Vention Medical

Produce an ultra-smooth "glass like" surface finish

The low shrink temperature and high melt temperature of polyester heat shrink tubing enables it to be used very effectively to form smooth tapered tips on the ends of catheters and other medical devices.

In the initial operation, a section of heat-shrink tubing is slid onto the end of a catheter tube, leaving a tail off the end. A coated metal rod or PTFE beading is inserted in the catheter to maintain the tip ID. Heat is then applied to shrink the tubing onto the substrate, causing the substrate to melt and flow. Pulling on the heat shrink tube draws the catheter tube to a very thin, smooth tip. Since the shrink tubing is clear, the operator can monitor the process. The shrink tubing is removed to complete the job, leaving an ultra-smooth finish.

In catheter tip forming, clear polyester heat shrink tube is first attached to the end of a catheter tube, then more heat is applied (with hot air torch extending from background), while a hemostat (at right) is used to pull and draw the shrink tube, forming a smooth tapered tip. A mandrel is used to prevent the tip I.D. from collapsing during the process.

Process Animation (Flash)

Key Properties

• Low shrink temperature and rapid shrinkage allows initial application without part distortion
• High melt temperature allows use of a high enough temperature to cause the substrate to melt and flow
• Ultra smooth surface finish after forming
• Easily removed
• Does not stick to most materials
• Clear material enables visual monitoring of the process
• Heat shrink tube can be drawn down when heated to get a very thin smooth taper

Process Steps

• Grab tube with one hand
• Place mandrel inside lumen which needs to be left open
• Place shrink tubing over tube end
• Hold the heat shrink tube over the multi lumen tube, then apply heat using a Hot Air Station and at the same time pull and draw the heat shrink tube using the tweezers. Caution: Ensure that the material does not touch the heat source.
• Allow product to cool
• Remove heat shrink tube and mandrel
• Trim tip as required

Equipment Used

• Tweezers
  Tweezers can be used to apply tension and draw the shrink tubing.
• Razor
  A razor can be used to trim the tip of the tube at the end of the process.
• Heat Source
  A heat gun or hot air station is typically used to heat the heat shrink tube and melt the substrate to be formed, thereby forming a thin smooth tip.

Materials Used

• Heat Shrink Tubing
  Advanced Polymers' thin-walled polyester heat shrink tubing is used in the tip forming/sealing process.
• Multi-Lumen Tube
  The multi-lumen tube to be tip formed and selectively sealed.
• Mandrel
  The mandrel is used to keep the selected lumen open.

Advanced Polymers' clear polyester heat shrink tubing can be used effectively in fusing tubes together. Typically, tubes of dissimilar properties — one stiff and one flexible — are joined. An easy way to accomplish this is to insert a mandrel in the tube ends to keep them from collapsing, butt the two ends together, and shrink a piece of tubing over them. Since polyester tubing has a low shrink temperature, the parts do not distort during this initial process.

In tube joining, clear polyester heat shrink tubing is used to hold a low durometer clear tube and high durometer white tube tightly together for fusing (top). The heat shrink tube is shown partially removed (middle) and completely removed from the joint (bottom). Thumbtack is for size reference.

The shrinking process squeezes the tubes and holds them together tightly during fusing. Because of polyester's high melt temperature, the high heat applied to fuse the tube ends does not melt the shrink tubing. After the tubes are joined, the shrink tubing can be left on or peeled off to leave an ultra smooth surface finish. Nicking the shrink tubing at one end before shrinking facilitates removal. Since the polyester tubing is clear, the operator can see when the tubes are fused. The ability to "see" the process is very useful in product development and production to avoid applying too much or too little heat.

Process Animation (Flash)

Key Properties

• Low shrink temperature and rapid shrinkage allows initial application without part distortion
• The high melt temperature of polyester allows use of a high enough temperature to get the substrates to melt and flow together
• Ultra smooth "glass like" surface finish after joining
• Easily removed if required or thin enough to leave in place. Tubing can be pre-cut without fear of splitting or propagating during the shrink process.
• Does not stick to most materials
• Optically clear material enables monitoring of the process

Process Steps

• Place both tubes next to each other (on a flat surface) and cut both tube ends evenly
• Grab one of the tubes with one hand and place Mandrel inside tube
• Slide other tube over the Mandrel
• Pre-cut end of shrink tubing "optional for easy removal"
• Place properly sized polyester heat shrink tube over the joint (formed by the two tubes). Please refer to our online catalog for proper sizing.
• Apply heat using Hot Air Station until shrink tubing shrinks over joined tubes. Ensure that material melts and flows uniformly. Caution: Ensure that the material does not touch the heat source.
• Allow product to cool for approximately one minute
• Slice end of heat shrink tube with scalpel or razor blade "if not previously done above"
• Use tweezers to peel shrink tubing off in a spiral manner
• Remove Mandrel

Equipment Used

• Tweezers
  The tweezers are used to remove the heat shrink tubing and mandrel from joined tubes.
• Razor
  The razor is used to make a clean cut on the end of the tubes.
• Heat Source
  The heat source is used to shrink the heat shrink tubing while melting and joining the tubes together. A heat gun or hot air station is typically used for this purpose.
• Scissors
  The scissors are used to pre-cut the edge or end of the heat shrink tubing to provide the starting point where the heat shrink tubing will be removed.

Materials Used

• Heat Shrink Tubing
  Advanced Polymers' thin-walled polyester heat shrink tube is used to form a joint between the two tubes. Also protects the tubes from the heat source.
• Green Tube
  Tubes to be joined together. For example: high and low durometer thermoplastics; Pebax^®, Polyurethane, PE, etc.
• Mandrel
  The mandrel is used to maintain the inside diameter of the tubes to be fused. Also helps to form a smooth joint. We recommend the use of a PTFE (Teflon®) beading or a Teflon coated metal mandrel.
• Orange Tube
  Tubes to be joined together. For example: high and low durometer thermoplastics; Pebax^®, Polyurethane, PE, etc.

Whenever very high radial shrinkage (up to 50% or more) is required, the drawing process can be used. This simply requires axial tension and stretching of the tube while it is being heated. Over 50% diameter reduction can be achieved at temperatures below 100°C (212°F). Higher diameter reductions can be achieved at higher temperatures, up to about 190°C (374°F).

Process Animation (Flash)

Process Steps

• Slide polyester heat shrink tubing over stepped mandrel (or product) so that it is overlapping the mandrel on both ends.
• Hold shrink tubing with one hand and use a hemostat in other hand (The hemostat should be held in the hand you will be drawing the tubing with)
• Move the product through the heat source, while pulling the material with the hemostats using sufficient tension to draw the heat shrink tube. Caution: Ensure that the material does not touch the heat source.
• Allow the product to cool as required
• Trim both ends accordingly

Equipment Used

• Hemostat
  Hemostats can be used to apply tention and draw the tubing
• Heat Source
  A heat gun or hot air station is used to heat the heat shrink tube, allowing it to shrink and be drawn over the mandrel or product.

Materials Used

• Heat Shrink Tube
  Advanced Polymers' thin-walled polyester heat shrink tubing is used in the drawing process.
• Mandrel
  The product to be covered with the heat shrink tube.

This is a simple but very effective application of polyester heat shrink tubing for masking areas during coating operations. One manufacturer requires a white coating over a clear balloon, but the neck must remain uncoated so that a UV curable adhesive can be used to bond it to the catheter. A piece of heat shrink tubing is applied to the neck, then the balloon is dipped in the coating. After it dries, the heat shrink is peeled away, leaving the neck uncoated. The key to this application is the thinness of the polyester tubing. A thicker shrink tubing would leave a thick edge of coating material on the balloon, unlike the ultra-thin wall polyester tubing.

Clear angioplasty balloons are shown after a white coating has been applied to one end. Polyester shrink tubing was used to mask the small diameter ends to prevent the balloon end from being coated. This enables the manufacturer to use a UV-curable adhesive for bonding the balloon to the catheter. Top view shows coated balloon prior to removal of the mask. The heat shrink tube is partially removed from the end of the middle balloon. Bottom view shows shrink tubing has been completely removed, thus leaving an uncoated clear neck ready for bonding.

Another manufacturer applies a slippery coating to a length of wire that has a fine spring coil at the end. Polyester heat shrink tubing is used to mask the spring to keep it from being coated during the dipping process. The low shrink temperature permits the masking operation without heat distortion, and the tight shrink fit prevents the coating from flowing into the spring. Afterwards, the polyester tubing is easily peeled away.

The key properties of polyester heat shrink tubing in masking applications are:

• Very thin wall to prevent thick build up at edge
• Low shrink temperature allows application without heat distortion
• Easily removed
• Tight shrink fit on substrate

Removal of polyester heat shrink tubing:

• Heat shrink tube is easily removed by pulling or peeling, and the mandrel is pulled out of the catheter tube
• The heat shrink tubing does not stick to most materials
• If necessary, the tip may easily be trimmed using a razor blade
• Observe the ultra, smooth glass-like surface finish of the taper produced using this process

Bands of heat shrink tubing can be used as micro hose clamps on balloon catheters and other devices to reinforce bonds and help prevent failure under pressure. A narrow band of heat shrink tubing is applied over the end of the balloon. The polyester tubing, with its high hoop strength, grips the part much like a hose clamp, reinforcing the bond and keeping it from lifting off. It also provides a smooth transition without adding significantly to the bond diameter. The tubing can also be used to terminate braiding, spring coils and other parts to provide a smooth transition.

Clear 1 mm bands of polyester shrink tubing are shrunk over both ends of this latex balloon (shown un-inflated and partially inflated). The shrink tubing acts like hose clamps to reinforce the bonds and therefore prevent the inflated balloon from peeling away from the catheter tube and leaking.

The key properties of polyester heat shrink tubing in micro hose clamp applications are:

• Has substantial hoop strength to reinforce bonds and other areas
• Very thin so it does not add significantly to the device diameter
• Can help smooth diameter transitions
• Can be used to terminate braiding, springs, etc.
• Adhesive can be UV-cured through the clear tubing

Polyester heat shrink tubing is often used to cover braided catheter shafts, spring coils, radio-opaque marker bands and other parts that require a thin, but tough protective covering.

It offers a quickly and easily applied reinforcement for smooth transitions over sharp edges, provides strain relief to prevent kinking, offers chemical protection and allows for the bundling of various components into the smallest possible space.

The tubing provides smooth transitions over sharp edges and can be sealed against fluid leakage. One manufacturer uses it over a rotary spring cutter to keep debris from clogging the coils and to act as a bearing surface inside the device. It provides a fluid seal, yet the cutter remains flexible. And the very thin walls add virtually no dimensional increase to the device.

The tubing is also used to provide strain relief on catheters and other tubes to prevent kinking. A braided catheter will tend to kink at the point where the braid ends, but encapsulation with heat shrink tubing provides a quick, easily applied reinforcement providing a smooth transition over the two surfaces. Using shrink tubing is a repeatable, consistent and efficient alternative to coatings. It eliminates the solvents and chemicals required in the coating process, as well as the inherent issues of uniformity and pin holes in coatings.

Endoscopes and other devices can be downsized or have more features added without a size increase with the use of ultra thin wall tubing. Unique devices can be produced using polyester heat shrink tubing to bundle various components into the smallest possible space. Components such as plastic and metal tubing, wires, optical fibers, etc. can be compressed and protected. Connecting tubes at the ends of a device can be made of thin wall polyester, too, to save valuable space. The thinner walls of polyester tubing can free up enough space to add another working channel inside an endoscope. Or it might enable the designer to reduce the size of the device by a whole French catheter size.

The key advantages of using polyester tubing as a protective cover or encapsulation material are:

• Very thin wall adds virtually no dimensional increase
• Smooth transitions made over sharp edges
• Provides strain relief to prevent kinking
• Easy, quick application
• Repeatable and consistent
• Adhesive can be UV-cured through the clear tubing
• Provides chemical protection

Depth marks and printing can easily be added to catheters and metal shafts with heat-shrink tubing. Typically, thin bands of colored shrink tubing are used for marking. They can be accurately positioned using the proper techniques. Labeling information can be added by pre-printing on the shrink tubing then applying it to the product. That avoids the need to send the devices themselves to a printer for labeling or to bring printing inks and solvents into the manufacturing facility for in-house printing.

Some products, such as catheters made from high-density polyethylene, cannot be readily printed without surface treatment, adding more complexity. Manufacturers who do print on their products can use clear heat shrink tubing over top of the printing to protect it. The ultra-thin wall of polyester heat-shrink tubing does not increase the diameter of the product substantially.

A clear tube (top) is marked with bands of transparent green heat shrink tube. Pre-printed polyester heat shrink tubing (middle two images) is shown before and after shrinkage in a labeling application. At the bottom, alternating white and black bands of polyester heat shrink tubing are shrunk onto a clear catheter tube.

The key properties of polyester heat shrink tubing influencing marking and printing are:

• Can be printed with any color and graphic
• Tubing is available in variety of colors
• Thin wall tubing adds little to the size of the product
• High-gloss surface provides quality appearance
• Can be accurately placed using proper techniques
• Clear tubing can be used to protect printing on the product

Create your own high-pressure, ultra-flexible catheter shaft by shrinking or drawing our polyester heat-shrink tubing over a coil spring formed from flat or round wire.