DE2045558A1 - Process for the manufacture of elastomeric silicone films - Google Patents

Description

DR. MÖLLER-BORG Dl PL-PHYS. DR. MAN ITZ D I PL-CHEM. D R. D EU FEL

DIPL-ING. FINSTERWALD D I PL-I NG. GRÄMKO W 2045558 PATENT LAWYERS

15. SE ?.

Lo / Sv - N 1032

NATIONAL RESEARCH DEVELOPMENT CORPORATION Kingsgate House, 66-74- Victoria Street, London S.W.1, England

Process for the production of elastomeric silicone films

Priority: Great Britain from September 15, 1969, No. 45411/69

The invention relates to polysiloxanes and, more particularly, to the manufacture of elastomeric silicone films.

The properties of silicone elastomers have been known for many years. The permeability of elastomeric silicone films particular attention was paid to certain gases and offered the possibility of new and improved ones Membrane for oxygen generators, gas separators and other devices in which this property is

to deliver.

turns we & j / some years ago it was shown possible is, strong (solid) elastomeric silicone films with a thickness of the order of a few hundredths

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To produce millimeters, which showed sensational properties in terms of oxygen permeability, however, the introduction of such films in practical use has been delayed by many problems related to the attempt occurred to adapt the procedure to the requirements of large-scale manufacture. In particular It turned out that the development of a continuous process for the production of such film having had numerous difficulties with the desired combination of properties, and despite considerable difficulties Efforts devoted to this problem have not resulted in a reliable and reproducible one Procedure.

It has now been found that it is possible to use elastomeric silicone films of remarkably good quality and by a continuous process to produce by one Attention to a number of important and in some cases critically essential factors and operating conditions was given, which are explained in more detail below.

The method according to the invention is based on a raw polysiloxane Rubber raw material which, in its commercially available form, is usually a suitable filler contains / adds strength to the finished film To give. It has been found that silica or any other conventional filler which in varying amounts, e.g. from about 30% by weight to about 50% by weight of the polymer, films with excellent Provides strength for the purposes of the invention. The amount of filler can be easily adjusted to the desired Value can be adjusted by adding unfilled or heavily filled rubber raw material as required is admixed.

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The raw rubber raw material is ground to soften it and produce a mass of homogeneous consistency, and then a catalyst is added and uniformly dispersed therein. Catalysts from the class of peroxides are commonly used for curing silicone elastomers and have been found to be particularly suitable for purposes of the invention. Benzoyl peroxide, dicumyl peroxide and 2,4-dichlorobenzoyl peroxide gave excellent results, the latter being particularly preferred. Catalyst concentrations of from about 1 to about 10 percent by weight of the rubber starting material have given very satisfactory results and within this range a concentration of from about 2 to about 4 percent has been found to be preferred in most cases. The preferred catalyst, 2,4-dichlorobenzoyl peroxide, was used in varying concentrations from about 1.5 to about 6 percent , and particularly excellent results were obtained with about 4 percent by weight of this catalyst. The catalyst can be effectively dispersed in the rubber raw material in a rubber kneader or equivalent device.

The elastomer provided with filler and catalyst is then brought into the form of a film solution with organic solvents. Suitable solvents are those which can be removed by evaporation below the temperature at which the catalytic curing reaction takes place at an appreciable rate. Solvents which easily evaporate at temperatures up to about 100 ^° C. are recommended, in particular hydrocarbon solvents and mixed solvents. Toluene and xylene are examples of aromatic hydrocarbons which can be used to advantage and these have given the best results when mixed with commercially available isoparaffin fractions.

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the. Mixtures of toluene or xylene with Esso 10, for example in equal parts by volume, gave excellent film-forming compositions. The concentration of the rubber starting material in the film solution is particularly important, and it has been found that it is preferred to operate with a solids content which is appreciably higher than would be expected. Thus, the solution or dispersion should contain no less than about 20% solids, and in fact the solids content can be increased up to as high as about 60 % . Conventional solutions with at least 30 % or more solids give better results than those obtained with dilute film solutions. Tests have shown that the solids content necessary to achieve the best films varies to a certain extent with the properties of the starting polymer, which is commercially available from a number of possibilities and in different types. For some materials, a solids content of 20 - 1 ) Q% is optimal, while with others better films are obtained from film solutions which contain 30 - 50% solids, with values in the range of 40 % producing outstanding films.

The importance of using stiffer film solutions is related to the fact that films with the desired Properties and the desired performance can be obtained by means of a single coating operation can. Indeed, studies have shown that films deposited in this manner are generally more superior show, compared to those obtained using successive coating steps, whereby a film of the desired thickness is built up in stages. Films of the latter type tend to Occurrence of decoating and other defects to show which they are less suitable for certain specialized applications make suitable.

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It has been found that to achieve the most reliable Results are highly desirable, slides off to deposit the film solution on a horizontal substrate or support, which one is continuous moving surface provides for continuous operation. A slight deviation from the horizontal position is sometimes permissible, but poorer results are obtained if the inclination of the wearer is opposite the horizontal is too strong. The coating of the solutions of the elastomeric films on a moving belt, which runs in the vertical direction has been found to be less than satisfactory for purposes of the invention. The support on which the film is deposited may be that of which the elastomeric Films are peeled off at the end of the process, e.g. "Melinex" film (Melinex is a trade name for a synthetic polyester film that is stretched during manufacture to improve strength and heated). Alternatively, the carrier may be one to which the elastomer adheres so that a backed or reinforced film is formed, and in this case the backing material should be such, that it itself has permeable properties. In any case, it is necessary that the carrier material is sufficient Has heat resistance to temperatures at which the "silastomer film" subsequently cures or is vulcanized to degenerate.

It has been found that the manner in which the film solution is applied to the substrate is very important. Preferably, the film solution is spread or poured onto the substrate, and a precisely ground one Squeegee is used to gauge the thickness of the layer of elastomer which is used in subsequent stages of the process is promoted to steer. The geometrical

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Draw between the squeegee and the carrier is also of great importance and it requires careful attention, to achieve a uniform and continuous film. Although it is possible the substrate to allow the squeegee to approach horizontally, it has been found that it is preferable to approach the squeegee from below and in is allowed to approach an ascending direction so that the film solution supplied to the substrate is subjected to a combination of forces as it approaches the doctor blade. As a result of their own weight the film solution tends to flow downward against the movement of the carrier, but this becomes downward movement the film solution counteracted by the upward movement of the carrier, and the resulting movement of the film solution represents a rotary movement in the direction of the doctor blade. It is assumed that this rotary flow within the film solution is of paramount importance to eliminate air pockets and foaming of the material, which cause irregularities in the layer of film solution that passes through the doctor blade.

The supported on the carrier elastomers layer is then subjected to heat treatment in two separate steps depending on the requirements in one or more treatment furnaces, the purpose of the first stage, mainly the removal of solvent by evaporation, and the solvents of the type described above, this takes at relatively low temperatures, for example temperatures not exceeding about 100 C, instead. In this process step, the elastomers is during and after the removal of the solvent in a very tacky state and must therefore not in contact ". If kick the elastomer is deposited on an impenetrable carrier from which it is to be printed later with any other surfaces, can carry the supporting fabric or belt through the oven by means of a number of

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the rollers are guided. However, if the elastomer has been deposited on a porous material, e.g. a textile product with enough open tissue to hold the silastomer solution To allow the goods to penetrate, the use of support rollers is completely inadequate. Another important one The feature of the invention, which relates to the coating of elastomers on porous supports, resides in the Technique for carrying the coated goods by means of a gaseous carrier, e.g. in the form of a "gas cushion" or can assume a range of gas flows. That to eradicate the The gaseous medium used is advantageously also used as a means for supplying heat to the goods Elastomer solution used to evaporate the solvent and flush it out of the system. Advantageously hot air is used for this purpose.

The second stage of the heat treatment is vulcanization or Curing stage, and for this purpose somewhat higher temperatures are used, for example from about 120 to 180 ^° C. The curing time naturally varies depending on the temperatures chosen, but it is usually not less than about 50 seconds and not more than about 30 minutes In practice, a period of about 1 to 4 minutes has been found to be particularly suitable for curing. Additional strength can be obtained by a further curing period between 130 ° - 180 ⁰ C are obtained. The optimal duration of post-curing depends on the catalyst concentration and the proportion of silicone elastomer in the film solution.

The invention is illustrated by means of the attached, schematic Drawing explained below.

The support on which the silicone elastomer film is to be deposited is a commodity 1 drawn by a roller 2

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which is driven by means of drive devices (not shown). The goods 1 pass over guide rollers 3 and 4 and then over an edge part 5 ^from which they migrate from left to right in the horizontal direction as shown in the figure. A doctor blade 6 cooperates with the edge part 5.

The direction in which the goods pass between the guide rollers 3 and 4 is at an angle "b" and the direction of the goods between the guide roller 4 and the edge part 5 is indicated at an angle "a". The angles a ™ and b represent the inclination of the goods in relation to the horizontal The angle "a" can be between 10 ° and 45 ° and the Angle "b" vary between about 10 ° and about 60 °.

Adjacent to the doctor blade 6 is a feed funnel 7, which feeds the film solution of the elastomer to the goods, while this moves in the direction of the doctor blade 6. The layer thickness of the film solution supplied to the product 1 of the elastomer is controlled by the distance between the doctor blade and the fabric, e.g. a gap of 0.1 to 0.89 mm (4 to 35 thou). However, the relationship between the distance of the doctor blade and the thickness of the film solution layer also depends on the ^ Viscosity of the film solution and the angles "a" and "b".

The coated goods 1 occurs at one end of a furnace designed in the form of two sections, an evaporation section 8 and a hardening section 9, which are passed through a Partition wall 10 with a central, transverse slot through which the coated goods from a section can pass through into the other.

In the oven, the coated goods are only carried by means of currents of hot air which hit the upper ones and lower surfaces of the goods, as indicated by the arrows in the drawing, impinge.

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The "coated goods leave the hardening section 9 and then pass over a guide roller 11, from which they run to a take-up roller 12. ***"

If an unsupported film is desired, a scraper 13 is provided and also a take-up roll 14 for winding up the removed film.

When working with a film solution which contains about 35 % solids and a doctor blade spacing of 0.25 mm (10 thou), the coated material is pulled through the evaporation section 8 and the hardening section 9 at a speed of 0.3-3 m / min, wherein the film or the film of a pre-cure of 20 see to 4 min at 70 - 8O ⁰ G, is followed by a same curing period at temperatures of 150 ° C 18O subjected. The film or the film is then subjected to post-cure from 5 "to 20 min at 150 - 180 ⁰ C subjected According to this method may membrane with a thickness of, for example eiftes-S ^ æske-v 0.005 -. 0.1 mm easily prepared . These are easily removed from a ftelinex-carriers, and they give remarkably good speed of so ^ ceiten in üauerstoffdiffusion and they are virtually free of voids and other defects. M

The invention has been carried out using the method described above with a wide variety of silicone elastomers, including e.g. dimethylvinylsilastomers, polydimethylsilastomers, Polymethylvinylsilastomers and polyphenylmethylsilastomers; these products are made by Midland Silicons Ltd. with the designations No. 2421 and 2421-U, 156, 2211, 2430, 2642, K9696 and K55, 2403, Polysil 2449 and ESP.2480 manufactured.

These are either unfilled, i.e. not provided with filler, rubber starting solutions or silica-filled rubber raw materials, with

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Exception to No. 2403, which is filled with polytetrafluoroethylene (trade name Fluon). These materials, with which the preferred catalyst 2,4-dichlorobenzoyl peroxide is rolled into the rubber starting material via a calender (twin roll mill) usually in a concentration of the order of 2 % , are carefully mixed with smoldering toluene, which is mixed with Esso 10 in such a way that a gel-free, clear dispersion is produced in a concentration preferably above 30 % and with a viscosity within the range from 40,000 to 120,000 cP. The dispersion is then filtered through a 0.1 mm (150 mesh) stainless steel filter. In order to produce backing-free films, the film solutions are spread out on a polyethylene terephthalate film (Melinex polyester) which has been treated with a 5% solution of the separating agent "Separoid" in acetone / water = 50/5. The knife gap is set so as to produce the desired layer thickness, and then the carrier film and the rubber starting material or the rubber stock successively through the ovens at 70 to 8O ⁰ C and 140 to 20O ⁰ C for from 2 to 8 min in each furnace, usually at a speed of at least 0.3 m / min (1 ft. per min). An excellent continuous sheet free of holes is produced which has the oxygen permeability usually in the range of 150 to 500 cc / m / min at a pressure of 55 mm Hg. Typical results are shown in the table below. These values were obtained with a catalyst concentration of 2.4% and a toluene / Esso 10 mixture of 50/50 and at take-up speeds of 0.61 m / min (2 feet per minute). The doctor blade gap and the film thickness are given in mm (1/1000 inch) and the values of the oxygen permeability in ecm /

m / min.

- 10 -

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Tabel

oilicer

Fcftr.toffe Yo

2421 Γ ρ 24 · ν; P 2 - ': - V?

2-421 + 2704 resin 2403 (fluorine,) 2421 U ESF 24S0 2421 TJ

2421 TJ (£ 3.0> cat.)

2421 TJ Ι5ό

2421 Z

35

35

35

50

31 20 25 60

gap

mm
(1 / 1CCC i:

2C)

Ut-. menu.!

abilit;

inch)

O'O 0.0 * 3 (1.7)

C, 31 (12) C, 0 ^ 3 (1, ^)

p. on, fi-Λ r. porrf ^ i -N

C, 102 (4th, C) 0.06 ^ (2.3) C, 07o (3, C)

, 7)

0.018 (0.7) 0.030 (1.2) 0.061 (2, ^) 0.076 (3.0)

"2" Z

Gaviebsn

To silicone elastomers nit reinforcing goods :: czv :. au laiui: Iieren (making laminates) can be a similar one Working method applied. The reinforcing material, which is a polyamide or polyester material or a Another type of porous ware can be lowered onto the elastomer film that is supported by the Helinex film so that it is propelled through the hot air passing through the oven and into the upper layers of the elastomer is embedded prior to curing. Alternatively, the goods can be passed through the doctor blade together with the elastomer dispersion v / ground and the impregnated product can be placed on a previously cast elastomeric film that is placed on the Melinex film is carried, lowered v / ground.

In all cases there are also other carriers than "Melinex" film possible, e.g. glass fabric, hose bodies, paper, cellulose, Acetate paper and other thermoplastics.

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BATH ORIGINAL

Claims (20)

2 Ü k 5 5 5 8 Claims (1. Approach to continuous or semi-continuous V "/ Production of elastomeric silicone foils or films, gekennz thereby that a silicone rubber starting material and catalyst in a solvent containing IiImIösung with a solids content of at least 20 wt.% Is applied to a practically horizontally moving carrier, the carrier and the the silicone layer located thereon in a first oven, in which the solvent present in the film solution is evaporated, and then in a second oven, in which the elastomer cured or vulcanized is carried out. 2. The method according to claim 1, characterized in that a film solution is used which contains 20 to 60 % solids. 3- The method according to claim 2, characterized in that that a film solution is used which contains 30 to 50% solids. 4. The method according to claim 1, 2 or 3, characterized in that a rubber starting material is used which contains 30 to 50% by weight of a filler, 5. The method according to any one of claims 1 to 4, characterized in that an elastomer is used which contains 1.5 to 6% by weight of a peroxide catalyst. 6. The method according to claim 5 »thereby marked, that used as a catalyst 2,4-dichlorobenzoyl peroxide will. - 12 - 109813/1213 7. The method according to claim 5 or 6, characterized in that the catalyst is used in an amount of 2 "to 4 % . 8. The method according to any one of the preceding claims, characterized marked that a hydrocarbon solvent is used. 9 · Method according to claim 8, characterized in that it is marked e t that a mixture of toluene or xylene is used together with an isoparaffin as a solvent. 10. The method according to any one of the preceding claims, characterized in that a carrier is used, from which the elastomer can be removed after vulcanization or curing. 11.Verfahren according to any one of the preceding claims, characterized marked that the film solution of the squeegee, which distributes the silicone on the carrier, is supplied in an increasing direction. 12. The method according to any one of the preceding claims, characterized gekennz eichnet that the solvent in the Ä first oven at 70 to 80 ⁰ C is evaporated and the curing or vulcanization in the second oven at 130 to 180 ⁰ G is carried out. 13. The method according to claim 12, characterized in that that the curing or vulcanization time 30 seconds to 30 min. 14-. Method according to claim 13, characterized in that that the curing or vulcanization time is 1 to 4 minutes. -13 - 2U45558 15. Method according to one of the preceding claims, characterized in that a carrier is used, which allows the passage of gas to create a gas cushion that binds the elastomeric film while he wears in a relatively fluid and sticky drawstring ir: I ;,. 16. The method according to claim 15, characterized in that that the cushion is supplied by the hot gas introduced into the oven to evaporate the solvent will. 17. Method according to one of Claims 1 to 1 -.-, characterized in that a polyester film is used as the carrier is used. 18. The method according to any one of the preceding claims, characterized in that a reinforcing product is laminated with the silicone film. 19 · The method according to claim 18, characterized in that it is eichri e t that the goods are allowed to float onto the silicone film before curing or vulcanization. 20. Continuous or semi-continuous process according to one of the preceding claims, characterized in that on a SXCh ₁ moving, separable or adhering carrier, a dispersion of a polysiloxane atom in a ^{hydrocarbon solvent which can be evaporated below 100 0} C at atmospheric pressure, which contains a filler and about 1 to about 10% by weight of a peroxide catalyst, the total solids content and viscosity of the dispersion being from about 20 % to about 60% and from about 40,000 to about 120,000 centipoise, respectively, by spreading the dispersion to a portion of the support is fed, which is at an angle of about 10 ° to about 45 ° relative to the horizontal in 10 9 813/1213 204SÜ58 Towards a doctor blade, the substrate and the elastomer being fed thereon in a practically horizontal direction from the doctor blade at a speed of at least 0.3 m / min (1 ft. Per min) through a first oven below 100 ° C, in which the hydrocarbon solvent is evaporated, and then into a second oven at a temperature of at least 130 ^° C., in which practical curing or vulcanization of the elastomer is achieved during a residence time of not more than 30 minutes, and the sheet or film obtained is taken up in rolls or other elongated lengths on the carrier or after removing % of the carrier. 1 0 9 B 1 3/1 ? 1 ? Blank page