Polyester resin and resin composition for molding, and formed product thereof

Abstract

In a saturated polyester resin or a composition with the saturated polyester resin as the main component for molding, the melt viscosity at 200° C. is at least 5 dPa.s and not more than 1000 dPa.s, and the product axb is at least 500 where a (N / cm2) is the tensile breaking strength and b (%) is the tensile breaking elongation of a film shape formed product. Preferably, the polyester resin has a glass transition temperature of not more than -10° C., a melting point of at least 70° C. and not more than 200° C., and an ester group concentration of at least 1000 equivalents / 106 g and not more than 8000 equivalents / 106 g. A material superior in water resistance, electrical insulation, durability, working environment and productivity as a molding material for an electric electronic component having a sophisticated configuration is provided.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to polyester resins and resin compositions directed to molding, and a formed product using the same. The polyester resins and resin compositions of the present invention are particularly suitable for low pressure molding applications to secure electrical electronic components in a waterproof manner.[0003] 2. Description of the Background Art[0004] Electrical electronic components widely used in the field of vehicles and electrical appliances must be electrically insulated in order to achieve the usage objective. For example, electric wires are covered with a resin that has electrical insulation. Reflecting the growing demand for incorporating many more sophisticated electrical components in a restricted small region such as cellular phones during the past several years, various approaches for electrical insulation thereof have been employed. Particularly in the case where resins and the like corresponding to an ele...

AI Technical Summary

Benefits of technology

[0024] "Molding" in the present specification refers to molding injected at the low pressure of 10 N / cm.sup.2 to 800 N / cm.sup.2. The molding process is carried out at an extremely low pressure as compared to injection molding carried out at a high pressure of the average of approximately 4000 N / cm.sup.2 conventionally employed for general plastic molding. The principle is similar to that of general injection molding, wherein a melted resin is injected to a mold cavity in which an electrical electronic component is set to encapsulate the component. Over molding can be effected without fracturing the delicate component.

[0045] It is desirable that the retention of the melt viscosity of the polyester resin composition of the present invention after a heat treatment test for 100 hours at 121.degree. C. and 0.2 MPa is at least 70% to the melt viscosity prior to being subjected to the heat treatment test. In the heat treatment test of the present invention, a resin or a composition thereof for molding is cut to a dimension of 1 cm.times.1 cm.times.1 cm, and processed under the condition of 121.degree. C..times.0.2 MPa.times.100 hours. The melt viscosity retention thereof is preferably at least 75%, more preferably at least 80%, and most preferably at least 90%. There is no restriction in the upper limit, and a value closer to 100% is favorable. If the retention of the melt viscosity is below 70%, the durability when used at high temperature may be degraded.

Problems solved by technology

However, this method had various problems such as bubbles remaining when the solvent is vaporized as well as degrading the working environment if an organic solution is used as the solvent.

However, it is known that this method imposes various problems such as the adverse effect of the epoxy towards the environment, requiring accurate adjustment of the mixing ratio of the two liquids, and the short available period of time prior to mixing being restricted to only one to two months.

Low productivity is also noted due to the requirement of a cure period of several days for hardening.

Furthermore, there was a problem of the stress caused by contraction in the resin after curing being concentrated at an area where the physical strength is relatively weak such as at the solder portion bonding an electrical electronic component and the wiring to cause delamination thereat.

The reason why a hot metal type resin having high potentiality as a resin for molding has not become the material to replace the conventionally-used two-part epoxy resin is due to the fact that a base material suitable therefor has not been proposed.

For example, the relatively economic EVA (Ethylene Vinyl Acetate) which is known as a hot melt type has insufficient heat resistance and durability in the environment where an electrical electronic component is used.

The inclusion of various additives to express adhesion may contaminate the electrical electronic component to reduce the electrical performance.

Thus, EVA is not suitable.

However it is known that polyamide is basically highly hygroscopic and will gradually absorb moisture.

Electrical insulation which is one of the most important property is often degraded over time.

There is a possibility of the electrical electronic components being fractured during the molding process.

Thus, a base material that meets the requirements of various capabilities as a resin for molding directed to electrical electronic components having complicated configurations was not conventionally proposed.

Although high resin cohesive force and durability can be achieved when the melt viscosity becomes as high as 1000 dPa.multidot.s or above, there is a possibility of the component being fractured since injection molding of high pressure is required for molding of a sophisticated configuration.

If the product a.times.b is less than 500, sufficient durability may not be achieved with respect to various impacts that will be received in various use conditions.

If the tensile breaking strength is too low, the electrical electronic component may not be held at the sufficient strength, inducing the possibility of being detached or the like.

Also, if the tensile breaking elongation is too low, the resin may be brittle and not capable of withstanding the mechanical load on the electrical electronic component, inducing the possibility of a crack or the like in the resin.

If the total amount thereof exceeds 180 mole %, the crystallization rate becomes so high that distortion during contraction easily occurs to reduce the adherence towards the electrical electronic component.

Delamination and generation of cracks will easily occur if the modulus of elasticity of the resin is increased during cooling.

In contrast, if the number-average molecular weight exceeds 10000, the compatibility with the polyester portion will be degraded to render copolymerization in blocks difficult.

In the case of an unsaturated polyester, there is a possibility of crosslinking or the like occurring during melting to degrade the melt stability during molding.

If the added amount is less than 0.1%, the effect of preventing thermal degradation will be inferior.

If the added amount exceeds 5%, the adhesion or the like may be adversely affected.