PROCEDURE FOR SYNTHESIS OF A WHITE OR LIGHT-COLOURED CROSS-LINKED HALOGEN CONTAINING POLYMER

Abstract: White or light-coloured cross-linked polymer and a procedure for synthesis of the same. The polymer consists of 30-98 weight percent halogen containing polymer, 0-60 weight percent plasticizer, 0.05-10 weight percent hydrolysable mercaptosilane, 0.1-10 weight percent lead stabilizer, 0-4 weight percent lubricant and 0.1-10 weight percent epoxy resin. The cross-linking is carried out in the presence of moisture after the processing of the polymer.

Description: Procedure for synthesis of a white or light-coloured cross- 1inked halogen containing polymer The present invention concerns white or light-coloured thermo¬ stable cross-linked halogen containing polymers and a procedure for producing them. There are several methods of cross-linking halogen containing polymers, including PVC. Among interesting methods that have appeared in recent years we can mention methods where organosilanes are used as cross-linkers. The patent application DE 3719151 describes the use of organosilanes, especially mercaptosilanes (e.g. mercaptopropyl trimethoxysilane (I)) as cross-linking agents for halogen containing polymers, especially the homopolyroer PVC. The cross-linking is done as follows: First trimethoxysilane (I) is grafted on to the polymer chain, and this should preferably be done by a normal process such as compounding, extrusion or rolling. CH 2 -CHC1~ CH 2 -CHC1~ / / HC-C1 + HS-(CH 2 ) 3 -Si-(OCH 3 ) 3 → HC-S-(CH 2 ) 3 -Si-(OCH 3 ) 3 + HCl \ \ CH 2 -CHC1~ CH 2 -CHC1~ (I) (ID (~ = polymer chain) The cross-linking reaction is then carried out in two steps: By hot water or steam treatment alkoxysilanes are hydrolysed and form silanols. Once the silanols have been formed they quickly react with one another and form the cross link through condensation of H 2 0: CH 2 -CHC1~ / (II) + 3H 2 0 → HC-S-(CH 2 ) 3 -Si-(OH) 3 + 3 CH3OH \ CH 2 -CHC1- (III) CH 2 -CHCl~ CH 2 _CHC1- / / 2 (III) → HC-S-(CH 2 ) 3 -Si(OH) 2 -0-Si(OH) 2 -(CH 2 ) 3 -S-CH + H 2 0 \ \ CH 2 _CHC1- CH 2 _CHC1- ( = polymer chain) In Norwegian Patent Application No. 890543 (Patent NO. 166189) halogen containing polymers are used which consist of copolymers of halogen containing monomer and glycidyl acrylates. The preferred copolymers are copolymers between vinyl chloride monomer (VCM) and glycidyl ethacrylate (GMA) . The Norwegian patent application first and foremost differs from DE 3719151 in that the epoxy group introduced by the glycidyl monomers facilitates the grafting of the organosilanes to the polymer chain. The dominant grafting reaction is assumed to take place as follows, where a copolymer of VCM and 0.05-10% of glycidyl methacrylate are used together with (I) : , O O ) « / \ CH 3 -C-C-C~CH 2 -CH-CH 2 + (I) . O OH ' " / ] → CH 3 -C-C-0-CH 2 -CH-CH 2 -S-(CH 2 ) 3 -Sι-(OCH) 3 () =ρolymer chain) In both the above-mentioned patent applications the cross-link¬ ing takes place after processing by exposing the material to hot water or steam. In NO 890543 it is stated that the use of glycidyl copolymers is considerably more effective than the use of the homopolymer PVC, inasmuch as the grafting of the organo- silane to the polymer is more effective. Both the cited patent applications emphasize the importance of using lead-based stabilizers so the cross-linking will be effective. An undesirable effect of the combination of lead stabilizer and mercaptosuane is that the material turns yel¬ low. This happens at room temperature as soon as the mercapto¬ suane and lead stabilizer come into contact with each other. It is therefore likely that the yellow colour comes from the formation of a compound or complex between the lead stabilizer and the mercaptosuane. Nor can the possibility be excluded that the formation of this compound/complex is a precondition of effective grafting. The yellow colour has a tendency to become stronger with increased addition of mercaptosuane. The colouring limits the usefulness of this cross-linking tech¬ nique, since even after the addition of large quantities of the white pigment titanium oxide there is still a yellowish tone. This means that the cross-linking method cannot be used when whiteness is an important requirement. The colour is moreover unstable, showing a tendency to change under the influence of sunlight, for example. It is also difficult to add other col¬ ours, especially light colours. The object of the invention is thus to avoid the disadvantages of the methods described above and to obtain a cross-linked halogen containing polymer with a white or light colour. In certain systems, especially with homopolymers, a further objective is to strengthen the network. These and other objects of the invention are achieved by the procedure described below, and the invention is characterized and defined by the accompanying patent claim. The present invention concerns a method of producing white or light-coloured thermostable cross-linked halogen containing polymer. Surprisingly, it was found that this polymer can be produced using mercaptosilane, lead stabilizer and a low- molecular epoxy compound. The low-molecular epoxy compound reacts with the mercaptosilane and/or the by-products which together with the lead stabilizer cause the colouring, and thus remedies the problem. The polymer consists of 30-98 weight % halogen containing polymer, 0-60 weight % plasticizer, 0.05-10 weight % hydrolysable mercaptosilane, 0.1-10 weight % lead stabilizer, 0-4 weight % lubricant and 0.1-10 weight % epoxy resin. The halogen containing polymer may be a homopolymer like PVC, or a copolymer based on halogen containing polymer and inactive or reactive comonomers with respect to the cross-linking. A copolymer between a halogen containing monomer and a glycidyl- containing acrylate is favoured. The content of glycidyl- containing acrylate is 0.05-10 weight %. Under 0.05 weight % the effect is too weak and over 10% the polymerization is too slow. The mercaptosilane is of the general formula: SH- '-Si-R 1 'n■ where: R r = a -CH 2 - -C 2 H - up to C 8 H 16 °r another non-functional group. R l ' = a freely selected, non-hydrolysable group Y = one or more hydrolysable groups such as -OCH 3 , -OC H5, -0C 3 H 7 , - OC 4 H 9 n = 0,1,2 The compound R" can be a freely selected non-hydrolysable group. Examples of usable groups are -CH 2 - up to CgH^, but the choice of groups in principle has no significance for the result. The lead stabilizer is a freely selected commercial stabilizer based on e.g. tribasic lead sulphate, tetrabasic lead sulphate, dibasic lead phosphite, dibasic lead carbonate, dibasic lead phthalate.or dibasic lead stearate. To obtain an effect, more than 0.1% should be added. The upper limit is fixed according to whatever is practical, there is no level that cannot be ex¬ ceeded. The disadvantages of high additions are more expense and higher density. A practical limit is 10 weight %. Ordinary commercial plasticizers in quantities up to 60 weight % are used. Above this limit the mixture cannot be handled. Commercial lubricants are used in quantities up to 4 weight %. Higher additions produce a mixture which is overlubricated and thus difficult to handle. The low-molecular epoxy compound may consist of e.g. monofunc- tional or multifunctional glycidyl ethers, glycidyl esters, glycidyl amines, or of a linear or cycloaliphatic type. This is added at 0.1-10 weight %. An addition of less than 0.1% has no effect and an addition over 10% produces too great a surplus of epoxy resin in proportion to the mercaptosilane. In addition the mixture may contain small quantities of the ordinary addi¬ tives used for this type of product. The invention will be clarified in more detail in the following examples. In the examples the quantities are expressed in pph (pph = parts per 100 parts of polymer) . EXAMPLE 1: Three different formulas were produced as in Table 1. Table 1 1 = commercial lead stabilizer and lubricant combination 2 = external lubricant 3 = commercial epoxy resin of diglycidyl ether-bisphenol A type, known as DGEBA resin. DOP = dioctyl phthalate The formulas were mixed/hot-mixed up to 110° C. They were then rolled at 170° C for 5 mins. The cross-linking was then carried out in an autoclave at 110° C for two hours. The following ana¬ lyses were carried out: Gel conten : Measured as the insoluble proportion of poly¬ mer in tetrahydrofuran (THF) at room tempera¬ ture. Hot-set: Measured as the deformation caused by a load of 0.1 MPa on a sample rod at 200° C after 15 mins., and as the residual deformation 5 mins. after the load has been removed from the sample. Colour : Measured visually. The results of the analyses are shown in Table 2 : Table 2 : The results in this example show that addition of 2 pph of DGEBA resin to a formula with 3% trimethoxysilane (I) can eli¬ minate all yellow colour. In the example no cross-linking has arisen for any formula. One probable reason for this is that the processing conditions were too mild for the grafting of mercaptosilane to the PVC chain to work. EXAMPLE 2: Three different formulas were produced as in Table 3. Table 3 The formulas were mixed/hot-mixed up to 110° C and rolled at 190°C for 5 mins. The same analyses were conducted as in Example 1, with the results shown in Table 4: Table 4 Here the higher processing temperature probably contributed to the achievement of grafting to the polymer chains and thus a certain amount of cross-linking. Addition of a small quantity of DGEBA resin appears to favour the cross-linking. The expla¬ nation of this could be that epoxy resin, for example, which has reacted with two ercaptosilanes can form a bridge: O CH 3 0 / \ / / \ 2 SH-(CH 2 ) 3 -Si-(OCH 3 ) 3 + CH 2 -CH-CH 2 -0-Ph-C-Ph-0-CH 2 -CH-CH 2 / CH 3 OH CH 3 OH / / / (OCH 3 ) 3 -Si-(CH 2 ) 3 -S-CH 2 -CH-CH 2 -0-Ph-C-Ph-0-CH 2 -CH-CH 2 -S- / CH 3 (CH 2 ) 3 -Si-(0CH 3 ) 3 (IV) Since in view of the low gel content there must be space between the grafted mercaptosilanes, after hydrolysis and condensation reactions with two mercaptopropyl trimethoxysi- lanes (I) grafted to the polymer chain, (IV) can form a bridge between these. At higher contents of epoxy resin the amount of (I) grafted to the polymer chains is probably reduced because it has mostly reacted with the epoxy resin instead. EXAMPLE 3: Three different formulas were produced as in Table 5. Table 5 The formulas were mixed/hot-mixed up to 110° C. They were then rolled at 170° C for two hours. The cross-linking was later carried out in an autoclave at 110°C for two hours. The same analysis as in Example 1 was done. The results appear in Table 6: Table 6 Example 3 shows that it is possible to produce white material which is strongly cross-linked by adding a low-molecular epoxy compound to the already familiar reaction between mercaptosi¬ lane, epoxy-containing halogen containing comono er and lead stabilizer. The fact that the gel content decreases through addition of epoxy resin and that the deformation by heat also becomes greater is very probably a function of the fact that the low-molecular epoxy compound "steals" mercaptosilane from the epoxy- groups bonded in the chain. We cannot exclude the possibility that hydrolysed and condensed compounds of type (IV) have a positive effect on the hot-set, but it is no less effective than if (I) were grafted to the polymer chains. Example 4 Three di ferent formulas were produced as in Table 7. Table 7 The formulas were mixed/hot-mixed up to 110° C. They were then rolled at 170° C for 5 mins. The cross-linking was later done in an autoclave at 110° C for two hours. The same analyses as in Example 1 were carried out. The results appear in Table 8: Table 8 Example 4 shows that an increase of the amount of epoxy in the polymer chains can produce a white material with lower low- molecular epoxy resin content. The example shows the same ten¬ dency as Example 3, inasmuch as addition of epoxy resin decrea¬ ses the gel content and increases the hot-set deformation. One can note that the formulas D2 and Cl in Example 3 have the same gel content, but D2 is considerably better in terms of hot-set. The explanation of this is probably that a higher proportion of (I) is bonded in the polymer chains. Example 5 Three different formulas were produced as in Table 9. Table 9 1 commercial cycloaliphatic epoxy resin. The formulas were mixed/hot-mixed up to 110° C. They were then rolled at 170° C for two hours. The same analyses as in Example 1 were carried out. The results appear in Table 10: Table 10 Cycloaliphatic epoxy resins are considered less reactive with mercaptan groups than for example diglycidyl ether-based epoxy resins like those of the DGEBA type. The higher gel content and the lower deformation than when DGEBA resin is used may be due to the fact that the cycloaliphatic epoxy resin does not com¬ pete as well with the polymer-based epoxy groups for (I) . In Examples 3-5 the addition of low-molecular epoxy resin has produced a lighter or white material at the expense of a rather poorer cross-linking. The epoxy resin in all these experiments has been difunctional, and the mercaptosilane has been tetra- functional. This has clearly not been sufficient to make an overall positive contribution to the mechanical durability of the network in terms of hot-set values. Example 6 : Three different formulas were produced as in Table 11, Table 11 1 Commercial tetrafunctional epoxy resin of glycidyl ether type. The formulas were mixed/hot-mixed up to 100° C. They were then rolled at 170°C for 5 mins. The cross-linking was later done in an autoclave at 110°C for two hours. The same analyses as in Example 1 were carried out. The results appear in Table 12: Table 12 Example 6 shows that the use of a tetrafunctional resin makes a contribution to the mechanical durability of the network, at least with additions of small quantities. The fact that the material turns light yellow is presumably due to the fact that Araldit 0163 itself is an intense yellow colour. The lower gel content than in Example 3 can be explained by the fact that the epoxy content is higher per weight unit in the tetrafunctional resin than in the DGEBA resin. In all examples where white material has been produced, it has only happened after autoclaving. Before autoclaving the mate¬ rial had a light yellow tone. On the other hand, material with no low-molecular epoxy content exhibits a tendency to develop a stronger yellow colour after autoclaving. With the present invention we have arrived at a method of pro¬ ducing white or light-coloured cross-linked material using hal¬ ogen containing polymers, mercaptosilanes, lead stabilizers and a low-molecular epoxy resin. In certain formulas, especially when tetrafunctional epoxy resin is used, a positive contribution to the mechanical properties of the network can be achieved.

Claims: Patent claims White or light-coloured cross-linked polymer, c h a r a c t e r i z e d b y consisting of 30-98 weight % halogen containing polymer, 0-60 weight % plasticizer, 0.05-10 weight % hydrolysable mercaptosilane, 0.1-10 weight % lead stabilizer, 0-4 weight % lubricant and 0.1-10 weight % epoxy resin. Halogen containing polymer according to claim 1, c h a r a c t e r i z e d b y containing a low-molecular epoxy resin which is mono- to tetrafunctional, of the glycidyl ether, glycidyl ester, glycidyl amine or linear or cycloaliphatic type. Halogen containing polymer according to claim 1, c h a r a c t e r i z e d b y the fact that the halogen containing polymer is PVC homopolymer. Halogen containing polymer according to claim 1, c h a r a c t e r i z e d b y the fact that it is a copolymer between a halogen containing monomer and a glycidyl-containing acrylate. Copolymer according to claim 3 , c h a r a c t e r i z e d b y a content of glycidyl-containing acrylate of 0.05- 10 weight %. 6. Procedure for production of white or light-coloured cross-linked halogen containing polymer using a mercaptosilane of the type: SH-R'-Si-R' ' n I Y (3-n) where: R' = a -CH 2 - -C 2 H4~ up to CgH^ or other non-functional group. R"= a freely selected (non-hydrolysable) group. Y = one or more hydrolysable groups such as -0CH 3 , -OC 2 H 5 , - OC 3 H7, -0C H 9 n = 0,1,2 as cross-linking agent and a lead stabilizer, and where the cross-linking is carried out in the presence of moisture after the processing of the polymer, c h a r a c t e r i z e d b y the fact that a low-molecular epoxy resin is added to the mixture. 7. Procedure according to claim 6 , c h a r a c t e r i z e d b y the use of a low-molecular epoxy resin which is mono- to tetrafunctional, of the glycidyl ether, glycidyl ester, glycidyl amine or linear or cycloaliphatic type. 8. Procedure according to claim 6, c h a r a c t e r i z e d b y the fact that 0.1-10 weight % epoxy resin is added. 9. Procedure according to claim 6 , c h a r a c t e r i z e d b y the use of vinyl chloride as the halogen containing polymer. 10. Procedure according to claim 6, c h a r a c t e r i z e d b y the use of a co¬ polymer of vinyl chloride and glycidyl methacrylate.

Inventors: DAHL ROGER, DAHL, ROGER
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1992
Main classification: C08L27
IPC codes: C08F4, C08F8, C08G59, C08K5, C08L27, C08L63