Why hot melt adhesive can stick things?

Why hot melt adhesive can stick things?

Only polymer Meite/Milan

Hotmelt glue can be called a "popular" glue that is widely used but rarely known to general public. It is widely used because I can easily find several items from your side that contain hot melt adhesive; it's not well known because most of them don't know that there is a glue that needs to be heated to get sticky. . For most people, hot melt is truly both familiar and unfamiliar!

What materials can be glued with hot melt adhesives has always been a concern for everyone. It must be necessary. If you want to know exactly what materials hot melt adhesive can stick to, you need to start with type of hot melt adhesive, because properties of different types of hot melt adhesives are different, and performance of bonding with materials is a matter. compatibility. Why do some people think that bonding effect is not good when using hot melt adhesive? It may be that type is not chosen correctly, resulting in incompatibility between them.

Why hot melt adhesive can stick things?
  • Relationship principle
  • Why adhesives can cause bonding, there have been many theories in theoretical circles about this, and there is still no conclusion. From a practical point of view, there is still no unified theory of adhesion that could explain all phenomena of bonding.

    1. Mechanical theory

    Mechanical theory is also called glue nail theory. In general, adhesive hardens by penetrating gaps in surface of material, forming small adhesive nails one after other, resulting in a mechanical bond that makes adhesive harden. The substrates are held together mechanically. Because behavior of a solid is not completely smooth, surface of a solid under a microscope is made up of numerous irregular peaks and troughs.

    The mechanical adhesion of adhesive is a major factor in bonding porous base materials such as foam. For bonding non-porous materials, mechanical sanding is much better than raw sanding. We often use this mechanical sanding method when bonding leather and rubber.

    Mechanical theory can very well explain adhesion mechanism of a rough surface, but it is difficult to explain adhesion mechanism of a smooth surface, which is its disadvantage.

    Why hot melt adhesive can stick things?

    2. Adsorption theory

    The adsorption theory states that adhesion is caused by molecular contact between two materials and creates surface forces. The process of contact between adhesive and adhesive surface is called "wetting". For adhesives, surface tension must be below critical surface tension of solid in order to achieve a wetting effect.

    Most organic adhesives readily wet metal solids. However, many solid organic substrates have a lower surface tension than commonly used adhesives. Good wetting requires adhesive to have a lower surface tension than substrate, a fact partly due to fact that organic adhesives such as epoxy adhesives have good adhesion to metals but not to untreated Poor adhesion to polymer substrates such as polyethylene, polypropylene and fluorocarbons.

    3. Electrostatic theory

    Electrostatic theory believes that existence of adhesion is due to presence of an electric double layer at interface between adhesive and adhesive, which is caused by formation of an electrostatic force. This electrostatic force is itself antiseparative. The plausibility of this theory is supported by electrical discharge that occurs when cured adhesive is pulled away from substrate.

    4. Diffusion theory

    Diffusion theory believes that existence of an adhesive force is due to mutual diffusion between adhesive and adhered molecules. This theory is plausible if both adhesive and adhesive are polymers with long movable molecular chains. For example, bonding of thermoplastics with a solvent or hot melt compound is considered to be result of interdiffusion between molecules.

    Although question of mechanism of communication is not yet settled, understanding various theories of communication will help us understand basic requirements for communication. Perhaps connection is not theory that can explain this. For hot melt adhesive films, different bonding theories should be used for bonding different materials, such as bonding textiles and plastics, different theoretical models will be applied. In general, among various bonding mechanisms, mechanical theory and diffusion theory are closest to actual situation of bonding hot-melt adhesive films.

  • Categories
  • 1. Polyethylene hot melt adhesive:

    ①Polyethylene Hot Melt

    Concept: hot melt adhesive polymerized from ethylene and a small amount of α-olefin or other monomers

    Features: good bonding, low price, easy bonding of porous surfaces, etc.

    ②Polypropylene hot melt adhesive

    Concept: thermoplastic resin polymerized from propylene, mostly random polypropylene

    Characteristics: certain cohesion; slow curing speed; low heat resistance; often blended with low molecular weight polyethylene or crystalline polypropylene to improve speedcuring and heat resistance.

    2. Ethylene and its copolymers

    ①EVA (ethylene vinyl acetate copolymer)

    Concept: EVA resin is a non-toxic white or light yellow odorless powder or granular low melting polymer. When MI index is large, molecular weight is small, and synthetic hot melt adhesive has low viscosity and good fluidity

    Properties: good adhesion, softness and fluidity when heated. Low strength, not heat resistant, not resistant to fatty oils, cannot be used as a structural adhesive

    ②EEA (ethylene ethyl acrylate copolymer)

    The ethyl acrylate content is about 23% in EEA resin used as base for hot melt adhesive. Its structure is similar to EVA, but it has a wide temperature range, good thermal stability and low polarity. It is often used in high temperature coatings where high toughness and strength are required, and has good adhesion to polar and non-polar substrates.

    ③EAA (ethylene acrylic acid copolymer)

    EAA contains a highly polar carboxyl group, which provides good adhesion to metals and non-metals.

    The properties of EAA resin are also related to content of acrylic acid monomer. By increasing acrylic acid content, transparency, low temperature heat sealability and low temperature hot toughness of film are improved, and adhesion to metal and tear strength of hot melt adhesive are improved.

    ④EVAL (ethylene vinyl acetate vinyl alcohol terpolymer)

    EVA is saponification product of EVA, which is a white or light yellow powder or granules.

    EVA molecules contain hydroxyl groups, which improves adhesion to many polar substrates, as well as improves stiffness, processability and colorability of resins.

    3. APAO (ethylene-propylene-1, butene polymer)

    APAO is an amorphous alpha olefin. Compared with EVA, it has a wider temperate zone, excellent adhesion to substrate, strong adhesion, and can be used for structural adhesives with high strength requirements. Because it is a copolymer, it can cover a wide range of properties (such as viscosity, softening point, and hardness). And it has good compatibility with many raw materials.

    4. Polyester (PES)

    Polyester is divided into two types: unsaturated polyester and thermoplastic polyester. As a hot melt adhesive, thermoplastic polyester is used as base material, that is, linear saturated polyester, which is formed by polycondensation of dibasic acid and dibasic alcohol or alkyd. The melting point and glass transition temperature of thermoplastic polyester are relatively high, and prepared hot melt adhesive has good heat resistance. Polyester hot melt adhesives are used alone as copolymers and generally do not require addition of other ingredients.

    5. Polyurethane (PU)

    Polyurethane is white irregular spherical or columnar particles, which are divided into two types: polyester type and polyester type. Polyether polyols are commonly used for polymerization with diisocyanates. The most characteristic features of polyurethane are excellent wear resistance, high hardness, high strength, good elasticity and low temperature resistance. Polyurethane reactive hot melt adhesives can be divided into hot melt adhesives and hot melt adhesives.

    6. Polyamide (PA)

    Polyamide hot melt adhesive has high adhesive strength, and larger molecular weight, higher strength and toughness, but melting temperature does not change much. Polyamide can be divided into two categories: one is dimeric acid (high molecular weight, high melt viscosity, high softening point, high strength, but workability of hot melt adhesive is reduced); other is nylon type (formaldehyde treatment is often used). for convenience) Made of hydroxymethylated nylon)

    7. Styrene and its block copolymers

    The characteristics of this type of copolymer: no vulcanization, but characteristics of vulcanized rubber, good creep properties and compatibility with various blended materials, but its heat resistance, UV resistance and resistance to hydrocarbon compounds. Low performance similar to solvents. It includes: SBS (styrene-butadiene-styrene block copolymer), SIS (styrene-isoprene-styrene block copolymer)

    Why hot melt adhesive can stick things?
  • Area of ​​application for hot melt adhesive
  • The materials that can be bonded with hot melt adhesives will definitely exceed most people's expectations because application of hot melt adhesives basically covers all aspects of our everyday clothing, housing and transportation. For example:

    (1) The clothes we wear contain hot glue: shirt cuffs, necklines, plackets, leather jackets, etc. need to be glued with hot glue;

    (2) The shoes we wear contain hot melt adhesive: whether it is leather shoes, sports shoes, canvas shoes, sandals or high-heeled shoes, hot melt adhesive is required as a composite adhesive;

    (3) Home decoration materials are also inseparable from hot melt adhesives: seamless wall coverings, curtain fabrics, tablecloths, home textile fabrics, wood furniture materials and even doors all need hot melt adhesives to bond composite ;

    (4) As an important means of transportation in our daily commute, hot melt adhesives are used more widely: car ceiling fabrics, seat covers, carpeting, damping soundproof panels, soundproof cotton, etc. are inseparable from each other . from a hot melt recipe.

    The types of materials that can be bonded with hot melt adhesives are much wider than those mentioned above. Thanks to constant improvement of hot melt adhesive technology, scope of their application is still expanding!

    Disclaimer: All text/images and other manuscripts marked "Source: XXX" are intended to provide additional information and facilitate industry discussion under this heading and do not constitute agreement with them. The content of article is for reference only. If there is any infringement, please contact us to have it removed. All texts/figures and other manuscripts in which author is indicated at beginning of article are originals with this heading number, if necessary, it is necessary to obtain authorization with this heading number.