Analysis of factors affecting the demolding of micro-structured devices in the injection molding process

Abstract

Abstract. The increasing demand for disposable ‚point-of-care' systems poses on-going challenges for health care industries to provide improvements in diagnosis and fabrication techniques. Regarding the fabrication in an injection molding process, the demolding stage is critical for success. For an in-depth investigation a tool for acquiring the demolding energies during the injection molding process was developed. This quantitative value in addition to injection molding simulations was used to describe the demolding stage. For easier classification the relevant parameters were grouped into four main influencing factors: polymer, machine parameters, microstructure design and the tool surface. Subsequently, several parameters affecting the demolding energy were attributed to each of those categories and examined systematically. One semi-crystalline polymer (PP), two amorphous polymers (COP and PMMA) and a thermoplastic COC-elastomer were investigated. It was found that the demolding energies were determined strongly by the polymer elasticity and less by its shrinkage. To investigate the machine parameters, the mold temperature and variothermal heating were analyzed. In this study a critical demolding temperature T dcr , as mentioned in literature, was confirmed for amorphous polymers. The investigation on the design of the micro-structures confirmed a favorable placement close to the gate and a preferable structure orientation in flow direction. However, a number of demolding effects that can distort the measurement had to be considered. These include part failure for brittle materials as well as strong deformation of elastic materials during the demolding stage. For the tool surface a TiN coating was found to lower demolding energies in a confined temperature range compared to the Ni surface. In general, TiN is advantageous at higher temperatures, although a thorough investigation for specific polymer-coating-combinations is necessary.

Rapid microfluidics prototyping through variotherm desktop injection molding for multiplex diagnostics

“…36 For the molds, we used metal ceramic heating (MCH) elements because of their thin profiles and high wattage; they have also been previously described for variotherm heating. [83][84][85][86] The portions of both A and B plates behind the cavities were hollowed out to enable the variotherm process (Fig. 2C).…”

Self-Assembled Monolayers of Alkanethiols on Nickel Insert: Characterization of Friction and Analysis on Demolding Quality in Microinjection Molding

“…Injection molding technology is a common method to fabricate plastic products in biomedicine [1][2][3], chemical detection [4,5], optical security [6,7], and photoelectric technology [8,9] with complex shape and size [10][11][12]. However, the process of demolding will directly affect the replication quality of the micro/nano structures [13][14][15].…”