Although YUPO® is a very durable synthetic paper, the longevity of the printed piece may ultimately depend on the durability of the printed image more than the durability of YUPO. For example, your application may require the inks to be any one or more of the following: light fast; heat resistant; alkali resistant; soap resistant; or alcohol resistant. Please consider the end-use for your piece during the planning stage.

A. General Guidelines
1. Pre-test inks for compatibility with proposed coatings, varnishes, adhesives, and laminations on samples of YUPO under end-use conditions.
2. Use fresh inks.
3. When a printed package includes YUPO and other substrates, print the entire job with YUPO formulated inks.
4. Ink formulated for YUPO should:
• consist of high solids, contain low solvents, and dry completely by oxidation.
• contain higher pigment load to allow for printing a thinner ink-film-thickness without sacrificing density or color.
• contain a high content of wax, slip-agents, and micronized Teflon®. However, if images are to be over-coated, imprinted, UV-coated or laminated, the inks must be compatible.
• be formulated to allow for a higher-water-pickup. This prevents them from over-emulsifying.
• set after 24 hours.
5. UV Inks or Coatings
• YUPO grades currently available are not recommended for UV offset or UV screen.
A suitable primer/anchor coating must be applied prior to UV printing and/or coating. Failure to do so would result in poor ink/coating adhesion.
• Yupo Corporation is planning to launch new grades that are appropriate for UV printing/coating. Please contact our customer service center for our most updated grade information.

B. Pigments to Avoid
These pigments, due to their properties, are usually not used for printing on YUPO. If your project calls for them, please contact your ink supplier for alternate formulations.
Color Properties
1. Red Lake-C (warm red) Poor light resistance.
2. Reflex Blue (alkali blue, used to tone Poor light resistance, may bleed, black inks and make blacks appear undergoes dramatic color shift blacker.) when UV-coated.
3. Purple, Violet, Rhodamine Red Clean and bright, but poor light resistance, may bleed, undergoes dramatic color shift when UV- coated.
4. Metallic Gold, Silver Made from copper/zinc alloys (bronze) and aluminum. Very opaque, with excellent light resistance, but challenging to print. Metallic inks generally have higher solvent levels than are acceptable for YUPO Papers and poor rub resistance.
5. Fluorescents Rapidly degrades photochemically; extremely poor light resistance; susceptible to many solvents and chemicals.

C. Ink Additives
Driers work with drying oils to turn wet ink film into a solid in a process known as oxidative polymerization. Three types of metal/salt catalysts are used, each of which initiates drying differently:
1. Manganese is a bottom- or through-drier, drying within the ink film. Manganese driers work best with YUPO Papers.
2. Cobalt is an aggressive top drier which dries the surface of the ink film. Cobalt agents blended with inks formulated for YUPO would have disastrous effects: by drying the top surface of the ink film, the oxygen required for the oxidation reaction below would be blocked from reaching the lower drying oils. As a result, inks would never dry, behaving much like the skin over pudding — dry on top, but wet underneath.
3. Zirconium is a weak drier that accelerates the action of cobalt and manganese driers.
4. Press-side driers such as Grapho drier (or x+y=DRY) should be used with YUPO Papers.
For two-sided printing, driers should be sparingly added to inks used on the first sided printed; wind the sheets immediately after the ink has set to eliminate the occurrence of gas ghosting. Driers may be used sparingly on the backside. Driers cannot be used to compensate for improperly formulated ink.

D. Comparison of Ink Components
The following guideline compares the components of conventional sheetfed offset printing ink used on coated papers with ink formulated for YUPO Synthetic Papers. This information is provided merely as a guideline for ink suppliers and is not intended to serve as a comprehensive resource.

• Solvents generated in preparation should not exceed 3%. Excessive solvent will penetrate YUPO Papers and cause distortion.
• Phenolic resin should be highly soluble to compensate for the ink's low mineral oil content.
• Linseed oil should have a very low viscosity and be mixed with chinawood (tung) oil to accelerate drying. Variations in pigment content may require varying proportions of resin and drying oils. Maintain the ink manufacturer's recommended ratio of resin to drying oils.
• Slow drying vegetable oils, such as soybean, should not be used in the formulation of inks for YUPO Papers. Inks formulated with these oils (1) take longer to dry, (2) compound the risk of ink setoff in the delivered lift and (3) increase the likelihood of gas ghosting on two-sided printing (discussed further in this section).

E. Factors Affecting Ink Dry Time
Because YUPO Papers are non-absorptive, drying times normally exceed that required for standard, wood fiber-based papers. However, drying times can be greatly reduced by solid planning, by properly controlling press conditions and by using the appropriate inks. The following categorically identifies common oversights that can greatly prolong drying times, and recommends preventative techniques about how to avoid them.
1. How planning may affect dry times.
• Cool pressroom temperatures (below 70ºF /210 C) or cold stock.
Allow YUPO to acclimate to pressroom conditions for at least 24 before unwrapping, and even longer during winter months. If cold YUPO is brought into a warm pressroom and immediately unwrapped, it will cool the surrounding air causing moisture to condense on the paper's surface (particularly along the edges). Although YUPO is non-hygroscopic, and therefore dimensionally stable, any surface condensation will severely inhibit ink transfer, and will prolong dry times.
• Ink coverage less than 10%.
When printing images that require a small amount of ink coverage, such as type, a larger amount of dampening water will be carried on press. This water has a tendency to migrate back into the ink train, causing the ink to over-emulsify; this tendency is amplified on synthetic stocks because they are non-absorbent. A solid color bar along the trailing edge of the sheet may be helpful in reducing ink emulsification by increasing the ink flow, improving uniformity of coverage.
• Gas ghosting on the backside.
Inks formulated for YUPO dry entirely by oxidation. Decomposition gases generated by the oxidation process during the topside run will alter the surface properties of the backside of the sheets. Areas directly above the printed image have a greater concentration of these gases.

You may experience poor ink transfer in these areas, which results in ghosted images (due to lighter density of ink) on the backside. We call this phenomenon gas ghosting. In addition to poor ink transfer longer drying time may be required as well.

These gases build up progressively on the surface of the backside throughout the ink drying process. Therefore, wind the printed lifts once or twice after the ink has set. This will reduce the risk of gas ghosting by releasing the gasses. Additionally, when printing YUPO on both sides, it is best not only to wind the printed lifts after the ink has set on the topside, but also to back up the job within 24 – 48 hours.

Avoid using excess driers on the topside; they will accelerate the generation of decomposition gases and increase the risk of gas ghosting. Use a grapho drier sparingly on the backside if necessary. Above all, consult your ink supplier before adding any driers to the ink. To minimize gas ghosting, print the image with the lightest level of ink coverage first.
• Multiple passes through the press.
Requires not only a sufficient amount of time for the inks to set between passes; gasses generated during the oxidation reaction increase drying time for subsequent passes as well. In addition, the risk of problems such as setoff, poor ink transfer increased static and void areas caused by offset powder from preceding passes will increase. Therefore, printing YUPO in one pass is highly recommended.

2. Press conditions which may prolong dry times.
• Too much dampening water on press.
Inks can emulsify, which will inhibit or stop the drying reaction. If the emulsified inks do dry, they will become soft and chalky. Therefore, run YUPO Paper with the least possible amount of dampening water— normally 5-10% less than that used on coated paper.
• Fountain solution with a low pH (below 4.5) or high conductivity.
A low pH will burn out the driers in ink. High conductivity, perhaps caused by using water with excessive mineral content, will also affect the drying capabilities of inks. Periodically checking the fountain solution pH (between 4.5-5.5, target 5.0) and conductivity is critical.
• Too little offset powder.
More powder is required than that used for coated paper depending on the following factors: total ink coverage, the thickness of YUPO being printed, the lift height, and the speed of the press. It is generally recommended to use 24 micron particle size on grades less than 10 mils, and to use a coarser powder on grades thicker than 10 mils.
• Not enough heat used.
As a general rule, for each 18º F increase in temperature, drying time is reduced by half. Blowing warm air on printed loads or using IR dryers also accelerates drying (Do not exceed normal pile temperatures).

3. How ink may affect dry times.
• Inks not specifically formulated for YUPO Synthetic Papers.
For example, the solvents contained in quick-set inks would penetrate YUPO's surface and cause it severe distortions.
• Old ink.
The potency of dryers in ink (especially black) will dissipate over time. As a general rule, any ink over one year old should be checked by your ink supplier.
• Inappropriate use of additives in inks or fountain solution.
For example, too much or using the wrong type of drier can actually result in drying problems. Consult your suppliers before altering ink or fountain solution.