Lightweight gypsum board
A lightweight wallboard whose second-largest ingredient is expanded perlite, glued to the gypsum matrix by starch — an alternative route to lower board weight that does not rely on foam alone.
- Assignee
- United States Gypsum Co
- Inventors
- Mirza A. Baig
- Jurisdiction
- United States (USPTO)
- Filed
- 1996-09-16
- Published
- 1999-07-13
- Priority
- 1996-09-16
Before the aggressive foam-void architectures of the 2000s, the classical way to bring board weight down was to displace gypsum with a lower-density mineral filler. Perlite is the obvious candidate: it is cheap, chemically inert to calcium sulphate hydration, and available at bulk densities of a few pcf.
The engineering problem with any filler in a gypsum core is bonding. Gypsum crystals grow into an interlocking network during set; a large fraction of an inert, low-density particle interrupts that network and drops nail-pull. This patent solves that with a starch bridge.
- 01Gypsum is kept as the largest single ingredient by dry weight (≥ 50 %), so the crystal network still dominates.
- 02Perlite is added as the second-largest ingredient (< 50 %), sized around a bulk density of roughly 3 – 3.5 pcf so its own porosity contributes to the board density drop.
- 03Starch — the patent notes it can be pre-cooked before mixing — disperses throughout the core and acts as a binder between the gypsum crystals and the perlite grains, recovering the mechanical anchorage that the inert filler would otherwise break.
- 04Fibres in the 0.5 – 5.6 % range provide additional reinforcement across the interfaces.
| Parameter | Value | Source |
|---|---|---|
| Gypsum content | ≥ 50 % of dry core weight (largest ingredient) | claim 1 |
| Perlite content | < 50 % (second-largest ingredient) | claim 1 |
| Perlite bulk density | ≈ 3 – 3.5 pcf | claim 1 |
| Fibre content | 0.5 – 5.6 % of dry core weight | claim 1 |
| Starch content | 0.25 – 6 % of dry core weight | claim 1 |
| Board density (claimed range) | 21.5 – 37.1 pcf | claim 1 |
- 01Perlite storage and dosing hardware is the biggest capex delta versus a pure foam-based lightweighting route.
- 02Perlite is highly abrasive to feed screws and to the paper: expect wear-plate replacement schedules to change.
- 03Because starch is doing structural work, moisture control across the perlite silo and the starch metering line becomes critical — wet starch clumps and stops metering evenly.
A lightweight gypsum board is provided, including, by dry weight, gypsum as the largest single ingredient, perlite as the second largest single ingredient, and starch as a minor ingredient, in the board. The starch may be pre-cooked prior to mixing, and is dispersed in the core of the board to act as a binder for binding the gypsum to the perlite. Gypsum board made according to the invention is lighter in weight, yet has a comparable nail pull value to conventional wallboard.
A lightweight gypsum wallboard comprising: a core including: a. gypsum, said gypsum being the largest single ingredient, by dry weight in the core, said gypsum comprising at least 50% of the dry weight of the core; b. perlite having a bulk density of approximately 3–3.5 pounds per cubic foot, said perlite being the second largest single ingredient, by dry weight, in the core, said perlite comprising less than 50% of the dry weight of the core and being distributed throughout said core; c. fibers comprising in the range of 0.5% to 5.6% of the dry weight of the core; d. starch comprising in the range of 0.25% to 6% of the dry weight of the core: and e. first and second sheets of face paper, said core being surfaced by said first and second sheets; wherein the wallboard has a density of between 21.5 and 37.1 pounds per cubic foot.
Further claims, drawings, prosecution history and legal status: see the official record.
- [1]US 5,922,447 A — Lightweight gypsum board — Google Patents · 1999-07-13