1. Introduction

Toughened grade poly (phthalamide) (PPA) has excellent mechanical properties - strength, hardness, fatigue resistance and creep resistance in a wide temperature range and high humidity environment. PPA combines superior toughness with a certain range of hardness and flexibility, the rigidity required for one-time use in fasteners, and a good choice of flexibility in repeated use.

PPA resin is a semi-aromatic polyamide with terephthalic acid or phthalic acid as raw material. There are both semi-crystalline and non-crystalline, and their glass transition temperature is about 255 ℃. Amorphous PPA is mainly used for occasions requiring barrier performance; The semi-crystalline PPA resin is mainly used for injection molding and other melt processing processes.

The following mainly introduces semi-crystalline PPA resin, unless otherwise noted. The melting point of semi-crystalline PPA is about 590 ℃, and it is supplied in the form of opaque rectangular slices.

PPA resin is stronger and harder than fatty polyamides such as nylon 66; The sensitivity to water is lower; Better thermal performance; Moreover, creep, fatigue and chemical resistance are also much better. For example, the tensile strength of PPA resin containing 45% short glass fiber is about 276 MPa, the bending modulus of elasticity is more than 13786 MPa, and the thermal deformation temperature (HDT) is 285 ℃. Even with mineral filler grade PPA, the tensile strength can reach 117 MPa. The ductility of PPA resin is not as good as that of nylon 66. However, the unreinforced impact modified PPA resin has been developed, and its notched cantilever impact strength is up to 1.1 kJ/m.

2. Processing technology

All polyamides absorb a certain amount of water, causing plasticization and size change. For example, nylon 66 can absorb 8.9% water at - 5 ℃ and 100% relative humidity, which reduces its glass transition temperature from 6.5 ℃ to - 20 ℃ and increases its size by 2.3%. Under the same conditions, PPA resin can absorb about 6% water, but its glass transition temperature will not be lower than 40 ℃, and the accompanying size growth will not exceed 1.0%.

Glass fiber reinforced PPA resin has a high HDT value and can withstand short-term effects of high temperature. For example, in a furnace or in the steam phase and in the process of infrared countercurrent consolidation, the thermal oxidation stability of PPA resin makes it able to withstand long-term high temperature effects. Glass fiber reinforced PPA, within 20 000 hours, its continuous use temperature can reach 165.5 ℃.

Under normal environmental conditions, PPA resin generally shows excellent solubility to aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, esters, ketones, alcohols and most aqueous solutions. This kind of resin cannot withstand the action of extremely strong acid and strong oxidant. Soluble in phenol and cresol. PPA is not inherently flame retardant. According to the vertical flame retardant standard, the flame retardant grade is UL 94 V-0, up to 0.7874 mm thick.

Most PPA resins are processed by traditional injection molding. Pre-dry the PPA raw material to a humidity level below 0.1%, and then put it into a heat-sealed metal bag or box. These containers can ensure that the PPA raw material does not need to be dried before processing. The acceptable humidity level for the processing process is 0.15% or less. Processing wet resin can reduce the molecular weight and cause the corresponding mechanical properties to decline. Using desiccant bucket dryer, it is easy to dry the resin to the dew point humidity of - 31.6 ℃ or even lower at 79.4 ℃. The drying time depends on the amount of water absorbed, generally within the range of 4~16 h.

During injection molding, the melting temperature is in the range of 323.7~343 ℃, and the retention time of the material in the barrel is not more than 600 s, so the mechanical properties of the product after injection molding are the best. The mold temperature is required to be at least 141.6 ℃ in order to obtain the product with the best crystallization and dimensional stability. Parts with partial thick wall can be injected at a lower mold temperature due to the slow cooling rate. The mold temperature is crucial for the optimization of surface appearance of finished parts. The mold surface temperature of mineral filler grade PPA resin used for vacuum metal plating to make electroplating metal is 176.6 ℃.

3. Scope of application

Because of its outstanding physical, thermal and electrical properties, especially its moderate cost, PPA resin has a wide range of applications. These properties and excellent chemical resistance make PPA used in the automobile industry. The trend towards better aerodynamic body design, together with higher performance engines, will increase the temperature of the engine case, making the traditional thermoplastic no longer applicable. These new requirements make PPA become one of the candidate materials for manufacturing the following components: automobile headlamp reflector, bearing seat, pulley, sensor housing, fuel pipeline components and electrical components.

The development direction of electrical components is miniaturization and high-temperature consolidation, such as infrared consolidation and vapor phase consolidation, which requires the superior performance of PPA. Flame retardant PPA has excellent electrical properties, high HDT value, high high temperature bending modulus, and can process thin wall parts with minimum overflow, so it is suitable for manufacturing switchgear. Connection piece, brush holder and motor bracket.

Mineral filler grade PPA is used for reflective surfaces and metal-plated applications, including automotive headlights, decorative pipe fittings and hardware. The unreinforced impact modified PPA has excellent balanced mechanical properties and high temperature properties. It has extraordinary toughness and these properties are extremely affected by humidity. Its uses include oil field components, military products, sporting goods, fan impellers and gears, and personal safety products.