Brush marks

The slushing compounds are a variant of the smearing types, and possess some Row properties at room temperature so that brush marks produced during application.are reduced- Some materials contain solvent, so that they ate free-flowing as applied, but sliBien wl n the solvent evaporates. 

Thixotropic behavior is responsible for the smooth flow of paints after the intense shear of a paint brush or spray. On standing without shear for a few moments, the fluid recovers" its original viscous nature. The former behavior is desirable to permit the smooth flow necessary for ease of application and for removal of brush marks. The high consistency at rest is needed to prevent flow after application to vertical surfaces (L2). 

The steady-state viscosity is a pragmatic way of predicting certain key properties of a sample. If the stresses used in the creep experiment are well chosen they will reflect the stresses applied to the sample by the action of gravity. Thus, the viscosity under these circumstances will help predict the ability of the material to resist sagging on a vertical surface (coatings). Other uses include prediction of sedimentation velocity or creaming velocity in two-phase dispersions. The ability of a paint to level out and therefore remove brush marks by... 

Bailer s argument is refuted by the fact that none of the colored walls shows any pattern of brush marks, and no identifiable coat of paint, since wall paint consists not only of pigment, but also of a not inconsiderable proportion of binding agents and other chemicals. The blue pigment is, however, simply one component of the lime paint and plaster. 

Brush marks. Lines of unevenness that remain in the dried paint film after brush application. Brush marks and ropiness are associated with poor flow and sticky application. These defects are more often encoimtered in highly pigmented products and in certain latex paint formulations. Tbo rapid recovery of consistency in a thixotropic system will also cause these defects. The remedy may be the addition of a flow promoter, reduction in consistency, or modification of the rheological properties. 

Figure 4.2 Water contact angle as a function of chemical functionality on brush-covered surfaces. Brushes were grafted from ETFE via free radical polymerization. Brushes marked with an asterisk were obtained via postfunctionalization. Source. Adapted from Neuhaus et al. [2], with permission from John Wiley Sons Inc.

Potential drop across the current-measuring shunt was measured on a 0—100,000 fiv L N White double potentiometer potential drop across the test piece was measured with an L N Wenner potentiometer, using a calibrated potential divider to reduce the. signal by a factor of 101.003. The unbalance signal from each of the potentiometers was amplified by dc chopper amplifiers and recorded simultaneously on a two-channel Brush Mark II recorder so that the resistance of the test piece could be determined at any instant. 

Leveling is the measure of the ability of a paint to flow out after application (e.g., to obliterate brush marks). It is measured by comb tests. Theoretical correlations have been established between viscosity measurements and practical results. Surface irregularities can be sensed mechanically and visualized with modern methods of image analysis [9.8]. 

Features Post-additive promotes film integrity improves enamel holdout helps eliminate brush marks Tallicin 1600 [Pfiaumer Bros.]... 

Leveling of a paint describes the flow-out of brush marks, etc. It can be estimated by drawing the paint down with a crenellated applicator and... 

Blender n. A round, softish brush of badger hair or similar material with a blunt tip, used for blending colors and removing brush marks left by coarser brushes. (2) A small laboratory mixer used to dispense pigment in a vehicle. 

Brush mark n. A small ridge or valley produced in a paint film by the combining action of the bristles of a brush. 

Photographing n. Brush marks or other irregularities in the previous coat or substrate that show through the dried topcoat. 

Ribs Raised ridge in the finish caused by heavy brush marks, which were not sanded or rubbed from underneath coats before finishing coats were applied. 

Ropy finish n. Finish in which the brush marks have not flowed out, this being the normal appearance of a paint or varnish having poor leveling properties. A similar appearance may also be produced in a paint, which normally has good levehng properties, by continuing to brush the paint after the film has begun to set. 

Stipple sti-p9l [D stippelen to spot, dot] (ca. 1762) vt. (1) To even out a coat of paint and remove brush marks and other imperfections, immediately after apphca-tion, by systematically dabbing the surface with a soft stippling brush. (2) To produce a broken color or textured effect, either by applying spots of a different color or by disturbing the surface of the paint coat, e.g., with a stipphng brush or rubber stippler. 

Boss Bossing. In the process of pottery decoration known as ground-laying (q.v.), brush marks are removed by BOSSING, i.e. striking, the ware with a pad, or Boss, made by stuffing cottonwool into a silk bag. 

Brush Marks. A surface imperfection found on the exterior of some bottles the marks resemble a series of fine vertical laps and are also known as SCRUB marks. 

Scrub Marks. A surface blemish on glass bottles see brush marks. 

Must give sufficient viscosity under low shear conditions such that sag of the coating is avoided on vertical surfaces. At the same time, the viscosity under these conditions should not be so high that brush marks and bubbles remain trapped in the coating and remain visible as defects after drying is complete. 

Brushing is nsefnl for prototypes and small or discontinuous production runs. However, brush application of rnbber to metal adhesives, while being the simplest method, is not recommended. This is because control of dry film thickness is very difficult to achieve over the part surface. Also, imperfections, such as brush marks or loose bristles in the adhesive film can interfere with performance. 

After appUcation, gelling should occur in a controlled time scale. If gelling is too fast, the coating may leave the brush marks (uneven coating). If gelling is too slow, the naU poUsh may drip. The relaxation time of the thixotropic system should be accurately controUed to ensure good levelling and this requires the use of surfactants. 

---