Research chemists investigated three UV-curable PSA formulations, making four modifications to each PSA to vary performance. Traditionally, PSA formulations have been solventborne and based upon modified rubber chemistry. Recently, Sartomer chemists investigated three UV-curable PSA formulations (Table 1), making four modifications to each PSA to vary performance for various reasons (Table 2). For base blend #3, the base formulation viscosity is higher than all of the modifications except for the addition of hydrocarbon resin, modification B. In base blend #2, the PSA has a relatively low tack of 100-200 grams in most of the samples (only slightly higher than the first blend). Essentially, the CN301 does seem to improve the SAFT, but for the most part has no affect on anything else – except in base blend #3 (which does not contain an oligomer). In all cases, the addition of hydrocarbon resin (S-135) yielded negative results for all physical properties. In short, the most positive impact made by any of the additives was the addition of more monomer to the blend.
The Handbook of Sealant Technology provides an in-depth examination of sealants, reviewing their historical developments and fundamentals, adhesion theories and properties, and today’s wide range of applications. Accurate bonding with printable adhesivesThanks to further developments in quality, screenprintable pressure-sensitive adhesives have made their mark in many industrial applications. For processing liquid adhesives, the screen printing method has established itself alongside the conventional systems like curtain coating, spraying, anilox and knife. Using the screenprinting method, the liquid adhesive is printed through a stencil with a squeegee on to the substrate. The advantages of solvent based systems lie mainly in good printability, very good surface flow and extraordinarily short drying times. The early screenprintable pressure-sensitive adhesives of the 1970a€™s had low adhesive properties and were mainly used for decorative applications. The economical rubber based pressure-sensitive adhesives have very high initial bond strength, but are yellow to brownish in colour, which intensifies when exposed to light. By being able to replace polyvinyl acetate by acrylic resin copolymers as a binding material for screenprintable pressure-sensitive adhesives, it was possible to advance into areas of application which were hitherto the reserve of the solvent based formulations. Only recently, liquid 100% systems have become available, which create pressure-sensitive adhesive when cured by UV rays after printing.
A special area of application for screenable, solvent based pressure-sensitive adhesives is the transfer. The main area of application for screenable adhesives is for the self-adhesive finish of instrument panels. Printing is normally done using mesh with a thread count between 21 and 43 per centimetre a€“ in special cases up to 8 threads per cm. In order to achieve the best and reproducible adhesive results for industrial applications, it is recommended that bonding is done with pressure through a heated silicone rubber stamp (e.g.
A further area of application is membrane switches, the upper film of which is for identifying and operating the circuits underneath. This overlay forms the second layer of the entire circuit and this is printed as required with e.g.
It is also possible to provide a self-adhesive finish to the underside of the complete membrane switch, in order to facilitate positioning when applying to the final product. It is possible to furnish films and foams with a partial finish of pressure-sensitive adhesive where previously adhesive tape was used as a means of fixing. Plastic film printed on both sides is used particularly for short term advertising campaigns in the fast food branch. To finalise from a selection of additional areas of application, we would like to mention foam bonding of mouse pads, screen dot shaped transfer adhesive film, rhomboid and line shaped adhesive systems for photo albums, tacky document security systems and rub-off letters and motifs. In the foreseeable future, when new raw materials can be combined with the relevant drying and cross-linking technologies in screen printing, we can look forward to even more areas of application for screenable pressure-sensitive adhesives. November 29, 2010 Kathie Zipp : A manufacturer of  pressure-sensitive adhesives offers high-strength solar bonding tapes designed for assembly solutions in solar cell applications.
Tested and shown to resist more than 400 degrees Fahrenheit while maintaining a secure bond, the free film adhesive featured on the new high-strength solar bonding tapes is an excellent substitute for liquid or complex cure adhesives and simplifies the manufacturing process. Browse the most current issue of Solar Power World and back issues in an easy to use high quality format.
In this podcast series, editors Kathie Zipp, Steven Bushong and Kelly Pickerel give you the opportunity to hear from the industry’s biggest newsmakers in their own words.
Solar Power World delivers your weekly dose of news and insight on Racking, Inverters, Panels, Software & Services and more.
Windpower Engineering & Development covers the design, technical content, and maintenance of wind turbines, wind farms, and the regulations and policies that make the industry function. Design World Online provides the latest design engineering news, articles, tutorials, videos, and products.
During recent years, market demand has been strong for liquid optically clear adhesives (LOCA) for display or touchscreen applications. UV-Vis spectra were collected for each laminating adhesive before and after weathering up to 2,000 hours.
Table 1 introduces nine new acrylate products using two commercial products, CN9018 and CN966J75, as controls. Peel strength and optical clarity are critical properties for electronic laminating adhesives.
Most experimental products, except for reactive polyvinyl acetal, present better durability than controls. As expected, these three oligomers are also the worst performers under freeze-thaw weathering conditions.
Consumer electronic adhesives usually require 1,000 hours durability, thus we continued the weathering tests to 1,000 hours and 2,000 hours.
The two best products were NTX12514, a urethane acrylate based on moisture-resistant polyester polyol, and PRO12546, a polycarbonate urethane acrylate.
We believe that the cloudiness of the adhesive based on PRO12546 is caused by moisture penetration. Thus, NTX12514 and PRO12546 are the best candidates for electronic or solar panel laminating adhesive applications. With the increasing popularity of smartphones and tablet PCs as enabling tools, the importance of display quality is becoming more important. The lower the dielectric constant of OCA layer, the thinner the OCA layer and the better the performance. In this study, NTX12514 and PRO12546 demonstrate high bonding strength to PET substrates and excellent durability under extreme weathering conditions.
Jin Lu is the manager of the Adhesives Sealants, Personal Care Platform R&D, Sartomer Division, at Arkema Inc.
The PSTI is a 4 mil textured matte lustre, pressure sensitive lamination film designed to protect prints from moisture and abrasion.

Due to today’s stricter environmental-compliance regulations, these solventborne PSAs are being challenged by low-VOC, fast-curing systems such as ultraviolet (UV) and electron beam (EB). In the first variation, polybutadiene dimethacrylate was added to try and improve shear adhesion failure temperature (SAFT).
Base Blend #1 Viscosity ProfileViscosity Profiles For each of the three base PSA blends, four different dilutions were made for reasons described previously. The addition of more monomers in modification D lowers the viscosity significantly where the 25 degrees C viscosity is around 1,000 cps. Base blend #1 used an aromatic urethane acrylate, whereas base blend #2 used an aliphatic urethane acrylate. However, it appears that the D modification still has the lower viscosity, with the 25 degrees C viscosity of about 290 cps.
All were in the range of a Gardener Color of 5-6, except those containing the CN301 polybutadiene dimethacrylate, which is a darker oligomer. Base Blend #3 Viscosity ProfileEvaluating Tack Tack was run in a similar manner to peel adhesion, in which aging the samples shows long-term stability or lack thereof. Blend #1 Modification, 180¿ Peel AdhesionEvaluating Shear Adhesion Failure Temperature Sartomer chemists next ran SAFT tests using each of the previous blends at each of the cure conditions. Blend #3 Modification, 180¿ Peel AdhesionKey Findings of the Study These experiments were designed to help formulators determine which additives will help them achieve the specific physical characteristics needed in their UV-curable PSAs. Additional oligomer only had a positive effect in the base blend #3, which did not contain an oligomer. Besides reducing the viscosity to a printable viscosity (300-900 cps), the monomer improved the peel adhesion and tack with every blend – even improving the SAFT for base blend #1.
Which screenprintable pressure-sensitive adhesives are available on the market and where are their preferred areas of application? The specific advantages of using the screenprinting method for processing adhesives was already recognised in the early 1970a€™s. The stencil is made from a woven polyester filament, in which the mesh area is only open for the pattern of the adhesive to be printed. After a short time, silicone paper can be applied or other processing steps can be carried out. The products available today have been optimised for industrial applications, with regard to their tear strength, tack value, UV and heat resistance. Good UV resistance, high heat resistance and the ability to prevent plasticiser migration are the advantages of this group. The advantages of this range are mainly to be found in the problem free application; long dwell times, good printability and excellent flow, fast a€?dryinga€? by chemical means and environmentally friendly processing, as the liquid is 100% adhesive. The particular advantage in using screenprinting for this class of adhesive lies mainly in the adhesive contours being exactly defined.
Here we mean a decal, which is used for decorative purposes or in the advertising business. Display texts, viewing windows and dials are then printed in different coloured and transparent inks. After drying in a convector oven or drying tunnel, the product is covered with silicone paper and if required, is subsequently die cut. On the bottom side, dispersion or rubber-based (containing solvents) pressure-sensitive adhesive is applied by screenprinting. The selection of the appropriate pressure-sensitive adhesive system depends on what it is going to be used for.
In applications behind glass, the film has to be able to be removed from the glass without leaving any residue a€“ and this can be best achieved by using cohesive and UV resistant acrylic systems.
MACtac Specialty Products’ Solarfast UV Cure Adhesive System is designed for concentrating and flexible solar applications. They can be used in a variety of applications, such as food packaging, aerospace, automobiles, electronics or solar panels. Key performance requirements include strong bonding strength to the substrates, excellent reliability, high optical clarity and superior moisture resistance. The key properties evaluated are optical clarity characterized by percentage of UV-Vis transmission and T-peel strength. Their adhesive and durability properties were evaluated using two commercial products, CN966J75 and CN9018, as controls.
CN9018 is well-accepted for pressure-sensitive adhesive applications, and CN966J75 for laminating adhesive applications.
As seen in the figure, the commercial control, polyester urethane acrylate CN966J75, has much higher initial peel strength than polyether urethane acrylate CN9018. The best candidates for extreme weathering conditions (freeze-thaw) are polycarbonate urethane acrylates PRO12546 and PRO12599. The high peel strength but low clarity of the adhesive based on PRO12599 indicates that the penetration of moisture into the films might also cause cloudiness.
The combination of high peel strength and excellent optical clarity of NTX12514 indicates that this oligomer is the best candidate for electronic adhesive applications. As predicted, the T-peel and clarity of the films after 1,000 hours weathering are better than those after 2,000 hours. Only four oligomers (NTX12321, CN9018, NTX12945 and NTX12514) could maintain optical clarity throughout 2,000 hours of all the weathering tests. Therefore, we collected UV-vis spectra again after the adhesive was equilibrated at room temperature for seven days. In particular, the need for better outdoor readability is emphasized.4 Filling the air gap between the touchscreen and the display by directly bonding the optically clear adhesives (OCAs) drastically improves both indoor and outdoor readability.
The PRO12184, PRO12507 and NTX12599 products demonstrate high bonding strength and reasonable reliability, which make them good candidates for conventional consumer or industrial electronics.
Each dilution with the original base blend PSA has a viscosity profile run from room temperature to 65 degrees C.
With the third grouping, the 20 percent addition of S-135 hydrocarbon resin into the base PSA, the 180 degree peel adhesion significantly decreases. With the third grouping, the 20 percent addition of S-135 hydrocarbon resin into the base PSA, the 180 degree peel adhesion decreases, this time with additional UV dosage reducing the 180 degree peel adhesion.
Sartomer scientists reviewed all the above samples and tested tack with the aging of the samples, along with a one-month aging sample. In the third grouping, which is the 20 percent addition of S-135 hydrocarbon resin into the base PSA, we see that tack is non-existent.
The best improvement of the SAFT was seen with CN301, but it was not as good as the other two bases.
Formulators looking to achieve excellent peel adhesion, increased tack and improved SAFT should review the key findings below and consider modifying their formulations accordingly. Today pressure-sensitive adhesives, which have been printed on substrates can be found in many industrial areas of application, as for example, the automotive industry, household white goods and the electronic industry.
The choice of mesh (the number of threads and thread diameter) determines the thickness of the adhesive deposit.

The disadvantages of the system lie mainly in the flammability of the solvents used, as well as fumes being breathed in. Rubber and acrylic resin based formulations are available, which differ in price and property profile.
Here additional equipment for drying and more comprehensive process monitoring is required. Exact positioning to within millimetres, as well as fine filigree and stand alone adhesive geometry, cannot be done with any other processing technology. Because of the smooth and even adhesive film, only solvent based rubber and acrylic resin formulations can be used.
Die cut parts, which have been finished with pressure-sensitive adhesives are then bonded to injection-moulded housings and fibre optics made from PMMA, PS, ABS, PA etc. In order to prevent contact with the underlayer film, a spacer is glued in between, which can be made self-adhesive by screenprinting.
Restrictions only apply as far as soft PVC is concerned, because there is a danger of plasticizer migration into the adhesive layer, as well as unusual compounds, which contain e.g. Adhering with hand roller (according to PSTC standard, roll weight 10 pounds, 5 x in each direction). The manufacturer says the bonding tapes (SF-1003 and SF-1005) can withstand a range of environmental conditions where a high-temperature, high-strength bond is required. The free film adhesive initially bonds similar to a typical pressure-sensitive adhesive, but the final bond is initiated through UV light.
The major technologies include solventborne, waterborne, two-component urethanes and UV-curable resins. The T-peel test was performed using an Instron 5543 and following the ASTM D1876-08 standard.
The dielectric constant was measured following the ASTM D150 method at a frequency of 1 kHz.
Using the standard formulation package (see Experimental section), adhesive samples were prepared for each oligomer. Due to the flexibility of the PET substrates, we chose the T-peel test to determine the strength of the adhesives. Similarly, the experimental oligomers with the highest initial peel strength are polyester urethane acrylates (PRO12184, PRO12507 and PRO12546) and polycarbonate urethane acrylates (PRO12384 and PRO12599).
Interestingly, even though the ester group was easily degraded at high humidity conditions, NTX12514, based on a moisture resistant polyester polyol, presents superior durability. Under this condition, the film based on PRO12546 exhibited superior optical clarity, supporting our hypothesis. Again, the same trends were observed with the same modifications that are in base blend #1. Each of the blends was fully evaluated with each of the four modifications for the 180 degree peel adhesion for 30 minutes, 24 hours and one week after UV cure. The fourth grouping evaluates the 20 percent addition of CN966J75, an aliphatic urethane acrylate oligomer. Each of the blends was fully evaluated for tack 30 minutes, 24 hours and one week after UV cure. In the second grouping, which has the 20 percent CN301 polybutadiene dimethacrylate added into the PSA blend, tack is lower than with the base PSA blend.
The addition of the CN966J75 also improved the SAFT, as expected, because it is similar to the base #2 blend. More can be found in the production of optical displays as well as the advertising and sign making industry.Peel strength of KIWOPRINT D 159 on various substratesThe variety of these areas of application calls for an even greater variety of substrates, which have to be made self-adhesive.
Dry coating thicknesses of 50Aµm are usual for technical applications today; for special applications where more thickness is required, it is possible to lay down 160Aµm. Both product groups have very high water and steam resistance, which is especially advantageous for use where condensation occurs.
The range of UV curable pressure-sensitive adhesives does not yet have the application variety of the dispersion based adhesives, but augmentation is being worked on at full speed. Where transparency and UV resistance are required, acrylic resin pressure-sensitive adhesives are used. The main areas of application are instrument panels in the automotive industry and operating components of a wide variety of electrical devices.
Still in evaluation is the development of a spacer, which can be completely printed as pressure-sensitive adhesive. Once cured, the manufacturer says the adhesive has extreme heat resistance, low creep and excellent peel. The adhesives were then laminated and cured between two PET films with controlled thickness at around 9 mils. The three weathering conditions reflect different levels of temperature, moisture and UV exposure. The best products with low dielectric constant and superior adhesion properties include CN9014 and CN823. Studies have shown that excellent peel strengths have been obtained with acrylate-terminated oligomers with molecular weights ranging from 1,000 to 6,000, and glass transition temperatures ranging from -74 degrees C to 13 degrees C. The 180 degree peel adhesion has greatly improved compared to the base PSA, although again we see that the increase in dose actually decreases the 180 degree peel adhesion. Again, the third grouping, which is the 20 percent addition of S-135 hydrocarbon resin into the base PSA, has essentially no tack.
Initial bond strength is not as high as with the rubber based adhesives, but develops within a few hours and then even exceeds the values of the rubber based adhesives.
For all of these PSAs, including the base PSAs, viscosity profiles, 180 degrees-peel adhesion, tack and SAFT, tests were all run to help better understand performance. As for the final group, the 20 percent addition of the SR256 (2-ethoxyethoxyethylacrylate) and SR504 (ethoxylated nonyl phenol acrylate) in a 1:1 blend, the results for the 180 degree peel adhesion are greatly improved over the base PSA.
Here film, foam and hard plastic made from the usual materials (PVC, polycarbonate, polyester, polyethylene, polypropylene, PMMA, PUR etc.) are to be given a self-adhesive finish.
Depending on the area of application and size of the motif, a differentiation is made between wet and dry transfers. This is necessary when bonding to injection moulded goods with their unavoidable pock holes. As in the case of the higher-dose sample modified with the S135, no adhesion was present to run the test. Specially formulated pressure-sensitive adhesives have an aggressive tack, which is important for successful bonding of difficult substrates.
Finally, the freeze-thaw weathering test is used to screen for adhesives that can survive very harsh conditions.

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