GB/T 40125-2021Liquid silicone rubber—Mold making (English PDF)

4.1 Type

Mold rubber is divided into four types according to its purpose:

a) Universal type It is used for decorative moulding and industrial moulding, specifically for the reproduction of statues, toys, candle holders, decorations, photo frames. It is represented by the letter G.

NOTE: The material for reproduction should be plaster, polyester, polyurethane foam, epoxy resin and so on.

b) Industrial prototype It is used to manufacture precision molds and casting molds, with high copy accuracy requirements and good simulation. It is represented by the letter I.

NOTE: The material for reproduction should be polyurethane resin, ABS, photosensitive resin and so on.

c) Building type It is used for building beautification, such as restoration of historical sites, sculpture decoration, stone marking, exterior decoration, building renovation. It is represented by the letter B.

NOTE: The material for reproduction should be liquid concrete, plaster, artificial stone, polyester and so on.

d) Pad printing type It is used to use pad printing technology to print color graphics on the surface of various objects, such as ceramic transfer, label or decal transfer. It is represented by the letter P.

NOTE: The material for reproduction should be ink and so on.

4.2 Designations

The naming of mold rubber designation is based on the provisions of GB/T 36804. It is expressed by liquid silicone rubber code, product component, vulcanization mechanism code, hardness, mold rubber code and type code.

6.1 Appearance inspection

Visually inspect under natural light.

6.2 Specimen preparation and adjustment

6.2.1 Specimen preparation

Weigh a certain amount of unvulcanized liquid silicone rubber. The components are mixed evenly according to the ratio specified in the product manual. After vacuum deaeration, put it into the cold-mold mold. Make it naturally leveling. If it cannot level naturally, add a cover plate. Vulcanization conditions are room temperature or heating (refer to product instructions for details). The made test piece shall be smooth and clean, uniform in thickness, and free of bubbles. The finished test piece shall be cooled at room temperature for at least 16h. Then prepare specimens according to the requirements of each test method.

6.2.2 Specimen adjustment

According to GB/T 2941, adjust the specimen temperature to 23°C±2°C, and the relative humidity to 50%±10%. The adjustment time is not less than 16h.

6.3 Viscosity

Determine according to GB/T 22235.

6.4 Shore hardness

Determine according to GB/T 531.1.

6.5 Tensile properties

According to GB/T 528, Take 5 type 1 specimens to determine the tensile strength and elongation at break.

6.6 Tear strength

Determine according to GB/T 529. Use a crescent-shaped specimen.

6.7 Linear shrinkage test

Determine in accordance with Annex A.

6.8 Durability

Determine in accordance with Annex B.

8.2 Packaging

Generally, the packaging of liquid mold rubber includes inner packaging (plastic bag) and outer packaging (metal drum, 25kg or 150kg). Other packaging methods agreed between the manufacturer and the user can also be used.

Each batch of products shall be accompanied by a product certificate, inspection report and product instruction manual. The product instruction manual includes at least the following content:

a) A description of the components;

b) The mixing ratio of the components;

c) Vulcanization conditions.

8.3 Transportation

During the transportation of the product, avoid rain and snow dipping and sun exposure. It is strictly forbidden to contact with oil, grease, acid, alkali.

8.4 Storage

When two-component or multi-component mold rubber is stored, each component shall be stored separately. The product is sealed and stored in a dark, clean, dry and ventilated warehouse. Avoid squeezing. From the date of production, the storage period shall not exceed 12 months.

B.1 Overview

The durability of the mold rubber is embodied in the number of mold reversals or the number of pad printing.

B.2 Equipment and materials

B.2.1 Male mole: The shape and size of the male mold can be negotiated by both parties (see Figure B.1).

B.2.2 Reproduction material: polyurethane resin or other reproduction material.

NOTE: The designation of the resin is determined through negotiation between the supplier and the purchaser.

B.3 Specimen preparation

Mix the various components of the mold rubber according to the ratio given in the product manual. Mix well. Put the mixed rubber in the vacuum chamber.

Properly adjust the vacuum to eliminate bubbles in the mixture. Then pour the mixed rubber into the male mold.

Vulcanize the rubber compound according to the conditions given in the product manual to make a silicone mold (female mold), printing roller or printing plate.

B.4 Test steps

B.4.1 Mold reversal

Pour or coat polyurethane resin (or other resin) on the silicone mold. Naturally or heat curing completely. Remove the reproduced resin product. Check whether the reproduced product meets the requirements. If it is reached, it will be counted as a mold reversal. Repeat this operation for N times, until the silicone mold is deformed, cracked, falling off, then stop using it. The number of mold reversal is recorded as N-1 times.

B.4.2 Pad printing

Use a roller or printing plate to dip the ink or other materials evenly. Print the desired pattern on the substrate. Check whether the pattern is clear and […]