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OLBRICH GmbH is one of the leading suppliers of customized converting machinery for a wide range of coating and laminating applications to the paper, film and foil converting industries. OLBRICH’s success is based on an ongoing effort to implement state of the art innovations within the fields of coating, laminating, drying and winding technology and always with the focus of the customer’s needs!
NanoPack’s FDA-compliant NanoSeal™ uses a patent-pending oxygen barrier that provides a clear barrier coating for meat and cheese packaging and delivers significant economic and environmental advantages.
NanoSeal technology also provides flavor and aroma barriers. Other markets include spices and coffee, as well as dry packaged products including nuts, crackers, cookies, confectionaries and mixes.
All of the current web coated products, battery, fuel cell components, printed electronics current products, packaging and window film, require a contaminant free film to function effectively. Also, contaminated coatings increase the manufacturing costs because they must scrapped. Therefore; it is essential that there be an ongoing program to clean and maintain the cleanliness of the entire coating facility.
Spots or point defects are caused by individual particulate contaminants in the film. They have a wide variety of names that are sometimes identified by apparent cause of defect or appearance. Typical names are:
Fisheyes, repellents, comets, pinholes, voids, gels, backing roll spots, applicators roll spots.
There are three basic mechanisms that cause these spots. The first cause is contaminants in the coating solution that are not removed during coating and end up in the final coating. There are several possible sources of contaminates in the coating solution:
• dirt, polymer chips oil or grease on the substrate surface, which dissolves in the coating solution during coating
• contaminants in raw materials, undissolved ingredients, oil, dirt, fibers, gels,
• contaminants in process vessels, transfer lines and on coating applicators and coating rolls.
Contamination on coating and backup rolls that create a disturbance of the coating bead leading to a spot. Contamination on any roll in contact with the running substrate. If there are wet side rolls, which normally do not contact wet film, can lead to defects if there is a tension upset in the coater and the wet surface deposits on the roll. This can diminish clearance and lead to spots defects. Particles in the drying air will deposit on the film surface, causing spot defects.
Particles in the air and from human skin debris can be deposited in the coating solution and on the substrate during the coating operation.
The important steps to maintain cleanliness in the coating process are as follows:
• clean the substrate before it enters the coating station. The majority of contaminants will be removed
• specify purity of raw materials
• filter all solutions and characterize the material that is removed to help locate source
• Clean all solution delivery lines. Consider disposable lines. It often is cheaper to do this then to clean permanent lines.
• Thoroughly clean all coating and solution delivery equipment. When the coater is not running, cleaning is a useful activity
• Clean all rolls in the coater
• Insure that the coater ambient air is appropriately filtered
• Insure that coater has effective static control so that dirt is not attracted into the dryer from the ambient air
• Insure high relative humidity to minimize static attraction
• Monitor dirt levels in process rooms to insure cleanliness is maintained.
All cleaning solutions and cleaning equipment should be tested to verify that they will not have an adverse effect on the product. Also when cleaning all safety and environmental must be followed.
The ongoing development of many new web coated products requires the ability to dry the coating without causing defects by damaging the wet coating These coatings can be fragile because they are often very low viscosity and fragile. This occurs because the desired dry coating weight is low and the coating solution must be diluted in order to obtain the flow rate that is required to coat in a stable region of the coating operability window.
These coatings can be easily damaged in the initial drying process, because the impinging g on the coating surface can disturb it leading to surface disruption and defects. Depending on drying air velocity and impingement air direction, a variety of defects can result. Low velocity impinging air will result in a mild distortion such as surface mottle defect. A high velocity impinging air will lead to large distortions such as chatter like bars, drying bands and spot defects.
There are two basic concepts to prevent these classes of defects. Initially dry the coating with minimum airflow until the coating viscosity increases to the point where impinging air will not disturb the coating. In addition, increasing the viscosity of the coating solution to increase the resistance to motion is effective. However, if this is done by concentrating the solution it can affect the coating quality. Therefore, the best approach is to use an additive to increase viscosity and maintain flow rate.
There are several approaches that can be used to modify drying conditions so that they can effectively dry fragile coatings. Install an infrared predryer to start the drying, thereby increasing viscosity thereby increasing resistance to impingement air in the first drying zone.
Use a dryer with several independent drying zones. The initial zone should have low velocity to reduce distortion and a low film temperature to increase viscosity. The subsequent zones can have higher velocities and drying air temperatures to maximize Drying efficiency when coating is resistant to damage
Rear-side drying with no front side drying in the initial drying zone is also effective. The coating dries with minimal front side impinging air while it is fragile so distortion is minimized. Figure 1 shows a commercially available. Rear side dryer.
An initial drying zone with low velocity air flowing parallel to the coating can also be effective. There will be drying but no impingement to disturb the coating.
The ability to rapidly characterize various aspects of a web coating line, when its producing defective or off-standard material is essential in all phases of the process, R&D experiments, Scale-up, and routine manufacturing is essential for commercials success. A coater running at 500 fpm can produce 150,000 sq ft. in an hour. As a result rapid diagnosis of a problem and eliminating it quickly is essential.
There are many analytical and characterization tools available. However many of them are in the analytical laboratory and can take a long time to characterize a defect. Meanwhile, the coater is either running or making no product or not running until the problem is s solved. Either case is expensive. One effective method to reduce this downtime and coats and it is a Rapid Response Characterization Toolkit available. This Toolkit contains several characterization instruments that can rapidly provide analytical capability. Therefore, reducing testing time in the laboratory. The expense of having this Toolkit available will have an excellent economic return when is drastically reduces downtime and off=standard material
Advances in technology has resulted in hand held instruments being available with excellent precision and reproducibility. Another justification is a principle that “One accurate measurement is much better than many hours in the Library or many hours discussing with a fellow students.
There are several instruments in this toolkit:
• A handheld XRF spectrometer that can quantify elements ranging from magnesium (Mg – element 12) through uranium (U – element 92. This effective for particulate defects and if metals are present the composition can be determined to identify the specific metal.
• An Advanced Digital Microscope System that is both a digital camera and portable microscope. This will record and store images of the process or film samples. Data can be downloaded to computers in internal company computers.
• Portable Infrared thermometers that can measure temperatures in any part of the coater hardware and coated film without contacting it.
• A hot wire Thermoanemometer With Datalogger. This can simultaneously measure dryer air velocity and temperature and store measurements.
• A portable data logger that can measure and store a range of properties over a long time period. This is useful to characterize a part of the process that is not being controlled or characterized.
• A digital recorder to visually record continuous action such as defects in the coating bead.
• A portable or tablet computer to analyze data as it is being generated and to easily retrieve previous data.
An Apple iPhone or tablet can do the last two functions.
One confusing aspect of the web coating process is that there are no standard naming conventions to define the many process variables that are needed to operate a successful process. As a result one process variable can have many different names, or a specific variable can have many different names and interpretations as to the meaning of the term. It is essential that when terms are used to describe a coating process term, that all interpret it in the same way to insure the selection of and the successful operation of a coating applicator.
An example is the various terms used to describe the weight of coating per unit area on the substrate. It is referred to as the coatweight, laydown, coverage or “coating thickness”. all refer to the same fundamental property, Whichever term is used it refers to two distinctly different properties, film coating thickness and the wet coating thickness. The dry film thickness is important for the end use and performance parameters of the product. If it is not as specified the product will not function as intended. The wet film thickness of the applied film is a fundamental property of the coating applicator. Each applicator has a range of wet thicknesses over which it can uniformly apply a specified thickness. Therefore, when selecting a coating method, the wet thickness is the key parameter that must be used. When determining coating method performance, the charts and tables the definitions should be verified so that a valid comparison is made
The dry film thickness that results from the wet coating thickness is a function of the percent solids in the wet layer. Thus, it is possible to obtain the same dry thicknesses from a variety of coating thicknesses depending on the solids content of the wet coating. Therefore the wet thickness can be adjusted to obtain a stable coating while still obtaining the desired dry thickness.
There are many units that are used to specify coating weight. Each industry has its own traditional preferred units). When comparing and discussing the units should be attached to insure consistent interpretation
COATING WEIGHT: The weight of coating per unit area. The specific units used depend on the industry. Typical units are as follows
•Lb/ream(3300ft2), grams/meter2 , oz/yd2, mg/dm2 mils thickness. or microns thickness.
The web coating process is used to continuously apply a layer or layers of liquid or solid functional material onto a substrate, in order to create a new structure with new novel properties. The process must be capable of applying a uniform coating over a wide range of thicknesses and quality levels on many different substrates such as a plastic film, paper, or metal foil. The process must also be economically effective, competitive cost and high productivity.
To achieve these objectives and, reproducibly manufacture defect free products; it is essential to understand what actually constitutes the total coating process. The reason for this is that the process is complex and has many modules with many variables all of which are important and can affect the final product. Often the focus of problem solving, optimizing performance and effectively scale up new products is limited to a few of major modules, coater, dryer etc and other modules which can be important are ignored.
The web coating system has 18 separate modules, which are shown in detail in the attached Coating Process Flow Sheet. The basic flow of the process is as follows:
Developing and optimizing the requires formulation
Acquiring and storing substrate and raw materials
Quality control testing
Delivering solution to the coating head
Drying to remove solvent
In process quality control systems
Wound roll storage
Product acceptance testing
Converting to final size
Within these modules there are many process hardware and control components which are required for the module to function effectively. All of these modules can influence the coater performance and product properties. These modules must function together, with no weak links. There are ~3,000-5,000 separate variables to control in these modules can lead to defects.
Often a problem occurs because there is a failure with in these modules. A defective bearing in the coating roll drive can lead to chatter. A variation in storage conditions can influence properties after the coating process. A malfunctioning vacuum roll in the coater drive system can lead to chatter. Uncalibrated dryer control set points can cause drying load variation if the temperatures on the control instruments are not accurate.
The solution delivery system is an example of a module with many components all of which will influence coater performance. A flow sheet of this module is attached.
Since the process is complex all personnel should understand the complete process and the coater operators should be trained so that they understand the total Web Coating Process.