Animal glues in Case making

01 Oct 2012

Animal Glue or Protein Glue, an adhesive commonly used for Case making is also called Gelatin Glue, Jelly glue or Glutin. It is made of connective tissue and bones and hides of animals.

It is manufactured using animal protein which is obtained by breaking, milling the bones and cooking or boiling the raw-materials. The major characteristics of Protein glue is that it has strong wet tack, strong cohesion power and is hygroscopic in nature.

If a comparison is made between Protein glue and water based emulsions for case making, it would be clearly understood that Protein glue is the most suited for the application. An illustration below will explain the theory, further 

Average glue application (coating weight) for laminating (example):

Emulsion adhesives:

Dry substance 
Water absorption 
50-70 g/m²
50-55 %
25-35 g/m²
Protein Glue:

Dry substance 
Water absorption
 + add. Restrain of water
 (modified glue)
Effective water absorption
35-40 g/m²
50-55 %
17-20 g/m²

12 %
15-18 g/m²
   Reduction of Water Absorption 40 %

This results in lesser warping of the case, better bonding and faster setting of the adhesive. Protein Glue keeps the water longer in the adhesive film which helps in improving the flatness of the case. Emulsion adhesive   creates an adhesive film by water absorption into the porous material like paper or cardboard while Protein Glue creates an adhesive film by cooling down the glue. One of the remarkable features of Protein Glue is to create an adhesive film very quickly!

The running temperature of Protein glue is 50-60°C. which helps in quick evaporation of water (This also results in viscosity rising and the glue getting thicker. Hence, Water must be added from time to time, manually or automatically) It is important to note here that Temperature affects the viscosity!

While choosing Protein Glue it is necessary to ensure that it has strong tack (The ability to hold two substances together when they come in contact), it is fast setting, gives good and safe edge bonding and no “hollow edges”. It coats completely without any blisters. There is no stringing / splashing and is easy to melt.

Below you will find some generally accepted guidelines to help increase tack and setting speed of Protein Glues during periods of high heat and humidity.

Operating Temperature

It is recommend that all Protein Glue are run between 60°C. to 65°C.  When you have high heat and humidity we suggest that you turn the temperature down to 55°C. to 57°C.  This will help increase tack and setting speed.

Water Addition

Cut back on the amount of water dilution.  The more water you put in Protein Glue the longer it will take to dry and set up during high heat and humidity.

Adhesive Application

Be sure operators are not putting on too much adhesive.  If too much adhesive is applied it will slow down tack and take longer to dry.  A thin, well covered adhesive application will provide the best performance during high heat and humidity. In order to obtain the very best results, the following is recommended


  1. Melt Protein Glue at 60°C. – 65°C. Heat it up slowly.  Stir the glue frequently.  Do not turn the temperature “way up” to accelerate melting.  Do not “cook” Protein Glue—this was already done during manufacturing.  “cooking” damages the glue.

  2. Use Protein Glue at 60°C. – 65°C.

    • At temperatures below 60°C. the glue is too “cold”—result:  increased viscosity (thickening), poor machining (excessive build-up), loss of tack (overdilution is required to obtain a workable viscosity)

    • At temperatures above 65°C., the glue is too “hot”---result: Break down of adhesive, foul odors, stringing, cottoning, poor adhesion, excessive stickiness, discoloration (darkening or blackening).

  3. Frequently monitor glue temperature with an accurate thermometer-DO NOT rely on gauges, “High-Medium-Low” settings etc.

  4. If the Protein Glue is jelled in a machine, heat it up slowly at the setting which gives you an eventual temperature of 60°C. to 65°C.  Don't Rush It!  Get the glue “moving” as quickly as possible, by stirring, so as to avoid “Frying Pan” effect.

  5. Too dark?  Smells funny (unusual)? Thoroughly clean out the machine, pan, etc., and start over with fresh Protein Glue.  Spoiled glue will contaminate fresh glue - so don't take chances.


Protein Glue is produced using an exact formula with precise specifications.  They are thus intended to be used without dilution or with a specific dilution for your application.  Should dilution be required it is advised to not exceed 10% by weight of the glue in the tank and it is also recommended to use warm water for dilution.

Equipmernt and Housekeeping

  1. Stainless Steel vessels (Glue meters, glue pots) are ideal.  However, vessels made of other metals are used successfully.

  2. Heating of Protein Glue must be indirect.  The temperature of the Protein Glue should be controlled, preferably by a Thermostat.

  3. The Protein Glue vessels should be kept very clean at all times.

  4. Never use stagnant water to dilute a Protein Glue or for clean up. Fresh water is to be used because there is far less chance of bacterial growth which can cause foul odors and a breakdown of adhesive properties.

Three parameters which have to be considered while using Animal Glue are:
  • Concentration of the animal glue (RF-Value) - 50 - 55 %
  • Running-temperature of the animal glue - 55 - 60°C
  • Glue application (adhesive coating weight) - 35 - 40 g/m²



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