Abstract:
Disclosed is a self-destructing syringe, comprising an outer casing, a core bar, a piston, a conical head component, a syringe needle and a protecting jacket. The syringe needle is fixed in the conical head component, and the conical head component consists of a threaded conical head, a sealing ring, a transition part and a hollow wedge. The protecting jacket is put around the syringe needle and is movably connected to the needle base of the syringe needle; the conical head component is fixed in the inner cavity at the front end of the outer casing; the piston is installed on the core bar; the main part of the core bar is sheathed inside the outer casing; and the front end of the core bar is inserted into the conical head component and is able to make the syringe needle return inside the outer casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the national phase of International Application No. PCT/CN2011/082337, titled “SELF-DESTRUCTING SYRINGE WITH HIGH LEVEL OF SAFETY AND CONVENIENT ASSEMBLY”, filed on Nov. 17, 2011, which claims the benefit of priority to Chinese patent application No. 201110320499.0 titled “SELF-DESTRUCTING SYRINGE WITH HIGH LEVEL OF SAFETY AND CONVENIENT ASSEMBLY”, filed with the Chinese State Intellectual Property Office on Oct. 20, 2011, both of which applications are incorporated herein in their entireties by this reference. 
     TECHNICAL FIELD 
     The present application relates to a medical instrument, in particular to a disposable syringe, and in more particular to an easily assembled and highly safe self-destructive syringe. 
     BACKGROUND 
     A disposable sterilized syringe is a new medical instrument introduced to China in 1980s, which may avoid cross-infection and is easy to use, thus is very popular with doctors and patients. However, due to mismanagement of some medical institutions or interest drive, the disposable syringe is recycled, resold and reused. The reuse of the syringe causes the transmission of diseases, such as hepatitis B and acquired immune deficiency syndrome (AIDS). 
     In recent years, as indicated by some experts, the danger level of the medical staff suffered the occupational infection depends on the prevalence rate of the blood-borne disease among people. China is one of the countries having high incidence of hepatitis B, the number of the hepatitis B carriers is about 120 million, the infection rate of hepatitis C is up to 1.7%, and the prevalence of AIDS in China has already entered the period of rapid growth. Therefore, the medical staff in China is facing serious occupational exposure danger. Based on the results of questionnaire survey in 13 hospitals in Beijing, 1111 needles stabs occur to 432 probationer nurses in 10 months, i.e., it is 2.6 times per nurse per month in average, and due to the accidental injury, some nurses have been infected by blood-borne diseases, such as hepatitis B and AIDS. 
     For using the disposable syringe safely, and completely solving the cross-infection and the occupational exposure of the medical staff caused by the reuse of the disposable syringe, at the end of the last century, the World Health Organization (WHO) has proposed concepts such as safe injection, harmless to people being injected, and no risk to the medical-care staff. China has dedicated to develop and popularize the safe self-destructive syringe since 2000. 
     A good utility model or an invention should have the following advantages, such as having a low manufacturing accuracy, being easy to manufacture, being suitable for automated machine assembly, having a stable quality control in mass production. The safe self-destructive syringe that is commercial available presently has the following disadvantages. 
     A component of a retraction assembly (corresponding to a “conical connector assembly”) for cooperating with an inner wall of a front end of a barrel to locate the retraction assembly is mostly designed as an integral loop structure or a small supporting jaw, the loop structure has a small expanding angle and the supporting jaw has a small body force, both of which may cause a low firmness of the location between the retraction assembly and the inner wall of the front end of the barrel, thereby causing a risk of the self-retraction of the retraction assembly during the injection process. 
     The retraction assembly has no shockproof design, thus the shock during the long-distance transportation may also cause the risk of the self-retraction of the retraction assembly. 
     The head of the barrel has no member for preventing the retraction assembly from being overly pushed forward or has too small force to prevent the retraction assembly from being pushed forward, such that in practical assembly process, the retraction assembly may be pushed out of the opening at the head of the barrel due to an excessive assembly force, thereby causing assembly problem. 
     In the retraction assembly, a conical connector, for assembling a syringe needle, and a structural member, for cooperating with the inner wall of the front end of the barrel to locate the retraction assembly, are formed integrally, and the locating structure is designed as a small supporting jaw. So that, firstly, a mould manufacturing accuracy is too high, the manufacture is difficult and the product fraction defective is high, and secondly, each mould has less cavities (for an injection machine of 180 tons, each mould can only produce 32 parts), thus the mass production is not suitable. 
     There is no sealing ring provided between the retraction assembly and the inner wall of the barrel, which may cause the leakage problem; or the sealing ring is provided, however due to the complicated design structure of the retraction assembly, the assembly of the sealing ring is difficult, thereby causing the conventional syringe having a low adaptability for automation and being not suitable for mass production with the automatic assembling machine. 
     The design of the retraction mechanism also has disadvantages. The conventional retraction mechanism mostly uses a three or more sequential retractions, which are formed in this way, the retracting force of the plunger is transmitted to a corresponding part, and then is transmitted to another corresponding part or to more corresponding parts via the first corresponding part, thus may cause a risk of unstable retraction operation. 
     Further, mostly there is no retraction restricting mechanism in the inner wall of the rear end of the barrel, such that if the medical staff operates carelessly, the needle tip may be retracted excessively to be pulled out, which may cause other accidents. 
     Due to above disadvantages, presently the safe self-destructive syringe has not been rapidly and widely used in China yet. Therefore, it is important to provide an easily manufactured and highly safe disposable syringe for improving the medical safety of China. 
     SUMMARY 
     An object of the present application is to provide a highly safe self-destructive syringe, which has a low manufacturing accuracy, is easy to assemble, has a high adaptability for automation, and is suitable for mass production, so as to solve problems of the existing disposable safe self-destructive syringe caused by unreasonable structural design, such as being not easy to manufacture and assemble, hard to adapt to the mass production, having a low qualified rate and a potential safety hazard during the self-destruction process. 
     A technical solution of the present application is as follow. 
     An easily assembled and highly safe self-destructive syringe includes a barrel  1 , a plunger  2 , a piston  3 , a conical connector assembly  8 , a syringe needle  9  and a protective cap  10 . The syringe needle  9  is mounted in the conical connector assembly  8 , the protective cap  10  is mounted above the syringe needle  9  to cover the syringe needle  9  and is movably connected to a needle seat of the syringe needle  9 , the conical connector assembly  8  is mounted in an inner cavity of a front end of the barrel  1 , the piston  3  is mounted on the plunger  2 , a main body portion of the plunger  2  is mounted in the barrel  1 , and a front end of the plunger  2  is configured to insert into the conical connector assembly  8  during the injection operation and drive the syringe needle  9  mounted on the conical connector assembly  8  to retract into the barrel  1 . The conical connector assembly  8  includes a thread conical connector  4 , a sealing ring  5 , a transition part  6  and a hollow wedge  7 . A lower portion of the thread conical connector  4  is inserted into an annular groove  621  and an annular recess  63  of the transition part  6 , and the sealing ring  5  is press fitted among joint surfaces of the thread conical connector  4 , the transition part  6  and an inner cavity wall surface of the front end of the barrel. The hollow wedge  7  is insertedly mounted in the transition part  6  and expands a blade  64  at a lower part of the transition part  6  via two annular inclined steps  73  on the hollow wedge  7 , so as to locate the conical connector assembly  8  in the inner cavity of the front end of the barrel  1 . 
     The hollow wedge  7  is of a hollow structure, and an upper portion of the hollow wedge  7  is a hollow cylinder  71 . Four elastic retaining teeth  72  protruding inwardly and upwardly are uniformly distributed along a circumference at an inner cavity opening of an end surface of a head portion of the hollow cylinder  71 . An annular groove  711  is provided on an outer wall surface of the cylinder  71 , and the two annular inclined steps  73  inclining outwardly and downwardly are provided on an outer side of a lower portion of the cylinder  71 . The transition part  6  is of a hollow structure, and an outer connecting body  61  and an inner connecting body  62  are provided on an upper portion of the transition part  6 . The inner connecting body  62  is hollow, the annular recess  63  is formed between the outer connecting body  61  and the inner connecting body  62 , and the annular groove  621  in communication with the recess  63  is provided on an outer wall surface of the inner connecting body  62 . Six spaced identical blades  64 , extending downward from an outer wall surface of the outer connecting body  61 , are provided at a lower portion of the transition part  6  and are uniformly distributed on a same circumference. A bottom surface of each blade  64  is a sloping surface, a groove  641  is provided in an inner wall surface of each blade  64  to form a fragile portion of the blade so as to facilitate the outward expanding of the blades being pushed. A big inwardly protruding portion  643  corresponding to the inclined step  73  of the hollow wedge  7  and a small inwardly protruding portion  642  corresponding to an annular groove  711  of the hollow wedge  7  are provided in the inner wall surface of each blade  64 , and the small inwardly protruding portion  642  is fitted in the annular groove  711  for preventing the shock during the product transportation. 
     A first annular flange  11  is provided on an inner wall at an end surface of a head portion of the barrel  1  for restricting the assembled conical connector assembly  8  from being pushed forward, and a second annular flange  12  is provided on the inner wall below the first annular flange  11  for restricting the assembled conical connector assembly  8  from being retracted. A retaining annular groove  13  and an annular protruding portion  14  are provided on an inner wall of a rear end of the barrel  1 , several longitudinal strip inwardly protruding ribs  15  are distributed uniformly on the inner wall of the barrel  1  below the first annular flange  11 , all the strip inwardly protruding ribs  15  are starting at a same circumference at a root portion of a bottom surface of the first annular flange  11  and have the same length, and an inwardly protruding height of the inwardly protruding ribs  15  is lower than an inwardly protruding height of the first annular flange  11 . 
     A first retaining member  21  corresponding to the retaining annular groove  13  at the rear end of the barrel  1  and a second retaining member  22  corresponding to the annular protruding portion  14  at the rear end of the barrel  1  are provided on the plunger  2 . The first retaining member  21  includes four arc sheets provided on a same circumference, a thickness side of the first retaining member  21  is tangent to a circumference of a bottom surface of the first retaining member  21 , and forms a chamfer angle with a circumference of a top surface of the first retaining member  21 , such that the first retaining member  21  can smoothly pass through the retaining annular groove  13  in the inner wall of the rear end of the barrel  1  when the plunger  2  is moving forward in the inner cavity of the barrel  1 , but can not pass through the retaining annular groove  13  when the plunger  2  is moving backward. The second retaining member  22  is an integral circle retaining member coaxial with the plunger  2 , a circumference diameter of the second retaining member  22  is slightly less than a circumference diameter of the first retaining member  21  and is slightly larger than a diameter of the inner cavity of the barrel  1  at the annular protruding portion  14 , and a thickness side of the second retaining member  22  also is tangent to a circumference of a bottom surface of the second retaining member  22 , and forms a chamfer angle with a circumference of a top surface of the second retaining member  22 . A reinforcing rib  23  is provided on the plunger  2  below the first retaining member  21 , a fragile portion  24  is provided on the plunger  2  below the reinforcing rib  23 , a first tapered boss  25  and a second tapered boss  26  are provided at a head portion of the plunger  2  sequentially along an axis, a circumference diameter of a bottom surface of the first tapered boss  25  is less than a circumference diameter of a bottom surface of the second tapered boss  26 , and a slip-resistant rib  28  is provided on a bottom surface of a pushing portion  27  of the plunger  2 . 
     An upper portion  41  of the thread conical connector  4  is a standard Luer locking conical connector which can cooperate with various standard syringe needles. Four elastic retaining teeth  412  are provided on an inner cavity wall surface of a conical connector hole  411  along a same circumference, several strip outwardly protruding ribs  413  are distributed uniformly on an outer surface of the upper portion  41  of the thread conical connector  4 , and all the outwardly protruding ribs  413  are starting at a same circumference and have the same length. An outwardly protruding height of the strip outwardly protruding ribs  413  of the thread conical connector  4  is equal to an inwardly protruding height of the strip inwardly protruding ribs  15  of the barrel  1 . An end portion of the upper portion  41  of the thread conical connector  4  has an outer diameter larger than a diameter of the inner cavity of the barrel  1  at the first annular flange  11 , and has an inner diameter equal to or less than a diameter of the inner cavity of the barrel  1  at the first annular flange  11 . A lower portion  42  of the thread conical connector  4  is a hollow cylinder, and an annular inward flange  421  is provided on a wall surface of an inner cavity of the lower portion  42  of the thread conical connector  4 . 
     The circumference diameter of the bottom surface of the first tapered boss  25  at the head portion of the plunger  1  is less than a diameter of a circle formed by a top inner wall of the elastic retaining teeth  72 , in a natural state, at the head portion of the hollow wedge  7 , and is larger than a diameter of a circle formed by a top inner wall of the elastic retaining teeth  412 , in a natural state, in an inner cavity of the thread conical connector  4 . The circumference diameter of the bottom surface of the second tapered boss  26  at the head portion of the plunger  2  is larger than the diameter of the circle formed by the top inner wall of the elastic retaining teeth  72 , in a natural state, at the head portion of the hollow wedge  7 . 
     The strip outwardly protruding ribs  413 , distributed uniformly on the outer wall surface of the thread conical connector  4 , cooperate with the strip inwardly protruding ribs  15 , provided on the inner wall of the barrel  1  below the first annular flange  11 , so as to ensure that the conical connector assembly  8  can not rotate, and meanwhile the conical connector assembly and the inner wall of the barrel  1  form an interference fit via the sealing ring  5  so as to achieve the sealing. 
     A distance from the bottom surface of the second tapered boss  26  at the front end of the plunger  2  to the bottom surface of the first tapered boss  25  is larger than a distance from a top surface of the elastic retaining teeth  72  of the hollow wedge  7  to a top surface of the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4  in an assembled conical connector assembly, and the distance difference is enough for the second tapered boss  26  to retract the hollow wedge  7  until the restriction to blades  64  of the transition part  6  from the hollow wedge  7  is removed after the liquid medicine injection is finished. The first tapered boss  25  at the head portion of the plunger corresponds to the elastic retaining teeth  413  in the thread conical connector  4 , and the second tapered boss  26  corresponds to the elastic retaining teeth  72  at the head portion of the hollow wedge  7 . When the plunger  2  moves forward in the inner cavity of the barrel  1 , the bosses  25  and  26  and the elastic retaining teeth  72  and  412  form a forward tooth shape, thus the plunger  2  can pass through successfully, and when the plunger  2  is retracted, the bosses  25  and  26  and the elastic retaining teeth  72  and  412  form a reversed tooth shape. 
     When the injection of predetermined liquid medicine in the syringe is finished, a head of the plunger  2  at the front end of the piston  3  is extended to the front of the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4 , so as to effectively reduce a residual amount of the liquid medicine. Meanwhile, when the liquid medicine injection is finished, the plunger  2  is retracted, firstly, the second tapered boss  26  hooks the elastic retaining teeth  72  at the head portion of the hollow wedge  7  to retract it, such that the restriction to the blades  64  of the transition part  6  from the hollow wedge  7  is removed. When the transition part  6  is not restricted by the hollow wedge  7 , the outwardly expanded blades  64  of the transition part  6  return to an original state, thereby breaking away from the restriction from the second annular flange  12  on the inner wall of the barrel  1 . Meanwhile the first tapered boss  25  at the head portion of the plunger  2  hooks the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4  and pulls back the conical connector assembly so as to retract the syringe needle into the barrel  1 , until the first retaining member  21  of the plunger  2  slides into the retaining annular groove  13  on the inner wall of the rear end of the barrel  1 . Meanwhile the second retaining member  22  is resisted by the annular protruding portion  14  on the inner wall of the rear end of the barrel  1 , such that the retraction-stopping force on the plunger  2  becomes larger, in this situation when pulling hard the plunger  2 , the plunger  2  is broken due to the fragile portion  24  provided on the plunger  2 , thereby achieving the self-destruction function of the syringe and the security protection function of the syringe needle. 
     Advantageous effects of the present application are as follows. 
     In the conical connector assembly, the thread conical connector, for assembling the syringe needle, and a structural member (i.e., the transition part), for cooperating with the inner wall of the front end of the barrel so as to locate the conical connector assembly, are designed as separate parts, such that the conical connector assembly has a simple structure, may facilitate the mould manufacture, and each mould can be designed as one hundred and eight cavities (i.e., for an injection molding machine of one hundred and eighty tons, each mould can produces one hundred and eight parts), thus the production efficiency is improved significantly. Meanwhile due to the separate structural design of the thread conical connector and the transition part, the sealing ring, assembled between the thread conical connector and the transition part for ensuring the sealing performance, is much easier to assemble (there is no need to enlarge a diameter of the sealing ring for assembling, which reduces the most difficult process), and is more suitable for assembling by an automatic assembling machine. 
     The provided transition part has a low manufacturing accuracy and is easy to machine, the transition part is designed as six (at least more than three) spaced large blades, which are easy to expand outward and return to an original state, thereby ensuring the firmness of the fitting between the conical connector assembly and the inner wall of the barrel and ensuring the effect of the retraction performance. 
     A retraction design, having a stable operation performance, is provided. After the liquid medicine injection is finished, the plunger directly retracts the conical connector assembly and the syringe needle into the barrel, thereby changing the unstable design in the current market, which includes three or more movable sequential retractions. 
     A member for preventing the assembled conical connector assembly from being overly pushed forward (such as the first annular flange) is provided on the inner wall of the head portion of the barrel. 
     A transportation shockproof design is improved in the fitting between the conical connector assembly and the inner wall of the barrel. 
     The retraction is safe. A retraction limiting mechanism for preventing the overly retraction of the plunger is provided at the inner wall of the rear end of the barrel. When the injection of the predetermined liquid medicine is finished, two bosses at the front end of the plunger respectively automatically slide into the retaining portions of two elastic retaining teeth for achieving the self-destruction, then the plunger is retracted manually to retract the used syringe needle into the inner cavity of the barrel together with the conical connector assembly, until the plunger falls into the retraction limiting mechanism, so as to ensure that the needle tip is locked inside the inner cavity of the barrel and will not be exposed, thereby effectively preventing the medical staff from being stabbed unintentionally and avoiding the risk of the syringe being reused. 
     The Luer thread conical connector can fit with various standard syringe needles and may form a tight and fixed fitting. The plunger at the front end of the piston is configured with an enough length, so as to ensure a less residual of the liquid medicine, thereby reducing the damage to the society caused by the waste after the injection. 
     For the integral design, the present application has a simple structure, a low mould manufacturing accuracy, is easy to machine, thus is more suitable for automatic assembly, and may facilitate the control of the quality stability of mass production and satisfy the market requirement, and meanwhile may avoid the risk of failure of the self-destruction performance caused by careless assembly or operation. 
     The operation is safe. The sharp needle tip is protected securely, thus the following refuse treatment operation is safe and reliable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of the planar structure of the present application (before use), wherein  FIGS. 1( a ) and ( b )  are partial enlarged views of  FIG. 1 ; 
         FIG. 2  is a schematic view of the structure of a barrel of the present application, wherein  FIG. 2( a )  is a front view of the barrel,  FIG. 2( b )  is a bottom view of the barrel, and  FIG. 2( c )  is a perspective view of the structure of the barrel; 
         FIG. 3  is a schematic view of the structure of a plunger of the present application, wherein  FIG. 3( a )  is a front view of the plunger,  FIG. 3( b )  is a bottom view of the plunger,  FIG. 3( c )  is a sectional view of the plunger taken along line A-A,  FIG. 3( d )  is a sectional view of the plunger taken along line B-B, and  FIG. 3( e )  is a sectional view of the plunger taken along line C-C; 
         FIG. 4  is a schematic view of the structure of a conical connector assembly of the present application; 
         FIG. 5  is a schematic view of the structure of a piston of the present application; 
         FIG. 6  is a schematic view of the structure of a thread conical connector of the present application, wherein  FIG. 6( a )  is a front view of the thread conical connector,  FIG. 6( b )  is a top view of the thread conical connector, and  FIG. 6( c )  is a perspective view of the thread conical connector; 
         FIG. 7  is a schematic view of the structure of a sealing ring of the present application, wherein  FIG. 7( a )  is a front view of the sealing ring, and  FIG. 7( b )  is a top view of the sealing ring; 
         FIG. 8  is a schematic view of the structure of a transition part of the present application, wherein  FIG. 8( a )  is a front view of the transition part,  FIG. 8( b )  is a bottom view of the transition part, and  FIG. 8( c )  is a perspective view of the transition part; 
         FIG. 9  is a schematic view of the structure of a hollow wedge of the present application, wherein  FIG. 9( a )  is a front view of the hollow wedge,  FIG. 9( b )  is a top view of the hollow wedge, and  FIG. 9( c )  is a perspective view of the hollow wedge; 
         FIG. 10  is a schematic view of a first using state of the present application, with the protective cap being removed; 
         FIG. 11  is a schematic view of a second using state of the present application, showing absorbing the liquid medicine; 
         FIG. 12  is a schematic view of a third using state of the present application, when the injection is finished, wherein a right side of  FIG. 12  is a partial enlarged view of the conical connector; 
         FIG. 13  is a schematic view of a fourth using state of the present application, with the plunger being pulled back, wherein a right side of  FIG. 13  is a partial enlarged view of the conical connector, and the hollow wedge is pulled downwardly by a second tapered boss such that the transition part returns to its original state and is no longer restricted by the second annular flange; 
         FIG. 14  is a schematic view of a fifth using state of the present application, wherein the plunger is pulled back until a retaining member of the plunger slides into an annular groove in an internal wall of a rear end of the barrel and the needle is retracted into the barrel, wherein a right side of  FIG. 14  is a partial enlarged view of a tail portion of the barrel; and 
         FIG. 15  is a schematic view of a fifth using state of the present application, with the plunger being broken. 
     
    
    
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 In FIG. 1: 
                   
               
               
                 1. barrel; 
                 2. plunger; 
               
               
                 3. piston; 
                 4. thread conical connector; 
               
               
                 5. sealing ring; 
                 6. transition part; 
               
               
                 7. hollow wedge; 
                 9. syringe needle; 
               
               
                 10. protective cap; 
                 11. first annular flange; 
               
               
                 12. second annular flange; 
                 13. retaining annular groove; 
               
               
                 14. annular protruding portion; 
                 21. first retaining member; 
               
               
                 22. second retaining member; 
                 23. reinforcing rib; 
               
               
                 24. fragile portion; 
                 25. first tapered boss; 
               
               
                 26. second tapered boss; 
                 27. plunger pushing portion; 
               
               
                 28. slip-resistant rib; 
               
               
                 In FIG. 2: 
                 15. strip inwardly protruding rib; 
               
               
                 In FIG. 4: 
                 8. conical connector assembly; 
               
               
                 In FIG. 6: 
               
               
                 41. upper portion of the thread 
                 411. conical connector hole; 
               
               
                 conical connector; 
               
               
                 412. elastic retaining teeth; 
                 413. strip outwardly protruding rib; 
               
               
                 42. lower portion of the thread 
                 421. annular inward flange; 
               
               
                 conical connector; 
               
               
                 In FIG. 8: 
               
               
                 61. outer connecting body; 
                 62. inner connecting body; 
               
               
                 621. annular groove; 
                 63. annular recess; 
               
               
                 64. blade; 
                 641. groove; 
               
               
                 642. small inwardly protruding 
                 643. big inwardly protruding 
               
               
                 portion; 
                 portion; 
               
               
                 In FIG. 9: 
               
               
                 71. hollow cylinder; 
                 711. annular groove; 
               
               
                 72. elastic retaining teeth; 
                 73. inclined step. 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     The present application is further described in conjunction with the drawings and embodiments. 
     As shown in  FIGS. 1 to 9 , the present application provides an easily assembled and highly safe self-destructive syringe. 
     As shown in  FIG. 1 , the easily assembled and highly safe self-destructive syringe includes a barrel  1 , a plunger  2 , a piston  3 , a conical connector assembly  8 , a syringe needle  9  and a protective cap  10 . The syringe needle  9  is mounted in the conical connector assembly  8 ; the protective cap  10  is mounted above the syringe needle  9  to cover the syringe needle  9  and is movably connected to a needle seat of the syringe needle  9 ; the conical connector assembly  8  is mounted in an inner cavity of a front end of the barrel  1 ; the piston  3  is mounted on the plunger  2 ; a main body portion of the plunger  2  is mounted in the barrel  1 , and a front end of the plunger  2  is inserted into the conical connector assembly  8  during the injection operation and then can drive the syringe needle  9  mounted on the conical connector assembly  8  to retract into the barrel  1  together. As shown in  FIG. 4 , the conical connector assembly  8  includes a thread conical connector  4 , a sealing ring  5  (as shown in  FIG. 7 ), a transition part  6  and a hollow wedge  7 . As shown in  FIG. 2 , a first annular flange  11  is provided on an inner wall at an end surface of a head portion of the barrel  1 , and a second annular flange  12  is provided on the inner wall below the first annular flange  11 ; a retaining annular groove  13  and an annular protruding portion  14  are provided on the inner wall of a rear end of the barrel  1 ; several longitudinal strip inwardly protruding ribs  15  are distributed uniformly on the inner wall of the barrel  1  below the first annular flange  11 , all the strip inwardly protruding ribs  15  are starting at a same circumference at a root portion of a bottom surface of the first annular flange  11  and have the same length, and an inwardly protruding height of the inwardly protruding ribs  15  is lower than an inwardly protruding height of the first annular flange  11 . A first retaining member  21  corresponding to the retaining annular groove  13  at the rear end of the barrel  1  and a second retaining member  22  corresponding to the annular protruding portion  14  at the rear end of the barrel  1  are provided on the plunger  2 , and the first retaining member  21  consists of four arc sheets provided on a same circumference (the number of the arc sheets is not limited to four, however there should be at least two arc sheets). A thickness side of the first retaining member  21  is tangent to a circumference of a bottom surface of the first retaining member  21 , and forms a chamfer angle with a circumference of a top surface of the first retaining member  21 , such that the first retaining member  21  can smoothly pass through the retaining annular groove  13  in the inner wall of the rear end of the barrel  1  when the plunger  2  is moving forward in the inner cavity of the barrel  1 , but can not pass through the retaining annular groove  13  when the plunger  2  is moving backward. The second retaining member  22  is an integral circle retaining member coaxial with the plunger  2 , a circumference diameter of the second retaining member  22  is slightly less than a circumference diameter of the first retaining member  21  and is slightly larger than a diameter of the inner cavity of the barrel  1  at the annular protruding portion  14 , and a thickness side of the second retaining member  22  also is tangent to a circumference of a bottom surface of the second retaining member  22 , and forms a chamfer angle with a circumference of a top surface of the second retaining member  22 . A reinforcing rib  23  is provided on the plunger below the first retaining member  21 , a fragile portion  24  is provided on the plunger below the reinforcing rib  23 , a first tapered boss  25  and a second tapered boss  26  are provided at the head portion of the plunger  2  sequentially along an axis, and a circumference diameter of a bottom surface of the first tapered boss  25  is less than a circumference diameter of a bottom surface of the second tapered boss  26 . As shown in  FIG. 3 , a slip-resistant rib  28  is provided on a bottom surface of a pushing portion  27  of the plunger  2 . As shown in  FIGS. 1 and 5 , the piston  3  is hollow, and the head portion of the plunger  2  passes through the piston  3  so as to mount the piston  3  at the front end of the plunger  2 . As shown in  FIG. 6 , an upper portion  41  of the thread conical connector  4  is a standard Luer locking conical connector which can cooperate with various standard syringe needles; four elastic retaining teeth  412  are provided on a wall surface of an inner cavity of a conical connector hole  411  along a same circumference (the number of the elastic retaining teeth is not limited to four, however there should be at least two elastic retaining teeth); several longitudinal strip outwardly protruding ribs  413  are distributed uniformly on an outer surface of the upper portion  41  of the thread conical connector  4 , and all the strip outwardly protruding ribs  413  are starting at a same circumference and have the same length; an outwardly protruding height of the strip outwardly protruding ribs  413  of the thread conical connector  4  is equal to an inwardly protruding height of the strip inwardly protruding ribs  15  of the barrel  1 ; an end portion of the upper portion  41  of the thread conical connector  4  has an outer diameter larger than a diameter of the inner cavity of the barrel  1  at the first annular flange  11 , and has an inner diameter equal to or less than a diameter of the inner cavity of the barrel  1  at the first annular flange  11 ; and, the lower portion  42  of the thread conical connector is a hollow cylinder, and an annular inward flange  421  is provided on a wall surface of an inner cavity of the lower portion  42  of the thread conical connector  4 . The transition part  6  has a hollow structure, an outer connecting body  61  and an inner connecting body  62  are provided on an upper portion of the transition part  6 , the inner connecting body  62  is hollow, an annular recess  63  is formed between the outer connecting body  61  and the inner connecting body  62 , an annular groove  621  in communication with the recess  63  is provided on an outer wall surface of the inner connecting body  62 . Six spaced identical blades  64  (the number of the blade is not limited to six, however there should be at least three blades), extending downward from an outer wall surface of the outer connecting body  61 , are provided at a lower portion of the transition part  6  and are uniformly distributed on a same circumference, a bottom surface of each blade  64  is a sloping surface, and a groove  641  is provided in an inner wall surface of each blade  64  to form a fragile portion of the blade so as to facilitate the outward expanding of the blades being pushed. As shown in  FIG. 8 , a big inwardly protruding portion  643  corresponding to an inclined step of the hollow wedge and a small inwardly protruding portion  642  corresponding to an annular groove of the hollow wedge are provided on the inner wall surface of each blade  64 , and the small inwardly protruding portions  642  are fitted in the annular groove  711  for preventing the shock during the product transportation. As shown in  FIG. 9 , the hollow wedge  7  has a hollow structure, an upper portion of the hollow wedge  7  is a hollow cylinder  71 , four elastic retaining teeth  72  protruding inwardly and upwardly are uniformly distributed along a circumference at an inner cavity opening of an end surface of a head portion of the hollow cylinder  71 , an annular groove  711  is provided on an outer wall surface of the cylinder  71 , and two annular inclined steps  73  inclining outwardly and downwardly are provided on an outer side of a lower portion of the cylinder  71 . 
     In specific implementation, it should be ensured that a circumference diameter of the bottom surface of the first tapered boss  25  is less than a diameter of a circle formed by a top inner wall of the elastic retaining teeth  72 , in a natural state, at the head portion of the hollow wedge  7 , and is larger than a diameter of a circle formed by a top inner wall of the elastic retaining teeth  412 , in a natural state, in the inner cavity of the thread conical connector  4 ; and a circumference diameter of the bottom surface of the second tapered boss  26  at the head portion of the plunger  2  is larger than the diameter of the circle formed by the top inner wall of the elastic retaining teeth  72 , in a natural state, at the head portion of the hollow wedge  7 . 
     The assembly of the conical connector assembly  8  is as follow. The lower portion  42  of the thread conical connector  4  is extended into the upper portion of the transition part  6  to fit with the annular recess  63 , and the thread conical connector  4  and the transition part  6  are connected via the snap-fit between the annular inward flange  421  and the annular groove  621 ; meanwhile a sealing ring  5  is mounted between the thread conical connector  4  and the transition part  6 , the sealing ring  5  is pressed tightly to form an interference fit so as to ensure the sealing among the thread conical connector  4 , the transition part  6  and the inner wall of the barrel  1 . The hollow wedge  7  is mounted under the transition part  6 , the inclined steps  73  at the lower portion of the hollow wedge  7  outwardly press the six blades  64  at the lower portion of the transition part  6  to be expanded outwardly, such that the thread conical connector  4 , the sealing ring  5  and the transition part  6  are tightly restricted between the first annular flange  11  and the second annular flange  12  on the inner wall of the barrel  1 . The outer wall surface of a tail portion of the hollow wedge  7  and the inner cavity, formed by the second annular flange  12  on the inner wall of the barrel  1 , form an interference fit, and the small inwardly protruding portion  642  and the annular groove  711  are snap fitted to further improve the cooperation, thereby achieving the transportation shockproof function. Due to the mutual restriction between the strip outwardly protruding ribs  413 , distributed uniformly on the outer wall surface of the thread conical connector  4 , and the strip inwardly protruding ribs  15 , on the inner wall of the barrel  1  below the first annular flange  11 , the conical connector assembly can not rotate, and meanwhile the conical connector assembly and the inner wall of the barrel  1  form an interference fit via the sealing ring  5  so as to achieve the sealing. 
     Further, it should also be ensured that a distance from the bottom surface of the second tapered boss  26  at the head portion of the plunger  2  to the bottom surface of the first tapered boss  25  is larger than a distance from the top surface of the elastic retaining teeth  72  of the hollow wedge  7  to the top surface of the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4  in an assembled conical connector assembly, and the distance difference should be enough for the second tapered boss  26  to retract the hollow wedge  7  until the restriction to the blades  64  of the transition part  6  from the hollow wedge  7  is removed after the liquid medicine injection is finished. The first tapered boss  25  at the head portion of the plunger  2  corresponds to the elastic retaining teeth  412  in the thread conical connector  4 , and the second tapered boss  26  corresponds to the elastic retaining teeth  72  at the head portion of the hollow wedge  7 . When the plunger  2  moves forward in the inner cavity of the barrel  1 , the bosses  25  and  26  and the elastic retaining teeth  72  and  412  form a forward tooth shape, thus the plunger  2  can pass through successfully, and when the plunger  2  is retracted, the bosses  25  and  26  and the elastic retaining teeth  72  and  412  form an reversed tooth shape. 
     When the injection of the predetermined liquid medicine in the syringe is finished, the head of the plunger  2  at the front end of the piston  3  is extended to the front of the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4 , so as to reduce the residual amount of the liquid medicine; meanwhile, when the liquid medicine injection is finished, the plunger  2  is retracted, firstly, the second tapered boss  26  hooks the elastic retaining teeth  72  at the head portion of the hollow wedge  7  to retract it, such that the restriction to the blades  64  of the transition part  6  from the hollow wedge  7  is removed; when the transition part  6  is not restricted by the hollow wedge  7 , the outwardly expanded blades  64  of the transition part  6  return to the original state, thereby breaking away from the restriction from the second annular flange  12  on the inner wall of the barrel  1 ; meanwhile the first tapered boss  25  at the head portion of the plunger  2  hooks the elastic retaining teeth  412  in the inner cavity of the thread conical connector  4  and pulls back the conical connector assembly  8  so as to retract the syringe needle into the barrel  1 , until the first retaining member  21  of the plunger  2  slides into the retaining annular groove  13  on the inner wall of the rear end of the barrel  1 ; meanwhile the second retaining member  22  is resisted by the annular protruding portion  14  on the inner wall of the rear end of the barrel  1 , such that the retraction-stopping force on the plunger  2  becomes larger, in this situation when pulling hard the plunger  2 , the plunger  2  may be broken due to the fragile portion  24  on the plunger  2 , thereby achieving the self-destruction function of the syringe and the security protection function of the syringe needle. 
     The using process of the present application is shown in  FIGS. 10 to 15 . 
     The portions that are not referred to in the present application are the same as that in the prior art or can be implemented by using the prior art.