Abstract:
A 3D printing pen for extruding and curing a radiation-curable pasty polymer composition has a housing that contains a disposable cartridge filled with the composition. The cartridge also contains a piston that is slidable in the cartridge due to engagement of the nut secured in the piston with a lead screw that is located in the cartridge and driven from a motor so that displacement of the piston inside the cartridge expels the composition from the pen through an orifice at the end of the cartridge opposite the motor. The front end of the housing also contains LEDs that emit light onto the thread of composition on exit of the composition from the device. The mode of operation of the 3D printing pen and viscosity of the composition are selected so that after curing the extruded thread maintains its shape without supports.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of three-dimensional printing (hereinafter referred to as “3D Printing”) and, in particular, to a pen for three-dimensional printing (hereinafter referred to as “3D printing pen”). 
     2. Description of the Related Art 
     A 3D printing pen is the latest innovative product that allows a 3D object to be drawn in space. A 3D pen can be used in many ways. Images or objects produced with a 3D pen can be created as flat forms that can be peeled from a piece of paper, as freestyle 3D objects, or as separate parts ready to be joined together. The creative opportunities are endless. In addition to manufacturing various ornamental designs, jewelry, etc., a 3D pen can be used for modeling, e.g., 3D prototyping. 
     Although 3D printing pens are relatively new products in the industry, some devices of this type are known in the art. 
     For example, Chinese Patent Application Publication CN103707511 (A) of Apr. 9, 2014 (inventor: Bao Huhe) describes a 3D printing pen that comprises a shell with an outlet nozzle on one end and a material-feeding opening on the other end. The material is fed through a feeding tube to the nozzle via an adjustable electric heater and is extruded through the orifice of the nozzle. In such a device the material can be supplied in the form of a viscous liquid (e.g., an oligomer) or in the form of solid matter. In the first case, the extruded material is cured when exiting the nozzle. In the second case the solid material melts by preheating and then returns to a pasty or solid state with the lapse of time after exiting the nozzle. 
     Chinese Utility Patent CN203449607 (U) of Feb. 26, 2014 (inventors: Haixiong, et al) describes a 3D printing pen that comprises a housing that contains a heating coil for heating a material which is fed through the feeding tube arranged along the housing and then extruded through the nozzle located on the side of the housing opposite the material inlet opening. The heating coil is located near the nozzle at the output end of the feeding tube. The device is provided with a sensor and a control circuit. The heating temperature is shown on a small display provided on the side of the housing. 
     Chinese Utility model CN203371791 (U) of Jan. 1, 2014 (inventor: Wenliang) discloses a 3D pen that comprises a printing pen body consisting of a shell and an internal hollow body, wherein the front end of the shell comprises a discharging nozzle and the rear end of the shell comprises a feeding port. The feeding port and the discharging nozzle are connected with a feeding channel arranged in the hollow body. The feeding channel is formed by connecting the feeding pipe at the tail part with the heating core at the front part. One end of the feeding pipe, which is close to the feeding port, is provided with a driving device in a linking manner. The driving device consists of a feeding control motor and a guiding wheel, which are linked. The space formed by the heating core and the shell is filled with insulated silica gel. A ventilating port is formed between the insulated silica gel and the shell in a blocking manner. The inner part of the hollow body also comprises a cooling fan, which communicates with the ventilating port. The 3D printing pen disclosed by the utility model has the advantage of a polymer material such as ABS (Acrylonitrile Butadiene Styrene), which is preheated or cooled to a certain temperature and continuously discharged. The temperature of the material is constantly adjusted and maintained at a required level. 
     Chinese Utility Patent CN203357906 of Dec. 25, 2013 (inventors: (Feizuo, et al) discloses a 3D printing pen that comprises a housing, an outlet head with a nozzle, a heating cavity, a drive motor, a material-feeding pipe, and a control panel with control buttons wherein the outlet head, the heating cavity, the drive motor, the material-feeding pipe, the control panel, and the control buttons are arranged in the housing. The outlet head is located at the front end of the housing. The heating cavity is arranged at the rear end of the outlet head. The control panel is provided with a control module, a power supply module, a heating module, and a motor module. 
     Chinese Patent Application Publication CN103341975 (A) of Oct. 9, 2013 (inventors: Feizuo, et al) discloses a 3D printing pen which in its structure and function is similar to one described in one of the aforementioned publications. 
     It can be seen that all known 3D printing pens are based on the use of a thermal process for softening and melting of the material to be extruded through the nozzle of the 3D printing pen. In case of a polymer. heating provides thermal curing, which is achieved by arranging a heater, such as an electric heater, inside the housing of the device. 
     SUMMARY OF THE INVENTION 
     The present invention relates to the field of D Printing and, in particular, to a pen for three-dimensional printing (hereinafter referred to as “3D printing pen”). 
     A 3D printing pen of the present invention is intended for extruding and curing a radiation-curable pasty polymer composition. The 3D printing pen has a housing that contains a disposable cartridge filled with the aforementioned composition. The cartridge also contains a piston that is slidable in the cartridge due to engagement of the nut secured in the piston with a lead screw that is located in the cartridge and driven from a motor so that displacement of the piston inside the cartridge expels the composition from the pen through an orifice at the end of the cartridge opposite the motor. 
     The front end of the housing also contains LEDs that emit light onto the thread of composition on exit of the composition from the device. The mode of operation of the 3D printing pen and viscosity of the composition are selected so that after curing the extruded thread maintains its shape without supports. The total power of LEDs ranges from 1 to 5 W. The hollow housing is further provided with a protective cap which can be connected to the front end of the hollow housing. The tapered nozzle has an output orifice with a diameter ranging from 0.6 to 1.5 mm and n the LEDs irradiate a light with a wavelength in the range of 390 to 410 nm. 
     An example of the radiation-curable pasty substance suitable for the 3D printing pen of the present invention is a polymer composition comprises 60 to 80 mass % of oligoester acrylate, 10 to 30 mass % of liquid polyethylene glycol, 7 to 9 mass % of nonliquid polyethylene glycol, and 0.1 to 1 mass % of a system of photopolymerization initiators, and has viscosity measured at room temperature by the capillarity method in the range of 7.00 to 10.00  MM   2 /c. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the inventive technique. Specifically: 
         FIG. 1  is a longitudinal and sectional view of a 3D printing pen of the present invention. 
         FIGS. 2A and 2B  show a protective cover to be fitted on the nozzle side of the 3D printing pen in  FIG. 1 . 
         FIG. 3  is a perspective view of the 3D printing pen of the invention with a part removed to show the inner arrangement of the parts. 
         FIG. 4  is a front view of the 3D printing pen  20  in the direction of arrow A in  FIG. 3 . 
         FIG. 5  is a view in the direction of arrow B in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference will be made to the accompanying drawing(s), in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific embodiments and implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes and/or substitutions of various elements may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense. 
       FIG. 1  shows the 3D printing pen of the present invention (hereinafter referred to as “3D printing pen”), which as a whole is designated by reference numeral  20 . Structurally, the 3D printing pen  20  comprises an elongated and hollowed housing  22  which has an inner surface  22   a ′ and a front end  22   a ″ and consists of two connectable/disconnectable parts  22   a  and  22   b . The housing parts  22   a  and  22   b  are molded from a hard plastic material such as polycarbonate, polytetrafluoroethylene, hard polyethylene, etc. The parts may have a snap or bayonet connection  22   c . In  FIG. 1 , reference numeral  22   d  designates a protective cap  23   c , which can be connected, e.g., by snapping, to the tapered and open front end of the housing part  22   a.    
     One of main components of the 3D printing pen is a prefilled and disposable cartridge  24 , which is filled with a pasty material to be used for 3D printing. In the context of the present invention, the term “pasty” means a radiation-curable polymer composition that has kinematic viscosity, measured at room temperature by capillarity method, in the range of 7.00 to 10.00  MM   2 /c. The measurements were conducted on a Viscosimeter VPZh-2, the product of Labtex, Moscow, Russia. 
     The cartridge casing is a single, hollow molded part having a cylindrical portion  24   a  with an open rear end and a tapered nozzle portion  24   b  at the front end. The disposable cartridge  24  is shown in  FIGS. 2A and 2B , where  FIG. 2A  is a perspective external view of the cartridge  24 , and  FIG. 2B  is a perspective, longitudinal and sectional view of the cartridge  24 . As seen in  FIGS. 2A and 2B , a part of the cylindrical wall of the part  24   a  has flats  24   c   1  and  24   c   2  on the outer surface of the cartridge and on the inner surface of the cartridge cavity, respectively. These flats extend along the entire length of the cylindrical part  24   a  of the cartridge  24 . The purpose of the flat  24   c   1  is to prevent rotation of the cartridge inside the housing portion  22   a  when the cartridge is inserted into this portion of the housing through the rear open end of the latter. A mating flat  22   a ′ is formed on the inner surface of the housing part  22   a.    
     The rear open end of cylindrical portion  24   a  of the cartridge casing is closed and sealed by a piston unit  26  which consists of a piston  26   a  and a sealing element  26   b  made from a resilient chemically-resistant material such as rubber, plastic, or the like. The sealing element hermetically seals the interior  24   d  of the cylindrical part  24   a , which contains the material to be used for extrusion through the nozzle part  24   b.    
     The device has a means that prevents rotation of the piston  26  inside the cartridge in the form of a flat  24   c   2  on the inner surface of the container portion of the cartridge and a flat  26 ″ on the outer surface of the piston  26 . 
     Inserted into the piston  26   a  in a cantilever manner is a lead screw  28  which has a diameter smaller than the inner diameter of the cylindrical portion  24   a  in order to provide enough room for the material to be extruded, filling the space between the inner surface of the cylindrical portion  24   a  of the cartridge and the outer surface of the screw. 
     The piston  26   a  contains a nut  30  that is engaged with the thread  28   a   1  of the lead screw  28 . Since the cartridge  24  is disposable and is intended for single use, the piston  26   a , the screw  28 , and the nut  30  can be molded from a plastic material, and the nut  30  can be embedded into the body of the piston  26   a . The free end  28   a   2  of the lead screw  28  is located close to the inlet opening  24   b   1  of the nozzle  28   b  but does not close it. 
     The end of the screw  28  opposite to the nozzle  24   b  extends outside the end of the piston end of the part  24   a  of the cartridge and is provided with elements for connection with the screw-drive motor, which is described below. In the illustrated modification of the 3D printing pen, these connection elements are shown as splines  32  ( FIG. 1 ). 
     The cartridge  24  is a disposable and interchangeable component of the 3D printing pen  20 . In other words, the cartridge  24  can be selected to match specific 3D printing conditions by using cartridges with nozzles having different diameters of the outlet orifices and by filling the cartridge interior with different pasty materials. Based on the plurality of experiments, the inventors herein found that the best results in conjunction with the 3D printing pen of the invention for obtaining the extruded thread capable of maintaining its shape without the of supports are obtained when the cartridge is filled with a predetermined radiation-curable polymer composition, which constitutes the subject of parent pending patent application Ser. No. 14/536,729 filed on Nov. 10, 2014. Such a composition comprises 60 to 80 mass % of oligoester acrylate; 10 to 30 mass % of liquid polyethylene glycol; 7 to 9 mass % of nonliquid polyethylene glycol; and 0.1 to 1 mass % of a system of photopolymerization initiators. It is also preferable that such a composition be extruded at an environmental temperature of 22° C. and an extrusion rate of 2.5 to 3.5 cm/sec through the nozzle  24   b  ( FIG. 1 ) having an output orifice with a diameter ranging from 0.6 to 1.5 mm, with irradiation before extrusion with light having a wavelength ranging from 390 to 410 nm emitted by LEDs  34   a  ( FIG. 1 ),  34   b  ( FIG. 3 ), and  34   c  ( FIG. 4 ). 
     The radiation curable polymer composition has a kinematic viscosity measured at room temperature by capillarity method in the range of 7.00 to 10.00  MM   2 /c. The measurements were conducted on the Viscosimeter VPZh-2, the product of Labtex, Moscow, Russia. 
     The determination of viscosity using a suitable capillary viscometer is carried out at a temperature of 20±0.1° C., unless otherwise prescribed. The time required for the level of the material to drop from one mark to the other is measured with a stopwatch to the nearest one-fifth of a second. The result is valid only if two consecutive readings do not differ by more than 1 percent. The average of no fewer than three readings gives the flow time of the material to be examined. 
     Calculate the dynamic viscosity η (2.2.8) in millipascal seconds using this formula:
 
η= kρt  
 
     where:
         k=constant of the viscometer, expressed in square millimeters per second squared,   ρ=density of composition to be examined expressed in milligrams per cubic millimeter, obtained by multiplying its relative density (d) by 0.9982,   t=flow time, in seconds, of the composition to be examined.       

     The constant k is determined using a suitable viscometer calibration liquid. The following formula is used to calculate the kinematic viscosity in mm 2 /s.
 
 v=kt  
 
       FIG. 3  is a perspective view of the 3D printing pen  20  of the invention with a part removed for showing the inner arrangement of parts.  FIG. 4  is a front view of the 3D printing pen  20  in the direction of arrow A in  FIG. 3 . The total power of the radiation energy emitting means, i.e., LEDs  34   a ,  34   b ,  34   c , ranges from 1 to 5 W. 
     The LEDs are circumferentially arranged around the tapered nozzle inside the hollow housing at equal angular spaces, i.e., when three LEDs are used, they are spaced at an angle of 120°. 
     The tip  24   b   1  of the nozzle  24   b  protrudes beyond the outlines of the housing part  22   a  ( FIG. 1 ) to a distance sufficient for observing the tip  24   b   1  by the user, and LEDs  34   a ,  34   b , and  34   c  are supported by the LED holder  34   d  that forms the front wall of the housing part  22   a . The LEDs are arranged so that the light beams (not shown) emitted by them are focused on the thread of the material extruded from the nozzle orifice at the most efficient point in curing the extruded thread. 
     The rear housing part  22   b  contains a rotary drive motor, which comprises, e.g., a DC rotary motor  36  that is powered by a 12V battery cell  38  which is inserted into the hollow housing, conveniently located, e.g., in the battery compartment  40  formed inside the hollow housing part  22   b . Alternatively, the drive power can be supplied to the motor from an external power supply source, e.g., through a mini USB  42  or an external control port  44  (shown in  FIGS. 1 and 5 ), which is a view in the direction of arrow B of  FIG. 3 . The output shaft  42  of the motor  36  rigidly supports a coupling sleeve  44  which is provided with spline slits into which the splines  32  of the lead screw  28  are inserted for transmitting rotation of the motor  36  to the lead screw  28 . 
     The rear housing part  22   b  also contains a control panel  46  that supports the switch On/Off button  48  and a speed switch button  50  ( FIG. 1 ), the upper ends of which are exposed to the outer surface of the housing part  22   b . The rear-end face of the housing part  22   b  is closed by an easily removable flat cover  52 . The control panel also contains a control circuit (not shown) for controlling operation of the motor  36  and LEDs  34   a ,  34   b , and  34   c . Reference numeral  54  designates rigidity fins. 
     Thus, it has been shown that the 3D printing pen for extruding and curing a radiation-curable pasty polymer composition comprises the hollow housing  22 , having an inner surface  22   a ′ and a front end  22   a ″; the cartridge  24  having an outer surface  24   a ′ and an inner surface  24   a ″ and being filled with the radiation-curable pasty polymer composition, the cartridge  24  having a container portion  24   a  and a tapered nozzle  24   b  for extruding the curable pasty polymer material; the lead screw  28  rotationally supported inside the container portion  24   a  of the cartridge  24 ; the piston  26  with the nut  30  that is secured in the piston and engages the lead screw  28 , the piston being slidingly fitted inside the container portion; the rotary drive unit in the form of a motor  36  kinematically connected to the lead screw for driving the lead screw into rotation; and the radiation energy emitting means in the form of LEDs  34   a ,  34   b , and  34   c  located inside the housing around the tapered nozzle and emitting radiation energy onto the material extruded through the nozzle  24   b  of the cartridge for curing this material. 
     Although the invention is described with reference to specific examples of the 3D printing pen, it is understood to those skilled in the art that various modifications and changes are still possible without deviation from the scope of the appended patent claims. For example, two or more LEDs can be used for curing the extruded material. Radiation sources other than LEDs, e.g., laser diodes, can be used for the purposes of the invention. The chemical composition is given as an example only, and other compositions can be used, e.g., polymers with various additives such as coloring agents or nonpolymers suitable for other 3D printing conditions. The 3D printing pen  20  may be attached to the end effector of a computer-controlled robot or to a stationary control device. The hollow housing can be made from a light metal or a metal alloy.