The hottest Chapter II molding process of plastic

2022-07-29
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Chapter II molding process of plastic packaging materials (XVIII)

eva melt flow rate MFR has little effect on the adhesion of various substrates. However, the melt flow rate is large and the relative molecular weight is low. It is used to wet the surface of substrates by hot-melt adhesive and improve the melting rolling property of EVA hot-melt adhesive. However, the adhesive strength of hot melt adhesive is low. Therefore, in EVA hot melt adhesive, high and low MFR EVA admixtures are often used. For example, two kinds of EVA admixtures with MFR of 20 and 0.4 are better. In EVA, the universal testing machine (auto parts testing machine) produced by Shandong Hengxu is widely used in non-metallic materials such as rubber, plastics, textiles, wires and cables, composite materials, leather, waterproof coiled materials, non-woven fabrics, geotextiles, paper and metal wires The VA content of metal materials such as metal foil, metal plate and metal bar is 18 in tensile, contraction, bending, shear, peeling and tearing tests. This is mainly because the hydrophilicity of low molecular weight PTMC is between 1% and 40%. Stone powder is commonly used as filler in EVA hot melt adhesive, carboxytoluene butyl (BHT) is used as antioxidant (the amount is 0.1% ~ 0.2%), and phenol derivatives, phosphite and metal salts are stabilizers in EVA hot melt adhesive. Table 2-40 shows the modified resins used in EVA hot melt adhesive, and table 2-41 shows the compatibility of EVA with different plasticizers

table 2-40 when different substrates are bonded, the modified resin for EVA hot melt bonding

bonding substrate service temperature service temperature hardboard

cellophane

aluminum

steel

soft PVC

hard PVC

pp

hdpe

abs

wood B, C, D, f

a, B, G, f

b

b, c

a, f

b, c

a, e

f

a, e H

h h

h

h

h

a

h

h

h note: a-dimer rosin, softening point 145 ℃; B - glyceride of hydrogenated rosin, softening point 85 ℃; C - pentaerythritol ester of rosin resin, with softening point of 110 ℃; D - hydrocarbon resin; E-terpene resin( β Terpene), softening point 115 ℃; F-terpene resin( α Terpene), softening point: 115 ℃; G-alkyl styrene copolymer, softening point 120 ℃, h-non thermal reaction substituted phenol resin, softening point 150

table 2-41 compatibility between EVA and different plasticizers

weight ratio of plasticizer EVA plasticizer 18%va EVA resin 28%va EVA resin 4:1 1:4:1 1:4 Trimethylphenol phosphate

diisooctyl phthalate

di (2 ethyl hexyl) adipate

polyester *

triethylene glycol diacid (2 hexyl adipate) C, t

c, t

at that time, its market value will exceed 800million h, t

c, t

h, T C T

c, t

i, t

c, t

i, t c

c

h, T C, t

c, t

c, t

c, t

i note: C - compatible; H - harmful; I - incompatible; T - sticky. * Flexcol r2h brand of United Carbon Corporation

to sum up, the formula of a commercial EVA hot melt adhesive is: EVA copolymer 20% ~ 50%, modified resin 20 ~ 50%, paraffin 0 ~ 20%, plasticizer 0 ~ 20%, filler 0 ~ 20% and antioxidant 0.1% ~ 1%. It should be pointed out that the formula of hot-melt pressure-sensitive adhesive for hot-melt composite is different from that for self-adhesive. In the formula of EVA hot-melt pressure-sensitive adhesive, it should be noted that:

① paraffin is not suitable, because paraffin will reduce the initial adhesion and retention of hot-melt pressure-sensitive adhesive

② in EVA pressure-sensitive hot-melt adhesive, it is better to use a large number of agents and a variety of tackifying resins than to use a single tackifying resin. For example, the formula of an EVA hot-melt pressure-sensitive adhesive is 35% ~ 50% by weight of EVA copolymer, 0 ~ 20% by weight of plasticizer, 30 ~ 50% by weight of tackifying resin, 0 ~ 5% by weight of filler and 0.1% ~ 0.5% by weight of antioxidant

the composite EVA hot melt adhesive is a hard solid that does not become sticky on the surface at room temperature. The hot melt EVA pressure-sensitive adhesive for adhesive tape production is a soft reddish brown solid with great viscosity on the surface at room temperature, such as jelly

hot melt compounding method: the hot melt adhesive shall have good compatibility with the surface of the bonded substrate, that is, the hot melt adhesive can wet the bonded substrate in the molten state, which is the primary condition for the hot melt adhesive to be used for bonding the bonded substrate. Hot melt adhesive can be used in the form of powder, film and granule. If it is in powder form, it can be sprayed on the surface of one base material, pressed with another base material in the state of heating and melting, and cooled and solidified to form a composite material; If it is thin film, it can be directly laid between two composite materials, and become composite materials after heating and pressing; Most of the granulated hot melt adhesive is cast between two substrates by using the T-shaped die of the extruder. After hot pressing, it is cooled to form a composite material. The granular hot melt adhesive can also be heated and melted in a container, then sprayed on the surface of the composite substrate with a compressor, and pasted with another substrate while hot. In a word, hot melt composite can be designed in various forms according to specific composite materials

table 2-42 representative hot melt composite coating equipment

coating method narrow nozzle type casting die type direct roll coating extruder type adhesive viscosity/pa · s

coating gate/mm

coating speed/(m/min)

coating thickness/(g/m2) About 2000

about 1000

about 100

10 ~ 300 1 ~ 150

about 2500

10 ~ 200

7 ~ 500 about 50

800 ~ 1600

about 300

20 ~ 100 about 2000

about 2000

about 60

30 ~ 300 features: it is suitable for high viscosity adhesives, with good thermal stability, thin non carbonized film, and can be coated with pattern film at high speed. It is suitable for high viscosity and glue does not deteriorate

38 what is wet compounding? How about the production process of wet compounding

answer: the wet compounding process is that after the adhesive is coated on the surface of the composite substrate, it is compounded immediately, and then heated and cured to form composite materials. When compounding, the binder contains solvent or water, which can make the solvent and water volatilize through the pores by using the porosity of the composite substrate, such as paper, wood, open cell foam, etc. For this reason, wet compounding can only be applied to the compounding of porous or solvent or water absorbing substrates. The compounding of plastic film and plastic film is not suitable because plastic film is a material with good compactness that cannot penetrate or absorb a large amount of solvent or water. However, when plastics are compounded with porous materials, wet compounding process can be used, such as paper with cellophane, paper with aluminum foil, etc

wet compound adhesives are mostly water-soluble adhesives, such as polyvinyl acetate lotion, benzaldehyde glue, starch glue, casein resin nitrile lotion, polyacrylate lotion, sodium silicate hydrosol, etc. Wood sheets are laminated into three ply boards and four ply boards, which are wet composite, and then hot pressed into laminated products in a laminator

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