Soft foam plastic are less compressible and can immediately return to their original shape after stress is removed, with almost no residual deformation. In contrast, rigid foam plastic are highly compressible and brittle, and cannot return to their original shape after deformation and stress removal. Semi-rigid foam plastic have properties between the above two. Commonly used soft foam plastic include polyurethane, soft polyvinyl chloride foam plastic, etc. They are characterized by light weight and good elasticity, and can be used as cushions and buffering packaging materials.

Classification of Foam Plastic

There are many ways to classify foam plastic, and there are three common ones.

1. Classification by hardness

It is divided into three categories: soft foam plastic, rigid foam plastic and semi-rigid foam plastic.

The elastic modulus of soft foam plastic is less than 70MPa

The elastic modulus of hard foam plastic is greater than 700MPa

The elastic modulus of semi-hard foam plastic is 70~700MPa

2. Classification by density

It is divided into three categories: low foaming, medium foaming and high foaming foam plastic.

The density of low foaming foam plastic is greater than 400kg/m

The density of medium foaming foam plastic is 100~400kg/m

The density of high foaming foam plastic is less than 100kg/m

3. Classification by pore structure

The pores that are interconnected are called open-cell foam plastic, and the pores that are closed are called closed-cell foam plastic.

Features

(1) Low bulk density, which can reduce packaging weight and transportation costs;

(2) Excellent absorption of impact and vibration energy, which can greatly reduce product damage when used for cushioning and shockproof packaging;

(3) Strong adaptability to changes in temperature and humidity, which can meet the requirements of general packaging conditions;

(4) Low water absorption, low hygroscopicity, good chemical stability, will not corrode the contents, and has strong tolerance to chemicals such as acids and alkalis;

(5) Low thermal conductivity, which can be used for heat insulation packaging, such as ice cream cups, fast food containers and insulated fish boxes;

(6) Convenient molding and processing, can be made into various foam pads, foam blocks, sheets, etc. by molding methods such as molding, extrusion, and injection. It is easy to carry out secondary molding, such as foam sheets can be made into various fast food containers by thermoforming. In addition, foam blocks can also be bonded to themselves or to other materials with adhesives to make various cushioning pads, etc.

Foaming method

¢Ù Use chemical foaming agents, which decompose and release gas when heated. Commonly used chemical foaming agents include azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, sodium bicarbonate, etc. Many thermoplastic can be made into foam plastic by this method.

For example, polyvinyl chloride foam shoes are made by putting the mixture made of resin, plasticizer, foaming agent and other additives into an injection molding machine, the foaming agent decomposes in the barrel, and the material foams in the mold. Foamed artificial leather is made by mixing the foaming agent into polyvinyl chloride paste, applying or calendering it on the fabric, and continuously passing through a tunnel heating furnace. The material is plasticized and melted, the foaming agent decomposes and foams, and after cooling and surface finishing, the foamed artificial leather is obtained. Rigid polyvinyl chloride low-foaming sheets, pipes or profiles are formed by extrusion. The foaming agent decomposes in the barrel. When the material leaves the machine head, the pressure drops to normal pressure, and the dissolved gas expands and foams. If the foaming process is properly coordinated with the cooling and shaping process, structural foam products can be obtained.

¢Ú Utilize the by-product gas in the polymerization process. A typical example is polyurethane foam. When isocyanate and polyester or polyether undergo polycondensation reaction, part of the isocyanate will react with water, hydroxyl or carboxyl to generate carbon dioxide. As long as the gas release rate and the polycondensation reaction rate are properly adjusted, a highly foamed product with very uniform pores can be produced. There are two types of polyurethane foam. The soft open-cell type is similar to sponge and is widely used as seat cushions for various seats and sofas, as well as sound-absorbing and filtering materials; the hard closed-cell type is an ideal thermal insulation, insulation, shock absorption and floating material.

Polyurethane soft foam plastic

Polyurethane soft foam plastic has the characteristics of light weight, softness, good elasticity, mildew resistance, mothproof, heat insulation, breathability, dust absorption, water absorption, sound absorption, oil resistance, soap water washing resistance, high strength, wear resistance, etc. It is an open-cell foam, the porosity and pore size can be controlled during production, with various colors, long-term ultraviolet radiation will fade, but the performance remains unchanged. The specifications, uses and technical indicators of polyurethane soft foam shells are as follows:

1) Pipe diameter: DN15~DN600; thickness: 15~50mm.

2) Application: chilled water system, cold water system, heating hot water system.

3) Main technical indicators:

Oxygen index: >27 Density: 32-38kg/m

Water repellency: 0.03kg/m Thermal conductivity: 0.022W/(m¡¤K)

Polyethylene soft foam plastic

1. Preparation method

After the raw materials are mixed, they are kneaded, pulled, pelletized, extruded, calendered, cross-linked foamed, shaped, washed, dried, and rolled to obtain the product.

2. Product characteristics

This product has the advantages of sound insulation, heat insulation, folding resistance, good chemical stability, etc., and has a closed-cell foam structure. It is suitable for use as a thermal insulation material for residential buildings, factory warehouses, vehicles, and agricultural greenhouses. The use temperature is -35-80¡æ.

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