WO1999033704A1

WO1999033704A1 - Method for packaging of hot melt adhesives

Info

Publication number: WO1999033704A1
Application number: PCT/GB1997/003545
Authority: WO
Inventors: Anthony Peter Rodgers; Jean Bernard Paul Massoutier; Thierry Fernand Calmes; Ronald James Lane
Original assignee: National Starch & Chemical Investment Holding Corporation
Priority date: 1997-12-24
Filing date: 1997-12-24
Publication date: 1999-07-08
Also published as: AU5332998A; JP2001527003A; EP1021341A1

Abstract

A continuous method of producing hot melt adhesive comprising the steps of: a) forming a plastics material film tube (14) with the inside coated with a non-tack substance; b) pumping or pouring molten hot melt adhesive in liquid form into the tube (14); c) cooling the tube (14) with a cooling fluid; sealing the hot melt adhesive filled tube; d) voiding the tube (14) to produce a series of cartridges (28) of adhesive with the film (10) being substantially free of adhesive between each cartridge (28) thus produced; e) allowing the hot melt adhesive to solidify; f) cutting the film (10) coating on the adhesive tube (14); and g) stripping the film (10) from the hot melt adhesive.

Description

Method for packaging of hot melt adhesives

The present invention relates to a continuous method of

packaging hot melt adhesive compositions and the resulting

packaged adhesive composition.

Hot melt adhesives are generally applied while in the molten

or liquid state, but are solid at room temperature. Typically,

these adhesives are produced in the form of blocks and because

of the nature of these materials, particularly the pressure

sensitive hot melts, there are problems associated with handling

and packaging them. These blocks not only stick or adhere to

hands and/or mechanical handling devices and to each other but

they also pick up dirt and other contaminates. Furthermore, when

these blocks are placed in the melt pot in order to prepare

application, such stickiness can often lead to dangers to the

hands of human operators due to the adhesion of the block being

added. There have been a number of previously proposed methods

and devices for overcoming these problems .

US-A-4 , 054 , 632 proposes a method of continuously extruding

hot melt adhesives under water, which adhesive upon extrusion forms a^' skin. The extrusion is then cut into pillow shaped

blocks by a cutter and the core of the thus produced block slowly

allowed to solidify in a water bath. This method produces blocks

of hot melt adhesives under clean conditions. However, it does

not tackle the problem of handling the blocks of adhesive between

production and use.

Subsequent to US-A-4 , 054 , 632 a number of methods have been

proposed to coat hot melt adhesives with a non-tacky substance.

A number of such methods, for example FR-A-2 , 801, 618 and EP-A-

0,748,673 propose lining a series of moulds with non-tacky

substances and then pouring in the hot melt adhesive and then

finally powdering or covering with a film the surface of mould

to ensure complete coating of the blocks. All of these methods

have the- disadvantage that they require the use of cooled moulds

and a large investment in such apparatus which is expensive to

use and hard to automate .

EP-A-0, 412 , 867 proposed a method of producing a continuous

cord which is coated while being extruded. This method requires

a considerable amount of hardware to ensure that both sides of the flat sheet are coated and also does not adequately cope with

coating the sides or edges of the sheets, leaving opportunities

for contaminants to be picked up or for adhesion to handling

apparatus and personnel .

A further method is proposed in EP-A-0 , 469 , 564 in which

fragments of hot melt adhesive are held in a larger bag of a

plastics material which can co-melt with the adhesive. This

method enables different weights of bag to be produced. However,

this method has problems with regard to the melting of the bag

in the melt pot, in that the bag may not necessarily melt at the

same time as the adhesive, resulting in the remains of the bag

floating to the surface of the melt pot due to trapped air. The

application describes overcoming this problem by evacuating the

bag. However, this ignores the problem associated with handling

such packages as they can easily be damaged with air seeping in

leading to the same problems with the air in the bag.

Furthermore this also requires the use of vacuum packaging

equipment which adds to the cost of production. Therefore, this

does not provide a suitable solution to the handling of hot melt adhesives .

US-A;- 5, 373 , 682 proposes a method of coating extruded hot

melt adhesive with a non-tacky hot melt film. During the

extrusion process the film which melts at a lower temperature

than the hot melt adhesive is constantly sprayed with water or

other coolant. The resultant extruded tube is then pinched, cut

into separate cartridges and allowed to slowly cool for later

use. This method while not having the co-melting problems of the

plastic bags described above still results in the coating film

being added to the melt pot.

WO-A-9700813 proposes modification of this method in which

a string of such cartridges is held under water until the

cartridges have cooled before cutting. This method is

unnecessary to produce the appropriate technical result .

US-A-5, 333,439 and US-A-5 , 392 , 592 propose further methods

of producing a tubular film which coats an extruded string of hot

melt adhesive. In US-A-5 , 392 , 592 such film is designed to co-

melt with the hot melt adhesive. However, in US-A-5 , 333 , 439 the

film is designed to be removed by hand before the block is added to the melt pot. US-A-5 , 333 , 439 has the disadvantage that

producing a coated silicon film is extremely difficult and

therefore the block produced may not necessarily be coated with

the non-tack substance leading to all the usual adhesion

problems, and the crimping of the tube to produce blocks may not

be successful.

It is an aim of the present invention to provide a method

for producing hot melt adhesives which overcomes the above

mentioned problems.

Accordingly the present invention is directed to a

continuous method of producing hot melt adhesive comprising the

steps of forming a plastics material film tube with the inside

coated with a non-tack substance; pumping or pouring molten hot

melt adhesive in liquid form into the tube; cooling the tube with

a cooling fluid; voiding the tube to produce a series of

cartridges of adhesive with the film being substantially free of

adhesive between each cartridge thus produced; allowing the hot

melt adhesive to solidify; cutting the film coating on the

adhesive tube; and stripping the film from the hot melt adhesive. This provides the advantage that films can be used which

will not co-melt with the hot melt adhesive allowing a far wider

choice of films which may be more durable and cheaper to produce.

This also enables a wider choice of operating temperatures for

the pumping of the hot melt adhesive. Thus allowing production

to be run faster if higher temperatures are used. Furthermore,

the film used can be removed in the factory and recycled. This

also ensures that the surface of the hot melt adhesive is coated

with a non-tacky substance which can be incorporated into the

surface of the adhesive without any of the disadvantages of the

aforementioned spraying techniques thus ensures that a small

amount of coating is necessary. This provides the further

advantage that the hot melt adhesive is produced in readily

usable sized blocks. Furthermore, no film is present when the

cartridge is placed in the hot melt pot thus removing the

problems associated with the co-melting of the film and the hot

me11 adhesi e .

Advantageously the plastics material tube is formed by

wrapping the film around a mandrel and forming a seal such that the seal is not inside the thus created tube. This provides the

advantage that when the film is removed the hot melt adhesive

does not retain any of the film inside it, nor does the removal

of the film result in damage to the surface of the hot melt

adhesive .

In the preferred embodiment the cutting of the film is

conducted by cutting means which are on the opposite side of the

tube to the seal .

Advantageously the film is wound off onto two spools as one

side of the tube is cut, on the other the seal is pulled apart

with the cartridge of hot melt adhesive ejected.

Advantageously the method includes the further step of

cooling the string of cartridges by floating them in a fluid bath

which is sprayed with cooling fluid from above. In the preferred

embodiment the cooling fluid is one selected from the following

list: water, cooled glycol, liquid or gaseous Nitrogen,

compressed Carbon Dioxide. Preferably the cooling fluid is

water. This has the advantage that the string of hot melt

cartridges floats on the surface of the water allowing slow consistent cooling of the hot melt adhesive.

Preferably the plastics material film is made from one or

more of the following substances, polypropylene, nylon and

polyurethane . This has the advantage that these film types are

easy to produce and recycle and are readily coated with a non-

tacky substance .

The method of the present invention is adaptable to the

packaging of most types of hot melt adhesive composition. It is

especially adapted to the packaging of thermoplastic or

thermosetting pressure sensitive adhesives where the handling

problems are most severe. As examples the method disclosed

herein may be used to package hot melt adhesives prepared from

polymers and copolymers of synthetic resins, rubbers,

polyethylene, polypropylene, polyurethane, acrylics, vinyl

acetate, ethylene vinyl acetate and polyvinyl alcohol. More

specific examples include hot melt adhesives prepared from the

following:

a. rubber polymers such as block copolymers of monovinyl

aromatic hydrocarbons and conjugated diene, e.g., styrene- butadiene, styrene-butadiene-styrene, styrene-isoprene-styrene,

styrene-ethylene-butylene-styrene and styrene-ethylene propylene-

styrene;

b. ethylene-vinyl acetate polymers, other ethylene esters and

copolymers, e.g., ethylene methacrylate, ethylene n-butyl

acrylate and ethylene acrylic acid;

c. polyolefins such as polyethylene and polypropylene;

d. polyvinyl acetate and random copolymers thereof;

e. polyacrylates ;

f . polyamides ;

g. polyesters;

h. polyvinyl alcohols and copolymers thereof;

i . polyurethanes ;

j. polystyrenes;

k. polyepoxides ;

1. graft copolymers of vinyl monomer (s) and polyalkylene oxide

polymers ; and

m. aldehyde containing resins such as phenol-aldehyde , urea-

aldehyde, melamine-aldehyde and the like. Most' often such adhesives are formulated with tackifying

resins in order to improve adhesion and introduce tack into the

adhesive. Such resin include, among other materials, (a) natural

and modified resins, (b) polyterpene resins, (c) phenolic

modified hydrocarbon resins, (d) coumarone-indene resins, (e)

aliphatic and aromatic petroleum hydrocarbon resins, (f)

phthalate esters and (g) hydrogentated hydrocarbons, hydrogenated

rosins and hydrogenated rosin esters.

Desirable optional ingredients include diluents, e.g.,

liquid polybutene or polypropylene, petroleum waxes such as

paraffin and microcrystalline waxes, polyethylene greases,

hydrogenated animal, fish and vegetable fats, mineral oil and

synthetic waxes as well as hydro-carbon oils such as naphthionic

or paraffinic mineral oils.

Other optional additives may include stabilizers, anti-

oxidants, colorants and fillers. The section of components and

amounts as well as the preparation thereof are well known in the

art and described in the literature.

In a preferred embodiment the film is coated with a release coating which integrates with the surface of the hot melt

adhesive. This provides the advantage that the integration of

the coating with the surface of the hot melt adhesive produces

a non-tack coating for the adhesive. Furthermore, when the

cartridges are produced the coating easily allows the film to be

pinched together to create voids with little adhesive in it.

Preferably the coating is a Fischer-Tropsh wax.

Advantageously the Fischer-Tropsh wax is Sasol HI™ wax. This

provides the advantage that suitable wax coating can be selected

which has improved non-tack characteristics whilst not being

required to hold a string of cartridges together.

Preferably the voiding of the tube is carried out

approximately perpendicularly to the direction of cutting of the

film. Preferably the seal is of an upward fin type.

Preferably the film is multi-layered. This provides the

advantage of giving the film considerably more strength in all

directions .

Advantageously the film comprises two layers of

polypropylene which are bonded together so that their lines of weakness are perpendicular to each other. Advantageously the

film can be tri-layered, comprising a sandwich of polypropylene,

nylon, polypropylene which provides the advantage that nylon has

considerable strength and gives the film considerably higher

strength.

An example of an apparatus used to produce hot melt adhesive

in accordance with present invention is shown in the attached

drawing in which:

Figure 1 shows a schematic view of such an apparatus .

A coated film 10 is fed through a mandrel 12 in which the

film 10 is fin sealed by a tack weld to form a tube 14. The tube

14 has the wax coating on its inside and has the seal on its

outside. The film 10 may be coloured for instance blue or red,

this aids checking that all the film 10 has been removed from the

molten hot melt adhesive at a later stage. The tube 14 is fed

through a heated injection machine 16 in which molten hot melt

adhesive 18 is pouring into it at between 10 and lOOpsi at a

temperature above the melting point of the film coating. The

pressure of pouring of the hot melt adhesive defines the speed of the film feed and is dependent on the adhesive being used.

During the injection process the tube 14 can be constantly

sprayed with water by spraying apparatus 20 which surrounds the

tube 14. This ensures that if the plastics material of the tube

14 melts at a temperature lower than that of the melting point

of the adhesive it does not melt. The tube 14 is then fed

through a voider 22 in which two rollers 24 are hydraulically

pressed together to create areas of the tube 14 where there is

minimum adhesive, thus creating pillow like cartridges 28 of

adhesive whose size is set by the time delay between each

pressing. Rollers 24 are used as they avoid breaks in the tube

14. This is facilitated by the still semi-liquid state of the

hot melt adhesive. Preferably the film seal is at approximately

90° to the rollers 24. The whole apparatus can still be

constantly sprayed with water. The voider 22 can be adapted to

create varying sizes of adhesive cartridge 28 depending upon

customer requirements. A string 26 of cartridges 28 is then

floated down a water bath 30 whilst its top surface is sprayed

with water. The string 26 concertinas in the water bath 30 thus allowing a greater use of the surface area of the bath 30 and

thus requiring a smaller bath 30 for cooling the cartridges 28.

The string 26 of cartridges 28 is then removed from the water

bath 30 and passed through a high pressure water cutter 32 in

which the jet of water cuts the film 10 on the top side of the

cartridge 28, approximately opposite to the location of the fin

seal. The water jet is at a pressure of between 200 and 500 bar,

if too much pressure is used the jet forces the film 10 into the

cartridge 28. Water cutters have the advantage that they follow

the contours of the string of cartridges 28 with no physical

contact. Other suitable cutting machines may be used such as

lasers. The film 10 is then pulled off the cartridges 28 by

rollers 34 which break at the fin seal on the uncut side of the

cartridge and wound onto two winders 36 on either side. The

speed of the winders 36 is the same as the speed of production.

The cartridges 28 ejected from the string 26 and pass onto a

conveyor 38 which is sprayed with water to wash away any surplus

material. The cartridges 28 are finally passed through a dryer

40 before they are packaged for supply to a customer. An example of hot melt adhesives that can be packaged using

the method comprises the following percentage constituents by

weight

20% Styrenic block copolymer e.g. SIS (Kraton D 1107) or Erichon

Sol T166

60% Hydrocarbon resin or resin blend e.g. Escorez 5300.

Kristallex 3115

19% Plasticiser e.g. mineral oil such as Odina 68.

1% Stabiliser package e.g. Irganox 1010, Polygard TNPP

An example of the film can comprise a sandwich with the

following thicknesses: 25 micrometers of polypropalene on top

of 15 micrometers of biaxial nylon on top of 47 micrometers of

blue polypropalene with 20 micrometers thickness of Sasol HI wax

present. The film is coated with the wax across its entire width

as the wax does not interfere with the fin seal when the tube is

created.- Another example of a film suitable for use with the

present method comprises the following - 50 micrometers of blue

tinted co-extruded polypropalene film, 44.9 grammes per square meter, with 1.5 grammes per square meter of adhesive on top of

50 micrometers of blue tinted co-extruded polypropalene film

which is orientated in a different direction to the top film at

44.9 grammes per square meter and coated with Sasol wax HI at 20

grammes per square meter. This film is designed to withstand

temperatures of 150 °C without distorting.

Claims

1. A continuous method of producing hot melt adhesive

comprising the steps of

a) forming a plastics material film tube with the inside coated

with a non-tack substance;

b) pumping or pouring molten hot melt adhesive in liquid form

into the tube;

c) cooling the tube with a cooling fluid; sealing the hot melt

adhesive filled tube;

d) voiding the tube to produce a series of cartridges of

adhesive with the film being substantially free of adhesive

between each cartridge thus produced;

e) allowing the hot melt adhesive to solidify;

f) cutting the film coating on the adhesive tube; and

g) stripping the film from the hot melt adhesive.

2. A method according to claim 1, in which the plastics

material tube is formed by wrapping the film around a mandrel and

forming a seal such that the seal is not inside the thus created tube .

3. A method according to claim 1 or claim 2, in which the

cutting of the film is conducted by cutting means which are on

the opposite side of the tube to the seal.

4. A method according to any preceding claim, in which the film

is wound off onto two spools as one side of the tube is cut, on

the other the seal is pulled apart with the cartridge of hot melt

adhesive ejected.

5. A method according to any preceding claim in which the

method includes the further step of cooling the string of

cartridges by floating them in a fluid bath which is sprayed with

cooling fluid from above.

6. A method according to any preceeding claim, in which the

cooling fluid is one selected from the following list: cooled

glycol, liquid or gaseous Nitrogen, compressed Carbon Dioxide,

water.

7. A method according to any preceeding claim, in which the

plastics material film is made from any one of the following

substances, polypropylene, nylon and polyurethane.

8. A method according to any preceeding claim, in which the

film is coated with a release coating which integrates with the

surface of the hot melt adhesive.

9. A method according to claim 8, in which the coating is a

Fischer-Tropsh wax.

10. A method according to any preceeding claim, in which the

voiding of the tube is carried out at approximately

perpendicularly to the direction of cutting of the film.

11. A method according to any preceding claim, in which the seal

is of an upward fin type.

12. A method according to any preceding claim, in which the film

is multi- layered.

13. A method according to claim 12, in which the film comprises

two layers of polypropylene which are bonded together so that

their lines of weakness are prependicular to each other.

14. A method according to claim 12, in which the film is tri-

layered comprising a sandwich of polypropylene, nylon,

polypropylene .

15. A package of hot melt adhesive produced according to any of the preceding claims.