Hot Melt News

In previous articles, the fundamental of viscoelasticity and the principle of adhesion were briefly discussed. A material must cold flow at room temperature in order to possess pressure sensitive features. Disregarding polymer bases and the use of tackifiers, all room temperature applied “general purpose” pressure sensitive adhesives (PSAs) should meet the following rheological criteria… Read Article>>

Rheological Criteria of Pressure Sensitive Adhesives
- by Pierce Covert, Glue Machinery Corporation

Most peel adhesion tests are carried out at 180 or 90 degree. However, in the real world application, nobody pays attention on the actual peel angles.

The peel adhesion force of all PSA tapes and labels are greatly affected by peel angles. Unfortunately, there is no simple quantitative relationship between peel force and peel angle. Some PSAs show the highest force at the lowest peel angle. Others may present the highest peel force at 30 to 40 degree peel angle. Normally, the minimum peel force appears at a peel angle of 120 to 140 degree. These differences are primarily caused by the radius of curvature of peeling backing materials at various peel angles.

In fact, besides peel test, both shear adhesion and tack are also related to test angles. Lap shear adhesion test is actually a zero (0) degree peel angle test. Shear adhesion force is extremely high because the total area of shearing is much greater than merely a peeling line of the typical peel test. A probe tack tester can determine the force change of a circular contact area. The circular contact area is diminished as the peel angle is altered upon separation. Loop tack test starts with a square contact area. The contact area is gradually reduced into a contact line upon separation. The peel angle of both probe and loop tack continues to change during the entire separation process. As a result, adhesion forces determined from both probe and loop tack tests constantly change during the separation process.

Although almost no tapes and labels are actually peeled at an angle of 180 or 90 degrees in our daily life, the true peel forces at different peel angles were never evaluated or reported by tape and label suppliers. To further understand the effect of peel angle, more fundamental studies are needed.

- by Pierce Covert, Glue Machinery Corporation

PVC floor tile is constructed with many layers of materials. Typically, from top to bottom, there is a transparent PVC film with various thickness (abrasion resistance), a printing film (aesthetic purpose), a white PVC film (background for printing film), and a composite PVC body (form a rigid shape).

The composite body is compounded with several components: recycled PVC, virgin PVC, plasticizer, calcium carbonate, stearic acid derivatives, PE wax, stabilizer, pigment, and etc. Since those recycled PVCs are received from various resources, the total content of plasticizer in the composite is always uncertain.

For self stick PVC floor tile, hot melt pressure sensitive adhesive (HMPSA) is coated on the top of the composite body piece by piece with a top feed roll coater. The coating speed is up to 160 pieces per minute for 1 square foot tiles. The adhesive surface is automatically covered with…Read Article>>

Hot Melt Pressure Sensitive Adhesives Used for PVC Floor Tiles
- by Pierce Covert, Glue Machinery Corporation

A tremendous amount of HMPSAs are used for making self stick labels. Although both solvent and water borne PSAs are also used in these application markets, HMPSAs offer the following advantages.

Environmental friendly and healthy - HMPSA is a PSA with 100% solids. It does not contain any harmful volatile organic compounds (VOC). Although most water-based PSAs do not contain any VOC, they include about 40% of water. Extra efforts are required to clean containers, coating equipment, and waste water treatment.

Fast coating - Since HMPSA has 100% solids, no drying oven is required for the adhesive coating line. HMPSA can cool and solidify immediately after coating. Consequently, it can be coated at very high speed up to 1500 feet per minute or even higher on a very short coating line.

High tack performance - Most general purpose HMPSAs impart relatively high tack versus their solvent and water based counterparts. This unique feature results…Read Article>>

Hot Melt Pressure Sensitive Adhesives (HMPSAs) Used for Labels
- by Pierce Covert, Glue Machinery Corporation

Hot Melt Pressure Sensitive Adhesive backed fastening tape is used heavily in assembly applications worldwide for automotive, packaging, aerospace and other applications. This adhesive is applied to the smooth surface back of the fastening tape then a removable release liner is laminated to the adhesive and the product wound on a reel or die cut to the size and length required.

The major concerns regarding the coating of fastening tape with hot melt adhesive…Read Article>>

Hot Melt PSA-backed Fastening Tape for Assembly Applications
- by Pierce Covert, Glue Machinery Corporation

Fastening tape (Velcro / Hook and Loop) is widely used in products we all use on a daily basis such as clothing, shoes, house wares, furniture, stationary, vehicles, construction, etc. While fastening tape can be sewn easily on most fabrics adhesive is required to bond onto substrates which cannot be sewn, such as metal, glass, concrete, wood, ceramic, rigid plastics, etc. Solvent borne, water borne, and hot melt pressure sensitive adhesives are all used for fastening tapes. However, HMPSA is the most favorable adhesive because it offers the following advantages:

1. Environmental friendly. No solvent evaporation and waste water generated from entire hot melt coating system.
2. High Coating Weight. Typical coating thickness for a fastening tape is 200-250 microns. It is very difficult to obtain such high coating weight from solvent and water borne adhesives at one shot. The maximum coating weight for HMPSA on fastening tapes can easily reach 500 microns.
3. Fast coating speed. HMPSA does not require a drying oven during process. It cools and sets right after coating by a series of cooling fans. A release paper is laminated on the sticky adhesive surface immediately after coating. The coating speed for a typical 1 inch wide tape is about 100 ft/min.
4. Controlled coating width. To avoid edge ooze of the thick and sticky surface, a slot coating die with a precise width is generally used. No adhesive is coated at both edges of the fastening tape for about 0.5-1 mm.

There is no universal HMPSA for all fastening tapes. Depending upon specific application areas, to introduce HMPSAs imparting different adhesion performances are normally required. For those applications requiring high temperature resistant, such as automotive, curable solvent or water borne adhesives are needed.

- by Pierce Covert, Glue Machinery Corporation

In 1995 hot melt adhesive (HMA) was aggressively introduced to the sport shoemaking industry. Different types of hot melt adhesives (SBC, EVA, APO-based HMAs, Polyesters, Polyamides and PUR) are used for bonding specific shoe components.

Basically, these adhesives are applied in three major process rooms: parts preparation, shoe upper stitching, and upper-sole assembly. Some parts, with pre-coated adhesives, are supplied from outsourcing coater/laminators.

The following table lists the bonding areas, type of applicators…Read Article>>

Hot Melt Adhesives for the Sport Shoemaking Industry
- by Pierce Covert, Glue Machinery Corporation

Removable hot melt adhesive, also called peelable hot melt or “Fugitive” adhesive offers temporary bonding between a range of substrates.

This product is used the majority of the time to temporarily attach paper to paper and plastics to paper. Great care must be taken in the application of this product to insure that the paper substrates are not stained with oily residue from the adhesive.

It is important to determine in advance if this problem can occur as many jobs in printing and mailing are refused or aesthetically defective at a later date due to the oils from the adhesive migrating through paper.

With most glossy or coated paper paper stock staining will not occur provided the correct adhesive is used and it is applied at the correct temperature.

Some removable hot melts contain higher concentrations of oils than others and must be evaluated in advance of use.

The application temperature of the hot melt is also critical. If a removable hot melt is applied too hot - the oils can be driven from the adhesive into the paper. Also, if the hot melt is melted and held at a higher than recommended temperature the adhesive can be adversely affected.

While staining of the paper substrates with removable hot melt may not affect the quality of the bonds or be of any issue - some customers see this aesthetic imperfection as unaccpetable.

-by Pierce Covert, Glue Machinery Corporation

A tremendous amount of PE and PP films are used in tapes, labels, envelopes, bags, packaging, and lamination markets. These materials are more difficult to bond than many other plastics due to their nature of low surface energies or polarities.

Some chemists believe that to gain good adhesion to low surface energy materials, the pressure sensitive hot melt adhesives used should have low polarities. This perception is coming from the principle of “like–dissolve-like” for mixing chemical substances. However, this principle is not able to describe the adhesion behavior for two dissimilar materials… Read Article>>

How to Adhere Low Surface Energy Substrates
- by Pierce Covert, Glue Machinery Corporation

Most hot melt adhesive users prefer clear or transparent hot melt. Below are two approaches to achieve this aesthetic goal.

1.To produce a transparent EVA-based HMA, one should first select EVAs and tackifiers possessing similar solubility parameters. In other words, the selected tackifiers should be very compatible with the soft VA (Vinyl Acetate) segment of the EVA. Natural tackifiers such as rosin and Terpene derivatives are more polar material and therefore are more compatible with VA. Disregarding the color, it is normally easier to make a transparent EVA-based HMA with natural tackifiers. Among various types of synthetic hydrocarbon tackifiers, C5 (aliphatic)/C9 (aromatic) or C10 (DCPD, di-cyclo-penta-diene)/C9 co-tackifiers are more compatible to VA and can be easier to make transparent EVA-based HMAs.

2.The production procedure is also critical to obtain transparent HMAs. During mixing, adhesive blends are normally transparent at elevated temperatures beyond the cloud point of the blends. When finished adhesive blends are suddenly chilled… Read Article>>

Clear EVA-based Hot Melt Adhesives
- by Pierce Covert, Glue Machinery Corporation