DE4111739A1 - Continuous prodn. of multicomponent EVA-based melt adhesive - using double screw extruder with two feed points - Google Patents

Abstract

A process and appts. are claimed for continuous prodn. of melt adhesives based on an (opt. modified) EVA copolymer, rosin and/or hydrocarbon resin, waxes and/or inorganic fillers as well as stabilisers. The process comprises (i) feeding the basis polymer and specific components to a first cylinder opening (2) of an extruder such that (a) the basis polymer has a flat viscosity-temp. curve in comparison to the further components; and (b) the specific components have a rheological behaviour to the basis polymer similar to that of the hydrocarbon resins as well as having the same or a higher softening pt.; (ii) pre-heating, plasticising, transporting and pre-homogenising these components over a 7-12 (pref. 8) D length of a screw mixer; (iii) introducing and de-gassing further components via a second cylinder opening (5) such that (a) the components have a steeper viscosity-temp. curve or lower softening pt. as compared with conditions (i)(a) and (i)(b) above; and (b) the required inorganic fillers and stabilisers are present; and (iv) homogenising the total mixt. and then processing it in an underwater strand-forming or granulating device. ADVANTAGE - A more homogeneous prod. with improved properties is obtd. as compared to when a discontinuous kneading process is used

Description

In the chemical or plastics processing industry, ver different discontinuous and continuous processes and corresponding devices for the production of enamel adhesives application, it being known that by melt homogenization of ethylene-vinyl acetate copolymers, colopho nium resins and / or hydrocarbon resins, waxes and / or Fillers these are generated.

In the batch process, the ingredients in batches, preferably one after the other in thermoplastic kneaders melted, intensely mixed, over discharge screws discharged and granulated using strand granulators (adhesion 13 (1969) 7).

According to patent specification SU 7 32 349, this will be gradual Adding the components to the mixer and a special tem temperature control practiced.

A batch process is also known (DD 1 00 014), which consists in that the components in the Measurements such as the melting temperature with a gradual increase the viscosity increases, be abandoned. It will be first submitted the low-viscosity components and the thermo plastic components as well as fillers at a higher dimensional mixing movement supplied. The disadvantage of ver driving is that the components that lead to thermo oxidative degradation tend to stay in the process the longest.

In the patents DE 29 26 642 and SU 8 19 143 a two-stage continuous process for hot melt adhesive manufacturing described, being in a first mixer base polymer and adhesion promoter at the melting temperature of the Base polymers melted and in a second mixer special additives are added. The second mixer is with  a 10 to 30 ° C lower temperature, based on the Melting temperature of the base polymer, and with a around 50 to 100% higher thrust rate gradients operated. This However, the process can only be carried out with recipes where the base polymer has a higher melting temperature than that other recipe ingredients. When using ethylene Vinyl acetate copolymers limit this to grades with a vinyl acetate content of 10 mass% or less. International however, above all become higher for many types of hot melt percent ethylene-vinyl acetate copolymers used.

The main disadvantage of kneading technology and its dis continuous operation consists in the long melting and Discharge times (up to 2 hours) and the associated thermal loads on the products, which negatively affect the Impact the quality of the hot melt adhesive. Furthermore are also continuous process for the production of hot melt adhesives in Mixing and kneading extruders known, the recipe inventory parts are in powder or granulate form or as a melt. The feed materials are premixed before being added to the extruder or into the extruder by means of single component metering feeds (Adhäsion 17 (1973) 9).

Such a procedure does not refer to the speci fish plasticizing and homogenizing requirements of the individual Components and conditions of the respective thermal loading resilience of the said substances. So for Example leads to the simultaneous addition of base polymers and Paraffin or wax in the extruder feed opening and that common melting of these substances due to completely taking different plasticizing processes and differentiated rheolo behavior towards heterogeneous melts; the easy melting and relatively low-viscosity paraffin and wax melt encase the granules of the base polymer and ver hesitate its consistent plasticization and homogeneous pre mix with the other components.  

The components are successively in different places fed along the kneading extruder and thereby a certain, the Viscosity course over the temperature corresponding rows if you do not follow, there will also be inhomogeneous Melting and corresponding loss of quality. In addition comes the different thermal and deformative resilience of the individual components and the corresponding necessity an adjustment of the respective residence times in the kneading extruder, otherwise damage to the material, and consequent loss of quality occur and therefore not the economics of the process is more secured.

The invention has for its object a method and a corresponding device for the production of hot melt adhesive to create substances in which the specific of the individual components Process steps a homogeneous product is produced.

The object is achieved in such a way that the plasticizing and to unite into a homogeneous melt and finally components to be assembled in one such a sequence metered into a twin screw extruder and in this melted and homogenized that the material-specific plasticization and viscosity curves as well the maximum thermal and deformative resilience be viewed. Accordingly, according to the invention in the Feed hopper of a twin screw extruder the base polymer that has a relatively flat drop in viscosity with the Has increased temperature, supplied and at the same time those recipe components are fed into the same place, which have a similar rheological behavior as well as the same or higher softening point, for example coal hydrogen resins. The said components are made in one Screw conveyor and mixing elements, for example kneading disks, existing screw section from 7D to 12D length before preferably 8D, preheated, plasticized, transported and subjected to pre-homogenization.  

Then the recipes at a second dosing point components that have a lower softening point and steeper viscosity-temperature curve than that on the first Dosing point supplied components and given if inorganic fillers and stabilizers are added.

At the second dosing point, the discharge can take place at the same time volatile substances via degassing outdoors consequences.

This is followed by an extruder length of 13D to 18D, preferably 17D, the incorporation of the last added compo elements into the already plasticized and homogenized, optionally degassed, mass and that for the extrusion required pressure build-up. The homogeneous hot melt adhesive is finally by means of an underwater strand or sub water pelletizer assembled.

The inventive device for producing the melt adhesive consists of a twin-screw extruder with two Openings along the extruder barrel for the purpose of feeding the one individual components. The extruder barrel is procedural can be cooled or heated in sections. The two extruders snails are designed in segment construction and the respective Process sections adapted. At the openings along the Extruder cylinders are single or double-shaft metering units in volumetric or gravimetric design for addition of the individual components. The dosing units can be done by a continuous speed adjustment of the conveyor adapted to the requirements of the extrusion process will. The component present as a liquid is through fed a metering pump. There is a molding at the end of the extruder stuff for forming the melt into strands and a sub water strand or underwater pelletizer can be arranged. The hot melt adhesives produced by this method have in Comparison to that after the discontinuous kneader technology produced a significantly lighter color.  

The properties in use are much better to Example, the tensile strength is two to four times higher and the heat resistance shows one by five to ten Degrees higher value.

The invention is based on an exemplary embodiment are explained in more detail: The accompanying drawing shows:

Fig. 1 shows the device for the continuous production of hot melt adhesives with a twin-screw extruder.

The device according to the invention shown in Fig. 1 is from the twin-screw extruder 1 , the two screws 3 , 3 ', the cylinder openings 2 and 5 , the temperature-controlled cylinder 4 , at the end of which the underwater strand or under water pelletizer 6 is connected. At the cylinder opening 2 two metering devices 7 and 8 are arranged; the metering device 9 and the metering pump 10 are installed at the cylinder opening 5 .

Via the cylinder opening 2 of the twin-screw extruder, the base polymer and the recipe component are fed in, which have a similar rheological behavior and an equal or higher softening point, for example hydrocarbon resin with the aid of the two metering devices 7 and 8 . The mixture is preheated and compressed, plasticized and pre-homogenized. Due to a similar rheological behavior, the two components are placed in a state that allows a largely uniform shear stress to be introduced into the initially plug-like, then viscous composite.

This results in a uniform and rapid plasticizing process and a homogeneous premix. The degassing of volatile substances takes place via the cylinder opening 5 . At the same time, the recipe component is fed via this opening by means of the metering device 9 , which has a lower softening point and a steeper viscosity-temperature curve than the components supplied in the first cylinder opening 2 , possibly also inorganic fillers. By means of the metering pump 10 through the cylinder opening 5, the feeding of a liquid component, for example of the Stabili crystallizer.

While being fed through the cylinder opening 2 of the extruder components are plasticized along portion _P and L vorhomogeni Siert, the cylinder portion L _{H is} used for homogenization tion of the total melt adhesive mixture and the required extrusion pressure buildup. The homo genized mixture is finally assembled by means of the underwater strand or underwater pelletizing device 6 .

According to a process example, a hot melt assembly adhesive manufactured, which consists of the following recipe components: 57.5% by mass of EVA copolymer with a vinyl acetate content of 23 96 and a melt index of 120 dg / min at 463 K, 33% Hydrocarbon resin with a softening point of 378-388 K, and 0.5% stabilizer. The production takes place after inventive method on a corresponding Vorrich device consisting of a twin screw extruder with a Diameter of 125 mm and an L: D ratio of 25, where the base polymer and the hydrocarbon resin in the task funnel of the extruder dosed, this mixture over a System length of 8D was plasticized and pre-homogenized, then via a second extruder opening Polyethylene wax and the stabilizer was made and finally homogenization over a system length of 17D the hot melt adhesive mixture and the required pressure build-up took place.

Volatile substances could pass through the second extruder escape opening into the open. The assembly was done with Using an underwater pelletizer at water temperature ratures of 283 K.  

The process parameters in this example were: screw speed 75 rpm, throughput 400 kg / h, temperature profile throughout 343 K, melt temperature at the head of the extruder 398 K. The same recipe was produced for comparison purposes on a thermoplastic kneader. In the oil-heated kneader of conventional design and a capacity of 0.45 m ³ , EVA-CP granulate was placed and melted. The rest of the recipe components were refilled into the melt, homogeneously mixed at melt temperatures between 453 and 463 K and finally carried out by means of discharge screws over a perforated plate and strand-granulated.

The end products of both processes were according to the usual test methods tested and the characteristic values compared:

According to a further process example, a polygraphic hot melt adhesive with the following composition was produced on the same device according to the invention with similar process parameters as in the previously mentioned example:
44.5 mass% BVA-CP modified with butyl acrylate with a VA content of 31% and a butyl acrylate content of 5% and a melt index of 40-48 dg / min at 463 K, 20% hydrocarbon resin with a softening point of 368- 378 K, 35% wax mixture of 50% EVA-CP wax and 50% paraffin with a softening point of approx. 343 K, 0.5% stabilizer. In this case too, the product was tested and the results compared with the values of a corresponding recipe made on a thermoplastic kneader:

The comparison shows that this according to the invention Method and manufactured on a corresponding device Product has a 2.5 times higher tear strength than the kneading product corresponding to the state of the art.  

List of the abbreviations used

1 twin screw extruder
2 cylinder opening
3; 3 ′ snail
4 temperable cylinders
5 cylinder opening
6 underwater strand or underwater pelletizer
7 gravimetric or volumetric dosing device
9 dosing device
10 dosing pump
L _H homogenizing section
L _P preheating, plasticizing, transporting and prehomogenizing section

Claims (2)

1. A process for the continuous production of hotmelt adhesives based on EVA copolymers or modified EVA copolymers, rosins and / or hydrocarbon resins, waxes and / or inorganic fillers and stabilizers, characterized in that

• 1. a base polymer and special formulation components are fed into a first cylinder opening of an extruder, where
  • 1.1. the base polymer has a relatively flat viscosity-temperature curve in comparison to the other formulation components and
  • 1.2. the special formulation components have a rheological behavior similar to that of the base polymer to that of hydrocarbon resins and an equal or higher softening point,
• 2. these components are preheated, plasticized, transported and subjected to prehomogenization in a screw section consisting of screw conveyor and mixing elements of 7 D to 12 D length, preferably 8 D,
• 3. Both the degassing and the supply of further components can take place via a second subsequent cylinder opening, wherein
  • 3.1. the corresponding formulation components have a steeper viscosity-temperature curve or a lower softening point than that in point 1.1. or 1.2. have and
  • 3.2. necessary inorganic fillers and stabilizers are included,
• 4. the entire mixture is then mixed homogeneously and
• 5. The assembly takes place via an underwater strand or underwater pelletizing device.

2. Device for the continuous production of hot melt adhesives, characterized by the following features:

• 1. a twin-screw extruder ( 1 ) with screws ( 3 , 3 ') be a first cylinder opening ( 2 ) with associated gravimetric or volumetric metering devices ( 7 , 8 ) and a second cylinder opening ( 5 ) to which a metering device ( 9 ) and a dosing pump ( 10 ) are connected;
• 2. the twin-screw extruder ( 1 ) has a preheating, plasticizing, transporting and prehomogenizing section L _P with a length of 7D to 12D, preferably 8D, and a homogenizing section L _H with a length of 13D to 18D, preferably 17D;
• 3. Finally, an underwater strand or underwater pelletizing device is arranged.