Matching relationship between polyurethane elastomer products and molding processing methods

Abstract

According to the general principle of molding process selection, the micro-phase separation of polyurethane elastomer can be realized to meet the requirements of excellent product performance. Referring to the influencing factors such as extrudability, moldability, ductility and spinnability, the molding process is carried out according to the following principles: four basic types of polyurethane rubber, polyurethane pouring rubber, polyurethane water emulsion and polyurethane thermoplastic, and the molding process is carried out according to rubber, pouring, coating and plastic respectively; Through the combination of classical molding methods, the molding methods of derivative rubber series are selected. This paper analyzes the dependence of the selection of polyurethane elastomer molding on deformation factors and curing factors, and shows that extrusion molding, injection molding and calendering are the key methods in molding.

keyword

Polyurethane elastomer; Microphase separation; Forming processing; Extrusion molding; Injection molding; Calendering forming

foreword

Polyurethane elastomer formed by the polymerization reaction of diisocyanate and active hydrogen compounds, a rigid chain segment containing urea group composed of diisocyanate and diamine chain extender, has a glass transition temperature much higher than room temperature, and is glassy, sub-crystalline or microcrystalline at room temperature, forming a plastic phase; The flexible segments of polyether or polyester are gathered together to form the matrix or matrix of polyurethane rubber, which is called rubber phase because its glass transition temperature is lower than room temperature. The microphase separation of polyurethane elastomer makes polyurethane elastomer have the advantages of good wear resistance, wide hardness range, high strength and elongation, large load supporting capacity, good shock absorption effect and excellent oil resistance. Choosing a suitable molding method can give full play to the properties of polyurethane elastomers, and prepare polyurethane elastomers with various excellent properties, which are widely used in plastics, rubber, fibers, adhesives and coatings, and even used as functional polymer materials such as medical polyurethane materials.

This paper summarizes the molding processing methods of polyurethane elastomer, and deduces the internal relations of its derivative molding processing methods.

1 the basic principles of polyurethane elastomer selection molding processing method

1.1 General principles for selecting molding processing methods

(1) Molding is usually a process of melting or deforming polymer compounds in solid state (powder or granule), paste or solution state, forming the required shape through a die, and keeping the obtained shape, and finally obtaining the product.

(2) Common molding process: ① the method of producing products by primary molding and secondary molding of polymer compound mixture; (2) the method of producing products by one-step molding of polymer compounds; (3) a method for producing products in one step from monomer mixture; ④ One-step production method of oligomer mixture.

(3) processability and its influencing factors: ① extrudability, that is, the ability to acquire and maintain the shape when the material is deformed by extrusion in the extruder, the barrel of the injection machine, the roller of the calender and the mold. Its restrictive factors: melt viscosity, processing equipment structure, melt rheology and melt flow speed. (2) Moldability refers to the ability of materials to deform and be molded in a mold under the action of temperature and pressure during the molding process under the action of an injection machine, an extruder and a molding machine. Its restrictive factors: rheology, thermal properties and other physical and mechanical properties and chemical reactivity of polymer compounds. ③ Ductility, that is, the deformability of materials subjected to calendering or stretching in one or two directions. Its restrictive factors: plastic capacity and strain hardening of materials. (4) spinnability, the nozzle in extrusion molding, the ability of materials to form continuous solid fibers through molding. Its restrictive factors: rheology, melt viscosity and strength, thermal stability and chemical stability.

1.2 General principles for selecting molding processing methods for polyurethane elastomers

Polyurethane elastomer molding processing system is divided into liquid system and solid system. Based on the rapid polymerization of diisocyanate and active hydrogen compounds, the molding method is beneficial to the microphase separation of polyurethane elastomer. , liquid system, polyurethane casting glue can be used for casting processing (manual casting, centrifugal casting and vacuum casting), reaction injection molding, spraying, scraping, roll coating, bonding, laminating, bonding, vulcanization, gluing and wiping; Solid system, polyurethane rubber compound can be vulcanized and laminated by mold, and polyurethane thermoplastic can be thermoplastic, hot injection, calendering, blow molding, spinning and laminating.

1.3 Matching principle between basic types and molding processing methods

Polyurethane elastomer is a kind of high polymer between plastic and rubber in terms of its modulus, which mainly includes polyurethane mixed rubber, polyurethane pouring rubber, polyurethane water emulsion and polyurethane thermoplastic. Polyurethane leather, polyurethane adhesive, polyurethane coating, polyurethane mixture, polyurethane casting glue, polyurethane fiber, polyurethane aqueous emulsion and polyurethane thermoplastic are all derived from the above four kinds of glue. The molding methods of polyurethane rubber, polyurethane water emulsion and polyurethane thermoplastic generally belong to the molding methods of rubber, paint and plastic.

1.4 Matching principle between the use and production continuity of polyurethane elastomer and molding processing method

The processing method of polyurethane elastomer is matched with the use of polyurethane elastomer, giving consideration to the continuity of production. For example, the processing method of polyurethane leather usually uses polyurethane pouring adhesive layer or foaming layer, polyurethane water emulsion and polyurethane thermoplastic as the surface layer; Polyurethane thermoplastic and polyurethane water emulsion can also be used as leather alone, which are based on the basic rubber molding method and supplemented by foaming molding. Calendering molding method is usually chosen. Polyurethane paving material is paved by polyurethane pouring glue, mainly for the sake of large product size and low precision requirements. Medical polyurethane materials have good chemical stability, histocompatibility and biological aging resistance, so dip coating, pouring and coating methods are used for molding.

2 basic types of polyurethane elastomer molding processing methods

2.1 Molding and processing method of polyurethane rubber compound

Polyurethane rubber compound, as rubber, has high elasticity, large molecular weight and crosslinking, so the molding process is compounding, raw rubber plasticizing, rubber mixing, molding and vulcanization. Polyurethane elastomer can be molded by press molding, extrusion molding, injection molding and calendering. Molding is usually carried out at low temperature, which is beneficial to morphological microfacies separation. The curing system of peroxide such as dicumyl peroxide and tert-butyl cumene can prolong the time and be carried out at low temperature, so that the permanent deformation of polyurethane rubber mixture is small, the compression deformation is small and the heat resistance is improved. Of course, choosing injection molding can improve the dimensional accuracy of products, and choosing extrusion molding can improve the continuity of production.

2.2 Polyurethane pouring glue molding processing method

Polyurethane pouring glue can be used for pouring and pouring complex products, and the method is simple. As long as liquid is injected into the mold and heated, it can be solidified into complex products. One-step synthesis of polyurethane pouring glue is to put polymer diol, diisocyanate and chain extender together, mix them thoroughly, pour them into a mold for heating and curing, and then vulcanize them after the size is stable. Polyurethane pouring glue is synthesized by prepolymerization. The prepolymer and chain extender are mixed together, and then injected into the mold for heating and curing after vacuum defoaming, and then vulcanized to obtain the product. The high-efficiency release agent is added for demoulding. Reactive injection molding is essentially a one-step reaction or semi-prepolymerization reaction, but its reaction is carried out under high pressure and full mixing, which greatly improves the strength and adhesion of the products.

2.3 Polyurethane water emulsion molding processing method

Polyurethane aqueous emulsion has good environmental protection, but poor film-forming property. It needs moderate crosslinking and can be molded by spraying.

2.4 Polyurethane Thermoplastic Molding Processing Method

Polyurethane thermoplastic is a kind of linear polymer, which can be reversibly molded by extrusion, injection molding, blow molding, calendering and wire drawing. Semi-prepolymerization can effectively separate microphase. Moderate adjustment of calendering temperature makes a balance between melt viscosity, fluidity and melt strength. In order to improve the hardness of polyurethane thermoplastic, micro-crosslinking is usually needed to improve the mechanical properties of polymer materials, especially solid materials on the basis of extrudability, moldability and ductility.

3. Molding and processing methods of derivatives of polyurethane elastomer system

3.1 One-to-one processing method of polyurethane fiber molding

Polyurethane fiber forming process is continuous production by using polyurethane thermoplastic through melt spinning, dry spinning and wet spinning, on the basis of extrudability, moldability and ductility.

3.2 Polyurethane system derived types of molding processing methods are many to one.

Polyurethane coating is a homogeneous polyurethane coating prepared by adding solvent to polyurethane thermoplastic or polyurethane pouring glue. Polyurethane aqueous emulsion is a heterogeneous polyurethane coating, and the polyurethane coating is molded by spray molding. Polyurethane adhesive can be made into homogeneous polyurethane coating by adding solvent to polyurethane thermoplastic. Polyurethane aqueous emulsion is heterogeneous polyurethane coating, and polyurethane adhesive is molded by spraying. Polyurethane foam rubber is made by mixing polyurethane rubber mixture, polyurethane thermoplastic and polyurethane pouring rubber with foaming agent, and combining foaming molding on the basis of molding processing method.

4 Difficulties in forming and processing methods of polyurethane elastomer

In order to choose a suitable molding method, the relationship between the two processes of deformation and curing of polyurethane elastomer and the restrictive factors such as extrudability, moldability, ductility and spinnability is still unclear. The research on the use of polyurethane elastomer needs to be further developed. There are still many difficulties in the combination and efficiency of the existing molding methods. In a word, there are still many difficulties in the industrial application of polyurethane elastomer molding and processing methods, which need to be further studied.

5 concluding remarks

It is the key to maximize the excellent performance of polyurethane elastomer by selecting suitable molding and processing methods to make polyurethane elastomer microphase separated. Based on the classic molding methods of polyurethane rubber compound, polyurethane pouring rubber, polyurethane aqueous emulsion and polyurethane thermoplastic, the core position of rubber, plastic, fiber and coating molding is emphasized. Derived polyurethane elastomers can be selected by combining classical molding methods because they are derived from four basic rubber types.

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