CA2125076A1 - Process for the production of heat-activatable mats free from supports and release agents and their use for bonding various substrates - Google Patents

Abstract

A PROCESS FOR THE PRODUCTION OF HEAT-ACTIVATABLE MATS
FREE FROM SUPPORTS AND RELEASE AGENTS AND THEIR USE FOR
BONDING VARIOUS SUBSTRATES

A b s t r a c t The invention relates to a process for the produc-tion of heat-activatable mats based on hydroxyl polyester polyurethanes which are free from supports and release agents and which have viscosities of 600 to 3500 mPa.s, measured as solution viscosity in methyl ethyl ketone (15% Brookfield LVT viscosimeter, spindle 3, 60 r.p.m., 23°C) and weights per unit area of 5 to 200 g/m2, charac-terized in that the mats are produced by melt blowing (for example REICOFIL? melt blowing process) at melt temperatures in the range from 230 to 260°C using a receiving conveyor belt of which the constituent material has a surface tension of 18.5x10-5 N/cm to 46x10-5 N/cm.
The mats produced by the process according to the invention can be wound into rolls without blocking despite the absence of release agents or spacers and are eminently suitable for bonding various substrates.

Description

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A PRoCEæs FOR THE PRODUCTION OF HEAT-ACTI~ATABLE MAT~
F~E~ FROM ~UPPORT~ ~ND RELEASE AGENTS AND THEIR USE ~OR
BONDING V~RIOUS ~UBSTRATES

This invention relates to a process for the produc-tion of heat-activatable mats based on hydroxyl polyester polyurethanes which are free from supports and release agents and to their use for bonding various substrates.
It is known that various substrates can be bonded with solvent-containing adhesive systems or with solvent-less adhesive systems based on hydroxyl polyester poly-urethanes, for example by using hotmelt films (see, for example, H.J. Studt in Coating 2/93, pages 34 et seq.).
The disadvantage of solvent-containing adhesive systems lies on the one hand in the pollution of the environment by solvents which are released during the bonding process and, on the other hand, in their long processing cycles which entail high subsequent costs. Accordingly, there is a tendency for economic and anti-pollution reasons to use solventless adhesive systems for bonding various substrates.
In the case of solventless adhesive systems, for example where heat-activatable films based on hydroxyl polyester polyurethanes are used, disadvantages include their low permeability to gases and their feel-hardening effect, which is particularly noticeable in the bonding of textiles, and also the relatively high weight per unit area which involves higher material costs.
For the reasons mentioned above, therefore, the use ~of heat-activatable films based on hydroxyl polyester polyurethanes is confined to industrial applications, for example laminated parts for the interior trim of motor vehicles. Although, in this field of application, more adhesive has to be continuously applied for some com-posite structures, for example to arrest elastic forces Le A 29 772 - 1 Foreign Countries .. . ~

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- , of thermoformed flexible PVC films, there are sufficient potential applications where adhesive can be applied in relatively small quantities and a continuous, film-like surface structure of the adhesive applied is a disad-vantage.
The heat-activatable films to be used for bonding various substrates may be produced by various methods.
The production of elastomeric films, for example from polyurethanes, by co-extrusion is generally known (DE-A 2 114 065, US 3,880,691). The flat materials obtained do not contain any release agents or spacers.
A major disadvantage of this process lies in the complex process technology involved (2 extruders and a blowing head with 2 concentric annular nozzles~ and in the accumulation of a release film which cannot be put to any subsequent use.
The production of films from thermoplastic elas-tomers, for example polyurethanes, by monofilm extrusion blow molding is also known.
To enable the advantage of this process in terms of lower capital investment in machinery to be fully util-ized, an internal release agent or spacer has to be added to the relatively very tacky thermoplastics before blow molding of the film because otherwise the lengths of film stick to one another after laying flat by means of a squeezing roller and can no longer be separated there-after.
In addition, these release agents or spacers are used to avoid blocking of the wound and separated lengths of film as a result of post-crystallization. At present, waxes and/or organic additives, as described for example in A) H. Saechtling, Kunststoff-Taschenbuch, 25th Edition, Carl-Hanser-Verlag Le A 29 772 2 . .
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B) Becker/Braun, Kunstst~ff-Handbuch Vol. 7, Polyure-thane, Carl-Hanser-Verlag C) Xunststoffe 80 (7), pages 827 et seq. (1990) D) Gachter/Muller, Kunststoffadditive, 3rd Edition, Carl-Hanser-Verlag, are suitable spacers or release agents. However, it is also known that, with certain substrates, the addition of release agents or spacers results in a reduction in adhesive strength. Polymeric spacers as described, for example, in EP 0 526 858 are also used. They are at-tended by the disadvantage that the mechanical properties of the resulting sheet-form materials can be undesirably affected. In addition, a distinct change in activat-ability compared with the starting material used andchanges in the specific adhesion to certain substrates cannot be ruled out.
Accordingly, the problem addressed by the present invention was to avoid the above-mentioned disadvantages attending the use of solvent-containing adhesives and also the use of solventless adhesives, such as films.
Some of the disadvantages mentioned can be avoided by using heat-activatable mats in the bonding of various substrates, particularly where the melt blowing process (for example REICOFIL~ melt blowing process) is used to produce the mats.
Accordingly, the present invention relates to a process for the production of heat-activatable mats based on hydroxyl polyester polyurethanes which are free from supports and release agents and which have viscosities of 600 to 3500 mPa.s, measured as solution viscosity in methyl ethyl ketone (15%), and weights per unit area of 5 to 200 g/m', characterized in that the mats are pro-duced by melt blowing (for example REIC0FILX melt blowing process) at melt temperatures in the range from 230 to Le A 29 772 3 .: ' ' , :

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212~76 260OC using a receiving conveyor belt of which the constituent material has a surface tension of 18.5x10-5 N/cm to 46x105 N/cm.
The present invention also relates to the use of the mats produced by the described method for bonding or coating various substrates.
The heat-activatable mats free from supports and release agents produced by the process according to the invention preferably have weights per unit area of 8 to 50 g/m2 and, more preferably, in the range from 10 to 30 g/m2. The weights per unit area of the mats are deter-mined by the substrates used in the bonding process and, if required, may even extend to relatively high weights per unit area, particularly when any unevenness is to be made level in the bonding process.
The raw materials based on hydroxyl polyester poly-urethanes used in the process according to the invention preferably a viscosity of 1500 to 2100 mPa.s, measured as solution viscosity (15%) in methyl ethyl ketone (Brook-field LVT viscosimeter, spindle 3, 60 r.p.m., 23OC3.
Particularly suitable hydroxyl polyester polyure-thanes are those obtainable by reaction of organic iso-cyanates with preferably difunctional polyester polyols containing alcoholic hydroxyl groups and low molecular weight diols as chain extending agents, an NCO:OH equiva-lent ratio of 0.9:1 to 0.999:1 being maintained during the reaction, as described in EP 0 158 086 and in DE-PSS
1 256 822, 2 161 340 and 3 502 379.
Particularly suitable dihydroxypolyesters are those having a molecular weight above 600, preferably in the range from 1200 to 6000 and more preferably in the range from 2000 to 4000 g/mol, which may be obtained in known manner from alkane dicarboxylic acids preferably contain-ing 6 carbon atoms and alkanediols preferably containing at least 4 carbon atoms. Suitable dicarboxylic acids Le A 29 772 4 . . ... .

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are, for example, adipic acid, sebacic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid. Suitable alkanediols are, for example, butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol. ~he chain extending agents are, in particular, diols or diol mixtures with molecular weights in the range from 62 to 300 and preferably in the range from 62 to 150 g/mol. Suitable diols such as these are, for example, alkanediols preferably containing 4 to 6 carbon atoms, such as butane-1,4-diol, pentane-1,5~diol and hexane-1,6-diol.
Examples of suitable diisocyanates are 1,6-diiso-cyanatohexane,1,4-diisocyanatocyclohexane,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane,methylene bis-(4-isocyanatocyclohexane), 2,4- and optionally 2,6-diisocyanatotoluene, 4,4'-diisocyanatodiphenyl methane, 4,4'-diisocyanatodiphenyl-2,2-propane and mixtures of such isocyanates. In a particularly preferred embodi-ment, 4,4'-diisocyanatodiphenyl methane is used as a reaction component.
As already mentioned, the mats according to the invention are produced by melt blowing, more particularly using melt temperatures (measured before the spinning nozzles) of 230 to 260C. The melt blowing process is described in detail in DE-OS 19 64 060 and in DE-OS 23 08 242 and consists essentially of a specially designed forming tool for polymer filaments which follows an extruder and of which the principal feature lies in the fact that a directed, heated airstream is associated with each individual nozzle, ensuring that the issuing polymer filaments are highly stretched and broken under con-trolled conditions. The hot air can be directed onto the polymer melt from slots closely adjacent on 2 sides or, alternatively, the polymer melt can flow from an annular bore around the inner melt bore.
The issuing filaments are deposited onto a moving Le A 29 772 5 , : ~' . ~: , . .... . .
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-` 212~076 receiving surface, for example in the form of a circulat-ing conveyor helt.
In the process according to the invention, it is important to use a conveyor belt of which the constituent material has a surface tension of preferably 18.5x10-5 to 33x105 N/cm. Teflon-coated textiles, for example, may be used as constituent materials for the conveyor belt.
The bonding of various substrates may of course also be carried out by directly coating the substrate to be bonded with the mat produced by the process according to the invention and initiating the bonding of the sub-strates by heat activation of the mat (for example by exposure to infrared radiation or by contact heat).
Various methods may be used for bonding substrates with the mat produced by the process according to the inventlon .
In the case of precoated substrates (for example flexible PVC foam sheets, TPU sheets), vacuum forming, thermoforming, vacuum thermoforming, are used for the production of molded articles for roof elements, side panel elements or back-foamable composites for the production of seats, etc. Such processes are known and are described in detail, for example, in Saechtling "Kunststoff Taschenbuch", 21st Edition, 1979, pages 140 25 to 184.
A large number of substrates can be bonded to substrates of the same kind or to substrates of different kinds with the mat produced by the process according to the invention. In addition to the flexible PVC and TPU
surface sheets mentioned, such substrates include in particular various textile materials based on cotton, cotton/wool blends, wool, wool blends, polyester and polyamide fabrics and polyolefins.
It was surprising to find that hydroxyl polyester polyurethanes could be processed to mats by melt blowing Le A 29 772 6 - , ~ i:: : - :
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because the high melt temperatures required for melt blowing, which are about 500C above the temperatures applied in conventional film production processes, had been expected to lead in hydroxyl polyester polyurethanes to such a pronounced shift in equilibrium in favor of the starting components that at best oligomeric products which could not longer be hardened to form a mat would be obtained.
In addition, it had been expected that cohesive strength would no longer be sufficiently present in bonds formed with the mats through degradation of the polymer.
This is not the case.
In the prior art, there is a limited number of known raw materials which can be made into mats by melt blow-ing. The raw materials in question are, in particular,polymers which completely solidify in amorphous or partly crystalline form, such as for example polypropylene and polystyrene. The polymers mentioned generally have the property of developing a completely tack-free surface immediately after falling below a temperature of around 70C. Hydroxyl polyester polyurethanes with a segmented soft segment/hard segment structure show more critical behavior in this regard. Thus, recrystallization of the hydroxyl polyester polyurethane processed by extrusion requires a much longer time compared with the polymers mentioned above and, in any event, requires a temperature below a melt temperature of 50c in the extrudate. This behavior of segmented polyester urethanes generally leads to the above-mentioned disadvantages of production in the presence of release agents or spacers and blocking of the extrudates on the roll.
It has surprisingly been found that the hydroxyl polyester polyurethanes mentioned, which are deposited as random fibers, develop a tack-free surface shortly after deposition onto the conveyor belt of the melt blowing Le A 29 772 7 . :
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By virtue of the minimal fiber denier (approximately O.l dtex), the mat obtained is distinguished by high surface coverage (covering power), even when applied in small quantities. Even if it is applied in large quanti-ties of 30 g/m2 to textiles, a soft feel is maintained.
Permeability to air can be selectively established, depending on the quantity applied.

Examples The tests described in the following were carried out in a commercial REICOFIL~ melt blowing machine (prod-uction width 1 meter). The thermoplastic elastomeric hydroxyl polyester polyurethanes were predried for 12 hours in a SOMOS~ air dryer.

Example 1 The extruder and mold temperature were adjusted to give a melt temperature of 250C before the spinning nozzles. The hydroxyl polyester polyurethane (solution viscosity 2000 mPa.s) was extruded at a screw speed of 5 r.p.m. The output of the spinning pump was adjusted to 4 r.p.m. The resultinq extruder output was 22 kg/h and the resulting extruder/nozzle melt pressure was 40~16 bar. After stretching by the compressed air preheated to 220C and the controlled filament breakage, the polymer filaments issuing from the melt nozzles were deposited 30 ~ onto a circulating conveyor belt with a surface tensionof 30-10-5 N/cm and delivered from there to an inter-mediate takeoff station where the edges were cut. The mat was then wound onto 1000 mm cardboard tubes. Dif-ferent weights per unit area were adjusted by varying the rate of travel of the mat and/or the throughput. The mat Le A 29 772 8 . .. :. , : , . . ~ - .
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was wound onto the tubes in lengths of 200 meters per ~ `
test. The mats could readily be offwound from the tubes at any time.

Bxample 2 The extruder and mold temperature were adjusted to give a melt temperature of 250C before the spinning nozzles. The hydroxyl polyester polyurethane (solution viscosity 1200 mPa.s) was extruded at a screw speed of 4 r.p.m. The output of the spinning pump was adjusted to 4 r.p.m~ The resulting extruder output was 22 kg/h and the resulting extruder/nozzle melt pressure was 40/30 bar. After stretching by the compressed air preheated to 220C and the controlled filament breakage, the polymer filaments issuing from the melt nozzles were deposited onto a circulating conveyor belt with a surface tension of 30-10-5 N/cm and delivered from there to an inter-mediate takeoff roller where the edges were cut. The mat was then wound onto 1000 mm cardboard tubes. Different weights per unit area were adjusted by varying the rate of travel of the mat and/or the throughput. The mat was wound onto the tubes in lengths of 200 meters per test.
The mats could readily be offwound from the tubes at any time.
Exampl~ 3 -In the same way as described in Example 1, the hydroxyl polyester polyurethane was directly applied as a mat to a TPU surface sheet (thickness 100 ~m). In this case, too, the mats were wound onto 1000 mm cardboard tubes after the intermediate takeoff and edge trimming stations. The mats could readily be offwound at any time.

Le A 29 772 9 Example 4 The procedure was as described in Example 3 using a flexible PVC (foam) sheet. The adhesion of the melt blown mat of the hydroxyl polyester polyurethane was sufficient to guarantee problem-free winding and offwind-ing of the coated mat.

Example 5 As in Example 3, the hydroxyl polyester polyurethane was directly applied in the form of a mat to a cotton fabric. The adhesion of the mat to the cotton fabric was again excellent. Bonds between this cotton fabric coated with varying quantities of material and an uncoated cotton Iabric produced the peel strengths shown in Table 1 below.

Table 1:
Bonding Sample Quantity Peel temperature code applied strength (C) ~~~~ (g/mZ) (N/5 cm) 100 PUR Example 1 10 12.5 100 PUR Example 1 24.0 100 PUR Example 1 30 38.5 120 PUR Example 1 10 16.5 120 PUR Example 1 20 31.0 120 PUR Example 1 30 35.0 140 PUR Example 1 10 16.5 , I
140 PUR Example 1 20 35.0 140 PUR Example 1 30 41.5 .
160 PUR Example 1 10 20.0 160 PUR Example 1 20 39.0 160 PUR Example 1 30 51.5 Le A 29 772 10 ,, , , -, .. .

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¦ 100 PUR Example 2 10 13.5 100 PUR Example 2 20 27.5 _ 100 PUR Example 2 30 46.0 I
¦ 120 PUR Example 2 10 16.5 120 PUR Example 2 20 29.0 I
120 PUR Example 2 30 42.5 140 PUR Example 2 10 14.0 140 PUR Example 2 20 30.0 140 PUR Example 2 30 43.5 160 PUR Example 2 10 16.0 160 PUR Example 2 20 36.0 160 PUR Example 2 30 53.5 ,:
Pressure applied: 1 bar : ~:
Pressing time: 20 seconds Le A 29 772 11

Claims (2)

1. A process for the production of heat-activatable mats based on hydroxyl polyester polyurethanes which are free from supports and release agents and which have viscosities of 600 to 3500 mPa.s, measured as solution viscosity in methyl ethyl ketone (15% Brookfield LVT
viscosimeter, spindle 3, 60 r.p.m., 23°C) and weights per unit area of 5 to 200 g/m2, characterized in that the mats are produced by melt blowing (for example REICOFIL?
melt blowing process) at melt temperatures in the range from 230 to 260°C using a receiving conveyor belt of which the constituent material has a surface tension of 18.5x10-5 N/cm to 46x10-5 N/cm.

2. The use of the mats produced by the process claimed in claim 1 for bonding and coating various substrates.