Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2001-11-27
2004-07-27
Colaianni, Michael (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S319000, C264S328130, C264S328100
Reexamination Certificate
active
06767496
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for producing a needle of plastic, a system for same as well as a needle of plastic, in particular a needle for medical purposes.
PRIOR ART
Needles or cannulas for medical purposes, such as injections of medicine, have been produced in various sizes depending on their intended use. For medicine to be injected frequently, such as several times a day, it is preferred to use the thinnest possible needle taking into account the viscosity of the medicine to be injected. Diabetics injecting insulin several times a day would preferably use a very thin needle, such as from gauge 26 to gauge 30, in order to reduce the pain as well as reduce the tissue damage resulting from each injection. In the present context the term “thin” refers to the diameter of the needle in question. Usually needles and other medical tubings are sized in gauges, wherein gauge 8 corresponds to 4.19 mm, and gauge 30 corresponds to 0.30 mm, for example.
In order to obtain a needle exhibiting the necessary strength for penetrating the skin and subcutis as part of the injection the very thin needles have usually been made from metal. Like many other medical articles it is of interest to produce the needles of a plastic material.
EP 452 595 discloses a method for producing a plastic medical tubing, such as a catheter, wherein a liquid crystalline polymer has been shear-thinned to such a viscosity allowing the melt to flow into and fill a mould. The plastic tubings produced have a gauge size of from 8 to 26, preferably from 14 to 20. The shear-thinning is provided by passing the plastic melt through an orifice before the melt reaches the mould. The patent describes a method for preparing the tubing by extruding the shear-thinned polymer into a mould, and describes further that the polymer melt may be forced under pressure through the orifice and thence directly into the mould.
However, in order to obtain very thin needles of the length relevant for injection of medicine very small volumes of plastic melt is used. It has been found, that merely extruding the melt, optionally under pressure will not result in the moulding of a needle of the dimensions in question with sufficient strength.
Injection moulding systems are often used for the production of large amount of articles. Injection moulding is a periodical process, in which a plastic granulate is being homogenized and melted by heating as well as by mechanical working. The plastic melt is injected into a mould cavity. The mould cavity has a temperature which is controlled to be lower than the melting point of the plastic. Hereby the melt injected into the mould cavity will solidify from the wall of the mould cavity to the centre of the article.
In the known injection moulding systems a screw may be used to the mechanical working of the melt as well as to introduce the melt into the mould cavity at a certain injection speed.
The screw movement or injection stroke is normally set to 1 to 4 times of the diameter of the screw. Hereby a right quality of the melt as well as a uniform shot volume will be ensured. By “shot volume” is meant the amount of melt necessary to at least fill the mould cavity to obtain a needle of predetermined dimensions.
The inertia of the screw as well as the hydraulic pressure transferred to the screw ensures in the known systems a pressure which is sufficient to fill large shot volumes.
However due to the small amount of melt necessary for producing a small article pressure applied to the screw cannot be timely transferred to the melt at the entrance of the mould cavity. The matter is that the hydraulic pressure behind the screw shall build up a pressure from the screw to the entrance of the mould cavity in approximately 1 to 10 msec, which has not been possible in known injection moulding system. Therefore, it has not previously been possible to obtain plastic needles or cannulas for medical purposes, for which the outer diameter of the needle or the cannula is 0.5 mm or less.
Furthermore, needles or cannulas of this diameter having an inner diameter is very thin-walled, a wall thickness of approximately 0.10-0.18 mm. This provides the problem of introducing the melt into the mould cavity in such a short time, that “freezing” of the melt is avoided. By “freezing” is meant that the melt solidifies rapidly due to the small thickness of the material. In case melt freezes in the first part of the mould cavity, the melt will not be able to fill the entire mould cavity and thereby a needle of predetermined dimensions will not be obtained.
By the known methods of injection moulding it has therefore not previously been possible to mould needles or cannulas having a wall thickness of material of approximately 0.10-0.18 mm.
The needles or cannulas are furthermore having a very large L/D ratio (wherein L is the length, and D is the diameter of the article) which further provides the problem of not only requiring a small shot volume but also of filling the “long” mould cavity as compared to a small diameter. Thus, in order to ensure that the mould cavity is filled totally with melt a very precise control of the energy reserve in the melt at the entrance of the mould cavity is necessary.
Certain requirements must be met for needles Or cannulas for medical purposes irrespective of the material used. One requirement is that the needle must not bend during insertion of the needle into the patient. Many plastic needles have lacked sufficiently strength when the diameter of the needle is decreased, so that in practice it has not been possible to use plastic needles for medical purposes unless very large needles, such as needles having a diameter of 1 mm or above.
CORE OF THE INVENTION
One aspect of the invention relates to a method for producing a plastic needle, which needle has two ends, wherein at least the outer diameter of one end is less than 0.50 mm, said needle further having a longitudinal lumen extending between two openings of the needle, in a moulding system having an assembly comprising a feed system and a mould cavity,
said method comprising the following steps:
introducing a melt of plastic into the feed system,
increasing the melt pressure gradually during melt passage through the feed system,
passing the melt into the mould cavity, whereby the melt substantially fills the mould cavity,
cooling the melt in the mould cavity whereby the melt solidifies to a needle, and
removing the needle from the mould cavity.
Another aspect of the invention is a system for producing a hollow plastic needle, having an assembly comprising a feed system and a mould cavity, and further comprising means for introducing a melt of plastic into the feed system, said feed system being arranged for increasing the melt pressure gradually during melt passage through the feed system, and means for passing the melt into the mould cavity, so that the melt substantially fills the mould cavity.
By the present invention it has been found that in order to produce small, thin and elongated articles by injection moulding whereby the shot volume is very small it is required to ensure a high energy reserve in the melt at the entrance of the mould cavity itself.
By gradually increasing the pressure through the feed system it is possible to meet the specific pressure demands at the entrance of the mould cavity in order to mould the thin and elongated articles in spite of the small shot volume, because the melt will then reach a sufficient pressure before it enters the mould cavity.
During injection moulding the melt is in motion in the feed system, i.e. flows, whereby the flow front of the melt has a pressure of approximately 0.1 MPa whereas the pressure in front of the screw is high. Accordingly, a high pressure gradient is present.
The high pressure gradient in the feed system ensures the high energy reserve in the melt. This energy reserve in the melt has the same function as for example a biased spring.
When the melt is introduced into the entrance of the mould cavity the energy reserve in the melt ensures, that the spring effec
Hansen Henrik Egesborg
Jensen Søren
Nielsen Poul E. B.
Papsøe Mogens
Sørensen Anne
Colaianni Michael
Fontaine Monica A.
Novo Nordisk A S
Petry Marvin
Stites & Harbison PLLC
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