The present invention relates to increasing the electrical conductivity of the printed layer by compression and annealing simulataneously. The system consists of compression rollers with creasent shaped heating plates and can be rotated either manually or by a motor. The nip gap between rollers can be adjusted using gear and hydualic.
Background
In the case of printed electronics conductive line resistance is an important property. It depends upon various parameters such as conductive particle, binder to conductor ratio, cohesion, etc. Further, it depends upon the percolation network of the conductive particles which depends upon the printed layer thickness and gap with in the particles. Consequently, for enhanced conductivity, gap between particles along with surface roughness should be minimum. It can be achieved by either heating or compression (US9803097B2, X Huang et al.).

Annealing is a heat treatment process in which molecular rearrangement phenomenon ocuurs as well as oxygen content got removed and less oxygenated groups leads to better electrical conductivity. Due to heat treatment at higher temperature the grain size increased which results in recrystallization which sometimes leads to better surface. On the other hand, compression results to the reduction in the size of the insulated air pores in-between the layers which increases the interconnection among the conductive film layers and enhance the electrical conductivity. However, the compression sometimes leads to the micro cracks in the film and these micro cracks can limit the increase in the electrical conductivity.

Additionally the hybrid method i.e. compression with annealing introduced by our product will be beneficial in multiple ways.

Annealing helps in improving the electrical conductivity of the printed layer at higher temperatures, however during annealing with compression desrired conductivity can be accomplished at lower temperature ranges.
Both, annealing and compression are physical phenomenon but impacts on the layer in different way (as discussed above). Combining the film compression along with annealing not only leads to multifold increase in the conductivity of the film but provides the structural stability. Therefore, to compress the layer with heating simultaneously there will be a requirement of shear force along with heating.
Here, we propose a shear compression system with the provision of heating to compress and anneal the printed conductive traces simultaneously. This system consists of two moving rollers with a similar speed with adjustable difference and heating is provided with the crescent-shaped plate heater (as shown in the figure below). The rollers can be moved either manually or with the help of a motor. The developed system can be efficiently utilized to compress and anneal the printed layers roll to roll or batch type resulting in enhanced conductivity and surface uniformity.
Statement of the invention
Electrical conductivity is the basic property of the printed circuit and devices. Higher conductivity is always required in various applications and to achieve this, post-processing parameters such as annealing, sintering, compression, etc. play a key role. Separate equipments are required to perform these tasks which is time-consuming as well as not cost effective. The present system provides a better solution which can perform both annealings as well as compression simultaneously.

Brief description of the drawings
The figure shown below describes the present innovation. It shows the rollers and the crescent-shaped plate heaters to compress and heat the printed layers. It also shows the two gearing systems; one to adjust the roller’s gap and the other to rotate the rollers.

Detailed description of the drawings
The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

The figure depicts building blocks of embodiments of the present invention; (101) represents the compression rollers with an adjustable nip gap between them to pass the printed layer. Depending upon the type of material used to compress, the roller could be made of any hard metals such as Stainless Steel, tungeston carbide, titanium, etc. with ultra-smooth surface to avoid discontinued compression of the layers. (102) represents the crescent-shaped plate heaters surrounding the rollers to heat them which annealled the printed layer during compression. (103) represents the PID temperature controller attached to the heater to adjust the temperature. (104) represents the wheel to adjust the gap between the rollers. The rotating wheel is attached to two big gears via a small gear to move the upper wheel equally from both sides so that nip gap between the rollers can be adjust as per our requirement. Beside gear, the nip gap can also be adjusted using hydraulic control. (105) represents the wheel with a handle to rotate the rollers manually. The wheel is connected to rollers by two similar size gear so that both wheels will move at equal speed to avoid any wear and tear in the printed layer. A pulley has been attached to another free end below the wheel to attach the motor so that the system can be used for roll to roll system.
Substrate is the platform where all the printing work is conducted, and in conventional printed electronics, silicon as substrate is one of the most used material. With numerous advantages, it have various limitations too such as higher cost, rigidity and fragile in nature. With advancement in the field of printed electronics, substrates that are common in graphic printing such as polymers, paper, metal films, etc. has been explored a lot. These substrates have advantages such as low cost, light weight, and flexible. Despite of these advantages, there are some shortcoming in respect of their handling, low annealing temperature, wettability, etc. Therefore, post processing parameters play a crucial role to enhance the electrical properties of printed layers on these substrates.
Functional ink is the key component of printed electronics and it is the major difference between the electronic and graphic printing. After printing, a functional ink have to perform desired task such as conductivity, photoluminence, magnetisim. etc. Metal nanoparticles, polymers, carbon allotropes, etc. are extensively used to formulate functional inks. It should posses certain physical properties such as viscosity, surface tension, particle size etc. to get printed through desired printing technology.
The rollers nip is the gap between two rollers at a place where they seems parallel to each other. As nip gap always remains the minimum gap between the rollers, therefore, the material passes inbetween the rollers experiences maximum force at nip gap. The layer compression also happen at the nip gap when it is smaller than the combine thickness of the substrate and the coated layer.
Nip gap can be measured manually using feller gauge; a metal strip of fixed thickness. It can also be measured more preciously using gap measurement sensors. The gap sensors works at different technologies such as air pressure, optical, capacitive methods, etc. Depending upon the classification of the system, a suitable gap measurement sensor can be choosen.
Electical motor is an electromechanic machine that uses electrical energy to provide a mechanical movement. The proposed system can also use an electrical motor to rotate the rollers. There are mainly two types of electrical motor i.e. AC and DC and their selection depends upon the required torque and force.
Gear is a revolving circular machine part having tooth around its circumference and used in transmitting movement/ force from driving shaft to driven shaft. Spur gears, helical gears, bevel gears, worm gears, gear rack, etc. are type of gears that can used for this purpose. In the developed system spur gears has been used to adjust th nip gap as well as to rotate the rollers using rotation wheel. Another method to adjust the nip gap could be the hydraulic system that uses imcompressible liquid to transfer the force. It can be attached to the top roller’s end and the desired nip gap can be adjusted accordingly.
Temperature sensor is used to determine the temperature of the rollers. It can be done by either contacting the surface of the rollers by sensing element or contactless by using IR based sensors. NTC thermistor, RTD, thermocouples, etc. are different type of sensors available to determine the temperature and each have a temperature sensing limit, physical size limation and sensitivity. Therefore, a suitable match with the equipment from the portfolio can be selected to accurately measure the real time temperature of the rollers.

CLAIMS:
We claim,
1. A system and process for simultaneous compression and annealing of printed layers to enhance the conductivity, wherein, the system consist of compression rollers with heating plates and the rollers nip gap can be adjusted using gear; printed layers on the substrate are passed through nip gap using rotation wheel manually and/or using electric motor.
2. A system as claimed in claim 1, wherein the nip gap between the rollers can be adjusted as per the requirement to process the large range of substrate and printed layer thickness.
3. A system as claimed in claim 2, wherein the nip gap can be adjusted manually using gear and/or automatic hydraulic system.
4. A system as claimed in claim 2, wherein the nip gap can be measured by using filler gauge and/or sensors.
5. A system as claimed in claim 1, wherein the temperature of the rollers can be varied from room temperature to 250°C.
6. A system as claimed in claim 1, wherein the system can be operated manually and/or with a motor.
7. A system as claimed in claim 4, wherein the motor can be a plurality of DC, AC, induction, stepper, etc.
8. A system as claimed in claim 1, wherein the system can be applied in both sheet to sheet and/or roll-to-roll printing process.
9. A system as claimed in claim 1, wherein the flexible substrate can be a plurality of paper, polymer, and metal sheet etc.
10. A system as claimed in claim 1, wherein the functional ink can be a plurality of copper, silver, gold, polymer and carbon allotropes etc.