GB2271115A

GB2271115A - Low compression set glazing seals

Info

Publication number: GB2271115A
Application number: GB9214969A
Authority: GB
Inventors: Joseph Gordon Robinson; Michael William Copson
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-07-14
Filing date: 1992-07-14
Publication date: 1994-04-06
Also published as: GB9214969D0

Abstract

Weatherstrip seals for insertion around the doors and windows of houses, offices, factories and other structures, based on PVC and, in the minor proportion, nitrile rubber, have been produced with compression set values of less than 50% when measured after 200 hours at 70 DEG C.

Description

LOW COMPRESSION SET GLAZING SEALS Strips of vulcanised elastomers are widely used as weatherstrips around the edges of doors and windows and other openings. These strips may be in the form of tubes or they may be solid strips or in some cases foamed strips or tubes.

Weatherstrips for some applications, such as for use as glazing seals around doors and windows in domestic buildings, offices, factories and other constructions, have often nowadays to meet demanding performance specifications. For example, it may be required, but depending on the particular application, that the compression set shall not exceed 50% measured, for example, after 200 hours at 70"C, the hardness shall not exceed 80 Shore A degrees (ASTM D2240), the ultimate tensile strength shall be not less than 8 mPa (ASTM D412A), the elongation at break shall not be less than 200% and the tear strength shall be greater than 11 kNIm (BS 7412).

Ethylene-propylene-diene terpolymer (EPDM) is commonly used to make glazing seals but this elastomer has serious drawbacks in that it is relatively costly, yields extrudates having an inferior surface finish and it has a relatively low tear strength.

Nevertheless, until now this has been the best material available for making glazing seals.

We have found that strips extruded from oxidatively and thermally stabilised blends of plasticised PVC and nitrile rubber (NBR), in which the nitrile rubber content, by weight, is not greater than the weight of the PVC polymer, which are cross-linked during melt mixing, have a compression set of less than 50% after 22 hours at 70"C. In other respects, too, the strips meet the requirements for the glazing seal market.

The amount of nitrile rubber present in the PVC is in the range 5 parts to 90 parts per 100 parts of PVC polymer and preferably in the range 10 parts to 50 parts per 100 parts of PVC polymer. The amount of plasticiser, which is preferably, but not exclusively, an ester such as di-octyl phthalate or a mixture of such esters, is in the range 20 parts to 250 parts per 100 parts of PVC but is preferably in the range 25 parts to 100 parts per 100 parts of PVC polymer.

The nitrile rubber has an acrylonitrile content which is preferably in the range 10 parts to 60 parts per 100 parts of rubber and is more preferably in the range 30 parts to 45 parts per 100 parts of rubber. The Mooney viscosity is preferably in the range 20 - 120 and more preferably in the range 40 - 100. Alternatively, the rubber may be partially cross-linked before blending with the PVC and other constituents of the formulation.

A liquid nitrile rubber of viscosity preferably in the range 9000 cP to 30,000 cP at 50"C may be used, either alone or in combination with solid nitrile rubber, for blending with the PVC.

The PVC suitable for the purpose of the present invention may be either a suspension grade or an emulsion-prepared grade or a mass polymerised grade or a mixture of any of these grades. The K-value is preferably in the range 45-90 (DIN 53726).

The PVC polymer, nitrile rubber and the other constituents of the formulation, including azobisisobutyronitrile (AZBN) and/or an organic peroxide, are thoroughly mixed together and thereafter melt-blended on a 2-roll mill or other suitable mixer, such as a Buss Ko-Kneader, at a temperature typically in the range 1200C to 1600C.

During this melt mixing process, the azobisisobutyronitrile (AZBN) or, if used, the organic peroxide, decomposes to generate free radicals. It is believed that these free radicals interact with the nitrile rubber and PVC to effect cross-linking. It is supposed, moreover, that the PVC becomes chemically attached through carbon-carbon covalent bonds to the nitrile rubber. It is speculated that it is these processes of cross-linking and, in particular, the grafting of the rubber onto the PVC polymer chains which endow the strips or weatherseals with uniquely low compression set values (less than 50% after 200 hours at 70"C) for PVC/nitrile rubber artifacts.This interpretation is believed by us to be consistent with our observation that if instead of incorporating AZBN and/or an organic peroxide in the formulation sulphur and a sulphur accelerator are used (Example 5), then the compression set values are not modified to any significant degree. This is probably due to the fact that PVC is unaffected by sulphur curing systems and consequently the PVC does not then have nitrile rubber segments grafted on to it.

These interpretations of the mechanisms whereby AZBN or peroxide, when incorporated in the formulation, enable artifacts with low compression set to be obtained are of a speculative nature only and they are not intended to constitute any part of the invention or to limit its scope.

The amount of AZBN or organic peroxide used in the polymer compound is preferably in the range 0.1 parts to 4.0 parts per 100 parts of polymer compound and more preferably in the range 0.02 parts to 0.5 parts per 100 parts of the polymer compound and is such that the blend remains thermoplastic after melt mixing and, moreover, that the AZBN or organic peroxide is essentially all consumed during mixing. The mixing conditions, viz. temperature and time, to achieve these requirements for AZBN or any particular peroxide are readily determined by persons skilled in the art.

Suitable peroxides for the purpose of the present invention include but are not restricted to: 2,2-ditertiarybutyl peroxybutane; 1,1-ditertiarybutyl peroxy-3,3,5-trimethylcyclohexane; 1,1,1-ditertiarybutyl peroxycyclohexane.

The cross-linking and grafting processes involving the PVC and NBR as described above, are preferably promoted by the inclusion of an activator in the formulation. Suitable activators include acrylate and methacrylate monomers such as 1,6-hexanediol diacrylate, trimethylolpropane trimethacrylate, 1,3-butylene glycol dimethacrylate and ethyleneglycol dimethacrylate. Other activators which may be used include triallylcyanurate and triallylisocyanurate. The level of activator is preferably in the range 0.5 parts to 15 parts per 100 parts of the polymer blend and more preferably in the range 2 parts to 10 parts per 100 parts of PVC/NBR blend and most preferably in the range 2.5 parts to 5 parts per 100 parts of the PVC/NBR blend.

In compounding, the PVC, plasticiser and nitrile rubber, together with the other components of the formulation, including AZBN or organic peroxide and, optionally, an activator, are melt mixed on a 2-roll mill or in a Banbury or in a twin-screw extruder at a temperature typically in the range 120-160"C and for a time typically in the range 0.5-10 minutes. The precise time depends on the initiator used and will be sufficient to completely decompose most of the initiator (greater than 7 half lives of the initiator at the melt mixing temperature). The thoroughly mixed blend leaving the mill or mixer is cooled and granulated. These granules are subsequently fed into an extruder from which emerges a strip having the required shape and dimensions. If a blowing agent such as, for example, azocarbonamide, is incorporated in the polymer compound then the strips will emerge as a closed-cell foamed strip.

In the course of compressive deformation of the extruded (or moulded) strips of the present invention, such as in permanent set measurements (ASTM D395B), it is speculated that strong elastic recovery forces of the cross-linked nitrile rubber, chemically attached to the PVC by carbon-carbon bonds, exert a strong recovery force on the compressively deformed thermoplastic elastomer strips.

It is further speculated that it is these strong elastic restoring forces that ensures that the sealing strips of the present invention have, advantageously, a relatively low compression set, thereby making them superior in this respect to conventional PVC/NBR weatherseals. These speculations are not intended to constitute any part of the invention or limit its scope.

The sealing strips of the present invention may be either solid or foamed.

The solid or foamed strips of PVC/NBR of the present invention may be used directly as glazing seals. Alternatively, a strip 1 of PVC/nitrile rubber of thickness typically 1.5-2.0mm may be attached to a solid rubber or rigid plastic strip 2, as shown in Figure 1.

This facilitates attachment via the protrusion 3 to the surrounds of windows, doors and other openings. The PVC/nitrile rubber weatherseal may be attached to the strip of rigid plastic or solid rubber using a contact rubber-based adhesive.

Example 1 One hundred parts by weight of PVC (Lacqvyl SK70), 40 parts of nitrile rubber (Chemigum P83), 40 parts of dioctyl phthalate, 0.6 parts of Irganox 1010, 5 parts of trimethylolpropane trimethacrylate, 12 parts of powdered chalk, 1.5 parts of tribasic lead sulphate, 1.5 parts of carbon black, 0.8 parts of calcium stearate, and 0.1 parts of 1,1-ditertiarybutyl peroxy-3,3,5-trimethylcyclohexane were melt mixed on a 2-roll mill at 1500C for 10 minutes. The hide, upon removal from the mill, was cooled to ambient temperature and granulated. The granules were fed into an extruder from which emerged a strip having a rectangular cross-section 3.0mm x 25mm. The mechanical properties of the strip were next determined when the following results were obtained.

Compression set after 200 hours & ommat; 70 C (%) ..... 43 Hardness (Shore A degrees) ..................... 64 Elongation at break (%) ....................... 380 Ultimate tensile strength (mPa) ............... 9.5 Tear strength (kN/m) .......................... 32 Example 2 The procedure described in Example 1 was repeated but the 1,1-ditertiarybutyl peroxy-3,3,5-trimethylcyclohexane was replaced by 0.05 parts of azobisisobutyronitrile and mixed on the mill for 10 minutes at 145eC.

The extruded strip had a compression set, measured after 200 hours at 70"C, of 42%.

Example 3 The procedure described in Example 1 was repeated but the 1,1-ditertiarybutyl peroxy-3,3,5-trimethylcyclohexane was replaced by the same quantity of 2,2-ditertiarybutyl peroxybutane.

The extruded strip had a compression set of 42% measured after 200 hours at 70"C.

Example 4 The procedure described in Example 1 was repeated except that the trimethylopropane trimethacrylate was omitted from the formulation.

The extruded strip had a compression set of 45% measured after 200 hours at 70"C.

Example 5 - Comparative Example The procedure described in Example 1 was repeated except that the 1,1-ditertiarybutyl peroxy-3,3,5-trimethylcyclohexane was replaced by 0.8 parts of stearic acid, 2.0 parts of zinc oxide, 0.4 parts of mercaptobenzthiazyl disulphide, 0.1 parts of tetramethylthiuram disulphide and 0.6 parts of sulphur.

The extruded strip was heated at 1500C for 10 minutes to effect vulcanisation or cross-linking. The resultant product had a compression set of 53% measured after 200 hours at 70"C.

Claims

What we claim is:

1 A method of producing plastic artefacts having a permanent compression set of less than 50% (ASTM D395-89, Method B), hardness less than 75 Shore A and meeting the requirements for glazing seals (British Standard 7412, 1991), comprising steps of:: l(a) dry-blending nitrile rubber with PVC, an ester for plasticizing the PVC, an ethylenically unsaturated compound and a reagent which generates free radicals on heating; l(b) incorporating by dry-blending one or more members of the group consisting of carbon black, an external lubricant, a rubber antioxidant, a heat stabilizer for PVC, clay, silica, calcium carbonate, titanium dioxide and pastel coloured pigments into the blend according to claim 1(a);; l(c) melt-mixing the blend according to claims l(a) and l(b) for sufficient time to achieve thorough mixing of the constituents and at the same time to decompose the reagent which generates free radicals on heating; l(d) extruding or moulding the meltemixed blend according to claim l(c) to give artefacts for subsequent use as glazing seals.

2 A composition as claimed in claim l(a) and l(b) wherein the nitrile rubber is a co-polymer of acrylonitrile and butadiene and has an acrylonitrile content of 10 parts to 60 parts per

100 parts of the nitrile rubber.

3 A camposition as claimed in claim l(a), l(b) and 2 wherein the nitrile rubber is cross-linked.

4 A composition as claimed in claim l(a), l(b) and 2 wherein the nitrile rubber is not cross-linked and has a Mooney viscosity in the range 20 to 120.

5 A camposition as claimed in the previous claims wherein there are 5 parts to 90 parts of nitrile rubber per 100 parts of PVC in the camplete formulation.

6 A canposition as claimed in claims 1 to 5 wherein the PVC has a K-value in the range 55 to 90 (DIN 53726).

7 A composition according to claims l(a) to l(d) wherein the PVC plasticizer is an organic ester having a molecular weight of more than 275 and which does not contain any ethylenically unsaturated groups in the molecule.

8 A composition according to claims l(a) to l(d) wherein the PVC plasticizer is a mixture of organic esters, each having a molecular weight of more than 275 and none of which contain ethylenically unsaturated groups in the molecules.

9 A camposition according to claims l(a) and l(b) wherein the ethylenically unsaturated compound is an organic compound which contains two or more ethylenically unsaturated groups per molecule.

10 A composition according to l(a), l(b) and 9 wherein the ethylenically unsaturated compound has a molecular weight in the range 120 to 450 and a boiling point greater than 1500C at 760mn pressure.

11 A coMposition according to claims l(a), l(b), 9 and 10 wherein there are 0.5 parts to 50 parts of the ethylenically unsaturated compound per 100 parts of PVC in the complete composition.

12 A composition according to claims l(a) and l(b) wherein the reagent which generates free radicals on heating is an organic peroxide having a half-life, measured in chlorobenzene, of more than 7 minutes at 80'C and less than

2 seconds at 240 C.

13 A composition according to claims l(a) and l(b) wherein the reagent which generates free radicals on heating is an azo compound having a half-life, measured in chlorobenzene, of

60 seconds at a temperature in the range 125 C to 145 C.

14 A composition according to claims l(a) and l(b) wherein the reagent which generates free radicals an heating is an inorganic persulphate.

15 A composition according to claims l(a), l(b), 12, 13 and 14 wherein there are 0.02 parts to 10 parts of the reagent which generates free radicals on heating per 100 parts of PVC in the formulation.

16 A procedure whereby a composition according to the previous claims is first dry-blended and thereafter melt-mixed at a temperature in the range 95C to 205'C so as to thoroughly mix and at the same time to generate free radicals in situ for chemical reaction with and between constituents of the formulation.

17 A procedure whereby compositions according to claims 1 to 15 which have been melt blended, and chemically reacted with free radicals 'in situ' according to claim 16 are thermoplastic elastomers having a compression set of less than 50% (ASTM D395-89, Method B), a hardness of less than 75 Shore A and meeting the requirements for glazing seals (British Standard 7412, 1991).

18 Hollow profiles produced by extrusion fran the thermoplastic elastomers according to claim 17.

19 Solid profiles produced by extrusion fran the thermoplastic elastaners according to claim 17.

20 Artefacts produced by injection moulding or compression moulding fran the thermoplastic elastaners according to claim 17.