A sliding stopper for a syringe

Abstract: A sliding stopper (1) for a syringe, consisting of a rubber elastic body (2) whose part to be contacted with a liquid medicament and sliding part on the inner wall of a barrel (8) are fully laminated with a film (3) of tetrafluoroethylene resin, ethylenetetrafluoroethylene resin or ultra-high molecular weight polyethylene resin, and having an excellent liquid tightness and gas tightness is provided in which the ratio of the length (Y) of such a surface that the outer circumferen­ tial part of the sliding stopper (1) and the inner wall of the barrel (8) are contacted to the length (L) of the sliding part (4) of the sliding stopper (1), i.e. Y/L is in the range of 0.80 to 1.00, and the ratio of the length (L) of the sliding part (4) to the outer diameter (D) of the sliding stopper (1), i.e. L/D is in the range of 0.25 to 1.00.

Description: This invention relates to a sliding or movable stopper for an injector or syringe used, eg, for dosing a human body or animal with a liquid medicament. An injector is generally constructed of a barrel 48 of a glass or thermoplastic plastic, a sliding stopper 41 of a glass, rubber or thermoplastic elastomer and a plunger rod 47, as shown in Fig. 5. A combination of a glass barrel and glass sliding stopper has rarely been used recently, but a combination of a glass barrel and elastomer sliding stopper has been used for a syringe additionally serving as a container to be filled with a liquid medicament and a combination of a plastic barrel and elastomer sliding stopper has ordinarily been used for a throwaway disposable syringe. Fig. 4 is a cross-sectional view of an elastomer sliding stopper 41 of the prior art, in which a sliding part on the inner wall of a barrel 48 has annular protrusions 45a and 45b which are contacted with the inner wall. Syringes or injectors must be germ-free and dust-free in view of the purpose of the object and must have special physical properties such as liquid tightness, gas tightness and sliding property, which depend on the degree of contacting of the inner wall of a hard barrel with a sliding stopper consisting of an elastic material. Since every barrel has different straightness, smoothness and circular deformation of the inner wall and some errors in dimension and shape corresponding to the position, i.e. front part, central part and rear part, however, the above described degree of contacting differs every barrel and every position of a barrel. In order to correct such a dispersion, the diameter of a sliding stopper is ordinarily rendered larger than the average inner diameter of a barrel and the degree of contacting is increased to improve the liquid tightness and gas tightness. In this case, however, it is required to coat the sliding part with a silicone oil as a lubricant to make up for the thus lowered sliding property and the use of this silicone oil causes a problem of fine particle contamination of a medicament to be dosed. Under the situation, the inventors have proposed a high quality syringe in which no silicone oil is required by laminating the surface of a sliding stopper with a fluoro resin and the contamination due to the silicone oil can thus be prevented, as disclosed in Japanese Patent Laid-Open Publication Nos. 243122/1986 (EP-A-0264273) and 139668/1987. The laminated sliding stopper the inventors have proposed can completely solve the problem of contamination with a silicone oil as described above, but in a case where there are errors passing the limit in dimension and shape as to the inner wall of a barrel, the laminated sliding stopper cannot fully follow up the surface fluctuation as compared with non-laminated sliding stoppers, thus often resulting in deterioration of the sealability or tightness during sliding, i.e. using the syringe. Furthermore, the laminated sliding stopper often meets with lowering of the tightness, in particular, in the case of twistdrawing when aspirating a liquid medicament or in the case of slant pushing when injecting a liquid medicament. It is an object of the present invention to provide a sliding stopper for a syringe used for the injection of a liquid medicament, whereby the above described problems of the prior art can be solved. It is another object of the present invention to provide a laminated sliding stopper with an improved sealability during sliding. These objects can be attained by a sliding stopper for a syringe, comprising a body of elastomeric material whose part to be contacted with a liquid medicament and sliding part on the inner wall of a barrel are laminated with a resin film, such as of tetrafluoroethylene resin, ethylenetetrafluoroethylene resin or ultra-high molecular weight polyethylene resin, wherein the ratio of the length (Y) of such a surface that the outer circumferential part of the sliding stopper and the inner wall of the barrel are contacted with each other to the length (L) of the sliding part of the sliding stopper, Y/L, is in the range of 0.80 to 1.00, and the ratio of the length (L) of the sliding part to the outer diameter (D) of the sliding stopper, L/D is in the range of 0.25 to 1.00. The accompanying drawings are to illustrate by way of example and embodiment of the present invention. Fig. 1 and Fig. 2 are cross-sectional views of preferred embodiments of the sliding stopper for a syringe according to the present invention. Fig. 3 is a cross-sectional view of another embodiment of the sliding stopper of the invention when applied to a syringe. Fig. 4 and Fig. 5 are respectively cross-sectional views of a sliding stopper of the prior art and a syringe using this sliding stopper. Referring to Fig. 1 and Fig. 2 showing cross-sectional views of preferred embodiments of the sliding stopper for a syringe according to the present invention and Fig. 3 showing a cross-sectional view of another embodiment of the sliding stopper of the present invention when applied to a syringe, a sliding stopper 1 consists of a rubber part 2 and a laminated resin film part 3 and is fitted to the end of a plunger rod 7 and inserted in a syringe barrel 8 as shown in Fig. 3. When the length of a sliding part 4 of the sliding stopper 1 is designated as L, the length of a part 5 of the sliding part 4, contacted with the inner wall of the syringe barrel 8, is designated as Y and the outer diameter of the sliding stopper is designated as D, Y is 80 to 100 % of L, that is, Y/L is 0.80 to 1.00, and L is 25 to 100 % of D, that is, L/D is 0.25 to 1.00. In the case of Fig. 1, the contact part 5 with the inner wall 8 of the syringe barrel 8 is an outer circumferential even surface of a cylinder and Y = L, i.e. Y is 100 % of L, while as shown in Fig. 2, an annular hollow part 6 can be provided between a contact part 51 (length Y₁) and another contact part 52 (length Y₂) in such a manner that the sum of Y₁ and Y₂ becomes 80 to almost 100 % of L. Generally, the length L of the sliding part 4 is adjusted to about 6 to 15 mm, since the volume of an ordinary syringe corresponds to an injection liquid of 10 ml and this range of L can cover a liquid quantity of 3 to 25 ml. In the laminated sliding stopper of the prior art, annular protrusions 45a and 45b are provided at both the ends of the sliding part of a stopper 41, as shown in Fig. 4 (laminated film not shown), so as to hold the sealability. In Fig. 5, 47 designates a plunger rod and 48, a barrel. In the present embodiment, on the contrary, the sealability can largely be improved by adjusting substantially the overall surface of the sliding stopper, i.e. 80 to 100 % of the length L of the sliding surface to the length Y of the contact surface with the inner wall of a barrel. Since the sliding surface has no or few unevenness, production of the sliding stopper by subjecting a rubber and resin film to molding and laminating can be accomplished without formation of scratches on convex parts and with a largely increased yield, thus lowering the production cost. Furthermore, the sealability can well be held even in incorrect operations such as twist drawing and slant pushing by adjusting L to 25 to 100 % of D. The factor having the largest influence upon the sliding property is the friction resistance of the surface of a sliding stopper. Thus, a fluoro resin film having a small friction coefficient such as tetrafluoroethylene resin films (hereinafter referred to as TFE) or ethylene-tetrafluoroethylene resin films (hereinafter referred to as ETFE) is preferably used as the laminated layer 3 of the surface of the sliding stopper. In addition, polyethylene resins (referred to as PE) having an ultra-high molecular weight, i.e. at least 100 x 10⁴, which have lately been developed, are also preferably used as the material of the laminated layer, because of having a similar friction coefficient to fluororesins, being sufficiently resistant to practical use and also resistant to a gamma-ray sterilization method which has lately been used often and being produced with a low cost. The laminated layer has preferably a thickness of 0.010 to 0.2 mm. Production of the sliding stopper can be carried out by placing a film for lamination on the surface of a rubber sheet and then simultaneously subjecting to molding and laminating. For this rubber sheet, for examples, natural rubber and synthetic rubbers can be used. The sliding stopper of the present embodiment has the following advantages: In the sliding stopper, the surface of an elastic rubber body is laminated with a resin film with an excellent chemical resistance, but the sealability or tightness of the sliding stopper can be rendered sufficient enough to resist dispersion of the inner diameter or shape of a syringe barrel and incorrect operation of the syringe during use by specifying the relationship between the length of such a surface that the outer circumferential part of the sliding stopper and the inner wall of the barrel are contacted with each other, and the relationship between the length of the sliding part of the sliding stopper and the outer diameter of the sliding stopper. Furthermore, the use of silicone oil is not required and contamination of a liquid medicament with fine particles due to it can be prevented. Therefore, the sliding stopper of the present embodiment can favorably be applied to a syringe or injector for dosing a high purity medicament with in high security as well as a syringe additionally serving as a container for a liquid medicament, because of its high chemical resistance and sealability. The following examples are given in order to illustrate the present invention in greater detail without limiting the same. Examples Sliding stoppers of the present invention, each having a shape as shown in Fig. 1 or Fig. 2 and a laminated layer consisting of TFE, ETFE or PE, were prepared while varying Y/L and L/D within the scope of the present invention (Examples 1 to 6). On the other hand, laminated layer-free stoppers as shown in Fig. 4 (Comparative Examples 1 to 3, commercially available) and a laminated stopper (Comparative Example 4) were prepared. These samples were subjected to the elution or extraction test according to the legal test method, as a physical property test of a sliding stopper itself, and to the legal physical test and the physical test and fine particle test according to the independence test standard to evaluate the properties when used for a syringe. The outlines of these test methods are illustrated below and the test results are shown in the following table with the standard values: Legal Test 1) According to the test methods described in Notification No. 442 of the Welfare Ministry, Standard for Syringe Barrel of Disposal type, extraction tests with water (A) or a solvent (B) and physical tests (C) including a pressure test, aspiration test and movement test were carried out. 2) According to 44 Test Method of Rubber Stopper for Liquid Transfusion of 11th Revision, Japanese Pharmacopoeia, an extraction test (D) was carried. Independent Test Method Twist Drawing Test: Leakage of air was examined when 2 ml of water was charged in a syringe barrel, a needle opening part was directed upward and clogged and a plunger rod was withdrawn by fingers while revolving it by about 90 degrees. Slant Pushing Test: Leakage of water was examined when 2 ml of water was charged in a syringe barrel, a plunger rod was positioned in such a manner that the sliding stopper be at the maximum scale mark, a needle opening was directed upward and clogged and the plunger rod was pushed under slant state. Sliding Test: When a syringe barrel to which an injection needle was not attached was fixed and a plunger rod was thrust to move the sliding stopper, the load (initial value and sliding value) was measured by an Autograph DCS-100 type (commercial name, manufactured by Shimazu Seisakusho KK). Knocking Test (Fluctuation of Sliding Value): "Good" means such a state that when a plunger rod is thrust in a syringe barrel by hand, it is moved in smooth and continuous manner, while "knocking" means such a state that the plunger rod is intermittently moved. The knocking property is an important property to judge whether an injection medicament is precisely dosed as predetermined or not. Deairing Test: After purified water was aspirated in a syringe to the maximum scale mark and then discharged by 1 ml by thrusting a plunger rod under such a state that a needle was directed upward, the presence or absence of bubbles was visually examined. Mark ○ shows bubble-free state and mark x shows a bubbled state. Fine Particle Test: This test was carried out by aspirating 5 ml of purified water by a syringe, discharging the water by thrusting and collecting, repeating this procedure three times to obtain a test liquid and after allowing to stand for 30 minutes, subjecting 12 ml of the test liquid to measurement using an optical fine particle tester (RION). In each Example, 20 samples were used and subjected to this test and the results are shown in the following table as mean values per one sample. The assessment of the results is represented by "Very Good" O ○, "Good" ○ , "Normal" ▵ and "Unsuitable" x. "ND" means an amount of lower than the limit which can be detected. As can be seen from these results, the commercially available laminated layer-free sliding stoppers as shown in Fig. 4 (Comparative Examples 1 to 3) all give good results in the physical tests, but inferior results in the fine particle test which will cause a problem on safety considering a bad influence on a human body and the sliding stopper having a laminated layer and a shape as shown in Fig. 4 (Comparative Example 4) exhibits a very high safety, but meets with a problem in the physical tests. On the other hand, the samples of the present invention give much better results in the tests, which can favorably be compared with those of Comparative Examples.

Claims: A sliding stopper (1) for a syringe, comprising a body (2) of elastomeric material, such as rubber, having a contact part, which in use contacts a liquid medicament, and a sliding part (4), which in use slides along an inner wall (8) of a barrel, which contact and sliding parts are laminated with a resin film (3) having a low friction co-efficient, wherein the resin film (3) is selected from the group consisting of films of tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer resins and ultra-high molecular weight polyethylene resin, characterised in that the ratio of Y/L of the length (Y) of the sliding part, which in use contacts the inner wall of the barrel, to the actual length (L) of the sliding part of the sliding stopper, is in the range of 0.8 to 1, and the ratio L/D of the length (L) of the sliding part to the outer diameter (D) of the sliding stopper is in the range of 0.25 to 1. A sliding stopper (1) for a syringe as claimed in claim 1 wherein the length (L) of the sliding part (4) is from 6mm to 15mm. A sliding stopper (1) for a syringe as claimed in claim 1, wherein the contacted part (5) of the sliding stopper with the inner wall (8) of the barrel, having the length (Y), is provided with an annular hollow part to divide into two contacted parts respectively having lengths Y₁ and Y₂ in such a manner that (Y₁+Y₂)/L is in the range of 0.8 to almost 1.

Inventors: OKUDA TAMOTSU, SUDO MASAMICHI, OKUDA, TAMOTSU, SUDO, MASAMICHI
Applicants: DAIKYO GOMU SEIKO KK, DAIKYO GOMU SEIKO LTD.
Application year: 1989
Main classification: A61M5
IPC codes: A61L31, A61M5, B29K23, B29K27