PL217098B1 - Method for bonding polycarbonate panels preserving their surface micro-structure - Google Patents

Abstract

Connecting polycarbonate elements, preferably polycarbonate plates, comprises subjecting the surfaces of the polycarbonate elements to be connected to the organic solvent and/or non-solvent, which induces the swelling of the upper polymer layer and connecting the surfaces of the modified polycarbonate elements at a temperature, which is lower than the glass transition temperature of polycarbonate.

Description

The subject of the invention is a method of gluing PC microcircuits, characterized by simplicity, high repeatability and the fact that it does not change the surface chemistry or geometry of microchannels, using the phenomenon of swelling of the top polymer layer, in contact of polycarbonate plates with solvent vapors and subsequent compression of the modified elements at a temperature significantly lower than the glass transition temperature Tg.

Miniaturization is an important trend in many fields of science and technology. The widespread pursuit of miniaturization aims to: save time, space, costs and materials. Since the last decade of the 20th century, there has been a rapid development of microfluidic techniques. Microfluidic systems (FLDs) are systems of miniature channels with transverse dimensions from fractions to multiples of millimeters used to guide the flows of fluids (liquids or gases). The use of microscale in the flows allows them to be controlled more easily. For example, flows characterized by low Reynolds number values, i.e. those for which the viscous effects are more or much more important than the inertial effects, are well approximated by equations that linearly relate applied forces (e.g. pressure gradients) to volumetric flow rates. Many applications of microflow systems involve reproducible and reliable dosing or processing of small fluid samples (e.g. in chemical analysis applications or the creation of monodisperse emulsions or suspensions). The most common geometry of microfluidic systems is planar geometry, which means that microchannel systems are located in / on one plane or on several flat, parallel layers that are connected by ports. Systems of this type are often preferably made from polymeric materials in a two-step process. In the first stage, micro-patterns (micro-impressions or micro-impressions) are prepared on a flat polymer plate or on multiple plates. The tiles are then joined together (pattern tiles and patternless tiles in any combination) to close the microchannel lumen. Gluing polymer tiles often leads to melting or significant dissolution of their surface, which contributes to the deformation of the microchannel cross-sections. In this application, we present a method of joining polycarbonate sheets, which in a repeatable way allows to obtain a permanent joint without disturbing the geometry of the microchannel sections.

The latest scientific and technological achievements as well as the most modern materials (mainly polymers) are used in the construction of miniature systems. Polymers such as: PDMS (polydimethylsiloxane), PC (polycarbonate), PMMA (polymethyl methacrylate), COC (cyclic polyolefin copolymer), PEEK (polyetheretherketone) or PI (plastic polyimide resin) have found wide application as raw materials for the production of miniature systems. The attractiveness of polymers is determined by their great variety, and the choice of construction material is most often dictated by its properties (eg ease of processing, chemical resistance or transparency) [1-4]. Polycarbonate is a polymer material that has recently been eagerly used for the construction of integrated microcircuits. Its popularity is due to market availability, low price, easy processing, mechanical resistance or transparency in the field of visible radiation. The disadvantages of PC include poor resistance to organic solvents and absorption of UV rays. PC is commonly used in the construction of μFLDs used in medical research or bioanalysis (eg PCR - polymerase chain reaction) [5,6]. The constructed microchips are often multi-element systems that require integration. Thermal bonding is commonly used to connect components with PC, which does not guarantee a strong bond and often significantly changes the geometry of the channels.

Creating permanent joints between system elements without disturbing their structure is one of the key problems in microfluidic techniques. There are three μFLDs bonding methods: thermal, chemical and adhesive. The use of thermal joining technique requires heating the glued polymer elements to the glass transition temperature (Tg) [7-11] or the use of additional materials, eg thin foils (so-called lamination) [12]. This method is often used to integrate glass [13] or polycarbonate components [9, 14]. Moreover, the technique can be extended and, for example, assisted by solvent bonding (e.g. before thermal bonding of PMMA elements, they are exposed to DMSO and liquid methanol) [15].

PL 217 098 B1

The thermal bonding method is simple, cheap and does not require the use of complex equipment. The main disadvantage of this technique is the necessity to perform the compression at a temperature close to Tg, i.e. around 145 - 150 ° C, which often distorts the geometry of the microchannels.

An alternative to thermal bonding is chemical bonding, which involves changing the surface chemistry of the integrated materials [15-18]. Such modification can be introduced by using UV / O3, plasma or introducing active functional groups (hydroxyl, carboxyl, amine or epoxy). UV / O3 or plasma are commonly used to connect elements made of PDMS or glass, polystyrene, polyethylene or PMMA [19, 20]. For PDMS, such a modification is extremely unstable - the surface is reconstructed under the influence of air, which means that the gluing process must be extremely fast [21]. Another possibility of integrating PDMS components is modifying their surface with the use of (3-aminopropy! O) triethoxysilane (APTES) and (3-glycidoxypropyl) trimethoxysilane (GPTMS) [22]. The reaction between the amine (APTES on one element) and epoxy (GPTMS on the other) groups leads to the formation of a strong chemical bond (covalent bond). The presented method of gluing was also used to join two different polymers: PDMS and PC [23].

The third main method of gluing is adhesive bonding. Various types of adhesives are used for this purpose. Most often they are resins or UV-curable materials that enable the integration of metals, glass, ceramics and polymers [24, 25]. For example, PDMS plates can be modified and various film layers can be formed on their surface, and then permanently joined by a chemical reaction between amino and aldehyde groups [26].

The main disadvantage of the chemical and adhesive methods is the arising or necessary modification of the surfaces to be joined. The introduced changes in the structure or chemistry of the channels are in most cases an undesirable effect.

Surprisingly, it turned out that it is possible to develop a method of gluing polycarbonate plates, characterized by extremely high repeatability and, compared to thermal bonding of PC, it allows to obtain a strong adhesive (withstands pressure exceeding 0.4 MPa) while maintaining the geometry of the microchannels.

The method of joining polycarbonate plates according to the invention is characterized by the fact that the surfaces to be joined are treated with vapors of an organic compound which is a solvent or precipitant of polycarbonate, selected from the group consisting of: methylene chloride (DCM), 2-butanone (MEK), acetone (MMK), benzene, toluene, chlorobenzene, dichlorobenzene, nitrobenzene, methylene chloride, chloroform, cyclohexanone, tetrachlorethane, dichloroethane, tetrahydrofuran, dimethylformamide, m-cresol and pyridine, causing the surface layer of the polymer to swell, and then the surfaces of the modified elements are joined at a temperature of 125 to 135 ° C and at a pressure of 0.05 to 0.4 MPa.

In the process according to the invention, the thickness of the intumescent layer is preferably controlled by controlling the exposure time of the surface to the organic compound being a solvent or precipitating polycarbonate, in the range from 1 minute to 24 hours.

Preferably, the swelling of the surface layer takes place in a vacuum chamber filled with a controlled amount of vapors of an organic compound that is a solvent or precipitant for polycarbonate, or vapor mixtures of such compounds.

The method according to the invention is characterized by simplicity, high repeatability and the fact that it does not change the surface chemistry or the geometry of the microchannels. The presented method uses the phenomenon of swelling of the top layer of the polymer, which is the result of the contact of the PC with vapors of the organic compound being a solvent or precipitant of polycarbonate, and the compression of the modified elements at a temperature much lower than the Tg.

The method uses the following organic substances: methylene chloride (DCM),

2-butanone (MEK) and acetone (MMK). DCM is a widely known and used PC solvent. Its popularity is due to its high chemical stability and low boiling point. In the presented methodology, apart from the PC solvent (DCM), its non-solvents (MEK and MMK) are also used, which cause swelling and not dissolution of PC [27].

The device for gluing polycarbonate microcircuits according to the invention consists of an optionally cooled tank 2 containing an organic compound being a solvent or precipitant of polycarbonate 4, connected by means of a three-way valve 6 to the reactor 1, preferably glass, and a vacuum diaphragm pump 3. Additionally, preferably, a reactor 1 is equipped with a shut-off valve 7 and an agitator 8 to ensure the homogeneity of the composition of the gas atmosphere.

PL 217 098 B1

The diagram of the device according to the invention is shown in Fig. 1. The gluing procedure includes the following steps: i) placing the PC elements 5 in the reactor 1, ii) pumping out the air from the reactor to a negative pressure, preferably p = 0.001 MPa by means of pump 3, iii) connecting the rector 1 with a solvent tank 2 and introducing the vapors of the compound into the reactor 1. During the whole process, in order to ensure the homogeneity of the vapors, the compound and the gas in the reactor are mixed by means of a stirrer 8. After which, the glued plates are uniformly compressed.

The vapors of the used compound cause the polymer to swell and produce a modified PC layer visible under the microscope. The observed thickness of the modified layer d reflects the kinetics of the diffusion process, which is strictly dependent on the exposure time and the volume of the compound used.

The developed method of gluing polycarbonate (PC) plates is based on a simple set of apparatus, commonly available and cheap reagents. The method is an exceptionally attractive tool for obtaining durable and durable joints between polycarbonate plates with patterns of microfluidic channels. The current state of the art allows for obtaining strong joints by means of thermal (pressing, welding) or chemical (dissolving and joining) joining. However, these joining procedures often result in a significant or complete deformation of the micropatterns etched on the surfaces of the plates. The procedure outlined in this proposal solves this technical problem. In particular, the method according to the invention is based on the controlled exposure of polycarbonate sheets to the action of vapors of organic compounds and homogeneous compression (compression) at a temperature significantly lower than the glass transition temperature characteristic of the polymer material used.

The method according to the invention, thanks to the exposure of the plates to the vapors of the compound, guarantees homogeneity of the material etching and better repeatability. But it is also much easier to use because it uses exposure to the vapors of the compound, and not to the solution itself in the liquid phase.

Embodiments of the invention are presented below.

P r z k ł a d I

In the apparatus shown in Fig. 1, samples from Macroclear and Macrolon polycarbonate plates (Bayer) were placed in the reactor 1, then air was pumped out of the rector to a negative pressure, about 0.001 MPa by means of pump 3, and the reactor 1 was connected to the compound reservoir 2 containing dichloromethane. and the vapors of the compound were introduced to the reactor 1. During the whole process, the compound and the gas in the reactor were mixed during the entire process to ensure the uniformity of the vapors. Next, the PC plates modified in the above-mentioned manner were welded using a thermal press. The gluing process was conditioned by temperature (T), pressure (p) and compression time. Parameters: T and p were variable, while the gluing time was set to 30 minutes. In addition, the minimum PC penetration depth (d) required for gluing polycarbonate components was determined, which was set at 20 μm regardless of T and p. The gluing process in the presented method is based on: i) conformal contact between PC plates and ii) mutual interdiffusion of polymer chains.

P r z x l a d II

In the device shown in Fig. 1, samples from Macroclear and Macrolon polycarbonate plates (Bayer) were placed in the reactor 1, then air was pumped out of the rector to a vacuum, about 0.001 MPa, by means of a pump 3, and the reactor 1 was connected with the compound reservoir 2 containing acetone. (or 2-butanone) and the compound vapors were introduced into the reactor 1. During the whole process, in order to ensure vapor uniformity, the compound and the gas in the reactor were mixed. After the softening stage was completed, the glued tiles were uniformly compressed to form a joint. Next, the PC plates modified in the above-mentioned manner were welded using a thermal press. The gluing process was conditioned by temperature (T), pressure (p) and compression time. Parameters: T and p were variable, while the gluing time was set to 30 minutes. In addition, the minimum PC penetration depth (d) required for gluing polycarbonate components was determined, which was set at 20 μm regardless of T and p. The gluing process in the presented method is based on: i) conformal contact between PC plates and ii) mutual interdiffusion of polymer chains.

Results submit.

Fig. 2 shows the dependence of the average thickness of the modified layer d on the exposure time t of MakroIon® PC (20x10x2 mm) to DCM (circles), MEK (triangles) and MMK (squares) pairs obtained by evaporating 1 mL of the corresponding compound. The number n represents the number of samples on the basis of which the average thickness was calculated. It seems that the observed profile d (t) is not a simple diffusion,

1/2 where (d) is proportional to t ^1/2 , but a more complex process [28]. The effect of saturation of PC in pairs

PL 217 098 B1 is clear. The presented profile d (t) shows the possibility of easy adjustment of the layer thickness d by changing the exposure time. During the experiments, it was additionally noticed that the surface of the PC plates was factory modified (Fig. 2). Penetration of the PC without a release liner (100 micron topsheet removed) (circles in Fig. 2) through the compound pairs was greater (approx. 15 Pm thick) than for PC with a release liner (circles in Fig. 2). Nevertheless, the qualitative profile of d (t) was similar in both cases. The observed effect may suggest that the presented method will require calibration depending on the type and origin of polycarbonate.

Then, the effect of the amount of DCM on d was examined, and the results are presented in Fig. 3 and Fig. 4. The experiment used MakroIon® PC plates with a thickness of: 0.75 mm (squares in Fig. 4), 2 mm (circles in Fig. 4). ) and 5 mm (triangles in Fig. 4). The exposure time was constant at 30 minutes. The obtained results show that the volume of DCM has a significant influence on the thickness of the penetrated layer. However, the use of DCM in an amount of 1 to 4 mL guarantees a repeatable layer with a constant thickness of the order of 20 μm (Fig. 4). In addition, it was checked that at a fixed amount of compound d, it was independent of the modified plate surface.

The evaporation process used to modify the PC is highly endoenergetic - the flask with the compound cools down significantly during the experiment. The observed effect can be explained by the occurrence of the cavitation phenomenon, which consists in a rapid phase transition from the liquid phase to the gas phase under the influence of pressure changes. It was investigated that the change in the temperature of the water bath (in which the flask with the solvent is immersed) in the range from 22 to 30 ° C did not significantly affect the thickness of the modified PC layer.

Next, the PC plates modified in the above-mentioned manner were welded using a thermal press. The gluing process depends on the temperature (T), pressure (p) or compression time. Parameters: T and p were variable, while the gluing time was set to 30 minutes. In addition, the minimum PC penetration depth (d) required for gluing polycarbonate components was determined, which was set at 20 μm regardless of Ti p. The gluing process in the presented method is based on: i) conformal contact between PC plates and ii) mutual interdiffusion of polymer chains. Since the diffusion of the polymer actually runs on a length scale significantly less than 20 μm, it was theoretically assumed that the difficulties in obtaining a reproducible joint for d <20 μm resulted from the lack of conformal contact between the plates.

In order to obtain a thinner joint (d <20 μm), it would be necessary to use tiles with a specially prepared - very smooth surface, allowing good contact at the selected temperature and compression pressure. In other words, for gluing the tiles with a thinner joint, a smaller depth of penetration of the tiles by the pairs of the compound will be required, and thus the possibility of having flatter tiles (more precisely made), then a smaller swelling depth would probably be enough to connect them. Importantly, it was shown that penetration and swelling of PC at a depth slightly above / exceeding 20 μm did not significantly translate into microchannel deformation. The presented method is particularly attractive because it enables the gluing of PC tiles made in a relatively simple standard of the construction industry, thanks to which they can be relatively cheap. The presented method allows to obtain a durable weld while maintaining the geometry of the system with an accuracy of single micrometers or sizes smaller than 10 to 20 micrometers.

The pi T sticking parameters were tested for the compound dichloromethane (DCM) in the ranges: 0.05-0.4 MPa and 125-135 ° C < Tg, respectively. For this purpose, systems with dimensions of 20x20 mm were prepared, equipped with a set of microchannels and an inlet opening leading to a chamber with a diameter of 10 mm, located in the central part of the chip. The gluing results obtained in the above-mentioned conditions confirmed the possibility of repeatedly obtaining a strong bond while maintaining the microchannel geometry (Fig. 5). The degree of channel deformation was estimated on the basis of the formula: S / S0 x 100%, where S0 and S - are the cross-sectional area of the channels, respectively, before and after bonding _2, expressed in μm. Minimal deformations were observed only for the highest T ip values (135 ° C and 0.4 MPa). The results of the pressure tests performed were the basis for determining the strength of the obtained bonds. It was shown that the obtained binders are relatively strong and resistant to pressure above 0.4 MPa. The strongest binder (~ 0.6 MPa) was obtained for the highest T ip value (135 ° C and 0.4 MPa).

Similar results, i.e. obtaining a strong binder with negligible deformation of the channel geometry, were obtained in the case of two non-solvents (precipitants) of polycarbonate, especially

PL 217 098 B1

2-butanone (MEK) and acetone (MMK). Fig. 6 shows the cross-sections of the channels before and after gluing the PC with the compounds: DCM, MEK and MMK.

Literature:

H. Becker and L. E. Locascio, Talanta, 2002, 56, 267.

J. M. Margolis, Engineering Thermoplastic: Properties and Applications, Marcel Dekker, USA,

1985.

O. Olabisi, Handbook of thermoplastics, Marcel Dekker, USA, 1997.

J. Brandrup, E. H. Immergut, E. A. Grulke, A. Eric and A. Abe, Polymer Handbook, J. Wiley &

Son, 1999.

Y. Liu, D. Ganser, A. Scheider, R. Liu, Piotr Grodzinski, N Kroutchinina, Anal. Chem., 2001,

73, 4196.

C. H. Chan, J. K. Chen and F. C. Chang, Sens. Actuators B, 2008, 133, 327.

Y. J. Liu, C. B. Rauch, R. Lenigk, J. Yang, D. B. Rhine and P. Grodzinski, Anal. Chem., 2002,

74, 3063.

K. S. Hong, J. Wang, A. Sharonov, D. Chandra, J. Aizenberg and S. Yang, J. Micromech.

Microeng., 2006, 16, 1660.

J. Yang, Y. Liu, C. B. Rauch, R. L. Stevens, R. H. Liu, R. Lenigk, P. Grodzinski, Lab Chip,

2002, 2, 179.

M. H. Sorouraddin, M. Amjadi and M. Safi-Shalamazari, Anal. Chim. Acta, 2007, 589, 84.

H. Shadpour, M. L. Hupert, D. Patterson, C. G. Liu, M. Galloway, W. Stryjewski, J. Goettert and S. A. Soper, Anal. Chem., 2007, 79, 870.

R. M. McCormick, R. J. Nelson, M. G. Alonso-Amigo, D. J. Benvegnu and H. H. Hooper,

Anal. Chem., 1997, 69, 2626.

T. McCreedy, Anal. Chim. Acta, 2001, 427, 39.

J. Chen, M. Wabuyele, H. Chen, D. Patterson, M. Hupert, H. Shadpour, D. Nikitopoulos and

S. A. Soper. Anal. Chem., 2005, 77, 658.

L. Brown, T. Koerner, J. H. Horton and R. D. Oleschuk, Lab Chip, 2006, 6, 66.

Y. Zhang, V. Bailey, C. M. Puleo, H. Easwaran, E. Griffiths, J. G. Herman, S. B. Baylinb and

T. H. Wang, Lab Chip, 2009, 9, 1059.

C. J. Easley, R. K. P. Benninger, J. H. Shaver, W. S. Head and D. W. Piston, Lab Chip,

2009, 9, 1119.

S. G. Im, K. W. Bong, C. H. Lee, P. S. Doylea and K. K. Gleason, Lab Chip, 2009, 9, 411.

J. C. McDonald and G. W. Whitesides, Acc. Chem. Res., 2002, 35, 491.

W. Zhang, S. Lin, C. Wang, J. Hu, C. Li, Z. Zhuang, Y. Zhou, R. A. Mathies and C. J. Yang,

Lab Chip, 2009, 9, 3088.

J. Kim, M. K. Chaudhury and M. J. Owen, J. Colloid Interface Sci., 2000, 226, 231.

N. Y. Lee and B. H. Chung, Langmuir, 2009, 25, 3861.

K. S. Lee and R. J. Ram, Lab Chip, 2009, 9, 1618.

A. Gerlach, H. Lambach and D. Seidel, Microsystem Technologies, 1999, 6, 19.

D. Maas, B. Bustgens, J. Fahrenberg, W. Keller, P. Ruther, D. Seidel, IEEE Xplore, 1996, 331.

H. Y. Chen, A. A. McClelland, Z. Chen and J. Lahann, Anal. Chem., 2008, 80, 4119.

J. Borkowski, Z. Dobkowski, B. Krajewski, S. Maczenski, Z. Wielgosz, Poliwęglany, WNT,

Warsaw, 1971.

M. Fialkowski, C. J. Campbell, I. T. Bensemann and B. A. Grzybowski, Langmuir, 2004, 20,

Claims (3)

The method of joining polycarbonate plates, characterized in that the surfaces to be joined are treated with vapors of an organic compound which is a solvent or precipitant of polycarbonate, selected from the group consisting of: methylene chloride, 2-butanone, acetone, benzene, toluene, chlorobenzene, dichlorobenzene, nitrobenzene, chloride methylene, chloroform, cyclohexanone, tetrachloroethane, dichloroethane, tetrahydrofuran, dimethylformamide, m-cresol and pyridine, causing swelling Then, the surfaces of the modified elements are joined at a temperature of 125 to 135 ° C and a pressure of 0.05 to 0.4 MPa. 2. The method according to p. The method of claim 1, wherein the thickness of the intumescent layer is controlled by controlling the exposure time of the surface to the organic compound being a solvent or precipitating polycarbonate, in the range from 1 minute to 24 hours. 3. The method according to p. The method of claim 1, characterized in that the process of swelling the surface layer takes place in a vacuum chamber filled with a controlled amount of vapors of an organic compound being a solvent or precipitant of polycarbonate or mixtures of vapors of such compounds.