Materials FAQs

What is the difference between PVC-C and PVC-U?

PVC-C (chlorinated PVC) and PVC-U (unplasticized PVC) differ mainly in their chemical composition, temperature resistance and areas of application. Here is an overview of the most important differences:

1. Chemical composition

PVC-C: This is PVC that has been modified by chlorination. This additional chlorination significantly improves the properties of the material.
PVC-U: PVC-U is unmodified, pure PVC without plasticizers or additional chlorine components.

2. Temperature resistance

PVC-C: Can withstand temperatures up to 95-100 °C , making it ideal for applications where higher temperatures occur, such as hot water piping.
PVC-U: Is temperature-resistant up to about 60 °C and is particularly suitable for applications where high temperatures are not expected.

3. Mechanical properties

PVC-C: Chlorination makes PVC-C stiffer and more resistant, especially at higher temperatures. Impact resistance is also improved.
PVC-U: PVC-U is also stable and durable, but becomes brittle more quickly at low temperatures and is less impact resistant.

4. Chemical resistance

PVC-C: Offers excellent resistance to corrosive substances and aggressive chemicals. It is therefore ideal for demanding industrial environments.
PVC-U: Is also chemically resistant, but less suitable for extreme chemical stress.

5. Areas of application

PVC-C: Is mainly used in areas that require high temperature or chemical resistance , e.g. in the chemical industry, in hot water pipes or in wastewater technology.
PVC-U: Used in standard applications such as drinking water pipes, sewage pipes or in construction.

6th prize

PVC-C: Due to its improved properties, PVC-C is more expensive than PVC-U.
PVC-U: Is more cost-effective and therefore ideal for applications where there are no special material requirements.
 

Advantages at a glance:
PVC-C is particularly suitable for demanding applications with high temperatures or aggressive chemicals.
PVC-U is the cost-effective choice for standard applications in the construction industry and for normal temperature loads.

What is EPDM?

EPDM  is a material whose short form stands for "ethylene-propylene-diene; M-group". A so-called synthetic rubber with a saturated main chain. Chemically speaking, its production involves a copolymerization of ethylene and propylene, and the addition of a third monomer (diene) creates EPDM. A distinction is made between sulfur-or peroxide-crosslinked EPDM . The latter has both an improved  compression set and a higher heat resistance.

What is the difference between EPDM and EPDM Krevolan®?

EPDM is the international abbreviation for the UV and weather-resistant ethylene-propylene-diene rubber , which can be obtained from compounders and semi-finished product suppliers as a processable compound for the manufacture of O-rings , molded parts , profiles or as sheet and roll goods for the manufacture of stamped parts and water jet cut seals . The recipes are as varied as the requirements to be met by the automotive industry, the electrical industry, the manufacturers of white goods, medical technology, the food industry or the fittings industry.

EPDM Krevolan® is a private label from KREMER and is also an ethylene-propylene-diene rubber with its typical material properties of UV and weather resistance for the production of extruded profiles for the door, window and facade construction , container and greenhouse construction sectors. The dedicated focus on these few sectors led to a concentration of tried and tested recipes and compounds, so that it seemed possible to offer a clear product line of EPDM types under the private label Krevolan®.

What properties do EPDM O-rings have?

EPDM O-rings are very flexible and are characterized by very good  ageing resistance,  even  when exposed to UV and ozone. This makes the material ideal for outdoor use. EPDM is also resistant to oxygen, hot water and hot air (up to approx. 150°C) and hot steam up to approx. 200°C, but above all to a wide range of chemicals, including:

• diluted acids
• alcohols, ketones and esters
• glycol-based brake fluids
• detergent
• Skydrol
• silicone oils and greases

You can find more information about the chemical resistance of our materials here. EPDM also has a wide temperature range.  However, EPDM is not resistant  to  mineral oil products . In addition, the material is very difficult to bond to other components due to its molecular structure.

Where is EPDM used?

The properties of the material make EPDM ideal for use in conjunction with food ,  hot water  and  hot air up to 150°C . And not just as O-rings, but also as  profiles  or  EPDM seals ,  e.g. for washing machines or dishwashers. EPDM is often used in conjunction with food (approvals according to FDA, KTW or WRC) and in pneumatics. In the automotive industry, EPDM is the most commonly used sealing material in terms of quantity. The material is also ideal for the manufacture of construction profiles, films and seals in facade construction and in the consumer goods industry.

What is NBR?

NBR - the English abbreviation stands for "Nitrile Butadiene Rubber" - is also known as acrylonitrile butadiene rubber or under the trade name Perbunan®. It is one of the classic elastomers. As a sealing material, the material is mainly used in applications where resistance to  oils, greases and fuels  is required. This is where NBR can show its advantages - it should not be exposed to the effects of weather and ozone.

What are the properties of NBR?

In addition to their high abrasion resistance and their high tensile and tear strength , O-rings made of NBR are characterized by a low compression set.
But NBR can do even more. It is resistant to:

• hydraulic oils
• mineral oils
• mineral oil products
• petrol
• vegetable and animal oils and fats
• oil-in-water emulsions
• flame-retardant oil-in-water emulsions (HFA fluid)
• water-in-oil emulsions (HFB fluid)
• Dissolution of polymers in water (HFC liquid), animal and vegetable oils and water glycolsThe low temperature behavior (depending on the mixture down to -50°C) is sufficiently good. More flexibility  at lower temperatures is achieved if the acrylonitrile content (ACN)  in the NBR mixture  is lower  . However, this comes at the expense of resistance to oils and fuels.

However, it improves with increasing ACN content, although the material loses flexibility at low temperatures. NBR is also  impermeable to gases and air , which is why the material is often used to make hoses. Because the material hardly builds up any electrostatic charge , tank or petrol hoses are often made from NBR.

The material is not resistant to glycol-based brake fluids, flame-retardant pressure fluids, chlorinated hydrocarbons, polar solvents, UV radiation and ozone.

If O-rings made of NBR  are stretched , the material becomes significantly more sensitive to ozone and light cracking.  There are various solutions to this challenge: One is to simply change the O-ring material and  use O-rings made of EPDM or  FKM O-rings. If the NBR material is retained, the O-rings should  be stored in accordance with DIN 7716  and protected from light and ozone immediately after installation. There are also  NBR types that are treated with ozone protection waxes. This additional processing comes at a price. O-rings made of H-NBR,  on the other hand, can be an interesting alternative to their NBR counterparts.

What are the properties of H-NBR?

H-NBR  is characterized by its resistance to mineral oils, ozone and acidic gases.  Above all, the material can withstand  higher temperatures  (approx. +150°C) than NBR (up to +110°C) and is resistant to the effects of ozone or UV radiation.

What is silicone?

Silicone is a group of synthetic polymers. The scientific term for this material is poly(organo)siloxanes, or siloxanes for short. Silicone can take on a liquid, semi-liquid or solid form. Due to their material properties, silicone rubbers and silicone elastomers are in demand in numerous areas of application as materials for O-rings , seals , molded parts or profiles .

What is soft PVC or plastisol?

Soft PVC - also called plastisol or PVC-plastisol - is a widely used thermoplastic polymer material. It is also known as "polyvinyl chloride with plasticizer" or PVC-P. The abbreviation P stands for "plasticized" and describes a plasticized material. PVC-U (U for "unplasticized"), i.e. hard PVC, is the counterpart to this. The plasticizer content in soft PVC ranges from 20 to 50 percent. PVC itself consists of 57 percent of the salt component chlorine, the remaining 43 percent is made up of carbon and hydrogen from petroleum products.

The term "plastisol" is used for both the uncured mixture and the end product. It also refers to the dispersion of powdered PVC resin in a plasticizer liquid. Pigments and fillers such as chalk and stabilizers are added to this, which can be used to specifically influence the properties of the material in terms of color, structure, strength and flexibility. Stabilizers increase the thermal stability and resistance to UV and thermal radiation. In the past, heavy metals such as cadmium and lead or organotin compounds were also used. However, for reasons of environmental compatibility and the EU REACH regulation, they have mostly been replaced by organic calcium-based additives.

The areas of application of soft PVC are very diverse and range from the production of films, linings, cover caps,  PVC round caps with pull-off tabs , covers, sheathing, bellows or hoses to the plastisol coating or  PVC dip coating of metal objects , for example handles, latches, hinges and many other metallic surfaces.

What properties does soft PVC have?

During the manufacture of plastisol, the individual components of the respective recipe - i.e. plasticizers, PVC particles, fillers, stabilizers, etc. - must be precisely matched to one another in type and proportion depending on the desired properties and intended use of the soft PVC products. Plasticizers reduce the intermolecular forces between the polymer chains, so that a soft and flexible plastic is produced. Untempered plastisol, on the other hand, is a liquid paste at room temperature that can be poured, sprayed and spread. Only after heating - usually at around 160-180 °C - does it harden into a tough, elastic plastic. With a density of (depending on the composition) around 1.2-1.35 g/cm³, soft PVC is a relatively heavy material.

Many of the material's properties are greatly influenced by the type and proportion of plasticizers and fillers. This starts with the consistency - there are easy-flowing mixtures with a hardness of 50 Shore A, as well as material settings of 85 Shore A, which are more viscous. PVC plastisol is generally flame-retardant and extinguishes when the flame is removed. The material PVC is fundamentally flame-retardant due to its halogen component chlorine (Cl).

However, depending on the type and proportion of plasticizer, both the flammability of the material and the substances that are released change. The strength and hardness of soft PVC also decreases significantly as the temperature rises. It can be used for low loads up to around +60°C, and in mixtures with special plasticizers it can sometimes be used up to around +105°C. Special applications require the use of materials with higher temperature resistance. Such PVC immersion parts made of HT materials can withstand a temperature of +225°C for a load duration of 30 minutes. Depending on the proportion of plasticizer, the material begins to become brittle in the range between -10°C and -50°C.

In contrast to rubber, PVC-U and PVC-P are very resistant to aging, as their molecules do not contain double bonds and therefore do not offer any surface for atmospheric oxygen or ozone to attack. Soft PVC is also very slip-resistant and resistant to light and weather. Depending on the material setting, water absorption is relatively low and is between 0.1 and around 1% after prolonged water storage. The light, weather and aging resistance can be further optimized by suitable coloring. For example, black coloring with soot leads to greater UV resistance, but the heat aging resistance decreases.

As far as the mechanical properties of the material are concerned, soft PVC is very tough and resistant to stretch cracks. While the material has good abrasion resistance, its tear resistance is comparatively low. However, stress cracks are not to be feared thanks to the high deformability. Nevertheless, the material can become brittle if the plasticizer sweats out - for example when it comes into contact with organic solvents and aqueous solutions. Soft PVC also has a high damping capacity, which is why it is very good at absorbing shocks and vibrations due to the associated recovery.

The electrical insulating properties of soft PVC are good, but worse than those of hard PVC. The surface resistance of the material is in the medium range, as is the dielectric strength. With special material settings, such as Krevosol ®  3842, the electrical surface resistance can be reduced from 10^12 ohms to 10^7 ohms for ESD applications. The dielectric losses are generally high in soft PVC, but it has a low tendency to become electrostatically charged. The dielectric strength of cured plastisols is around 15-25 kV/mm material thickness.

If you look at the chemical resistance, this is also lower for soft PVC than for unplasticized PVC. The material is resistant to corrosive salt solutions and medium-concentrated inorganic acids, but only to a limited extent to alkalis. This also applies to petrol, oils and fats, which can cause the material to lose plasticizer if they come into contact for a long time. Therefore, with products such as caps and molded parts or injection molded parts made of soft PVC or parts coated with it, care should be taken to ensure that during assembly or use these only come into contact with surfaces where there is no risk of plasticizer migration, as the plasticizer molecules are not chemically bound to the material.

Accordingly, according to the Food Act, only certain types of plasticizer with a higher boiling point are permitted for contact with food, children's toys and clothing. Special types of soft PVC such as Krevosol ®  are ideal for sheathing and coating as well as for the production of customized dipped parts, for example for therapeutic devices and hospital accessories, but also for children's toys and other applications in which phthalate-free products are required. In addition, Krevosol ®  1649, for example, has very good resistance to disinfectants, which is particularly relevant for use in the medical and therapeutic field. Other types of Krevosol, on the other hand, have a higher ozone or UV resistance or are tailored to ESD applications. Last but not least, dipped parts made of soft PVC are also visually aesthetic, as they have a glossy surface, no weld lines and can be produced in many different colors, signal colors and even luminescent colors.

What advantages does soft PVC offer as a material?

Viewed holistically, soft PVC is an interesting material, particularly from an economic and practical perspective. Compared to materials such as glass, metal and ceramics, it can be processed at low temperatures, which means that the energy consumption is relatively low. Products such as PVC dipped parts, but also coatings on metal parts, can be implemented and adapted to the desired properties with relatively little time and financial expenditure. Given its durability, soft PVC is a very economical material over its entire life cycle.

This applies, for example, to floor coverings, underground and outdoor cables, wallpaper or sealing membranes, which, thanks to their ease of care and robustness, also have lower operating costs than other materials. In addition, soft PVC is very easy and uncomplicated to handle and the amount of work involved in handling the material is reduced to a minimum: for example, lining films, floor coverings, stretch ceilings or protective films can be attached and laid quickly and do not require any complex post-treatment.

What are plasticizers in soft PVC?

In general, plasticizers are used to give plastics softness, flexibility, suppleness and elasticity. Without plasticizers, soft PVC would not be soft, but hard and brittle. Plasticizers are also supposed to have other properties that affect the material, such as light, temperature and moisture resistance or flame retardancy. If the plasticizer escapes, the material shrinks and becomes brittle, hard and, in some cases, cracked. If the material containing the plasticizer comes into contact with a neighboring material, the plasticizer can migrate into the other material. This can make it sticky and discolor.

However, there is no such thing as a single  plasticizer. In fact, there are a large number of plasticizers that differ from one another in many ways and are therefore assessed differently by the authorities. The most commonly used plasticizer is diisononyl phthalate, or DINP for short, and is considered to be of no concern by experts in all EU member states.

A distinction is made between low molecular weight and high molecular weight plasticizers. The former include BBP, DBP, DEHP and DIBP. High molecular weight plasticizers include DIDP, DINP and DPHP, as well as specialty plasticizers, adipates, polymer plasticizers based on adipic acid, terephthalates and other plasticizers outside the phthalate group of substances. Today, high molecular weight plasticizers are predominantly used. Plasticizers are often the subject of discussions regarding health risks, and the focus is often on their phthalate content. However, a distinction must be made here: whether a health risk is possible depends primarily on whether the substance is able to escape from the product and enter the body - less on the concentration of the substance in a product. However, limit values ​​and restrictions keep the maximum permitted proportion of phthalate plasticizers within limits.

The addition and admixture of some phthalates, e.g. BBP, DBP and DEHP, is generally prohibited in cosmetics, food packaging, toys, baby bottles and other baby products. Soft PVC materials such as Krevosol ®  1649 or Krevosol ®  3069 are phthalate-free and suitable for the manufacture of immersion parts for therapeutic devices, hospital accessories, children's toys and phthalate-free, biocompatible products. In addition, both types of soft PVC are resistant to disinfectants, which is particularly important in the medical and therapeutic fields.

How is soft PVC or plastisol produced?

Pure PVC is very hard and brittle - the material begins to decompose even before it reaches its melting temperature. To obtain soft PVC, stabilizers, plasticizers, lubricants and pigments are added to the PVC powder, which can be used to adjust the desired properties. The PVC powder can then be broken down through the subsequent gelling process - an intensive dissolving and swelling process. Gelling essentially consists of the following steps:

• Mixing of PVC powder and plasticizer
• swelling
• thickening
• pre-gelation
• gelling

At room temperature, untempered plastisol is a liquid paste that can be poured, sprayed and spread and, depending on its composition, can be stored for weeks or months without gelling. In the first step, the PVC powder is mixed with the plasticizer liquid. This untempered paste matures at a maximum of 40 °C, during which the swelling process begins: the plasticizer penetrates and the PVC dissolves slightly in the plasticizer. If the paste is now heated to 60 °C, it thickens - from around 100 to 120 °C, the PVC particles dissolve while the viscosity of the paste increases sharply. At temperatures of 160 to 180 °C, PVC and plasticizer are finally homogeneously mixed, creating a permanently tough, elastic material. This gelling process is irreversible.

How are soft PVC products manufactured?

Among the products made from soft PVC, we will use protective caps as an example in this case to roughly describe the production of soft PVC products. Such protective caps, whether as PVC round caps or rectangular caps , are also called dip caps - and this already indicates the manufacturing process: the dip process. In this process, shaping mandrels made of steel or aluminum are dipped into liquid PVC plastisol. The advantage of the dip molding process is clearly the comparatively simple principle, which is somewhat reminiscent of the production of candles and also enables a seamless and visually appealing product.

To do this, the mandrels are first preheated to a certain temperature - the coordinated combination of mandrel temperature and immersion time affects the wall thickness of the immersion caps. Therefore, depending on the shape of the mandrel and the cap to be produced, it may be necessary to adjust the immersion speed during immersion in order to achieve the most uniform result possible. The mandrels are then immersed in the liquid soft PVC. As this is very sensitive to temperature, it adheres to the hot surface of the immersed mandrels. Once the mandrels have been removed from the plastisol immersion bath together with the adhering PVC layer after the specified immersion time, the next step is to heat them up in special ovens. This hardens the PVC layer.

After cooling in a water bath, the soft PVC caps are removed from the mandrels. For more complex shapes, such as bellows, the presence of residual heat is an advantage, as this makes removal easier. This way, a product is obtained that has the exact shape of the mandrel on the inside. PVC dip coating or the coating of metal parts is also carried out according to this principle, but without the final step of forming. PVC coating can be necessary, for example, if soft PVC round or rectangular caps cannot be mounted (captive) due to the geometry of the part to be protected. But PVC dip coating is also a tried and tested method for the general protection of surfaces, such as latches, levers, handles, baskets and many other parts.

For certain applications, it may also be useful to apply two soft PVC layers, which can differ in terms of hardness, electrical conductivity and color. If the first plastisol layer applied to the component becomes visible due to wear, this signals that this component must now be replaced with a new one.

What are the advantages of producing PVC parts using the dipping process?

The dipping process is a cost-effective alternative to injection molding, especially for the production of dipped parts in small and medium batch sizes - both for geometrically simple dipped caps and more complex dipped parts. This also applies in particular to the tool costs, which represent only a fraction of injection molding tools. This means that prototypes can also be produced at comparatively low cost. Another advantage is of course the flexibility of the relatively simple process, which offers both rapid replenishment and a wide range of options in terms of shapes and colors. Subsequent adjustments to protective caps, for example in the first production phase of a new product, can be implemented more quickly and more cost-effectively than with injection molding.

Diving caps and other products made of soft PVC, as well as components coated with it, are extremely durable, have versatile material properties and therefore have a long service life, which also has a positive effect on production costs. Since dipped parts and dipped coatings made of plastisol have no seams, they are also an excellent choice in terms of appearance. In addition, both small PVC caps in the millimeter range and - assuming a lot of know-how and sensitivity - diving caps over 1.50 meters long can be produced.

What should be considered when dipping PVC?

There are many typical applications for PVC dip coatings: levers, hooks, pipe clamps, handles, wall hooks or baskets in electroplating. In general, PVC coating is possible for components and products of almost all sizes. Since the object to be coated - just like the mandrel for making PVC dip caps - has to be heated before being immersed in the plastisol bath, it should be ensured that it can be exposed to the necessary pre-heating and heating temperatures without any problems. If thicker-walled coatings of significantly more than two or three millimeters are required, the part to be coated must also be heated more strongly. However, it must also have the necessary heat storage capacity to achieve a satisfactory coating result.

The part made of metal, glass or plastic made of high temperature resistant plastic types such as PEEK must be able to withstand a heating phase of several minutes during the coating process without affecting or changing the shape, appearance and mechanical properties. To ensure that the coating bonds inseparably to the part, it can also be treated with a primer. This ensures that only mechanical or thermal overload can destroy the coating. In general, the tolerances in terms of wall thickness and immersion depth depend heavily on the geometry of the part to be coated. Therefore, the dimensional tolerances can only be determined after a test coating.

What are the advantages of PVC dip coating?

Dip coating with soft PVC offers advantages such as the high coefficient of sliding friction of the surface and the easy and quick cleaning of smooth, glossy coatings. However, a skin-friendly, matt surface with a pearl structure can also be achieved. Coated parts and surfaces are protected from dirt and corrosion as well as the effects of chemicals and other substances. In addition, the PVC coating offers protection against scratches or other damage when subjected to mechanical stress and also eliminates potential sources of danger such as sharp edges.

The surface is electrically insulating and, with a surface resistance of 10^7 ohms, ESD-capable for packaging or transporting electrical equipment. Movable parts such as bellows also gain more flexibility thanks to a PVC type with a lower hardness. The safety factor can also come into play: parts coated with signal colors are easier to see. For greater safety in the dark, luminescent PVC coatings and caps are recommended. This is made possible by a color pigment that makes coated or coated parts such as door handles or levers appear milky white in daylight, absorbs the energy of the light and makes the coating glow green in the event of sudden darkness - for example in the event of a power failure. The color pigment can be mixed into phthalate-free material types such as Krevosol ®  1649, but is not compatible with ESD applications because black color is required to achieve the necessary electrical surface resistance.

Where is soft PVC used?

Thanks to its excellent material properties, soft PVC is used in many different industries and areas, in every conceivable form. Cables and wires with sheathing and insulation made of soft PVC form the largest product group. In the automotive sector, for example, such cable sets must withstand high mechanical loads and at the same time ensure that complex processes function in a very small space. Soft PVC-sheathed or insulated cables can also be found in energy supplies, in communications, in the industrial sector for function control or as special cables in chemical plants. Shrink tubing and insulating tape are also used in the electrical engineering sector.

In the construction industry, soft PVC is in demand as floor covering, wire sheathing, roof or building protection film, as edge strips, in stretch ceilings, for coating door handles and also as window or door seals. In agriculture, it is mostly found in the form of hoses or silo and cover films. Furthermore, artificial leather covers, decorative films for surface finishing or decorative profiles made of soft PVC are also used in the furniture industry. Plastisol is also very suitable for linings and coatings, for example to protect tool handles and other metal parts from damage or corrosion.

Transparent designs, such as display covers or hoses in food technology, can be produced, as can products and coatings with a pearl structure look. The latter gives them a more grippy surface and improves the visual appearance. Protective caps made of soft PVC protect the parts and surfaces underneath from dirt, corrosion or damage and insulate them electrically.

In the medical and medical technology sector, soft PVC is used in the form of disposable gloves, tubes or flexible containers such as easily sterilizable infusion, dialysis and blood bags. Other application and product examples range from conveyor belts, transport containers, shoe soles, curtains, swing and pendulum doors to suction cups, panels, damping elements or as underbody protection in automobile construction.

PVC dipped parts as paint protection also represent an interesting alternative to masking with adhesive tape in terms of time and cost. This is particularly the case with more complicated geometries of the object to be protected. A paint protection as a PVC dipped part fits precisely on the part to be protected and fully fulfills its protective function - also against damage and dirt. It can be easily removed or reapplied and reused, so that less waste is generated overall.