What Are the Different Types of Permanent Adhesive?

Bonding agent is one of the most important auxiliary materials, which is widely used in packaging operations. An adhesive is a sticky substance that joins two separate materials together by virtue of its tackiness. There are many types of adhesives.

Chinese name: Adhesive

Foreign name: Bonding agent
Attributes: Chemical agent

Introduction to adhesives

Adhesive is actually a general term for a variety of stress materials that connect or adhere the same or different materials. There are three types of liquid, paste and solid.

Adhesive classification

There are many types of adhesives, which can generally be classified as follows:

Source material of adhesive

Natural adhesive

It is taken from matter in nature. Includes starch, protein, dextrin, animal gum, shellac, skin rubber, rosin and other biological adhesives; also includes mineral adhesives such as asphalt.

synthetic adhesive

Mainly refers to synthetic substances, including inorganic binders such as water glass, and organic binders such as synthetic resins and synthetic rubbers.

Adhesive use characteristics

Water-soluble adhesive

Adhesives using water as a solvent include starch, dextrin, polyvinyl alcohol, carboxymethyl cellulose, and the like.

Hot melt adhesive

It is used after melting the adhesive by heating. It is a solid adhesive. General thermoplastic resins can be used, such as polyurethane, polystyrene, polyacrylate, ethylene-vinyl acetate copolymer, etc.

Solvent-based adhesive

Adhesive that is insoluble in water and soluble in some solvents. Such as shellac, butyl rubber, etc.

Emulsion adhesive

Most are suspended in water, such as vinyl acetate resin, acrylic resin, chlorinated rubber and so on.

Solvent-free liquid adhesive

Viscous liquid at normal temperature, such as epoxy resin.

Adhesive is the intermediary between the label material and the bonding substrate and acts as a bond. According to its characteristics can be divided into two kinds of permanent and removable. It has a variety of formulations, suitable for different surface materials and different occasions. Adhesive is the most important component in the technology of self-adhesive materials, and it is the key to label application technology.

Adhesives by raw material

1 MS modified silane

The end of the modified silane polymer is methoxysilane. It was invented by Zhongyuan Group in 1978. The company is the only supplier of modified silane raw materials in the world. Produce a series of high-quality sealants and adhesives used in construction, industry, automobile transportation, civil and so on.

2 Polyurethane

The full name of polyurethane is polyurethane, which is a collective name for macromolecular compounds containing repeating urethane groups on the main chain. It is made by adding organic diisocyanate or polyisocyanate with dihydroxy or polyhydroxy compound.

3 Silicone

Silicones are commonly known as silicone oil or dimethyl silicone oil. The molecular formula: (CH ₃ ) ₃ SiO (CH ₃ ) ₂ SiO _n Si (CH ₃ ) ₃ is a polymer of organic silicon oxides. It is a series of polymers with different molecular weights. Polydimethylsiloxane, viscosity increases with molecular weight.

Some performance comparisons of the three

performance	MS modified silane	Polyurethane	Silicone
Not frothy	10	9	5
Dispensing at low temperature	10	6	10
Drop resistance	10	10	10
Curing speed	10	7	10
Storage stability	10	7	9
Anti-aging	9	6	10
Stickiness to various substrates	10	5	8
Mechanical behavior	10	10	10
Temperature resistance	9	8	10
Antifouling	10	10	5
Affinity to water-based paints	10	10	3
Impermeability	8	8	3

* The numbers in the table indicate specific scores, with a maximum of 10 points.

Adhesives by packaging material

Paper-based material adhesive

It mainly includes original (natural) starch, dextrin, casein, and various water-based latexes that are currently chemically synthesized and environmentally friendly. Widely used in color boxes, cigarette packages, paper bags, gift boxes, hardcover boxes and various handmade boxes, as well as wooden furniture.

Plastic adhesive

It mainly includes solvent-based adhesives such as styrene-butadiene rubber, polyurethane, nitrocellulose, and polyvinyl acetate; water-soluble adhesives such as ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer; emulsion types such as vinyl acetate resin and acrylic resin Adhesives; hot-melt adhesives made of thermoplastic resins such as polystyrene, polyurethane, and polyacrylate.

wood adhesive

It mainly includes animal glue such as bone glue, leather glue, peony, casein, and blood glue; it also includes synthetic resin glue such as phenolic resin glue, polyvinyl acetate resin glue, urea resin glue, and vegetable glue such as bean gum.

Adhesives and adhesives are a general term for non-metallic materials that can bind one solid surface to another solid surface due to surface bonding and internal forces (adhesion, cohesion, etc.).

Adhesives by application

Industrial adhesive

It is mainly used in color printing packaging, architectural decoration and wooden furniture to achieve the combination of objects and objects.

Agricultural and forestry adhesives

It is mainly used for slope greening or other soil structure improvement, which can make the soil form a granular structure and achieve the effect of preserving soil moisture. At the same time, it can enhance soil water permeability, prevent soil loss caused by surface runoff, increase soil permeability, protect soil and fertilizer, alleviate and regulate soil moisture evaporation, and allow better crop growth.

Adhesive formula

Starch binder is a mixture of water, raw starch, cooked paste, caustic soda, borax and formaldehyde. The approximate ratio is: 80% water; 20% starch (of which 85% is raw starch and 15% is cooked starch); caustic Sodium (total starch) 2.4-2.8%; Borax (total starch) 2.7-3.2%, about 10 moles; trace amounts of formaldehyde.

Most of the starch used by some carton factories in the United States is corn starch. Some are untreated pure corn flour, and some are chemically treated. Especially, the processed special starch has good stable viscosity and excellent water content. Some starches are powdery and some are granular. The granules are just loose blocks surrounded by powder, which is used to prepare the whole batch of paste.

Some factories use specially treated corn starch to make a single-viscosity adhesive. Its gelation point starts at 61 ° C and is completed at 63 ° C. Although the gelation point is lower, the adhesive gels quickly like ordinary double-sided machine paste when bonded. The viscosity is usually between 27 and 32 seconds. 680 gallons of paste with 500 kg of starch.

After the starch is stirred in normal temperature water, its particles are dispersed into a milky state, but it will not dissolve and will not absorb water. If the agitation is stopped, the starch will precipitate at the bottom and gradually become lumps. Once the lumps are formed, redispersion will not be so easy. Starch dispersed in water starts to absorb moisture and swell when heated. Raw starch is used in the adhesive formulation, which begins to swell at about 70 ° C. The temperature was raised to 90 ° C, and the swelling effect was completed. The gelatinized starch is very sticky, the degree of which depends on the amount of starch in the water.

Adhesive raw material technology

Binder borax

Borax is also divided into powder and granular. Fine-grained borax is the best. Borax is divided into two levels based on strength. 10 moles of borax has 10 water molecules, which is called grade 10 water borax. 5 moles of borax has 5 water molecules, which is called Grade 5 water borax. The concentration of 5 moles of borax is higher. 0.35 kg of 5 moles of borax is equivalent to 0.454 kg of 10 moles of borax. If the same amount of two borax is used wrongly, the consequences will be serious. If borax is added to the raw starch and water emulsion, and the mixture is heated, the starch swells quickly after absorbing water, and becomes more viscous than without borax.

There is a certain limit to the amount of borax added, otherwise it will affect the swelling of the starch, the gelatinized paste will become brittle, and it will be in a powder state when dry.

As long as the caustic soda contains 76% sodium oxide without any commercial grade of additives, crumbs or flakes can be used. The composition is equivalent to 98% sodium hydroxide. Caustic soda absorbs moisture from the air and reduces its strength. Therefore, if the drum is damaged, it should not be used. After opening the bucket lid and taking the material, the lid should be tightly closed immediately.

Caustic soda

Caustic soda is a strong base, which can seriously burn the skin when dry or dissolved in water. Wear a mask and rubber gloves when handling caustic soda, and always have a bottle of vinegar ready to deal with caustic-contaminated skin immediately. Caustic soda will emit smoke when dissolved in water. Do not inhale the emitted smoke, which is toxic.

Caustic soda is added to the emulsion of raw starch and water, and the mixture is heated to reduce the temperature of starch swelling and gelling. According to this feature, the amount of caustic soda can be used to precisely control the temperature of starch swelling and gelling. However, if the added amount is too large, the gelatinized particles will be split, the viscosity will be reduced, and the raw starch in the paste will be gelled in advance.

Formaldehyde

Formaldehyde is in the state of 37% aqueous solution, and it is measured according to the volume or wet weight specified by the formula. Formaldehyde is used in general adhesives for corrosion protection. Used as a chemical crosslinker in some waterproof adhesive formulations. Protective equipment must be worn when handling formaldehyde, as formaldehyde is strongly irritating to the eyes and skin. Absolutely avoid inhalation.

Water-resistant adhesive

The difference between water-resistant adhesives and ordinary adhesives is that they usually contain more raw starch, less caustic soda, and no or little borax. Of course, water-resistant adhesives are added with a certain amount of waterproofing agent. There are many waterproofing agents that can be used, all of which are water-soluble resins. After the resin is chemically cross-linked with formaldehyde, it will become a water-insoluble, water-resistant adhesive when heated on the paste line.

Most water-resistant adhesives have a limited life. Some gradually thicken over time, and cannot be avoided even with agitation. Some mechanical operation performance is good, but the degree of water resistance is greatly reduced. Therefore, the adhesive must be used as soon as possible after preparation.

Adhesive considerations

The precautions for increasing the performance of waterproof cardboard are as follows:

The pH of the waterproof adhesive must be controlled within specified limits;
Must be heavier than normal paste lines;
Use as much heat as possible when producing cardboard;
The moisture of tissue paper should not be too high;
There must be more agitation and the waterproof adhesive in the tank must be used as soon as possible;
If the effect is still not good, the only remedy is to add more resin.

Adhesive water

Drying or bonding is mainly accomplished by absorbing water on the surface. The raw solid starch in the binder gels on the paste line to absorb moisture. The bonding time is from a few seconds to about a minute. Moisture is gradually absorbed by the surrounding air and paper fibers. This traditional adhesive is generally used in corrugated board production lines and can immediately produce a strong bonding effect.

To achieve a satisfactory cohesive effect, a slightly viscous suspoemulsion must be added to the starch and water emulsion, which contains pregelatinized starch. This suspoemulsion can suspend raw starch in water and prevent its precipitation; increase the concentration to facilitate being coated on the sizing roller and form a paste film of appropriate thickness on the roller; adjust the viscosity so that the paper fibers are properly wet and initially adhere; There is a lot of water around the starch molecules, so that the starch can swell to the maximum and completely gelatinize when heated; caustic soda must be added to adjust and control the gelatinization temperature of the starch to a minimum.

In order to achieve a satisfactory bonding effect, borax must also be added to make the raw starch absorb all available water when heated; make the starch gelatinous to produce appropriate viscosity and toughness; act as a buffer to prevent caustic soda from A portion of the raw starch swells below the minimum gelatinization temperature.

Adhesive storage

Most of the adhesives are made of high-molecular substances as soil, and some need to be added with a certain solvent. Relying on chemical reactions or physical effects to achieve curing, these will occur slowly during the adhesive storage process. Adhesives have a certain shelf life, which is related to storage conditions, such as humidity, temperature, and ventilation. In order to ensure that the performance of the adhesive is basically unchanged within the specified period, it is necessary to strictly pay attention to the method of storing the adhesive. For different types of adhesives, because of their different properties, storage conditions are also different.

The following are the precautions for keeping several commonly used adhesives:

The epoxy resin adhesive should be stored in a ventilated, dry, cool, room temperature environment for a period of six months to one year.
The phenolic resin adhesive should be stored in a closed container and stored in a cool place away from the fire. The period is six months to one year.
Polyisocyanate glue should be packed in brown bottles, stored in a dark place and protected from light. Do not use metal containers. Do not use rubber and cork stoppers. It must be strictly waterproof and prevent entering, otherwise polymerization deterioration will occur; the prepolymer polyurethane adhesive must not be stored at low temperature to prevent condensation. The storage period of component A is 2 years. The component must be protected from moisture and avoid contact with moisture or other substances Substances exposed to active hydrogen have a period of six months to one year.
The storage temperature of urea-formaldehyde resin adhesive should be as low as possible. Add 5% methanol to improve storage stability.
Neoprene adhesive containers should be tightly sealed. Store at room temperature. Do not leave the temperature too high (> 30 ) or too low (<5 ). Keep away from fire. The storage period is from March to June.
The a-cyanoacrylate adhesive should be stored in a sealed, low temperature, dry, dark and cool place for a period of one year. Glass bottles have a longer shelf life than plastic bottles.
Anaerobic adhesive should be stored in a cool, dark place. The storage period is half a year. The material of the packaging container should be polyethylene. Do not use iron containers. Do not fill it up.
The SGA adhesive should be stored in a sealed container. The two components must be separated and stored in a cool, ventilated, low-temperature and dry place. The period is six months to one year.
Polyvinyl ester emulsion (milk white glue) should be packaged in glass, ceramic, and plastic containers. The storage temperature is 5-30c. Pay attention to antifreeze. The storage period is 1 year.
Hot-melt adhesives should be stored at room temperature, protected from light and heat.
Inorganic adhesives should be stored tightly to prevent moisture absorption.

Adhesives and adhesives

The procedure of the bonding process :: surface treatment For different types of adherends and different conditions, surface treatment. Strict can be divided into general methods, chemical methods and physical methods. In the decoration industry, simple processing is mainly performed on adhered objects. Such as: dust, oil, rough surface, moisture and other aspects to be treated to ensure that the adhered surface is clean, dry and free of oil.
The glued surface to be glued should be evenly glued to ensure wetting, to avoid the generation of air bubbles as much as possible, and the adhesion strength is greatly reduced due to air holes, leading to degumming. Attention should be paid to the alignment position once. It should not be shifted. It can be pressurized to remove air and make it in close contact.
The process of curing an adhesive to make its adhesive layer solid through chemical and physical action. Curing is the last step to obtain adhesive properties, which has a great influence on the adhesive strength. During the curing process, temperature, pressure and time are the three important parameters of the curing process. The change of each parameter has a direct impact on the bonding strength. (Each adhesive has a specific curing temperature and time). When applying a certain pressure, it should be said that it is necessary for all adhesives, because pressurization is conducive to the diffusion and penetration of the adhesive, and it is in close contact with the adherend. The layer is uniform and the position of the adherend is fixed. Regardless of whether the chemical reaction or physical action is used to complete the curing of the adhesive layer, a certain amount of time is required. In order to fully obtain the maximum bonding strength, sufficient curing time must be ensured. (This is usually required to make the adhesive a certain time. To reach the final adhesion).