Learn about the glass frosting screen printing process in one article

Introduction: Frosted glass products are deeply loved by consumers because of their uniform and delicate surface, smooth feel, hazy and beautiful appearance, and soft light transmission.In recent years, frosted bottles have also been widely used in cosmetic bottle packaging.This article briefly introduces the relevant knowledge of glass frosting screen printing. The content is for reference by friends who purchase and supply high-quality packaging material systems:
Glass frosting refers to a method that uses chemical methods to obtain the effect of glass sand surface.
Chemical frosting is essentially a matte etching method, and glass frosting is also a type of glass etching.The difference between it and etching is that frosting is a shallow etching, and the surface is foggy; while etching has a deeper etching layer, and the etched graphics and text are transparent.Matte surface etching is limited to part of the glass product, while frosting is a matte surface that is formed by erosion of the entire outer surface of the glass product.The generated insoluble reactants become small particle crystals, which are firmly attached to the glass surface. Depending on the degree of contact between the glass surface below the particles and the acid liquid in the gap between the particles, the degree of erosion will be different, making the surface uneven.A rough matte surface or a fine matte surface can be obtained by controlling the size and number of crystals attached to the glass surface.Chemical frosting uses frosting liquid (powder) or frosting paste as materials, and is produced by immersion, screen printing, spraying and laying techniques.
This article introduces a paste prepared with chemicals that have an etching effect on glass. It is printed on the glass through screen printing. After obtaining the graphics and text, the printing material is removed by washing with water, and the glass is printed on the glass. The surface will appear sandy.This paste is commonly known as glass frosting mortar.

Pre-press glass surface treatment
Slight oil stains, dust, etc. on the glass surface generally do not have a great impact on frosting. Usually, you can just wipe it with cotton cloth for printing. If you want to obtain an excellent and exquisite frosting effect, you can use industrial sulfuric acid to prepare a 5% solution. To carry out the dipping and pickling process, it is best to equip a compressed air agitator to perform turbulent cleaning of the acid liquid in the acid pool. The cleaning time is about 2 minutes.Especially when frosting a large area for screen printing, in order to ensure the uniformity of the surface, the cleaning process cannot be ignored.After processing, hang the glass on the stand and let it dry naturally for later use.
On-press printing and post-press processing
Glass frosted screen printing can be done in two ways: manual and mechanical printing.General screen printing machinery has fully automatic or semi-automatic machines.The fully automatic machine is suitable for multi-color brushing and is equipped with an automatic stop device controlled by a photoelectric tube. It is very suitable for printing glass products and various types of sheets.The selection of a scraper mainly depends on its acid resistance and hardness. Generally speaking, mechanical printing speed is fast, easy to operate, and the printing accuracy is high, but the equipment investment is large.Hand printing is the opposite.
To ensure the quality of manual printing, the key is to control the thickness of the frosted printing material passing through the screen and keep the frosting time constant.In order to ensure smooth operation of the scraper during the printing process and to store the remaining printing paste in a certain position on the printing plate after scraping once, it should be considered during plate making that the empty screen inside the screen should be larger than the area occupied by the printed graphics and text.
Before formal printing, a trial printing is first carried out to check whether the screen, substrate position, scraper angle, strength, and stroke are appropriate, and necessary adjustments can be made before official printing.After printing, let the printing material stay on the glass surface. The time should not be too long, otherwise the printing material will increase the amount of corrosion and make it difficult to clean. It will also affect the frosting effect of the entire glass surface and produce non-uniformity.
During the frosting printing process, be careful not to splash the ink paste on people because the ink paste is a strong acidic substance and will burn the skin.After printing, rinse the ink with water to leave traces of corrosion. If necessary, wipe it with a brush. Place the printed glass on a stand to dry naturally and the finished product is ready.

Precautions
Pay attention to personal safety during frosted glass screen printing operations
Because frosting liquid (paste) and other substances are strongly acidic substances, they are corrosive to the human body.To avoid contact with people, acid-resistant rubber gloves, protective masks, glasses, aprons, etc. should be worn during operation.The operation movements must be steady, accurate and slow. Concentrated sulfuric acid is a strong dehydrating agent and has a serious burning effect on the skin. Be extremely careful when preparing and using printing materials.For frosting agents with a high concentration, they release a lot of heat when dissolved in water. Therefore, when adding, you can only add them to the frosting agent slowly and stir while adding to prevent boiling and splashing.If frosting agent is accidentally splashed on your skin or in your mouth, nose, or eyes, rinse immediately with plenty of running water.The wastewater from washing the printed glass is still acidic, so it can be neutralized with slaked lime to neutral (pH = about 7) before being discharged.
Glass frosted etching screen printing is different from ordinary printing
Ordinary printing retains the image formed by the printing ink, while the final product of etching screen printing is the corrosion trace left by washing away the ink on the imprint, and the attached sediment (printing paste) is washed away, revealing the pattern of corroded glass.Generally, it can be cleaned and dried within 1 minute after printing.
Frosting agents made from fluoride and fluorosilicate have poor uniformity and are prone to sedimentation.
In order to overcome this shortcoming, some thickening agents such as barium sulfate, sawdust powder, modified starch, cellulose, cryolite and organic matter can be appropriately added to increase the frosting effect.
Hydrofluoric acid corrodes silicate glass to varying degrees
Ordinary soda-lime glass is easier to frost, especially high-lime glass.Borate glass and phosphate glass are not suitable for frosting because they contain less Si02.
Be careful when using frosting paste
1) The glass surface to be printed must be degreased, decontaminated, defrosted and dehumidified. Avoid touching the clean surface to be printed directly with your hands.
2) The frosting paste should be stirred thoroughly and evenly. If there are crystals in the printing paste, it should be heated with hot water.