尼龙润滑剂:内润滑和外润滑错一个,脱模和强度都要出事

应用领域 发布时间: 2026-09-15 3261 阅读

Regarding the nylon lubricant, the most typical situation on site is that a batch of parts, after being left for three days, develops a layer of white on the surface.

This spring, a customer who makes electric tool housings brought two housings, each wrapped in a layer of newspaper.

The part is made of dark gray fiberglass-reinforced nylon. When it just came off the production line, the surface was quite clean. The customer said that by the third day, near the edges and the weld lines it started to turn white, and a layer could be wiped off by hand.

On the phone, he judged very decisively: 'There might be impurities in the material, can you help me check if it has been mixed with recycled material?'

I first asked him three questions.

Is the lubricant added together with the main ingredient, or added later in the process?

In this system, is the external lubricant of the calcium stearate type, or of the silicone type?

After this part is completed, does it need to be painted or ultrasonically welded?

He answered quickly: The ones we invested in together, calcium stearate, we want both.

That white layer isn't impurities, but lubricant that has reached the surface. And this is exactly where nylon lubricants are most easily misunderstood.

Understand in two minutes: internal lubrication and external lubrication are two opposite actions

Lubricants stay in the melt, and their position determines what they do.

Those that are highly compatible with the resin will drill into the melt, staying between the molecular chains, allowing the chains to slide past each other more easily.

This is called internal lubrication, which makes the melt 'smoother'—the viscosity decreases, it flows better, and the shear heat also reduces accordingly.

Those with poor compatibility with the resin cannot stay and will migrate to the surface of the melt, forming a layer between the melt and the metal wall.

This is called external lubrication, which makes the material 'not stick to the iron' — easy demolding, shiny surface, and less buildup at the mold opening.

A plain summary: Whether the inner lubricating tubing slides on its own, and whether the outer lubricating tubing sticks to iron. Both are called lubricants, but the work they do is almost opposite.

Why is this matter important? Because when the client says 'not lubricated well,' it points in two directions: if it's not fully applied, that's an issue with internal lubrication; if it can't be removed, that's an issue with external lubrication.

Asking in the wrong direction, adding the wrong ingredients, that's how frosting comes about.

1. Why frost always appears on the surface first

First explain that layer of white.

External lubricants naturally don't like to stay in the resin; during processing, they are pushed to the surface, and during use, they continue to move toward the surface.

Once the temperature rises and time passes, it starts to accumulate on the surface of the parts, and when it builds up to a certain extent, it becomes the layer of white you see.

This layer of white has several characteristics: it first appears near corners, weld lines, and gates; even after being wiped away, it comes back after a few days; and it becomes more noticeable as summer approaches.

Why does it come back after being wiped off? Because there is still a stock of material inside, and the channel is not broken, it will continue to flow out.

This point is very crucial: frosting is not an appearance issue; it is the external manifestation of the material 'expelling something'.

Since it is being expelled outward, the things it expels will also appear on the welding interface and the painting interface.

So when you see the spray cream, don't just think about wiping it; first think about what else it might affect.

2. Temperament Chart of Main Breeds

The functions and ranges in the table are based on commonly available information from public sources. The actual dosage should be determined by your grade, molding method, and subsequent processes, and cannot be copied directly.

VarietyInclined towardMain functionPublicly add intervalThe cost to watch out for
Diethylenetriamine distearamideHaving both inner and outer qualitiesImprove flow and demolding, interface-oriented alignment0.2%–0.8%Add more external lubrication, spraying and welding become weaker
Calcium stearates (metal soaps)Outer-biased lubricationDemolding, and it also has some acid-absorbing effect0.1%–0.5%Migration is obvious; electrical components need to be evaluated
SiliconePartial internal lubricationReduce friction, improve surface and forming0.3%–1.0%Impact on Coating and Printing Adhesion After Migration
Polyol estersPartial internal lubricationGood temperature resistance, wide processing window0.1%–0.5%The cost is higher than soap-based products and requires an evaluation of cost-effectiveness.

This table only provides the public addition ranges for single-type additives. The formula is the customer's confidential information, and the proportion combinations must be determined per item, so they are not written here, nor should they be.

The upper limit of the range does not mean 'maximum input.' Section 7 will explain clearly why maxing out often causes problems first.

One more reminder: Different models within the same category have different polarities, and the internal and external orientations will also change accordingly. When selecting a model, refer to the technical specifications for the specific model, not just the category name.

3. What happens with internal and external mismatches: both ends are blocked

Take that client mentioned at the beginning. His parts need painting and ultrasonic welding, yet he used an external lubrication metal soap, and in a considerable amount.

Excess external lubrication will cause three things to happen.

The frosting comes out first because it is being pushed out.

The welding strength decreases because the interface originally relies on mutual wetting of the molten material, and this surface layer is equivalent to having something padded in between.

The paint adhesion will also decrease, for the same reason—the coating sticks to a layer of lubricant, not the plastic.

Insufficient internal lubrication can also cause three things to happen.

High melt viscosity and poor flow cause thin-walled and long-flow areas to fill incompletely at first.

Excessive shear heat causes the glass fibers in the barrel to be over-sheared, reducing their retained length and consequently weakening the mechanical properties.

When the two streams of material converge at the welding line, the temperature has already dropped, so the interface does not fuse firmly, and the part cracks along this line under stress.

Excess internal lubrication also comes at a cost.

If the viscosity drops too low, the screw's dispersive shear is insufficient, the glass fiber bundles do not open, and fiber ends begin to appear on the surface of the part, causing uneven properties.

At the same time, the excess part still needs to go to the surface, and spraying frost will happen as usual.

So this is never a question of 'how much to add,' but a question of 'how to balance the inside and outside.' And balancing must follow the piece, according to the forming method and subsequent processes.

4. Demand Corresponding to Category: Lubricant Selection Table

This table puts common requirements, verification methods, common failures, and 'who will clash with whom' together.

Your needsWhich category should I look atHow to verifyCommon FailuresWhich types of additives or processes would conflict
Difficulty demolding, mold mouth buildupA type of external lubricationContinuously run 200 molds to observe buildup and ejectionExcessive demolding and dimensional bleachingMoves in the opposite direction to welding strength and paint adhesion
Thin walls cannot be fully formed, long processInner-type lubricationFlow length ratio and short shot locationFiber ends appear on the surface, dispersion worsensConflicts with the shear required for fiberglass dispersion
The welding line strength is insufficientBoth internal and external aspects need to be balancedStretching after short-shot samplingCracking along the weld lineDirectly conflicts with excessive external lubrication
Poor glass fiber dispersion, rough surfaceFirst, check if the internal lubrication is sufficientAsh Uniformity and Surface ObservationExposed fiber ends, uneven performanceIn conflict with too low melt viscosity
The item needs to be painted or printedChoose a low-migration modelConduct adhesion test after spray paintingShrinkage cavities, paint peelingThe migration of silicone has a significant impact on the spraying line
The part needs ultrasonic weldingControl the total amount of external lubricationWelded spline strength and weld cross-sectionWeld subsurface laminationClearly incompatible with metallic soaps and waxes
High-voltage electrical componentsUse metal soaps with cautionComparison between leakage tracking and insulation resistanceElectrical performance degradationConflicts with electrical specifications

Using this table, first look at the last column. Lubricants are different from other additives; their problems are mostly not that they 'spoil themselves,' but that they 'mess up others' work.'

5. Four types of failures all originate from the lubrication system

Failure 1: Surface frosting.

Most people's first reaction is 'the material was mixed with recycled material' or 'the substrate is unstable', but in fact, frosting is a typical manifestation of external lubrication being expelled outward.

The method of judgment is very straightforward: wipe it once, wait a few days, and then check. If the white frost comes back, it’s migration, not dirt.

The solution is to reduce external lubrication, replace part of it with internal lubrication or low-migration types, rather than changing the base material.

Failure 2: The weld line strength dropped, and the part shows white marks with just one bend.

The root cause is on the interface. The external lubricant forms a layer on the surface of the melt, which happens to cover the weld line and the welding surface.

After leveling the lubrication system for this type of component, its strength can quickly recover.

Failure three: Poor dispersion of fiberglass, rough surface, uneven performance.

Many people's first reaction is that the coupling agent is insufficient or the glass fiber quality is poor, but actually, you should first check if there is enough internal lubricant.

When internal lubrication is insufficient, the shear is too great, and the glass fibers are excessively broken; when internal lubrication is excessive, the viscosity is too low, the shear is insufficient, and the glass fiber bundles cannot open.

Problems can occur at both ends, so this item can only be determined based on trial mold data, not added based on experience.

Failure 4: Smoke appears as soon as the processing temperature rises, and the mold gate accumulates serious residue.

The root cause is that the lubricant's temperature tolerance limit was exceeded. These types generally have a low melting point, and prolonged exposure to high temperatures can cause them to decompose or evaporate.

The solution is to bring the material barrel temperature back within the window, or switch to a higher temperature-resistant setting.

There is one thing I want to make clear: difficulty in demolding does not necessarily mean insufficient lubrication.

Low mold temperature, insufficient draft angle, and excessive holding pressure can all cause demolding difficulties. In these three cases, adding a lubricant is equivalent to using an additive to make up for deficiencies in the mold and process.

Being able to get a good patch is luck, while getting a frost spray is normal.

6. Methods of adding: dispersion, temperature resistance, and order of feeding

The effectiveness of a lubricant is half in choosing the type and half in how it is applied.

Dispersed. The melting points of this type of variety are generally low, making them prone to clumping when mixed. The consequence of clumping is local overdosing, and the consequence of local overdosing is frosting.

It is recommended to first do a high-speed premix with the resin, or make it into a pre-dispersed masterbatch.

Maximum temperature resistance. Try to keep the processing temperature close to the lower limit of the window, and don't keep increasing it just for flowability. The portion of the lubricant that is lost in the barrel cannot be seen on the part, but the welding strength will keep track of it for you.

Masterbatching. Using low-melting-point components to make masterbatches is more stable and can also reduce dust and loss.

The general order of feeding is as follows: resin drying → high-speed premixing of main antioxidant with resin → other functional additives → lubrication system added in the later stage → glass fiber fed from the side port.

Why is the lubrication system placed in the later stage? Because it forms a surface film, if added too early, the film will first coat the resin and fibers, blocking the necessary dispersion and shearing.

Glass fibers are added from the side feed port to prevent the additives from being absorbed by the fiber surface first.

Storage. Soaps are hygroscopic and prone to caking, so sealing, keeping dry, and following the first-in, first-out principle should be included in the warehouse regulations.

Our approach is to record these few items on a single ingredient operation card; whoever prepares the ingredients signs it, so if there is frosting, we can trace it back to which batch it came from.

7. What happens if you add it incorrectly, and when you shouldn't add it

This part is the one people most want to remember in the additive line.

Excess leads to ineffectiveness. This sentence means that when it comes to lubricants, all four lines have problems at the same time.

The first is frosting. The second is a decrease in welding strength. The third is a decrease in the adhesion of painting and printing. The fourth is over-demolding—part dimensions drift, there are more flashings, and sometimes the part deforms directly when ejected.

There is also a hidden cost: when the lubricant migrates outward, it carries some other components with it, making the surface condition uncontrollable.

When shouldn't [it] be added?

First, the parts need ultrasonic welding or laser welding, and the welding strength is the main criterion. The total amount of external lubrication on these parts must be controlled; it cannot be released just to make demolding easier.

Secondly, the parts need to be painted, printed, or undergo surface treatment afterwards. It is an industry consensus that the migration of silicone affects the spraying line, so when selecting these parts, the subsequent processes should be clarified in advance.

Third, high-voltage electrical components. Metal soaps need to be assessed separately in terms of electrical performance and cannot be selected according to the standard for general components.

Fourth, it involves items that come into contact with food or medical devices. Additives cannot generate their own safety conclusions; they must be verified against the relevant regulatory context, such as national standards for food contact and the biological evaluation requirements for medical devices.

A final note: additives are one of the variables, not the solution. The direction of this route is to improve flow and demolding; whether it works depends on the results verified by your parts.

8. How to account for this lubricant expense

According to the common calculation method for modified plastics, the total cost of additives accounts for about one to five percent of the cost per ton.

Lubricants are usually one of the lower-priced categories here, and the reference price in 2026 will fluctuate with the market. The specific price is subject to the inquiry on the day.

Precisely because it is cheap, it is most easily treated as the 'just add a little' item, and it is also the most likely to cause problems.

Looking at it from another perspective: a batch of items may be judged visually defective due to frosting, or the entire batch may be reworked because the welding strength is insufficient, resulting in losses in material costs, processing fees, shipping costs, and customer trust.

These two accounts are not on the same scale. Therefore, for the lubricant item, it is worth spending an extra two hours during the formulation stage to balance the inside and outside.

The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the materials and auxiliaries are prepared together at once.

Several frequently asked questions

Question: For internal lubrication and external lubrication, is it possible to use only one type?

Answer: Yes, but it depends on which end you are lacking. If you only supplement one end, the problem at the other end will surface; balancing is the norm.

Question: Can the sprayed parts be washed and then reused?

Answer: You can wash off the surface layer, but there is still material inside, and it will come back after a few days. Also, the surface condition of washed parts has already changed.

Question: If demolding is difficult, should I just add a lubricant?

Answer: First check mold temperature, demold angle, and holding pressure. If any of these three are off, adding lubricant is just using an additive to compensate for process issues.

Question: How to achieve batch consistency?

Answer: For key grades, keep samples of every batch, conduct spray tests, melt flow index, and mechanical testing, and issue reports for each batch. Any drift in any item will put the whole batch on hold.

What we deliver is not just a bag of material — the earlier you inquire about material selection, the easier it is.

The lubrication system should be matched according to the part's molding method and subsequent processes, not by "adding more to be safer."

The formulation and validation of these parts can be discussed together.

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