Material selection: The secret of self-adhesive label

Self-adhesive sticker material is also called self-adhesive label. It is a composite material with paper, film or special materials as facestock, adhesive on the back, and silicon-coated backing paper as the protective paper. It is printed, die-cut, etc. After processing, it becomes a finished product label.

There are many types, mainly arising from the different compositions of the three components of self-adhesive label, namely : facestock, adhesive, and liner. Different facestock ,adhesive, and liner can be combined with many self-adhesive label.

Non-professional users often only focus on choosing facestock because they can directly display design and visual effects. In fact, the most important thing for high-quality self-adhesive labels is the adhesive and liner.

After all, before the finished label leaves the factory, the quality of the facestock is easily checked in pre-press, printing and finished product inspection,while the adhesive is easily affected by labeling or the use environment (temperature, humidity, etc.) Affected by the characteristics of different objects to be pasted, there are also different choices of adhesives.

01：Facestock

(1)Offset paper: Also known as writing paper and molded paper, the surface is uncoated matte paper. It is generally used for single-color printing or printing, and barcode information labels.

(2)Coated paper: It is coated paper. The surface of the surface paper is medium-gloss paper that has been coated. It has high flatness and the surface brightness is lower than that of mirror-coated paper. It is currently used in the pharmaceutical industry and food industry under color printing. The best printing material for transferring barcode labels.

(3)Mirror coated paper: super calendered, with high surface gloss, used for product labels that require bright printing colors. Such as pharmaceuticals, health care products and other industries.

(4)Thermal direct paper: Commonly used as information labels in supermarkets, it is also currently used in thermal printing information labels for large logistics companies.

(5)Thermal transfer paper: A self-adhesive label specially developed for thermal transfer printing ,The surface of the paper has been specially coated. It has excellent printing effect especially for small barcodes, so that when scanning product barcodes, there will be no breakpoints and broken lines of the barcode cannot be recognized. Moreover, the facestock is not easy to change color and lasts longer than the coated paper.

(6)Office laser printing paper: The most common laser printer material in the market uses offset paper. However, the high temperature and high speed of the printer make the adhesive prone to glue leakage failure under the action of high temperature, and it is easy to damage the printer. Special laser printing paper label can solve this problem. There are also some uncommon paper self-adhesive label facestock such as fragile paper, aluminum foil, etc., which are also used in food, health products, alcoholic products, etc.

(7)PE film: Polyethylene film. The surface is bright white, sub-white, bright silver and transparent. It is soft and has the characteristics of water resistance, oil resistance and extrusion resistance. It should be widely used in daily chemical products, such as Shampoo, shower gel and other products.

(8)PP film: Polypropylene film, the surface is bright white, sub-white, bright silver, and transparent. It has the characteristics of water resistance, oil resistance, and good stiffness. Ultra-transparent PP self-adhesive label, due to its high transparency, is attached to the transparent bottle body and looks like a label-free visual effect. It is also widely used in daily chemical products and cosmetics and other fields.

(9)PET film: Polyester film, with or without surface treatment. The surface includes bright white, sub-white, transparent and various metallized bright silver, sub-silver, etc. Due to its high stiffness and characteristics such as water resistance, temperature resistance, oil resistance, and solvent resistance, it is suitable for labeling materials for various types of electronic products and machinery that are attached to flat surfaces.

(10)PVC film: Polyvinyl chloride film, with transparent, white, and sub-white surfaces. It is water-resistant, oil-resistant, and solvent-resistant. It is mainly used in chemical products. PVC film with shrinkage properties can be used as a material for battery shrink labels.

02:Adhesives

 The main factors to consider when selecting adhesives are the following.

(1) The material of the object to be pasted: paper, plastic, metal, glass, ceramics, etc. (surface tension is different).

(2) The shape of the object to be attached: plane, curved surface, the size of the curvature of the curved surface, the diameter of the bottle, etc.

(3) The condition of the surface of the object to be pasted: flatness, roughness, cleanliness, humidity, etc.

(4) Labeling method: manual, self-labeling, labeling speed and labeling pressure, etc.

(5) Labeling environment: the temperature and humidity during labeling, the cleanliness of the labeling site and whether there is dust in the space, etc.

(6) Storage environment: the humidity, ultraviolet rays, etc. of the self-adhesive label materials stored after labeling and before labeling.

In the labeling process, what is easily overlooked is that labeling personnel care about the chemical viscosity of the self-adhesive label material itself, but underestimate the mechanical viscosity. In fact, under a certain labeling pressure, the use of suitable adhesives can make labeling safe. A special case is that hot melt adhesive series adhesives are not suitable for sticking to PVC materials. Due to the chemical reaction between the chemical components of the adhesive itself and the plasticizer component of PVC itself, glue bleeding occurs and the surface is damaged.

Glues with different properties have different prices and applications. For everyone to make a better choice, let’s introduce the common self-adhesive glues, which are divided into three types: hot melt glue, hydrosol glue (usually called water glue), and oil glue.

Hot melt adhesive is a rubber-based adhesive. It has strong fluidity and viscosity, is suitable for low-temperature labeling (minus 5 to 10 degrees), and is environmentally friendly and non-toxic; the labeling effect is better than that of hydrosol when there is a trace amount of oil or water on the surface of the object to be pasted.

A. Not resistant to high temperatures and can only be used below 70 degrees.

B. It is sensitive to temperature during processing. In winter, if the temperature of processing and storage is lower than 15 degrees Celsius, it will become hard and brittle.

C. Poor re-postability

D. It cannot be affixed to PVC materials in labeling environments that do not require too high temperatures, such as food, medicine, supermarket labels, etc.

Hydrosol is an acrylic adhesive. Strong viscosity, most hydrosols are environmentally friendly and non-toxic. At the same time, water-soluble glues have stronger temperature resistance than hot melt glues. Most hydrosols can withstand temperatures below 90 degrees Celsius, and some hydrosols can withstand high temperatures of about 150 degrees. The low-temperature labeling performance is poor. There are slight water stains or oil stains on the label, and it is difficult for the hydrosol to exert its viscosity. This is because the fluidity of the hydrosol is poor. It is used in food, medicine, daily chemical products and some environmentally friendly products. In addition to the characteristics listed in the table for strict industrial product labels, when the self-adhesive label is first pasted, the stickiness of hot melt adhesive is much stronger than that of water glue. However, if it is left for 24 hours, you can Try it and you will find that labels using water glue are far more difficult to peel off than hot melt glue. This is because the water glue flows slowly. Within more than 20 hours after labeling, the glue under the label finally disappears. Completely adheres to the surface of the adherend.

The difference between oil-based self-adhesive labels and water-based self-adhesive labels is the degree of waterproofing and aging. Oil-based glue itself is not "oil". We generally use soft monomers such as acrylate or vinyl acetate to maintain stickiness after curing. It can be pasted repeatedly and has strong adhesion. Water-based adhesives generally have inferior adhesion, and the adhesive surface may lose tack at high or low temperatures. In fact, in addition to polyvinyl alcohol, water-based glue is also a hydrated emulsion of oil-based glue, but the solvent is changed from MIBK, DBE or butyl acetate to water. It can be used indoors where it does not need to be exposed to humidity. It can be used all day long. Roll-up banners or outdoor photos outside in the wind and rain will not work. Generally, PP paper is made of oil-based glue. In order to increase the bonding fastness with PP, there is also a certain amount of chlorinated polypropylene, that is, CPP, as an adhesion promoter.