DD255992A1 - Method for assessing belt or plate fatigue subject - Google Patents

Method for assessing belt or plate fatigue subject Download PDF

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Publication number
DD255992A1
DD255992A1 DD29615386A DD29615386A DD255992A1 DD 255992 A1 DD255992 A1 DD 255992A1 DD 29615386 A DD29615386 A DD 29615386A DD 29615386 A DD29615386 A DD 29615386A DD 255992 A1 DD255992 A1 DD 255992A1
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DD
German Democratic Republic
Prior art keywords
wettability
wetting
speed
plate
uniformity
Prior art date
Application number
DD29615386A
Other languages
German (de)
Inventor
Ludwig Grader
Reinhard Kaermer
Wolfgang Hopf
Ernst-Otto Reher
Original Assignee
Wolfen Filmfab Veb
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Wolfen Filmfab Veb filed Critical Wolfen Filmfab Veb
Priority to DD29615386A priority Critical patent/DD255992A1/en
Publication of DD255992A1 publication Critical patent/DD255992A1/en

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Abstract

The invention relates to a method for determining the wettability of a tape or plate-like base by pulling a strip of the substrate to be examined from a test liquid which is incompletely wetting in the stationary state. According to the invention, the pulling speed is increased from a small value in the area of incomplete wetting in small steps or even with low acceleration, and one measures the speed of incipient and complete film formation. The average of the two measured velocities includes a criterion for wettability and the difference between the two measured velocities contains a measure of the uniformity of the wettability.

Description

Field of application of the invention
The invention relates to a method for determining the wettability of a tape or plate-shaped pad by an incompletely wetting liquid. The determination of the wettability of solid surfaces is needed in coatings and other processes where solid surfaces and liquids come into contact.
Characteristic of the known state of the art
The determination of the wettability of a tape or plate-shaped pad is often made by measuring the static contact angle between the pad and an incompletely wetting test liquid. The contact angle can be measured both on a drop of liquid which is placed on the uncovered pad and on an air bubble on the otherwise completely liquid-covered pad. The size of the static contact angle is a measure of the static wettability of the underlay.
In DE 2053390 a method for determining the wettability of a surface is described in which a plurality of drops applied to the surface are illuminated and the illumination angle is changed until reaching the critical angle of reflection to the observer. With this method, the contact angle of a static liquid can be determined with sufficient accuracy.
In many technical processes, eg. As in coating processes, not the static, but the dynamic wettability of the pad is of interest. It is known that the dynamic wettability differs significantly from the static. A measure of the dynamic wettability is the dynamic contact angle whose measurement was summarized by Johnson and Dettre in Surface and Colloid Science 2 (1969) 85.
It is further known that for dynamic wetting there are two limiting speeds, the minimum wetting speed below which no dynamic wetting film is formed any longer, and the maximum wetting speed above which air bubbles are sucked.
Like the investigations of Gutoff and Kendrick in AIChE-J. 28 (1982) 3,459, the maximum wetting rate is determined essentially only by the properties of the test liquid and is thus not suitable for characterizing the wettability of a substrate.
For the determination of the dynamic wetting ability, a method is described according to DD 117528, in which a hanging meniscus is generated on a rotating test cylinder. The maximum peripheral speed serves as a measure of the wettability. Since this speed corresponds to the maximum wetting speed, the method has the disadvantage of providing only statements about the wettability of the test liquid, but not about the wettability of the surface of the test cylinder.
In order to determine the dynamic wettability, DD 147 414 proposes a method in which a drop of liquid runs on a plane inclined to the horizontal. The shape of the surface of the liquid running in the wetting area and its speed are detected, wherein the dynamic contact angle serves as a measure of the wettability. This method is well suited for determining the dynamic wettability of sheet or plate-like documents, but has the disadvantage that only a narrow strip of the base can always be measured.
Statements of local variations in wettability can only be obtained from a variety of experiments.
In contrast, a method for the determination of surface inhomogeneities is described in DD 217313, in which the positional fluctuations of the advancing meniscus between a capillary and the moving surface are detected optoelectronically. This method is very well suited for determining the wettability uniformity, but has the disadvantages that the absolute level of dynamic wettability can only be determined by the additional photographic measurement of the dynamic contact angle and that a very long sample must be cut for each measurement.
Object of the invention
The object of the invention is to allow a simple, rapid and accurate determination of the dynamic wettability and its uniformity of a band- or plate-shaped pad to avoid wetting disturbances and to make coating processes more effective.
Explanation of the essence of the invention
The invention has for its object to provide a method for wettability determination of a band- or plate-shaped pad, which is simple and which allows the determination of the wettability and its uniformity for a band- or plate-shaped pad. According to the invention, the object is achieved by increasing the drawing speed from a small incomplete wetting level in small steps or evenly with low acceleration, and by measuring the rates of incipient and complete filming. The average of the two measured velocities is a criterion for the wettability and the difference of the two measured velocities is a measure of the uniformity of the wettability.
From a to be examined tape or plate-shaped pad a strip by means of a dipping device in a test liquid, eg. B. least. Immersed in water. The test fluid is in a beaker.
After a certain dwell time, the strip is slowly withdrawn, increasing the speed in small increments.
The wetting line is constantly observed by means of a stereomicroscope and a light source. The rates of incipient and complete film formation are measured.
The pull rate at which the strip is pulled out of the test fluid is increased from a small incomplete wetting level in small increments or evenly with very small acceleration. At the same time, the dynamic retraction angle decreases until a film is drawn up at an angle of 0 °. The rate of film formation depends on both the properties of the liquid and the substrate. Surprisingly, it has been found that with constant properties of the test liquid, the film-forming speed is a very sensitive criterion for the wetting properties of the substrate. The smaller the film forming speed, the better the substrate is wettable. Observing the wetting line by means of a microscope and a suitable light source, it can be seen very accurately from which speed Ui on the wettable areas of the pad a film is mounted and from which speed U 2 over the entire width of the sample, a film is mounted. The mean value Um = (U 1 + U 2 ) / 2 is used as a criterion for the average wettability of the substrate and the difference AU = U 2 -U 1 as a criterion for the uniformity of the wettability. The pad is all the better wettable, the smaller the difference AU is. The advantage is that the method according to the invention is applicable to all types of tape or plate-shaped documents, that it at the same time allows statements on the uniformity and the absolute size of the wettability and that it is easy to perform and at the same time highly sensitive.
embodiment
The invention will be explained in more detail below using an exemplary embodiment. Fig. 1 shows an embodiment of the method according to the invention.
In a beaker 1, which is filled to the brim with distilled water as test liquid, a test strip 3 of the size 15 x 80 mm of the acetyl cellulose pad to be examined is immersed by means of a diving device 2, not shown. After a residence time of 1 min, it is slowly pulled out again, the speed initially being 50 / xm / s and increasing in steps of δμΓη / β. The wetting line 4 is in this case viewed with a stereomicroscope 5 in 2X magnification at an angle of 45 ° to the wetting line. The microscopy 6 is arranged so that when the surface of the test strip unw wetted in the stereomicroscope just no reflection is observed. The various base samples are measured the velocities U 1 of the incipient film formation in the form of individually collecting droplets and the velocities U v of the complete film formation, cf. Table 1.
Table 1 Sample No. U 1 [μΙΤΐ / s] U 2 u M [μη-i / s] AU ΙμΓΓΐ / s]
1 2 3 95 60 100 125 130 140 110 95 120 30 70 40
For each sample the mean values U M = (U 1 + U 2 ) / 2 and the differences of these velocities AU = U 2 - U 1 are formed, whereby the average characterizes the absolute height and the difference the uniformity of the wettability.
The results show that Sample 2, while having the best wettability, is at the same time wettable most unevenly.
Although sample 1 has a lower wettability, it is the most uniform.
The worst wettability has sample 3.

Claims (1)

  1. A method of determining the wettability of a tape-like or plate-like substrate by pulling a strip of the test material from a test liquid that is incompletely wetting in the stationary state, characterized in that the drawing speed is of a small value in the region of incomplete wetting in small steps or uniformly with low acceleration increases one measures the speed of incipient and complete film formation, and that the average of the two measured velocities, one criterion of wettability and the difference of the two measured velocities, provides a measure of the uniformity of wettability.
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DD29615386A 1986-11-11 1986-11-11 Method for assessing belt or plate fatigue subject DD255992A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DD29615386A DD255992A1 (en) 1986-11-11 1986-11-11 Method for assessing belt or plate fatigue subject

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DD29615386A DD255992A1 (en) 1986-11-11 1986-11-11 Method for assessing belt or plate fatigue subject

Publications (1)

Publication Number Publication Date
DD255992A1 true DD255992A1 (en) 1988-04-20

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Family Applications (1)

Application Number Title Priority Date Filing Date
DD29615386A DD255992A1 (en) 1986-11-11 1986-11-11 Method for assessing belt or plate fatigue subject

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DD (1) DD255992A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3825416A1 (en) * 1988-07-27 1990-02-01 Ahlbrandt Andreas Method for the determination of the surface tension of solid materials, and device for carrying out the method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3825416A1 (en) * 1988-07-27 1990-02-01 Ahlbrandt Andreas Method for the determination of the surface tension of solid materials, and device for carrying out the method

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