(1) Definition of an adhesive
- An adhesive is a material which is not solidified and is in a semi-liquid state in order to be attached easily to the object to be bonded with by only slight finger pressure or a material of viscoelasticity which maintains adhesive power all the time, maintaining semi-permanent elasticity. (Products for which an adhesive is used have many uses as labels, double-sided tape, adhesive tape, and post-its. The reason why the use of adhesive products varies is due to the precise function and convenience of the adhesive and from the fact that the product is developed in various fields by assigning various functions according to its use.)
(2) Three major physical properties of an adhesive
-(TACK) Initial adhesive power (TACK)
Having only a transient adhesive property, it is related to ease of adhesion and is measured by the power that is necessary for detaching the adhesive from the bonded object in a short time.
This is a physical property that represents resistance generated when separating the adhesive or adhesive tape from the surface of a bonded object, i.e. it is the coherence power between the interface of the adhesive and the bonded object and is standard whether adhesive tape is attached firmly or not.
This refers to the internal cohesion of the cohesive itself. It means the degree that adhesive resists internal destruction, as resistance against being pushed under a certain load. It is related to the thickness of the adhesive, the power between the molecular, bridge condition and the molecular weight.
(3) Classification according to the function of the adhesive
- An adhesive can be classified into a permanent type adhesive which is attached permanently or a removable-type adhesive which can be separated again.
||Classification of adhesive
||PE, PP injected materials, drums, pallets.
||Glass bottles, boxes, computer sheets, plastic-injected materials.
||Study papers, teaching materials, aluminum plates, glass, etc.
||Steel plates, shopping bags, hangers, boxes, diskettes, video indexes, etc.
||Cassettes, tape indexes, portable wet tissues, electronic products, etc.
||Study papers, teaching materials, glass, general plastic-injected materials
(4) considerations when selecting an adhesive
- The important point in all label products is that an optimal product can be manufactured only when several factors are considered, i.e. what kind of original paper is used, by which method is it printed, under which condition is the product used after printing, to what substance is the object to be bonded and what kind of physical property of adhesive is required. A sufficient review and inspection are also necessary because even the same product may represent various physical properties, depending on the kind of adhesive, method of adhesion and improvement of performance. Though there may be factors for selection according to various changes, let us examine several points briefly.
||Factors for selection of adhesive
|Quality of material of original paper, surface condition of original paper
||Is adhesion with material excellent?
Is there any interaction with the adhesive?
Is there any problem in forming adhesive layer?
|Condition of release paper
||Is the peel strength excellent?
Does transfer phenomenon occur?
Does the adhesive affect the release paper?
|Quality and condition of surface
of material to be bonded
||Is the surface flat or round?
What is the quality of the material to be bonded?
Is it flat or embossed?
Is there any water, or other pollutant?
Is there a possibility that the label can be spoiled after attachment?
|Performance of physical property
||Are initial adhesion, later adhesion, heat resistance, cold resistance,
water resistance, moisture resistance, acid resistance, or chemical resistance called for?
Which characteristic is preferred-adhesive power or cohesive force?
|Condition about additional function
||Are fire retardant, conductivity, water solubility and light resistance is required separately?
||Is aging resistance excellent?
Is there a dryness problem?
Is aging condition excellent?
Are the processing capabilities of the adhesive coating excellent?
|Usage suitability for use
||Is the adhesive glue flow excellent?
Does it smell after adhesion?
Is it selected according to the most economical design?
(5) Basic explanations about adhesives
a. Rubber adhesives
- This is an adhesive which is designed to have adhesive power at ordinary temperatures by mixing macromolecule (rubber) having –Tg with resin which has an adhesive providing a +Tg characteristic.
- This adhesive has excellent adhesive power, cohesive force and TACK.
b. Acrylic adhesives
- The main monomer is composed of acryl ester of carbon numbers 2~10, and for cross-linkage, the polymer is generally used which a monomer with calling for a small amount to be copolymerized.
- It is used in a place where cohesive force is enhanced with a select monomer that provides improvement in adhesive power and transparency.
c. Silicon adhesives
These are adhesives which have greatly different characteristics from that of other adhesive due to the Si-O combined structure.
These are stable adhesives that resist oxidation and heat.
The flexibility and adhesion of the basic material is excellent at low temperatures due to the low power between molecules, but the mechanical strength is low.
They can be used where such characteristics as heat resistance, cold resistance, weather resistance, electricity resistance are required.
d. Hot melt adhesives
- There adhesives, being 100% solid at ordinary temperature, are made by non-volatile, non-flammable, thermoplastic resins without any solvent at all.
- Being a solventless adhesive, there is no danger of pollution and fire.
- There are several kinds of this adhesive such as EVA, PE, POLYURETHANE, POLYAMIDE POLYESTER.
e. Solvent adhesives
This is used more often for various adhesive products than other adhesive type.
It has the advantage of demonstrating variable performance and excellent effectiveness of its physical properties.
A hydrocarbon system is widely used as a common.
f. Emulsion adhesives
When an acryl emulsion-type adhesive is polymerized, the emulsifying agent (surface active agent), a high molecule protecting colloid polymerization initiator is commonly used in addition to the monomer.
After the polymerization reaction, the pH conditioning agent, thickener, and defoaming agent is used.
It has the advantage of low price compared with that of a solvent type but water resistance is low.
Reference: KOSTIC, "Label technology”,http://eng.kostic.co.kr/technology/01_labelinfo_01.html, 2014. 1. 29
>> Click to download Adhesive