METHOD FOR THE PRODUCTION AND METALIZATION OF A POLYMER COMPOSITE

Description

[0001] The subject of the invention is the method of manufacturing and metallizing polymer composites.

[0002] The described method assumes utilization of conventional methods of manufacturing thermoplastic polymer materials (extrusion, injection moulding) as well as modification of surface electric conductivity of the composite using laser radiation.

[0003] The description in the patent application WO2016007898A1 presents a composite including a polymer matrix, containing tin particles in the amount of 25 wt%; copper particles, also in the form of fibers, in the amount of 40 wt%; and solder flux mixed with polymer matrix at the concentration of at least 0.2 wt% used to limit or eliminate oxides in particles containing copper. This description lacks information about susceptibility of the composite to electroplating, particularly aided with laser modification.

[0004] The description of a Chinese patent application CN101407637A presents a polymer-coated composite material strengthened with fibers, including copper fibers. This composite is characterized by its content of solder (i.e. tin), which connects fibers dispersed in the polymer matrix. However, in this solution solder covers the fiber surfaces or fiber ends. Like the previous one, this description lacks information about susceptibility of the composite to electroplating, particularly aided with laser modification.

[0005] In "Direct electroplating of plastic for advanced electrical applications", Islam Aminul et al. describe a method of electroplating an injection moulded conductive plastic composite consisting of 56 vol.% (15 wt.%) Polyamide 6 (PA6), 25 vol.% (52 wt.%) of fine copper fibres (average length 0.65 mm, diameter 35 µm) and 19 vol.% (33 wt. %) of a low-melting Tin / Zinc alloy (Aminul Islam et al., CIRP Annals, Volume 66, Issue 1, 2017, Pages 209-212).

[0006] The aim of the invention was to develop a new method of producing and metallizing polymer composites using laser ablative modification and then electroplating, with the latter being a standard method for conductive materials only.

[0007] The essential element of the invention is the method of producing and metallizing polymer composite where a thermoplastic polymer material, in particular polycarbonate, polyethylene terephthalate, polylactide, polyamide, polystyrene or poly(acrylonitrile-butadiene-styrene) is fed, together with filler containing copper fibers and powdered tin at in the amount of 10-25 vol%, into the barrel of an extruder (Step I). Then the polymer material and the conductive filler are plasticized and mixed together (Step II), and the plasticized material composition is formed into the composite material (Step III). During the last step, the formed composite material is irradiated with laser beam whose power is equal to or greater than the laser ablation threshold of the thermoplastic polymer material that forms the matrix of the composite, and then electroplated (Step IV). Using poly(acrylonitrile-butadiene-styrene) as the thermoplastic polymer material is a very favorable option. Copper fibers have the length in the range from 200 to 1000 µm and diameter from 10 to 100 µm and the average diameter of tin particles is from 10 to 500 µm. It is beneficial if composite material is formed during Step III, first through extrusion and granulation, and then from the resulting granulate by injecting it into a form of injection moulder. For irradiating composite material whose matrix is poly(acrylonitrile-butadiene-styrene), it is beneficial to use a laser beam with the wavelength of 1064 nm and the power of at least 7.5 W, at the scanning speed of 2 m / s. The composite with polystyrene matrix, is preferably irradiated with laser beam at wavelength of 1064 nm, power of at least 7.3 W, and scanning speed of 2 m / s. The composite with polycarbonate matrix, is preferably irradiated with laser beam at wavelength of 1064 nm and power of at least 12.3 W, and the scanning speed of 2 m / s. The composite with poly(ethylene terephthalate) matrix is preferably irradiated with laser beam at wavelength of 1064 nm, power of at least 9.7 W, and scanning speed of 2 m / s. The composite with polylactide matrix is preferably irradiated with laser beam at wavelength of 1064 nm, power of at least 16.0 W, and scanning speed of 2 m / s. The composite with polyamide matrix, is preferably irradiated with laser beam wavelength at 1064 nm, power of at least 12.7 W, and scanning speed of 2 m / s. It is beneficial if the composite is electroplated in a solution containing sulfuric acid and copper sulfate, with the cathodic current density of 1-15 A / dm 2< , and with anode made of copper.

[0008] The advantageous outcome of the invented method is the possibility to electroplate composites efficiently and directly due to the increased electric conductivity resulting from laser ablation of the composite matrix and from copper fibers being laser-soldered to each other with tin. Optionally, with appropriately low content of the conductive filler, the presented invention enables also selective electroplating, i.e. electroplating limited only to areas irradiated with laser. Thus, the resulting product is a composite with dielectric properties, whose irradiated areas are characterized by electrical conductivity and therefore are susceptible to electroplating, which is a conventional method for conductive materials.

[0009] The invention in its embodiment has been illustrated by auxiliary figures, which present: Fig.1. Adhesion strength of glued joints to laser-modified thermoplastic materials; Fig. 2. Scanning electron microscopy (SEM) images of preliminarily selected polymer materials susceptible to laser ablation; Fig. 3. Characteristics of laser ablation of ABS, with SEM images illustrating selected parameters of ablation; Fig. 4. Surface resistivity of ABS depending on the content of copper fibers and tin powder; Fig. 5. Photo of ABS composite containing a mixture of copper fibers and tin powder (25 vol%) after direct electroplating; Fig. 6. Surface resistivity as a function of the number of laser beam scans; Fig. 7. Optical microscope images of selective electroplating. Example of embodiment

[0010] During the first stage of the exemplary method, investigations were conducted using polycarbonate (PC), polyethylene terephthalate (PET), polylactide (PLA) polyamide (PA6), polystyrene (PS) and poly(acrylonitrile-butadiene-styrene) (ABS) in order to select a polymer matrix most susceptible to laser ablation. The technical characteristics of the tested materials are summarized in Table 1. Tab. 1. Materials used and their basic parametersMaterial Density (g / cm 3< ) Melt flow index (g / 10 min) Melting point (°C) ABS1.0432 g / 10min190-230PS1.084.50180-260PLA1.247.44210PA61.3544.0230-290PET1.3825.0280PC1.2015.0260-280

[0011] The samples were prepared by injection moulding technique, using the standard process parameters recommended for these thermoplastic materials.

[0012] Next, the samples were modified with fiber laser at the wavelength from near-infrared range (λ=1064 nm), frequency 20 kHz, scanning speed 2 m / s, and maximum power up to 20 W. Based on the conducted laser ablation tests, laser ablation thresholds, ablation energy and effective absorption coefficient were determined for the investigated polymer materials (Tab. 2). Tab. 2. Values of ablation threshold and effective absorption coefficient of the tested polymer materials, determined for scanning speed of 2 m / sMaterial Ablation threshold (W) Effective absorption coefficient (cm -1< ) ABS7.56.50PS7.36.06PLA16.01.15PA612.72.79PET9.76.67PC12.35.57

[0013] Based on the conducted tests, the matrices selected as particularly beneficial due to susceptibility to ablation processes were ABS, PC, PS and PET, which were characterized by the highest effective absorption coefficient. However, microscopic analysis and tests of adhesive strength demonstrated that the best results were achieved for ABS (Fig. 1, 2 and 3), thus ABS was used as polymer matrix in further investigations.

[0014] Therefore, in the main exemplary implementation the polymer composite contained ABS as thermoplastic polymer matrix. For this polymer matrix conductive filler was co-compounded (at the beneficial content from 10 to 40 vol%) in the form of copper fibers and tin powder. What should be understood in this patent description as "copper fibers" includes also generally understood alloys of this element where copper is a dominant (over 50%) component; "tin powder" should be understood in the same way. The minimum and maximum content of conductive fillers was determined based on the research on percolation thresholds of the fillers used (Fig. 4).

[0015] The most effective filler turned out to be the one containing a mixture of copper fibers and tin powder. In the sample implementation the average length of copper fibers was 550±100 µm and their diameter was ca. 65±5 µm, while the average size of particles of tin was ca. 40±25 µm. In the examples of embodiments different amounts of conductive filler were used, but the most interesting results were obtained for the content up to 25%. The volume ratio of copper fibers to tin powder should be equal or proportionally larger. In the sample implementations this ratio was in the range from 1:1 to 10:1 respectively. The share of specific elements in the composites tested in detail is summarized in Table 3. Tab. 3. The content of composites tested in detailABS (% vol.) Copper fibers (% vol.) Tin powder (% vol.) 801010801467515107522.52.5

[0016] The above composites were manufactured through the extrusion and granulation techniques, and then, from the obtained granulates, plates were produced by injection moulding. For extrusion, a twin-screw extruder was used. Before extrusion, ABS was dried at 90°C for 24h. ABS with the mixture of copper fibers and tin powder were fed at an appropriate ratio from calibrated volumetric metering screw units into the plasticizing zone of a twin-screw extruder. As the mixture entered the feeder of the extruder, it was moved by the turning screws along the barrel, where it was plasticized, mixed and transported to the extrusion die. The extrusion process took place at the screw speed of 100 rpm, with the temperature of the barrel and the feed pipe 180-208°C. The streams of composite leaving the die were cooled down and then granulated with a mill blade. Thus obtained granulates were injection moulded, forming the plates of the size 60x60x1 mm. The injection parameters were as follows: injection temperature was between 210°C and 225°C (210, 215, 220, 225) and the mould temperature was 60°C.

[0017] The composites manufactured according to the invention with the filler content above 25% could be electroplated directly, with the known electroplating techniques for conductive materials. The plating bath was the solution of sulfuric acid and copper sulfate (1.0M H 2 SO 4 / 1.0M CuSO 4 ) with the cathodic current density up to 10 A / dm 2< , or a commercial galvanizing bath for initial nickel plating (Wieland, art. no. 3050400402) with the cathodic current density up to 4 A / dm 2< , with a copper or nickel anode. An example of effective electroplating of composite is presented in Fig. 5 (filler content >25 vol%).

[0018] What proved as particularly good option, however, was when the conductive filler content was equal to or lower than 25 vol%, and the electrical conductivity was then significantly increased by laser irradiation. The composites were irradiated with a laser beam at wavelength of 1064 nm, scanning speed 2m / s and the power 8W, and with a different number of scanning repetitions, in order to achieve the lowest possible surface resistivity (the greatest conductivity) so as to enable electroplating of such composite in the irradiated areas. As shown, after only 2 scans with the laser beam, the surface resistivity decreased 100 million times (Fig. 6), and the composite (with copper fibers and tin powder comprising 22.5 vol% and 2.5 vol%) became electrically conductive, and thus could be electroplated selectively, that is, only on the laser scanned surface (Fig. 7). The composite was copper- or nickel-plated with conventional electroplating techniques. The solution of sulfuric acid and copper sulfate (1.0M H 2 SO 4 / 1.0M CuSO 4 ) was used as plating bath and the cathodic current density was up to 10 A / dm 2< ; alternatively, a commercial galvanizing bath for initial nickel plating was used, and the cathodic current density was up to 4 A / dm 2< ; and a copper or nickel anode was used. The obtained composites are characterized by high electromagnetic shielding capability. They can have relatively high surface resistivity (when the conductive filler share does not exceed 25% vol.), which can be significantly reduced through laser irradiation.

[0019] The unexpected effects were mainly the result of using the laser beam power that caused polymer matrix ablation, and using a special mixture of conductive materials. The tin exposed by laser ablation of polymer matrix melts, which enables joining (soldering) of copper fibers. As a result, due to the invented method, the electrical conductivity increased in the irradiated areas of the composite. The joining (soldering) itself can partially occur already during the processes of extrusion and injection moulding, thus, if the content of such filler is large enough, the composite can be electroplated directly.

Claims

1. The method of manufacturing and metallizing polymer composites, in which: • Step I : thermoplastic polymer material, particularly polycarbonate, polyethylene terephthalate, polylactide, polyamide, polystyrene or poly(acrylonitrile-butadienestyrene), together with conductive filler is fed into the plasticizing zone of an extruder; then • Step II : the polymer material is plasticized and mixed together with the conductive filler; next • Step III : from the plasticized mixture composite material is formed, characterized in that the conductive filler contains copper fibers and tin powder that together comprise from 10 to 25 vol%, and Step IV : the composite material formed in Step III is irradiated with laser beam whose power is equal to or greater than the laser ablation threshold of the thermoplastic polymer material that forms the matrix of the composite, and then electroplated with the use of conventional techniques for conductive materials.

2. The method of processing polymer composite according to Claim 1, characterized in that the thermoplastic polymer material is poly(acrylonitrile-butadiene-styrene).

3. The method of processing polymer composite according to Claim 1 or 2, characterized in that the copper fibers have length in the range from 200 to 1000 µm and a diameter from 10 to 100 µm while the average size of tin particles is ranging from 10 to 500 µm.

4. The method of processing polymer composite according to Claim 1, 2 or 3, characterized in that the composite material is formed in Step III, first with the method of extrusion with granulation, and subsequently, form the obtained granulates, with the method of injection moulding.

5. The method of processing polymer composite according to Claim 1, characterized in that the composite material with poly(acrylonitrile-butadiene-styrene) matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 7.5 W, at the scanning speed of 2 m / s.

6. The method of processing polymer composite according to Claim 1, characterized in that the composite material with polystyrene matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 7.3 W, at the scanning speed of 2 m / s.

7. The method of processing polymer composite according to Claim 1, characterized in that the composite material with polycarbonate matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 12.3 W, at the scanning speed of 2 m / s.

8. The method of processing polymer composite according to Claim 1, characterized in that the composite material with polyethylene terephthalate matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 9.7 W, at the scanning speed of 2 m / s.

9. The method of processing polymer composite according to Claim 1, characterized in that the composite material with polylactide matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 16.0 W, at the scanning speed of 2 m / s.

10. The method of processing polymer composite according to Claim 1, characterized in that the composite material with polyamide matrix is irradiated with laser beam with the wavelength of 1064 nm and the power of at least 12.7 W, at the scanning speed of 2 m / s.

11. The method of processing polymer composite according to any of the Claims 1-10, characterized in that the composite is metallized in a solution containing sulfuric acid and copper sulfate, with the cathodic current density up to 10 A / dm2, and with the use of a copper anode.