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The practical application of hot melt pressure sensitive adhesive in production

Home    行业前沿    The practical application of hot melt pressure sensitive adhesive in production

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Abstract Mainly introduces the application of HMPSA in the manufacture of hot melt labels and the production of sanitary napkins and baby diapers

 

Keywords: #production application, #performance index, #control process #HMPSA

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Pressure-sensitive adhesives are mainly acrylic or rubber-based solvent-based or latex-based adhesives. In recent years, hot-melt pressure-sensitive adhesives have been developed due to the need for high-speed operation, reasonable coating, and elimination of solvent pollution. Hot-melt pressure-sensitive adhesive is an adhesive mainly composed of thermoplastic polymer (mostly styrene-based thermoplastic elastomer). It integrates the performance of hot-melt adhesive and pressure-sensitive adhesive. It is solvent-free, pollution-free and easy to use. It is coated in the molten state, used after cooling and solidification, and it can play a role of adhesion with slight finger pressure. It has a wide range of applications, and can be used in diapers, women's products, double-sided tape, labels, packaging, medical and health, book binding, surface protection films, forestry processing, wallpaper and shoemaking. This article mainly discusses the application of hot melt pressure sensitive adhesive (HMPSA) in labels and sanitary napkins and baby diapers.

 

1. Manufacturing hot melt labels

 

Bottles, jars and other containers are often stored and used under conditions of high humidity or moisture, so hot-melt pressure-sensitive labels can be used.

 

The glue application process for evenly attaching plastic labels on plastic bottles includes the following steps:

 

a Coat a layer of hot melt pressure sensitive adhesive on the printed surface of the printed plastic film label

 

b Heat the plastic bottle to be labeled with the temperature slightly higher than the activation temperature of the hot melt pressure sensitive adhesive on the plastic film label.

 

c Bond the hot plastic bottle to the surface of the glued label.

 

d Flatten the plastic label on the surface of the bottle.

 

It is usually desirable to heat the plastic bottle to a temperature slightly higher than the activation temperature of the hot-melt pressure-sensitive adhesive on the label. In fact, a slightly lower temperature is also feasible. For example, applying pressure-sensitive adhesive on the surface of a hot bottle or on a label, and then rolling it after the label is applied can also achieve the goal. It is best to use PE plastic bottles, and use the flame treatment process to heat the bottles. As a label, a plastic with a low coefficient of sliding friction should be selected to generate small static electricity and facilitate separation from each other. In addition, the label material should have greater stiffness. Linear polyethylene film is very suitable as a label material. Other label materials include polyester film, composite film of polyester and polyethylene, and composite material of cellophane and polyethylene.

 

Use hot-melt pressure-sensitive adhesive and apply it on the label or bottle to attach the label. It should be heated and activated before being applied to the label. The composition of this pressure-sensitive adhesive is generally 50 / 50EVA copolymer, which is relatively The molecular mass is about 5000-10000, which can be applied to the bottle with a brush.

 

For example: take a linear PE plastic bottle, the plastic bottle is first treated by flame, heated to the surface temperature of the bottle, which is slightly higher than the melting point of PE, and then coated on the surface of the bottle, coated with a fine EVA hot melt pressure sensitive adhesive The bottle rolls and contacts the plastic label coated with hot-melt pressure-sensitive adhesive, and then rolls through the hot smooth metal plate to eliminate bubbles and wrinkles on the surface. The quality of this label is very high.

 

2. Application of HMPSA in disposable hygiene products

 

Disposable hygiene products mainly include disposable gloves or finger cots (excluding medical gloves and finger cots) sanitary napkins, sanitary wipes, phone membranes, hats, masks, sanitary pads, diapers, etc. The appearance must be clean and tidy, conform to the inherent shape of sanitary products, must not have abnormal smells and foreign bodies, and must not cause adverse irritation and allergic reactions and other damage to the skin and mucous membranes. The application of HMPSA in women's sanitary napkins and baby diapers is discussed.

 

Sanitary napkins and baby diapers mainly use HMPSA and can be divided into structural adhesive and adhesive.

 

2.1 The purpose of structural adhesive is to stick the surface, bottom material and internal structural materials of the sanitary napkin together so that they do not move or break, and generally have a higher viscosity. Structural glue can not be sprayed too much. The main ways of spraying glue are: spiral spraying glue, coating scraping glue, fiber spraying glue and so on. Since the production speed of sanitary napkins and diapers produced in China is not too high, the spraying method of structural adhesives often uses spiral spraying. The molding principle of spiral spraying is that multiple air holes in the spiral nozzle spray compressed air at different angles. In order to make the strip-shaped rubber filaments spirally formed, pay attention to the built-in air heating device when purchasing the spiral spray gun. Otherwise, the cold air is blown out, the hot melt adhesive cools quickly, the viscosity increases, the rubber filament is not easy to stretch, the rubber strip will be thicker, the spiral forming is more difficult, and it is not easy to reach a larger spray width.

 

2.2 In sanitary products such as sanitary napkins, diapers, etc., in addition to the structural adhesive required for structural functions, there is also adhesive required for the use of functions.

 

Adhesive is used on the outside of sanitary napkins and its role is to stick to the underwear so that it does not move. The adhesive must be firmly attached, and must not be sticky or too sticky. Adhesive is a part of the product that requires higher use. The viscosity of the adhesive is generally lower than the viscosity of the structural adhesive, and it is easy to apply thinner. The spraying method used is scraping. The method of squeegee coating requires fast reaction speed. Only high-speed reaction and rapid shutdown can reduce the occurrence of wire drawing.

 

2.3 Sanitary napkins and diapers generally have the following stations that need to be sprayed:

 

a Adhesive for sanitary napkins (using a coating gun)

 

b Surface layer non-woven fabric or perforated film (using spiral coating or fiber spraying)

 

c Internal structural glue, toilet paper, wooden paddle, dust-free paper and other internal structural layers between layers of glue (generally spiral spray glue)

 

d Base film structure (generally using spiral fiber coating squeegee)

 

e Three-dimensional protective rubber band or diaper leg rubber band (generally spiral spray glue or fiber spray glue)

 

f Wings, sanitary napkins, wings fixed glue (scraping glue)

 

g Three-dimensional guarding fixed or three-piece fixed (usually strip glue spraying and scraping glue)

 

3. Performance requirements of HMPSA

 

HMPSA used for disposable hygiene products should be appropriately selected according to the raw materials and production processes used. For HMPSA, it should have the following characteristics:

 

 It has good adhesion to certain fiber or fibers, and it has certain softness.

 

 According to the final use of the product, it meets certain temperature, elasticity, solvent resistance, heat resistance, aging resistance and other requirements.

 

 It has good maneuverability, that is, it meets the requirements of sizing process.

 

 Good fluidity, conducive to infiltration.

 

The properties and coating conditions of commonly used solvent-based acrylate pressure-sensitive adhesives, water-emulsion acrylate pressure-sensitive adhesives and hot-melt pressure-sensitive adhesives are as follows:

 

Item

Exterior

Solid content /%

Viscosity /mpa.s

Abnormal toxin

Solvent type acrylic pressure sensitive adhesive

Transparent

45

2000~3000

No

Water emulsion acrylic pressure sensitive adhesive

Milk white

52

1200~1800

No

Hot melt pressure sensitive adhesive

Light Yellow

100

2000~4000

No

3-2 Coating conditions for pressure-sensitive adhesives

item

PaintingDry/g.m-2

Speed/m.min-1

Drying temperature

Solvent type acrylic pressure sensitive adhesive

30~40

13

12080

Water emulsion acrylic pressure-sensitive adhesive

50~60

5

8011070

Hot melt pressure sensitive adhesive

20~40

>40

160~170

 

Hot-melt pressure-sensitive adhesive does not contain any solvent, will not be polluted by solvent evaporation, no heating and curing, no drying process, easy to use, high production efficiency, to avoid additional occupation of the production plant, production using transfer coating method, The air permeability of the product can be effectively controlled through the coating process, thereby maximizing the air permeability of the product, and the air permeability is greater than 500g / (m2.24h).

 

       From the actual situation, the disposable hygiene products produced by HMPSA have minimized the skin allergy to the product and reduced the chance of skin allergy.

 

4. Process control of HMPSA used in production

 

The main function of HMPSA is to bond the sanitary napkin to the underwear to prevent the sanitary napkin from moving and deforming. The suitable temperature for production control provided by general hot-melt adhesive factories is 145 ~ 160 , but after many trial and error in actual production, the best control temperature is 170 ~ 180 . This is because: when the lower melting temperature is controlled (<160 ) It is very easy to cause "back glue" phenomenon, that is, after the melted glue is transferred to the sanitary napkin under this condition, it will cause the glue on the sanitary napkin or the cloth containing the glue to stay on the underwear and cannot be removed When the melting temperature is too high (> 190 ° C) or repeated heating, the viscosity of the glue will decrease significantly, and the color of the glue will become brownish yellow, which will give people a feeling of uncleanness. In addition, if the melting temperature of the glue is too high, it is easy to cause gelation and burning and fire.

2020-05-19 11:22
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