The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760



### 100% SOLIDS LAMINATING

Michael L. Leib

Technical Service Manager Packaging and Converting The Dow Chemical Company

Midwest Technical Center Elgin, IL 60123



### INTRODUCTION

100% solids laminating adhesives were developed in the mid

- 1970's to meet converters’ need to cut their solvent cost, energy cost, and to meet environmental regulations. Their choices to reduce emissions included: running high solids adhesives, solvent incineration, solvent recovery, aqueous adhesives or 100% solids adhes ives. 100% solids adhesives were the only alterative which not only eliminates solvent emissions from the adhesive, but also lowered the converters’ energy cost. It eliminated the cost associated with the solvent recovery and incineration equipment.

Addi tional benefits to the converter include:

~lower adhesive coating weight

~no use of solvent diluents

~no retain solvents due to the adhesive ~faster line speeds ~favorable health and safety characteristics

100% solids adhesives are an extension of ure thane chemistry which is well known for packaging adhesives. The primary difference between 100% solids adhesives and resins used in traditional solvent based dry bond adhesives is the adhesive molecular weight. The molecular weight of the 100% solids adh esives is significantly lower. Due to the lower molecular weights, initial bonds are significantly lower than those obtained with

the solvent

- based analogs. Therefore, laminating equipment with sensitive tension control and rewind systems are required to apply and laminate 100% solids adhesives. Furthermore, due to the reactivity of the two

- component reactive 100% solids adhesive systems, meter, mix and dispense (MMD) equipment is required to handle the adhesive.

Guidelines for making successful laminate s with 100% solids adhesives will be discussed in this paper.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 

### THE ADHESIVES

100% solids adhesives are analogs to one and two

- component solvent

- based adhesives.

Traditional one and two

- component solvent

- based adhesives are medium to high molecular weight resins which are solubilized in an organic solvent. The solvent is present for many reasons: it may be used as a polymerization medium, solubilizing agent for the resins, viscosity control, adhesive application weight control, substrate wetting,

and the a dhesive film forming properties.

100% solids adhesives have good flow and film forming properties without the aide of solvents. In addition to having good runnability, they quickly develop bonds bond strength and the laminate can often be slit after 24 h ours cure. Full cure is usually

achieved in 7

- 10 days depending on the storage conditions and the adhesive used.

100% solids adhesives are supplied as both single

- component and two

- component systems. Some are applied at room temperature while others req uire heating.

SINGLE

- COMPONENT ADHESIVES

Single

- component adhesive systems are generally polyether urethane based on aromatic isocyanate and are commonly used in low performance applications. They need to be

heated to 60

- 90  C to reduce their viscosity for application. They require moisture to cure. The moisture enters the adhesive from atmospheric moisture, the film surfaces or that which is resident in the film (i.e. Nylon and PVOH film). A minimum amount of ambient moisture must be present for comp lete cure. This is not a concern in a warmer humid climate. For consistent performance humidification at the laminating nip is recommended to assure adequate moisture is present to complete the cure. Humidification is accomplished by introducing humidit y as a very fine water spray or steam. The humidification system is usually directed at the secondary web. Do not spray directly on the adhesive. Care has to be taken so that water droplets are not sprayed or dropped onto the web.

TWO

- COMPONENT ADHESI VES

The two

- component adhesive systems can be either polyether and/or polyester urethane which is based on either aromatic or aliphatic isocyanate. These adhesives are targeted to replace two

- component solvent

- based adhesives which would be used in media n and some higher performance applications. The two

- component systems generally have better heat and chemical resistance that the single

- component adhesives. Some of the adhesives are room temperature applied while others require heating to lower theThe Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 ap plication viscosity and to improve their flow. The two

- component systems are designed so that their cure is mostly chemical and are not dependant on atmospheric moisture. Therefore, humidification is not required.

The room temperature systems are applied at slightly above the hottest ambient conditions (i.e. Room temperature is defined as the hottest ambient temperature) and can be pumped at ambient conditions. These systems are lower molecular weight than the single

- component systems and are typically applied at 40

- 50  C. The actual running temperature is dependant on the adhesive and line speed of the laminator.

The heated systems are higher molecular weight than the room temperature applied products. They are applied above 50  C. Due to their high v iscosity, they must be preheated to facilitate transfer to the MMD pump and to completely empty the containers.

The room temperature and heated two

- component adhesive systems require the use of MMD equipment to ensure that the adhesive is properly and uni formly mixed. Most two

component systems are designed to have a mixed working time of 15

- 20 minutes. Batch mixing, as done with the solvent

- based systems, is not recommended due to the high reactivity of the adhesive system. The 15

- 20 minute working tim e allows the machine operator time to make machine adjustments, web changes, etc., without having to completely clean the application unit when the laminator is restarted. Laminator stoppages of greater than 15

- 20 minutes would necessitate complete cleanin g of the adhesive application unit and flushing of the adhesive meter, mix and dispense unit from the mixing head on.



### SUBSTRATES

Most laminations currently made using dry bond adhesives can be made using 100% solids adhesive technology. The adhesive su pplier should be contacted to determine the best adhesive for the application. As with dry bond adhesive technology the more stable substrate is generally coated. Often, this is the printed web. The secondary web is typically the sealant film.

EXAMPLES OF COMMERCIAL APPLICATIONS

~ Polyethylene / Polyethylene for personal care products, potting soil ~ Metalized Polyester / High Slip Polyethylene for coffee portion packaging ~ Polypropylene / Polypropylene for beverage bottle label, salty snacks ~ Polypr opylene / Metalized Polypropylene for dry snack filling ~ Polypropylene / Polystyrene for beverage bottle labelsThe Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 ~ Polypropylene / Polyethylene for fresh produce ~ Polyester / Aluminum Foil / Polyethylene for coffee ~ PVDC coated Nylon / Polyethylene for meat and cheese ~ Nylon / Coextruded sealant film for thermoformed webs, meats ~ Polyester / Aluminum Foil / Coextruded sealant film for retort applications ~ Polyester / Polyethylene for hot fill ~ Many others



### CORONA TREATMENT

Surface tension control of the substrates to be laminated is critical. Some film will be treated to the appropriate level prior to laminating, while others films will need additional treatment at the laminator to promote adhesion. In

- line corona treatment at the laminator

is reco mmended to raise the surface energy and to clean the film surfaces of film additives or other contaminates which may hinder adhesion. For example, on high slip polyethylene, the slip additive will migrate to the film surface over time and it will

adverse ly affect adhesion. Polyethylene and polypropylene films have to be treated to a minimum surface energy level of 38 dynes/cm. When in

- line treating films, care has to be taken to assure that you do not get backside treatment of the sealant film to avoid sealing problems.

Nylon and polyester films should be in

- line corona treated to assure good adhesion. Zippery bonds may occur, depending on the adhesive, without retreatment.



### PRINTING

Both Flexographic and Gravure printing processes are used to print s ubstrates which are

laminated with 100% solids adhesives. The inks which are used must be suitable for laminating. Complete drying of the inks is vital, especially with inks which contain

alcohol diluents. Retain alcohols will react with the adhesive and alter the cure. CG analyses for retain solvents is recommended to ensure that the printing has been adequately dried. If the printed ink contains a high level of retain alcohol, the adhesive will not cure properly. It will have poorer heat resistance. It will have poorer product resistance. It will have and lower bond strengths in the printed areas. In contrast, adhesive performance in the non

- printed areas will be largely unaffected because there is

no retain in these areas to alter the adhesive cur e. In addition, ink components which contain hydroxyl (

- OH) groups or other functional groups which will react with the

adhesive will alter the adhesive cure in a manner similar to that noted with alcohols.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760



### ADHESIVE HANDLING

The adhesive should be sto red in their original containers at 20±10  C in a dry

environment.

Depending on the adhesive system, one of the components will contain isocyanate groups. The isocyanate groups are chemically reactive and will react with water, alcohol, amines

and similar materials which have active hydrogen. Opened containers should be resealed and kept tightly closed to maximize the storage life. Nitrogen purging of the containers will maximize the storage life after opening. If the adhesive is supplied in drums, a

de siccant tube should be fitted on the drum to insure the makeup air entering the drum, as the adhesive is withdrawn, is dry.



### ADHESIVE MIXING

METER, MIX AND DISPENSE EQUIPMENT

Two part 100% solids adhesives require the use of a meter/mix/dispense unit (MM D) to supply the adhesive to the laminator.

There are a number of suppliers of MMD equipment for reactive two component adhesive systems on the market. Equipment is available which will run both the room temperature applied and heated adhesive systems.

Most MMD pumps are variable ratio units which allow for the use of a variety of adhesives. The MMD units keep the adhesive components separate until the pump receives an electronic signal from the laminator that adhesive is needed. The adhesive is

then m ixed in the mixing block and supplied to the laminator.

ADHESIVE MIX RATIO

Running the adhesive at the recommended ratio is critical to assure that the adhesive performs as designed. The mix ratio should be monitored on a regular basis. Some of

the MMD units are supplied with automatic mix ratio monitoring which will trigger an alarm when the pump is out of ratio. Others require manual ratio checks. Regular checking of the adhesive mix ratio will verify that the adhesive is properly mixed and

will ide ntify if an out

- of

- ratio situation has developed. Regular mix ratio checks will also help you identify when the MMD unit needs servicing. This will minimize suspect material. The mix ratio tolerance is dependant on the adhesive system being used.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 IMPL ICATION OF USING THE WRONG MIX RATIO

Laminations made using adhesive which contains excess amount of hydroxyl (

- OH) component will not cure properly. The adhesive may remain tacky. The adhesive will exhibit reduced heat resistance, poorer product resist ance and poorer bond strengths.

Lamination made with an improperly mixed adhesive which contains an excess amount of isocyanate (

- NCO) component will be dependant on atmospheric moisture to complete the cure and may take a long time to cure, especially in a low humidity environment. The adhesive may remain tacky until an adequate amount of moisture has entered the laminate to complete the cure. In addition, if the adhesive is MDI (diphenylmethane diisocyanate) based, the potential for developing sealing p roblems due to the extended

cure time is increased.



### THE LAMINATOR

100% solids adhesives are coated by multi

- roll differential speed smooth roll coaters. In this section I will discuss aspects of the adhesive application unit which will affect the qualit y of the laminate. I will also review the impact that tension control ha s on laminate quality.

THE APPLICATION UNIT

The application unit consists of a series of polished rubber and metal rollers which deposit the adhesive on the primary substrate. The roll temperature and quality will impact the adhesive flow properties and influence the coating appearance. In addition to the application rolls, the application unit also contains an exhaust system to vent vapors.

There is also an adhesive distribution s ystem with adhesive level control, and a laminating nipping station. I will also review adhesive coating weight typically run on various structures and aspects of housekeeping.

Roller temperatures

The application rollers are heated to reduce the adhesiv e viscosity to a suitable level which has good flow properties. Maintenance of a constant temperature on the application rolls is critical to controlling the adhesive coating weight. Precise temperature control is needed for both the hot applied and the room temperature applied systems. Temperature control for the heated systems must be very exact. Small changes in the temperature will cause larger changes in the viscosity of the heated systems. Viscosity changes will alter the adhesive flow, the coati ng weight, and appearance.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 Typical temperatures of the heated steel rolls:

~Single component systems

-- 60

- 90  C

~Two

- component room temperature applied systems

-- 40

- 50  C ~Two component heated systems

-- >60  C

The actual application temperature used to run the adhesive will depend on the adhesive system which and the line speed. Higher line speeds typically require higher roll temperatures. The rubber rollers on most application units are not directly heated. These rolls are heated through roller c ontact or supplemental IR heating.

Application Roll Quality

The quality of the application rolls will influence the flow of the adhesive onto the substrate. Defects in the rolls such as cracks, pits, lumps or hard adhesive residue will be

seen in the la mination.

Exhaust

Good ventilation around the coating head is needed. It is important to assure that any vapors which may develop around the coating head are safely vented. At higher line speeds the 100% solid adhesive may exhibit misting in the applic ation unit. Misting is atomization of the adhesive caused by adhesive splitting between the rollers. The mist must be exhausted when it occurs. It can be easily controlled by increasing the application roll temperature or slowing the line speed. If the application roll temperature is increased, the coating weight will drop and may have to be brought back into your targeted range. The exhaust is also needed while cleaning the application unit to remove any solvent vapors which are generated.

Adhesive Di stribution and Level Control

The mixed adhesive should be delivered to the adhesive nip by a transverse feed mechanism to assure fresh adhesive is supplied to the entire width of the adhesive puddle. The application unit should also have a level sensor w hich is interfaced with the MMD unit to automatically supply adhesive as the adhesive level drops. The adhesive level should be kept as low as practical, especially for more reactive systems to minimize coating variations due to changes in the adhesive vi scosity while running.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 Coating weight control

Differential speed multi

- roll coaters are a very good method of precisely applying adhesive.. The coating weight is control by a combination of the relative roll gaps and roll speeds. The application rol ls must have true roundness and very low total indicated

run out (TIR). Freshly mixed adhesive must be used whenever checking the adhesive coating weight. Freshly mixed adhesive will always have lower viscosity than mixed adhesive that has aged on the ap plication unit. The lower viscosity material will coat at a lower coating weight than higher viscosity adhesive using the same application conditions. The coating weight may vary depending on the line speed and rheological properties of the adhesive. T he coating weight should be check on material which was run at the target line speed. Coating weight adjustments are fine tuned by adjusting the speed of the applicator rolls. Ideally, the lowest possible coating weight to achieve the required laminate p erformance is desired.

Below are typical coating weights used in laminates:

~Unprinted film/film laminates

-- 1.3

- 1.8 g/m 2

~Printed film/film laminates

-- 1.5

- 2.0 g/m 2

~Printed film/metalized film laminates

-- 1.8

- 2.5 g/m 2
The coating weight use d in laminated with high ink coverage is governed by the laminates optical appearance.

~Film/ Paper

-- 2.5

- 5.0 g/m 2
~AF/Paper

-- 2.5

- 5.0 g/m 2
The coating weight on paper containing laminates is governed by porosity of the paper. More porous papers require higher coating weights

.

~Film/AF

-- 1.5

- 2.5 g/m 2
The coating weight depends on the laminates’ end use application and adhesive.

The coating weight has an influence on the cured laminate appearance. High coating weights will generally yield a laminate which has an orange skin like appearance in the unprinted areas. Low coating weights will have a bubble like appearance in the printed areas, especially with metalized film structures. Continuous unprinted areas of a laminate oriented in the machine direction are under lower rewind pressure that the unprinted areas which are oriented transverse machine direction. Therefore, the unprinted machine direction areas may have poorer optical appearance.The Dow Chemical Company

2531 Technology Drive, Suite 301, Elgin, IL 60124 Phone: 847

- 649

- 3800 Fax: 847

- 649

- 3760 Nip conditions

The laminat ion nip will influence the laminate appearance. The actual nip temperature is determined by the substrates used in the structure. Optimal appearance is typically achieved by using the hottest nip temperature possible. Excessively hot nips may lead to

te nsion control problems or laminate curl. Roll hardness and impression pressure also influence appearance.

The condition of the lamination nip rollers, like the application nip rollers, will affect the laminate appearance. The nip rollers should be clean and free of defects for optimum laminate appearance.

Tension Control

Good web tension control is very important in making a laminate with good appearance. Because the adhesives have low initial bonds and shear strength, it is critical that the

laminato r is designed to precisely control the tension on the substrates. Tension has to

be well controlled from the unwinds to the rewind to avoid folds and creases in the finished roll. Laminates which are made without good tension control will typically

exhi bit severs curling or tunneling.



### FINISHED ROLL STORAGE

It is a good idea to suspend the master rolls while they cure. Finished rolls of laminate should be stored at room temperature or above to cure. If the laminate is stored in too

cold of an environm ent, the curing rate will be slowed or even stopped in some cases.

The cure will continue once the roll is warmed. Most laminates can be slits after 2

- 3 days cure and will achieve complete cure in 7

- 10 days depending on the storage condition and

the adh esive used.