PLASTIC

Plastics are excellent materials with unique and very useful properties. You can produce just about anything you can imagine using plastics.

Characteristics of Plastics

History Of Plastics:

1. Before Plastics—Age of the Natural Resins

• Rubber—Tough elastic substance (light cream or dark amber
  colored) from the milky juice (sap) of rubber tree
• Ebonite—Hard black rubber; natural rubber + sulfur
• Gutta-Percha—Dark brown substance like natural rubber
• Shellac—dark-brown material from lac insects

2. Bakelite—The First True Synthetic Plastics

• Leo Hendrik Baekeland invented Bakelite from coal
• Bakelite helped make 20th century “The Age of Electricity”

3. Industrialization of Major Plastics

Year	Type of plastics	Note
1872	Celluloid (Hyatt, USA)	Semi-synthetic
1910	Phenolic resin, “Bakelite” (Baekeland, USA)	From coal
1931	Polymethyl methacrylate (PMMA) (Rohm and Haas, Ger-many)	From coal
1935	Polyvinyl chloride (PVC) (IG Farben, Germany)	From coal
1935	Polystyrene (IG Farben, Germany)	From oil
1938	Nylon 6 (IG Farben, Germany)
1939	Nylon 66 (DuPont, USA)	From coal
1939	High-pressure low-density polyethylene (LDPE) (ICI, Eng-land)
1953	Polyethylene terephthalate (PET) (DuPont, USA)
1953	Low-pressure high-density polyethylene (HDPE) (Montecatini, Italy)	Ziegler catalyst
1955	Medium-pressure high-density polyethylene (HDPE) (Phillips, USA)	Phillips catalyst
1957	Low-pressure high-density polyethylene (HDPE) (Hoechst, Germany)	Ziegler catalyst
1959	Polypropylene (Montecatini, Italy)
1977	Linear low-density polyethylene (LLDPE) (UCC, USA)
1991	Metallocene very-low-density polyethylene (VLDPE) (Exxon, USA)	Metallocene cata-lyst

4. Concept of High Molecular Weight Compounds & Polymers

• Herman Staudinger, German chemist, proposed a new theory that several thousands of reactive units bonded together in chains and form giant molecules to make up cellulose and rubber
• In 1920, Staudinger proposed calling such materials: high molecular weight compounds, macromolecules, or polymers.

5. Nylon—The First Tailor-Made Plastics

• 1931 – Fiber 66 was produced, later called Nylon 66 in 1938

PRESSURE FORMING

Material & Description

ABS

Good general purpose material, very tough yet very hard and rigid, good impact and electrical. Available in gauges from .040 to .475 with several extruded textures. Comes opaque and can be matched in custom colors.

ABS/PC

A blend or alloy of ABS and polycarbonate that thermoforms well, weathers well, good color retention, very hard, excellent impact.

ABS/PVC

Flame retardant, tough.

Acrylic

Outstanding weather resistance, excellent optics and electrical properties, poor impact, high gloss and deep luster. Available in standard gauges from .080 to over 1″. Available in clear, transparent and opaque colors.

Acrylic, cell cast

Excellent optics and hot strength, more expensive. Acrylic, continuous and extrusion cast.
Large volume use and best price, good optics.

Acrylic film

3 or 6 mil film for laminating, decorating, and weathering of extruded ABS.

DR Acrylic

Modified acrylic with higher impact properties.

Acrylic/PVC

A blend of acrylic and PVC that is a tough, chemical-resistant material that weathers well and is flame resistant. Available in custom colors.

HDPE (high-density polyethylene)

Crystalline, very tough materials, good weather resistance with UV inhibitors, resistant to many chemicals. Available in standard gauges from .040 to .500. Available in opaque custom colors. Tough and stiff. Good low temperature. Economical.

HMWPE (high molecular weight)

Excellent environmental stress crack properties, thermoforms well, good low temperature.

HIPS (high impact polystyrene)

Good general-purpose material, rigid. Available in clear but usually opaque custom colors from .030 to .350, low cost.

PVC (vinyl)

Good general-purpose material, good abrasion and chemical resistance. Available in clear but usually opaque custom colors from .030 to .125.

Expanded PVC

Stiff, light, flat, thermoformable. Available in stock colors and gauges, generally 3 and 6 mm but others also available.

PETG

Clear, higher impact than acrylic, easy to form. Available in gauges from .030 to .500.

Pressure Forming:

Pressure Forming is the method used to produce injection mold quality, high definition plastic component parts, housings and containers without the huge expense of tooling. It involves positive pressure to force the heated plastic into the mold cavity. This is called pressure thermoforming or blow forming

Pressure Forming Working Operation:

The highly versatile pressure forming process utilizes air pressure, from 20 to 150 psi, to force the heated sheet into a temperature controlled mold cavity. Vent holes are provided in the mold to exhaust the trapped air. The final part features sharp definition of intricate contours and tight radii. Textures and accurate details are built right into the tooling. Low-cost, highly aesthetic plastic parts of varying sizes are possible due to the application of air pressure, as well as more sophisticated process controls that better monitor tool and sheet temperatures while controlling material shrinkage during forming.

Types Of Molding operation:

• Positive Mold
• Negative Mold

Negative molds  have concave cavities. A positive mold has a convex shape.

Pressure Forming over Thermo Forming:

The basic advantage of Pressure Forming over Thermo forming is the cost advantage for small production items. The mould cost for thermo forming is considerably higher in comparison to pressure forming thus for a lower quantity precision job the best suitable method used is pressure forming.

Application:

Pressure forming is used to create in a wide array of plastic products used for packaging of food trays, blisters, covers, internal parts, housings equipment, bezels, bases, and spare parts for use in business machines, electronics, computers and peripherals, bio-medical applications, and instruments.

Features:

Pressure forming achieves features beyond the capabilities of vacuum forming including louvers, ribs, recessed areas, crisp details and logos.

Pressure forming is ideal for small to medium sized production runs that do not justify the high cost of injection molding dies. Additionally, because the aluminum tooling used in pressure forming has an unlimited lifecycle, due to the non-abrasive process versus injection, it saves a great deal of money over many years of continued use. Pressure form tooling usually costs less than 10% the cost of an injection tool. There is also a significant time savings (sometimes 25%) in tooling lead time. Sheet gauges .020″ – .500″ are capable of being pressure formed.