Professional technology of adhesive common used technical indexes
1. Why does adhesive can stick?
A. Mechanical theory. Mechanical theory think that adhesive must infiltrate into the surface gap of adherend and eliminate the adsorptive air on the interface which can produce cohesive action. Mechanical inlay is an important element for bonding porous adherend such as foamed plastic. Bonding result for bonding density materials of polished surface is better than density materials of smooth surface. That's because: (1) mechanical inlay. (2) produce clean surface. (3) produce reactivity surface. (4) surface area increases. Polishing makes the surface rough. We can think the physical and chemical property of surface layer change, thus improving the bonding strength.
B. Adsorption theory. Adsorption theory think that bonding is caused by molecule touching between two materials and interfacial force. Bonding power mainly comes from intermolecular force which include hydrogen bonds and Van der Waals force. The continuous touching process between adhesive and adherend is called wetting. When the surface tension of adhesive is lower than critical surface tension of solid, adhesive will wet solid surface. Adhesive infiltrate into the hollows and gapes of solid surface, it will produce good wetting. If adhesive are overhead in surface hollow which produce the actual touching area between adhesive and adherend and the bonding strength of joint.
Many synthetic adhesive are easy to wet metal adherend, but most solid adherend which surface tension is lower than surface tension of adhesive. In factual , the condition of getting good wetting is the surface tension of adhesive lower than adherend. Also, this is why epoxy resin adhesive can bond metal well but is difficult to bond with untreated polymers, such as PE, PP and fluoro plastic.
To make close contact between adhesive and adherend by wetting is mainly produced by intermolecular force which produces permanent bonding. Chemical bond which included by adhesion force and cohesion force have four types: (1) ionic bond. (2) covalent bond. (3) metallic bond. (4) Van der Waals force.
C. Diffusion theory.? Diffusion theory think that bonding is produced by molecular diffusion of adhesive and interface of adherend. When both adhesive and adherend are possessed of motive long-chain macromolecular polymer, the diffusion theory is basically suitable. The bonding and heat sealing of thermo plastics can be regarded as the result of diffusion theory.
D. Electrostatic theory. Forming of electric double layer on? the interface of adhesive and adherend produces electrostatic attraction, also the discrete resistance. When adhesive are peeled from adherend, it has obvious electric charge which is the powerful authenticate fro this theory.
E. Weak boundary layer theory. Weak boundary layer theory think that if bonding destruction is regarded as boundary layer destruction, in fact, it is cohesion destruction or weak boundary layer destruction. Weak boundary layer comes from adhesive, adherend, environment or any combination during this three. If the impurity concentrate near bonding interface and insecure bonding with adherend, it will produce weak boundary layer for the inside of adhesive and adherend. When destroying, though many conditions happened on the interface of adhesive and adherend, in fact, it's the destruction of weak boundary layer.
Bonding between PE and metal oxides is the example of weak boundary layer effect. PE contains low-intensity oxygen-impurity and low molecule which makes few destruction effect existing on interface. It eliminating the low molecule or oxygen-impurity by surface processing, the bonding strength will improve largely. It is proved that weak boundary layer exists on interface which reduces bonding strength.
2. Adhesive classification
There are many adhesive classification method. According to applying method, it can be classified by thermal curable, hot-melt, room-curing type, pressure-sensitive and etc. According to application objects, it can be divided into structural, non-structural or special adhesive. According to morphology, it can be divided into water-soluble, water-emulsion, solvent-type and all kinds of solid form and etc. Synthetic chemical workers refer to classifying it according to chemical composition.
1. Inorganic adhesive
1. Silicate: sodium silicate; portland cement
2. Phosphate: sodium phosphate cupric oxide
3. Ceramics: lead oxide, aluminium oxide
4. Low melting metal: tin lead alloy
2. Natural adhesive
1. Animal glue: skin glue, bone glue, lac, casein glue, blood albumin glue, fish glue and etc.
2. Vegetable glue: starch, dextrin, rosin, arabic gum, natural gum, natural rubber and etc.
3. Mineral rubber: mineral wax, pitch and etc.
3. Synthetic adhesive
1. Synthetic resin
(1) . Thermo plastic: cellulose ester, vinyl polymer( PVAc, PVA, HPVC, PIB and etc), polyester, PA, polyacrylates, α-cyanaacrylate, P.V.B., EVA and etc
(2). Thermosetting: epoxy resin, PF, UF, melamine formaldhyde resin, organic silicon resin, furan resin, unsaturated polyester, acrylic resin, polyimide, PBI, PF-P.V.B., PF-PA, PF- epoxy resin, epoxy-PA and etc.
2. Synthetic rubber: CR, SBR, IIR, buna rubber, IR, GP-R, PU rubber, CSM elastomer sillico rubber and etc.
3. Several main technical indexes of adhesive
A. PH value
PH is the criteria for acid-base degree of emulsion. The closer the PH value tends to zero, the stronger of acid for emulsion, on the contrary, it tends to 14 which shows strong alkali of emulsion. Under common temperature, if PH value equals to 7, if means neutral emulsion.
There are many methods to measure the PH value of emulsion.
1. Add PH indicator into measured emulsion. Different indicators can change color according to different PH value. So we can make sure the range of PH according to indicator.
2. Making use of PH test paper which is divided into comprehensive test paper and sophisticated test paper. To dip a little tested liquor on the test paper, then compare the color of test paper with color card which can get PH of liquor. PH test paper can't show oily PH, that's because PH test paper is made by h-iron and measure PH of liquor by h-iron, but there is no h-iron in oil, this is why PH test paper can't show oily PH.
3. Making use of PH meter. PH meter is an instrument which measures PH value of liquor by choosing electrode(such as glass electrode). PH meter can accurate to 2 decimal places.
B. Solid content
This method rests on GB/T 2793-1995 <adhesive non-volatile matter content>.
1. Principle
To heat adhesive sample under certain temperature for certain time, the percentage of mass for after heating and before heating is adhesive non-volatile matter content.
2. Instrument
Electric constant-temperature drying oven, the temperature fluctuation should be less than ±2℃; thermometer 0~150℃; division value 1℃; low-type weighting bottle 50mm, height 30mm; maximum weight os analytical balance is 200g, division value is 0.1mg; glass desiccator is 24cm which contains anhydrous calcium chloride and hydranal-humidity absorber drying agent.
3. Experimental procedure
(1). Drying temperature and time of adhesive and sample quality see table.
Drying condition of different adhesive types.

(2). To weight sample according to requirement and accurate to 0.001g. Place it under experimental temperature and go through constant weight, clean and drying weighting bottle, to heat in drying oven under stated experimental temperature, then take out sample and put it into desiccator till room temperature and weight.
C. Viscosity
1. Tu-4 cups viscosity meter method
This method is suitable for testing products which outflowing time is 10-150s. Such as Zili-2 adhesive used by aviation which stipulates viscosity of Tu-4 cups is 60~90s.
1. Principle
Measuring 100ml adhesive filled in a special conical vessel and measure its outflowing time by orifice which diameter is (4±0.2) mm.
2. Instrument
Tu-4 cups viscosity meter is produced by plastic or yellow metal, but subject to metal viscosity meter. Its top is cylindrical, the bottom is conical. The roughness of wall surface is 0.4um. At the bottom of conical, there is a discharge spout. Its height is(4±0.02)mm, diameter is (4±0.02)mm, which is made from stainless steel. The cone inside angle of viscosity meter is 81°±15’, total height is 73mm, the internal diameter of cylinder is 50+2mm, volume is 100ml, division of thermometer is 0.1℃, accuracy of stopwatch is 0.2s.
3. Experimental procedure
1. Sample should be no clotting, no gelling and even fluid. Put the sample at constant temperature (such as 25℃) in advance.
2. To clean the internal surface by gauze which dipped solvent before testing, then dry by cold air. To set the viscosity meter on horizontal position and put a 100ml measuring glass under it. Heating the adhesive sample to 25+0.5℃ in advance, then plug up the hole of discharge spout by middle finger of left hand and dip sample into glass immediately. Sweeping bubble and redundant sample into groove and make oven for liquid surface and glass edge. If the temperature is above 25℃, it should control sample at 25-0.5 in advance. Letting go of middle finger of left hand and making adhesive flowing out. At the same time, starting stopwatch to record time from flowing out to break off.
2. Rotational viscometer
NDJ-1 rotational viscometer (pointer type)
NDJ-1 rotational viscometer is used to measure the viscosity resistance and absolute viscosity of liquid. Being accompanied by No. 1-4 four kinds of rotor which can be applied according to height of tested liquid and travel speed.
1. Viscosity measuring range: 10~100000mpa.s
2. Measuring error: ±5％ (Newton-type liquid)
3. Measuring rotor: No. 1~4 four kinds