If you are reading this article, you may just a newcomer to the eyewear industry or a veteran who has been purchasing sunglasses for 5 or 10 years or even longer. But if you think through, ask yourself, do you really know how a pair of sunglasses are produced? Are you truly familiar with its production technology and processes, even if you know well about sunglasses products?
Before writing this article, I have searched for information about sunglasses production on Google, but honestly speaking none of those came up to my expectations due to its wide description and partially explained sunglasses manufacturing procedure. That is why I decided to compile a comprehensive and detailed spectacle production guideline (some diversified and complex technics involved in the eyewear-making process will be explained separately in our future articles). I am pretty sure you would never find a second one that is more specific and more comprehensive on the internet. Well, let’s get started!
The material of sunglasses varies, we only discuss about the common plastic sunglasses production which will be explained in the following article.
Raw material selection.
Raw material procurement:
Our factory(GM Sunglasses)adopted the latest Polycarbonates as raw materials for production (transparent color, as shown on the left below).
Raw material coloring:
The coloring comes after the purchasing stage. For instance, if a customer requires a pair of purple-colored glasses, the raw materials have to be colorized in purple (we are capable of matching any color from Pantone number). You will certainly think of other coloring technics such as spraying and pattern drawing. These are more complicated technics which we will be explaining in our future articles. In this article, we only focus on the simplest process.
Other raw materials classification:
Sunglasses are available in several materials. Apart from the latest materials we mentioned above, we will NEVER consider second-hand and even third-hand materials as our ingredients, which will result in low toughness and high brittleness of products.
The first step is to put colorized ingredients into a special oven for heating and softening. Then pour into the injection molding machine to heat it up again until it becomes malleable as liquid form. The liquid is pressed by the barrel into the mould for shaping (the barrel temperature needs to be controlled between 270℃-320℃. The range can be adjusted depending on the mould structure and product features). After moulding, the semi-processed frame will be dipped into cold water for cooling. (PS: The output of an injection molding machine is around 5,000 to 8,000 pairs in 24 hours)
1st round Polishing:
Due to its rough surface, the frame needs to be polished by the small stones that are installed in the machine for the first round (watch below video, and the size of the stone varies depends on the level of roughness). While the machine vibrates, water is constantly added to keep the frame clean.
The 1st round of polishing is followed by embedding metal hinge into the frame and temples in the right position at very high temperatures. In this stage, some factories outsource this part of the business to external partners while we process it fully on our own.
To fasten the hinged frame and hinged temples together by using screws (some complex colorized glasses will be locked with screws after its frame and temples are stained).
1st round Cleaning:
Clean the hinged frame and temples and let it dry naturally, then get ready for spraying.
Remove the possible dust from the frame with an air gun before painting and then fix the frame. The frame will be sent to the spraying room for painting. There are two different ways of painting – auto spray and manual spray. The auto spraying machine can only paint a simple color, such as transparent or black. However, complicated colors must be handled manually.
The sprayed frames are ready for the next step of drying. In the drying room, it usually takes 8-24 hours to air-dry (the duration varies based on outside temperature). The chamber can be heated to speed up drying if necessary.
1st round of Quality Control:
When the frame is dried, they will be sent for the first round quality control(QC process), i.e. workers will pick out defective frames with pitted particles or wet paint.
2nd round Polishing:
Unqualified frames will be polished for a second time (white wax polishing), the purpose of which is to smooth the surface of the frames and temples to meet the quality standards (as shown in the figure below). After the second polishing, the frames will be painted for a second time too. This process will remain repeated until each pair of glasses is ready for the next step.
The finishing stage starts with logo printing, which can be done in many ways (silkscreen printing, pad printing, heat transfer printing, laser printing, metal logo inserted, etc.). Here we will show the most commonly adopted and simplest printing method – Silkscreen. The information required to be printed will be engraved on a metal plate and then fixed on the printer. The previously adjusted ink will be painted on the glasses through a silkscreen (the ink is usually in white, gold, or silver color, or can be mixed according to Pantone number).
Lens cutting and installation:
The CNC cutting machine shall be debugged several times before cutting the original lens into a shape that matches the frame. After cutting, the pieces will be manually inserted into the frame (The lenses are available with different types according to its material: PC, AC, TAC, and CR39. Different glasses match lenses with different curvatures ranged from 2C-8C. Type 6C-8C is widely used in sports sunglasses. In addition, different lenses have different levels of thickness. For instance, PC and AC are usually with a thickness of 1.6 mm to 2 mm, while TAC usually with a thickness of 0.74 mm and 1.1 mm)
2nd round of Quality Control:
The second round quality inspection is mainly to screen out the glasses with minor defects like asymmetric temples, loose screws, a few pitting points on the frame and slight scratches on the lens, to ensure that the final product is qualified and fully ready.
2nd round Cleaning and Drying:
After inspection, all the fingerprints and dirt on the frame and lenses will be cleaned in an ultrasonic cleaning machine. This will be done before putting glasses into the dryer.
This stage comes after the drying, where customers’ packaging requirements differ. Usually, they ask for bespoke tags, lens stickers, or customized packing box and bags. After the completion of putting a single package into the white inner box (in general 12 pairs for one box, the inner box can be printed with customers’ brand info or common labels), they will be packed into the 7 layers of corrugated standard export outer boxes, and the labels required by customers will be printed on the outer boxes as well.
So above all are the standard manufacturing process of plastic sunglasses. We will regularly update some technical related articles in the future. We really appreciate that you take your time to read our article and if you have any questions or suggested contents to add, please feel free to leave your comment and we will happy to get back to you very shortly.
Otherwise, if you are looking for a Chinese sunglasses manufacturer, please contact GM Sunglasses, and let’s make your eyewear business more prosperous together, Cheers!