PVC Resin SG-3 (K 71-72): Specification and Applications
SG-3 is the highest molecular weight grade we supply, and it is bought by one kind of customer: the one making soft or flexible products. Cable compound, film, artificial leather, hose, footwear, foam. If your formulation carries a large plasticiser load, SG-3 is built to hold it.
We ship SG-3 as a first-tier distributor out of Shandong, China. We do not polymerise it. The batch certificate is issued by the producing plant, and we obtain it for you.
Quick answer: SG-3 is defined by GB/T 5761-2018 as a viscosity number band of 127–135 mL/g, which is the same thing as a K value of 71–72 and an average degree of polymerisation of 1251–1370. Its defining property for buying purposes is plasticiser absorption of at least 26 g per 100 g, more than any other grade in the range. It goes into cable insulation and sheathing, film, artificial leather, hose, footwear and foam.
1. What SG-3 actually is
SG-3 is the top of the molecular weight ladder in the grades we hold. Long chains buy you flexibility and toughness, and they cost you flow.
The three expressions of the band, all from the same measurement:
- Viscosity number: the standard defines SG-3 as 127–135 mL/g.
- K value: 71–72. Buyers outside China usually write K71 or K70.
- Average degree of polymerisation: 1251–1370.
What actually decides whether SG-3 works on your line is not the K value alone. It is how much plasticiser the powder will take up, and how long it takes to fuse. SG-3 has the highest porosity in the range, which is why its plasticiser absorption requirement, at least 26 g per 100 g, is the highest of the four grades we supply. A formulation with 60 phr plasticiser is normal on SG-3 and unworkable on SG-7. The powder simply cannot absorb that much oil and stay dry and free-flowing.
The trade-off is real and worth planning for. High molecular weight means higher melt viscosity and higher fusion torque. Expect to run more stabiliser and lubricant than a rigid-product formulation, and expect a narrower processing window: SG-3 tolerates less abuse on temperature than a low-K grade does. Overshoot the temperature and you will see it in colour before you see it in the physicals.
2. Specification
Values below are the requirement figures for the SG-3 band under GB/T 5761-2018.
| Property | SG-3 requirement |
|---|---|
| K value | 71 – 72 |
| Viscosity number (mL/g) | 127 – 135 |
| Average degree of polymerisation | 1251 – 1370 |
| Impurity particles (per 100 g) | ≤ 16 |
| Volatile matter incl. water (%) | ≤ 0.30 |
| Apparent density (g/mL) | ≥ 0.45 |
| Sieve residue, 0.25 mm (%) | ≤ 1.6 |
| Sieve pass, 0.063 mm (%) | ≥ 97 |
| Fish eyes (per 400 cm²) | ≤ 20 |
| Plasticiser absorption (g per 100 g) | ≥ 26 |
| VCM residue (ppm) | ≤ 5 |
| Whiteness, 160 °C / 10 min (%) | ≥ 78 |
Three notes on reading this table.
These figures define the SG-3 band under GB/T 5761-2018. Every conforming batch has to sit inside them. What an individual lot actually measured is on that lot's certificate. Your incoming inspection compares the measured figure against your own acceptance range, not against these boundary values.
The volatile matter limit is tighter than on SG-5. ≤ 0.30 % against ≤ 0.40 %. On a flexible formulation this matters more than it looks: retained moisture and volatiles show up as bubbles and silver streaking in a thick extruded section, and they are difficult to blame on anything else once the compound is made.
Batch COA comes from the producing plant. Tell us at enquiry stage and we will obtain the certificate for the lot we are offering and send it to you before you commit. We do not issue certificates ourselves.
Standards note: GB/T 5761-2018 remains in force. The official record shows it was reviewed on 1 July 2025 with a conclusion of continuing validity. The designation and test-method standards GB/T 3402.1-2026 and GB/T 3402.2-2026 take effect on 1 February 2027 in place of the 2005 and 2010 editions, which changes the test methods written on a certificate. We wrote up what a buyer should now check.
3. Where SG-3 goes, and how it is processed
| Process | Typical end products | Why SG-3 suits it |
|---|---|---|
| Cable extrusion | Insulation and sheathing for wire and cable | Long chains give the flexibility and ageing performance a plasticised insulation compound needs |
| Calendering | Flexible film, artificial leather, coated fabric | High plasticiser uptake lets a heavily plasticised formulation stay dry and processable |
| Extrusion: profile and tube | Soft hose, garden hose, gaskets, seals | Flexibility in the finished part without resorting to an unworkable plasticiser load |
| Injection and moulding | Footwear, soles, technical mouldings | Toughness and low-temperature flexibility in the finished article |
| Foam and expansion | Foamed sheet and board | Melt strength holds the cell structure during expansion |
One point that comes up on almost every switch of source: SG-3 is bought for a behaviour. If a supplier offers you a resin whose K value sits at the top of SG-5 and calls it "equivalent to SG-3 for soft products", the plasticiser absorption figure is what settles the argument. Ask for it.
4. Naming it correctly on a purchase order
| What goes on the document | What it means | Note |
|---|---|---|
| SG-3 | The GB/T 5761-2018 grade | The designation we quote and ship under |
| K 71 – 72 / K71 | The same band, expressed as K value | Conservative buyers write the full band |
| Viscosity number 127–135 mL/g | The same band, expressed directly | Best form when the contract has an acceptance clause |
| Soft product grade / 软制品 | Trade shorthand | Not a specification on its own |
| SG-3 + plasticiser absorption minimum + standard edition | A complete order line | What we recommend for flexible formulations |
For a soft-product line, we would add one more field to the order line than a rigid-product buyer needs: the plasticiser absorption minimum. It is the property your formulation actually depends on.
5. Packaging, marking and documents
| Item | Detail | Who provides it |
|---|---|---|
| Standard packing | 25 kg PP woven or kraft paper bags with inner liner | Us |
| Bulk packing | 800 kg jumbo bags, or palletised, on request | Us |
| Private label | Your own bag design for volume orders | Us, on request |
| Batch certificate | Certificate of Analysis for the specific lot | The producing plant, obtained by us on request |
| Trade documents | Commercial invoice, packing list, bill of lading | Us and the carrier |
| Origin and preference documents | Certificate of Origin, Form E and similar | Issued on request, lead time applies |
| Third-party inspection | Arranged at loading, buyer-nominated agency welcome | Coordinates with your inspector |
The inner liner is not cosmetic on this grade. SG-3 with a heavy plasticiser load is more sensitive to what it picks up in transit than a rigid grade, and a torn liner is the first thing to look for when you open a container. How to read the markings on a PVC resin bag covers the fields your own incoming sheet should be recording.
6. What to send us for a firm offer
- Grade and position in the band: SG-3, plus a viscosity number or K value target.
- End product and process: cable, film, leather, hose, footwear; extrusion, calendering or moulding.
- Plasticiser load: phr or percentage in your formulation. This is the number that decides whether SG-3 is right.
- Quantity: first order and expected monthly volume. FCL and LCL are both workable.
- Packaging: 25 kg bags, jumbo bags, palletised, or private label.
- Discharge port: name it and we will quote FOB, CFR or CIF against it.
- Documents you need: Certificate of Origin, Form E, third-party inspection at loading.
- Payment terms: so we can show you the total cost of the order.
7. Frequently asked
What is the difference between SG-3 and SG-5? SG-3 is higher in molecular weight (K 71–72 against K 66–68) and has a much higher plasticiser absorption requirement, at least 26 g per 100 g against at least 19. SG-3 is for flexible, plasticiser-rich products; SG-5 is for rigid pipe, profile and sheet. The full comparison across all four grades is here.
Why does the volatile matter limit matter so much on this grade? Because you are extruding thicker, softer sections with a high plasticiser load. Moisture and volatiles that would vent harmlessly from a thin rigid profile show up as bubbles and surface streaking in a soft compound, and once the compound is made it is hard to attribute the fault.
Can I get the COA before I place the order? Yes. Tell us the quantity you are considering and we will obtain the certificate for the lot we are offering from the producing plant and send it for review. If the measured plasticiser absorption or viscosity number does not sit inside your acceptance range, you have spent nothing.
Do you supply in jumbo bags, or with our own bag design? Both are possible. 800 kg jumbo bags and palletised loading on request; private-label bag printing for volume orders. Send the artwork and we will confirm against the quantity.
What does the price depend on? The feedstock route the lot came from, volume and packaging, delivery basis, payment terms, and timing. PVC quotes hold for a shorter window than most plastics. Give us the parameters above and we will put a dated offer in front of you.
Get a firm offer for this grade
Send the end product, the position in the band you need, the quantity and the discharge port. We will come back with a dated offer and the COA for the lot we are offering.