled device sensor and analysis hardware and software
6.1 The wetting tension of a polymer film in contact with a
appropriate for subsequent analysis.
drop of liquid in the presence of air is a function of the surface
energies of both the air-film and film-liquid interfaces; any
8. Reagents and Materials
trace of surface-active impurities in the test liquid or on the
8.1 Purity of Water—Deionized ultra filtered water should
film may affect the results. It is therefore important that the
be used for testing purposes. The test liquid must be kept in
portion of the film surface to be tested not be touched or
scrupulously clean containers.
rubbed, that all equipment be scrupulously clean, and that
water purity be guarded carefully. Glass apparatus, in particu-
9. Sampling
lar, is likely to be contaminated with detergents having very
9.1 The minimum amount of film required for this test is an
low surface tension, unless specific precautions are taken to
approximately 25-mm wide and 300-mm long sample strip. If
ensure their absence, such as cleaning with chromic sulfuric
a sample is taken from a roll, the direction of the sample
acid and rinsing with distilled water.
relative to the machine direction of the web must be noted.
6.2 The presence of slip, antistatic, or antiblocking and
9.2 Extreme care must be taken to prevent the surface of the
other additives can change the surface of the film since these
film sample from being touched or handled in the areas upon
additives leach out to the surface with time.
which the test is to be made.
6.3 Finely embossed films add more variability to the
9.3 The number of measurements per film sample can be
measurements.
determined using published tables for sampling plans. Com-
6.4 Polymer films often generate static charges when they 7
plete tables can be found in most books on quality control.
are processed. Corona treatment usually exacerbates the prob-
The recommended number of readings per sample is ten.
lems. The film sample for surface measurement may carry the
9.4 For the purpose of determining the contact angle profile
static charge generated in processing or may acquire a charge
across the width of the roll, one contact angle measurement can
by friction when sliding over the specimen holder surface.
be taken every 25 mm (1 in.) across the sample.
6.4.1 The static charges may cause errors in contact angle
measurements. These errors occur as the electrostatic field
10. Conditioning
generated by the charged sample pulls the water droplet to the
10.1 Conditioning is not generally required for routine
film surface stronger than it would be in the absence of charges.
quality assurance (QA) or process control measurements since
6.4.2 To prevent measurement errors, the film sample must
conditioning may affect the measured value and misrepresent
be kept free of static buildup before and during measurements
the actual conditions.
by placing an air ionizer, also known as a static eliminator, in
10.2 Conditioning is required for interlaboratory measure-
the vicinity of the specimen holder. These devices produce air
ments intended to compare the results. Condition the test
ions of positive and negative polarity. The charged object in the
specimens at 23 6 2°C (73.4 6 3.6°F) and 50 6 5 % relative
vicinity of the ionizer will attract ions of the opposite polarity
humidity for not less than 40 h prior to testing in accordance
and will be neutralized.
with Procedure A of Practice D 618, for those tests in which
6.5 The transfer
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