1 Introduction
Transparent ABS material having a high fluidity and low shrinkage, so the processing performance, and dimensional stability of the product is better, and also better performance of the chemical resistance and, therefore, the transparent ABS new materials have the potential capacity to become poly carbonate alternative materials. Makes the production of injection products due to our transparent of ABS development and application late in the development of raw materials, molding equipment and technology research compared with foreign countries also there is a gap, poor transparency and not achieve the desired effect. In this paper, the impact of transparent ABS injection products transparency factor to explore and improve transparency.
2 transparency
A transparency of the material is good or bad, there are many performance indicators need to be considered. Commonly used indicators are: transmittance, haze, refractive index, birefringence, and dispersion. In the above indicators, light transmittance and haze of the two indicators is the most important, main characterization translucent material.
2.1 transmittance
The transmittance is the characterization of the resin an important performance index of the degree of transparency the higher the transmittance of a resin, and its transparency is better. The light transmittance is defined as: the material on the surface of the percentage of the luminous flux by the luminous flux incident to the material.
2.2 haze
The haze is also called turbidity, it can measure the degree of transparent or translucent material is not clear or turbid. Haze generated inside the material or the outer surface of the light scattering caused by cloudy or muddy appearance. The haze is defined as: through material scattered luminous flux and luminous flux through the material percentage.
Described above, light transmittance and haze are measured important indicator of the transparency of the material, the relationship between the two is as follows: Generally speaking, the inverse relationship between the transmittance and the haze, i.e. light-transmissive material having a high, and its low haze, and vice versa.
3 transparent ABS transparent mechanism
Transparent ABS is developed on the basis of the ordinary ABS, to add transparent agent to increase transparency in its composition. Increase transparency of transparent agent transparent agent (Clarifier) is an efficient nucleating agent. Its advantage is in the case of shortened nucleation time, to maintain the mechanical properties of products obtained in the best optical effect. Transparent agent can be dissolved in the polymer melt to form a homogeneous solution, but several orders than the traditional nucleating agent as a seed crystal to stage, after cooling, the transparency agent is the formation of a ternary “mesh structure”. This structure as nuclei, increase in the density of nucleation. Meanwhile, forming a grid structure “” fibers “, the size of only a few thousand nanometers, entirely in the range of wavelength of visible light, therefore, can make products transparent. “Molding System” 1998 U.S. Dacial Polymers Company developed transparent ABS new material called a T-140, which has a light transmittance rate of 88%.
4 Factors Affecting
ABS products due to the production of transparent, not only to ensure that the dimensional accuracy of the article, the appearance of quality and strength, but also to ensure the transmittance of the article, and therefore, transparent ABS with ordinary ABS injection molding tool and process parameters are different, with own characteristics.
4.1 Mold
The transparent ABS products the level of transparency and mold design and machining accuracy is closely related to it directly affects the optical effect of the product surface. In order to obtain the desired shape of a high transparency, high gloss products, in the mold structure design, the position and size of the gate, the size of the wedge blocks should focus consider. In the case of allowable costs, hot runner technology, design, should pay attention to thermal expansion and thermal insulation 2. The arrangement of the mold cooling channels should be as balanced, to ensure that the balance of the article is heated, is conducive to the rapid crystallization of the article.
Mold processing, on the one hand to improve the machining accuracy, on the other hand try to improve the quality of the mold cavity surface. First molding section should enable highly smooth, the shaping surface chromium plating or to achieve the mirror-polished, so that the molded surface is rough, and an unlimited number of irregular pores and micro-scratches affect the degree of the refraction of light, thus affecting the transparency of the article.
4.2 molding process
4 2.1, cylinder temperature, and the nozzle temperature
Like ordinary ABS transparent ABS plasticizing role in the barrel by the heat and shear, the uniformity of the plasticized mainly depends on the temperature and the heating time, while the barrel temperature directly affects the temperature of the material and flowability. In order to ensure stable operation even plasticizing, avoid high temperature materials group slip inside the screw is difficult to control the pressure and injection volume. While avoiding the injection process due to high temperature degradation and additive decomposition. Gloss when the melt temperature is too low, affecting the surface of the article, the material temperature is higher than 240 ℃ above, the haze will increase, decreased transparency. Plasticized transparent ABS high-speed flow through the flow channel of the nozzle and the mold to achieve the maximum flow resistance and good mold filling, for materials with a higher melt flow rate, the barrel temperature should be controlled to be lower for the via barrel. For materials with a lower melt flow rate, barrel temperature control required high. Cylinder temperature divided into three control, ending close to the hopper at one end to the nozzle, the temperature is gradually increased, so that the material gradually plasticized. The nozzle temperature is generally slightly below the barrel tip temperature is too high, prone the salivation phenomenon (should not exceed 230 ° C), but the nozzle temperature is too low, otherwise blocked or cold material into the mold, affecting the product transparency.
Mold temperature of 4, 2.2.
The level of influence of the mold temperature of the product size, performance, the degree of crystallinity and other process conditions. The transparent ABS is a crystalline polymer, the elevated mold temperature can increase the density and crystallinity of the article, and is conducive to the improvement of the mechanical strength and the article surface finish, but the article molding shrinkage increases, the article is easily deformed. Therefore, the mold temperature should not be too high, and generally take 40 to 55 ° C. But also not be too low, otherwise it will not completely cured, so that a large anisotropy of the products produced, and have defects such as bubbles, voids. In order to enhance surface gloss, and to reduce the degree of uneven shrinkage, the mold surface temperature can be maintained at about 50 ℃.
A 4.2 injection pressure and injection speed
Filling plays a decisive role of the injection pressure and injection speed of the materials, injection molding a transparent ABS, in order to improve product surface quality, and shorten the curing time, thereby increasing the transparency, higher injection speed should be used, adding a nitrogen-assisted growth. The pressing device is more desirable. Better mobility transparent ABS, crystallization speed, injection and holding pressure should not be too large, to prevent the edges of the the mist, destruction transparent effect.
Molding cycle of 4, 2.4.
The transparent ABS containing transparent agent, the crystallization speed, high temperature curing, to complete the first injection time required is shorter than the ordinary ABS, thereby reducing the molding time and reduce the cost of the product.
5 Application Examples
Injection moldings for the transparent ABS medical blood bottles body (Figure 1), the mouthpiece portion of the bottle body is oval, the bottom portion is circular, the smooth transition of the neck, the upper and lower hollow, requested transmission rate of more than 80%. To ensure the light-transmitting, using a mold structure of Figure 2. Has been able to ensure that the light transmittance, mainly taken the following measures:
(1) cavity and core chrome plated, to reduce pores and micro-scratches, and improve the transmission rate.
(2) Locking block large thickness, in order to prevent the injection pressure, the burrs.
(3) the use of the wedge strip to ensure the locking pressure of the locking block.
(4) the injection pressure is as large as possible, improve the filling speed and to reduce heat loss, whichever is not to produce burrs.
(5) a nozzle temperature of 230 ° C, degradation temperature lower than the clarifying agent, a mold temperature of 55 ° C.
(6) cooling water channel is disposed in balanced, watercourse larger diameter, so that the products cooling speed, faster crystallization, the transparency can be guaranteed.
