NO173337B - WHITE OR BRIGHT COLORED CROSS-HALOGENED POLYMER MATERIAL AND PREPARATION OF THIS - Google Patents

Abstract

White or light colored crosslinked polymer and process for the preparation of the same. The polymer consists of 30-98% by weight of halogen-containing polymer, 0-60. weight% plasticizer, 0.05-10% by weight hydrolyzable mercaptosilane, 0.1-10% by weight lead stabilizer, 0-4. wt% lubricant and 0.1-10 wt% epoxy resin. The crosslinking is performed in the presence of moisture after processing of the polymer.

Description

The present invention relates to white or light-coloured thermostable cross-linked halogen-containing polymer materials and a method for their production.

There are several ways to crosslink halogen-containing polymers, including PVC. Of the interesting methods that have emerged in recent years, methods where organosilanes are used as crosslinkers can be mentioned. DE official publication 3719151 describes the use of organosilanes, especially mercaptosilanes (e.g. mercaptopropyl trimethoxysilane (I)) as crosslinkers for halogen-containing polymers, especially the homopolymer PVC.

The cross-linking takes place in the following way:

First, trimethoxysilane (I) is grafted onto the polymer chain, and this should preferably be done by a normal processing process such as compounding, extrusion or rolling.

The cross-linking reaction is then carried out in two steps:

During hot water or steam treatment, alkoxysilanes are hydrolysed and form silanols. When silanols are formed, they quickly react with each other and form a cross-link through condensation of H20:

In Norwegian patent document no. 166189, halogen-containing polymers are used which consist of copolymers of halogen-containing monomer and glycidyl-containing acrylate. The preferred ones are copolymers between vinyl chloride monomer (VCM) and glycidyl methacrylate (GMA). The Norwegian patent differs primarily from DE 3719151 in that the epoxy group which is introduced via glycidyline-containing monomers facilitates the grafting of organosilanes to the polymer chain. The dominant grafting reaction is assumed to take place in the following way, where a copolymer of VCM and 0.05-10% of glycidyl methacrylate is used together with (I):

In both of these patent publications, the cross-linking takes place after shaping by exposing the material to hot water or steam. In NO 166189 it is stated; the fact that the use of glycidyl-containing copolymers is significantly more effective than the use of the homopolymer PVC, in that the grafting of organosilane to the polymer becomes more effective.

In both of the featured patent documents, the importance of using lead-containing stabilizers is emphasized in order for the cross-linking to be effective. An undesirable effect of the combination of lead stabilizer and mercaptosilane is that the material becomes yellow. This happens immediately already at room temperature when the mercaptosilane and the lead stabilizer come into contact with each other. It is therefore likely that the yellow color comes from the formation of a compound or complex between the lead stabilizer and mercaptosilane. Nor can it be ruled out that the formation of this compound/complex is a prerequisite for grafting to take place in an efficient manner. The yellow color shows a tendency to become stronger with increasing addition of mercaptosilane.

The color limits the application of this cross-linking technique as even after a large addition of white pigment, titanium oxide, there is still a yellow tint. This means that this cross-linking method cannot be used where great demands are made on whiteness. Since the color is not stable either, but shows a tendency to change under the influence of e.g. sunlight, it becomes difficult to add other colors, especially bright colors.

The purpose of the invention is thus to avoid the disadvantages of the previously described methods and to be able to obtain a cross-linked halogen-containing polymer with a white or light color. In certain systems, particularly with homopolymer, the aim is to be able to reinforce the network.

These and other purposes of the invention are achieved with the method described below, and the invention is characterized and defined by the accompanying patent claims.

The present invention relates to a method for the production of white or light-coloured cross-linked halogen-containing polymers. It was surprisingly found that these polymers can be prepared using mercaptosilane, lead stabilizer and a low molecular weight epoxy compound. The low molecular weight epoxy compound reacts with the mercaptosilane and/or the by-products which together with the lead stabilizer give rise to colour, thereby remedying the problem.

The polymer material consists of 30-98 wt% halogenated polymer, 0-60 wt% plasticizer, 0.05-10 wt% hydrolyzable mercaptosilane, 0.1-10 wt% lead stabilizer, 0-4 wt% lubricant and 0.1-10 wt% epoxy resin. The halogen-containing polymer can be a homopolymer such as e.g. PVC, or a copolymer based on halogen-containing polymer and inactive or reactive comonomers with respect to the cross-linking. A preferred compound is a copolymer between halogen-containing monomer and a glycidyl-containing acrylate. The content of glycidyl-containing acrylate is 0.05%-10% by weight. Below 0.05% by weight the effect is too small and above 10% the polymerization becomes too slow.

The mercaptosilane is of the general formula:

where:

R1 = a -CH2- -C2H4- up to -C8H16_ or another non- functional group.

R 11 = a freely selected, non-hydrolyzable group

Y = one or more hydrolyzable groups, e.g. -OCH3, -

OC2H5, -OC3H7, -OC4H9

n = 0.1 or 2

The compound R" can be a freely chosen non-hydrolyzable group. An example of usable groups can be -CH2- up to -CsHi7_, but the choice of groups has no meaning in principle-

ning for the result.

The lead stabilizer is a freely chosen commercial stabilizer based on e.g. tribasic lead sulfate, tetrabasic lead sulfate, dibasic lead phosphite, dibasic lead carbonate, dibasic lead phthalate or dibasic lead stearate. To achieve an effect, more than 0.1% must be added. The upper limit is determined according to what is practical, there is no level that cannot be exceeded. The disadvantages of high additions are an increase in price and a higher density. A practical limit can be set at 10% by weight.

Commercial plasticizers are usually used in quantities of up to 60% by weight. Above this limit, the mixture becomes unmanageable. Commercial lubricants are used in amounts up to 4% by weight. Higher additions give a mixture that is over-lubricated and therefore difficult to handle.

The low molecular weight epoxy compound can consist of e.g. mono- or polyfunctional glycidyl ethers, glycidyl esters, glycidyl amines, or of the linear or cycloaliphatic type. This is added at 0.1-10% by weight. An addition of less than 0.1% has no effect and an addition of more than 10% gives an excess of epoxy resin in relation to the mercaptosilane. In addition, the mixture may contain small amounts of common additives used for this type of product.

The invention will be explained in more detail in the following examples. In the examples, amounts are given in phr (phr = parts per 100 parts polymer).

EXAMPLE 1:

Three different formulations were prepared according to table 1.

<1><=> commercial lead stabilizer and lubricant combination

2 = external lubricant

<3> = commercial diglycidyl ether bisphenol A epoxy resin

type, sk, DGEBA resin.

DOP = dioctyl phthalate

The formulations were mixed/hot mixed up to 110° C. They were then rolled at 170° C for 5 min. The cross-linking was then carried out in an autoclave at 110° C. for 2 hours.

The following analyzes were done:

Gel content: Measured as the insoluble proportion of polymer in tetrahydro- furan (THF) at room temperature.

Hot set: Measured as the strain as a load of 0.1

MPa stock on a test rod at 200° C after 15 min., as well as the remaining strain 5 min. after the load is removed from the specimen.

Color i Measured visually.

The results of the analyzes appear in table 2:

The results in this example show that by adding 2 phr of DGEBA resin to a formulation with 3% trimethoxysilane (I) all yellow color can be eliminated. In the example, cross-linking has not occurred for any formulation. A likely reason for this is that the processing conditions have been too mild for the grafting of mercaptosilane to the PVC chain to work.

EXAMPLE 2:

Three different formulations were prepared according to table 3.

The formulations were mixed/hot mixed up to 110° C and rolled at 190° C for 5 min. The same analyzes as Example 1 were performed with the following results shown in Table 4:

The higher processing temperature here has probably contributed to the fact that we have obtained grafting to the polymer chains and that we have thus obtained a certain amount of cross-linking. A minor addition of DGEBA resin appears to be beneficial to the cross-linking. This can be explained by the fact that e.g. epoxy resin that has reacted with two mercaptosilanes can form a bridge:

(CH2)3-Si-(OCH3)3 (IV)

Since in view of the low gel content there must be spaces between grafted mercaptosilanes, (IV) can form a bridge between these after hydrolysis and co-condensation reactions with two mercaptopropyltrimethoxysilanes (I) grafted to the polymer chain.

With a higher content of epoxy resin, the number of (I) grafted to the polymer chains probably decreases because most have reacted with the epoxy resin instead.

EXAMPLE 3:

Three different formulations were prepared according to table 5.

The formulations were mixed/hot mixed up to 110° C. They were then rolled at 170° C for 2 hours. The crosslinking was later carried out in an autoclave at 110°C for two hours. The same analysis as in example 1 was carried out. The result appears in table 6:

Example 3 shows that it is possible to produce white material that is strongly cross-linked through the addition of a low molecular weight epoxy compound to the previously known reaction between mercaptosilane, epoxy-containing halogen-containing comonomer and lead stabilizer. The fact that gel contents decrease with the addition of epoxy resin and that the elongation in heat also increases is very likely a function of the low molecular weight epoxy compound "stole" mercaptosilane from the epoxy groups anchored in the chain. It cannot be ruled out that hydrolyzed and condensed compounds of the type (IV) have a positive effect on the hot seat, but that there is also no less than if (I) is grafted to

the polymer chains.

EXAMPLE 4

Three different formulations were prepared according to table 7.

The formulations were mixed/hot mixed up to 110° C. They were then rolled at 170° C for 5 min. The cross-linking was then carried out in an autoclave at 110° C. for 2 hours. The same analyzes as in example 1 were carried out. The result appears in table 8:

Example 4 shows that by increasing the amount of epoxy in the polymer chains, a white material with a lower content of low molecular weight epoxy resin can be obtained. The example shows the same tendency as example 3, in that the addition of epoxy resin lowers the gel content and increases the strain during hot-set. It can be noted that formulation D2 and Cl in example 3 have the same gel content, but D2 is significantly better in hot-set. This can probably be explained by the fact that a larger proportion of (I) is anchored in the polymer chains.

EXAMPLE 5

Three different formulations were prepared according to table 9.

The formulations were mixed/hot mixed up to 110° C. They were then rolled at 170° C for 2 hours. The same analyzes as in example 1 were carried out. The result is shown in table 10: Cycloaliphatic epoxy resins are considered to be less reactive towards mercapto groups than e.g. dyglycidether-based epoxy resins such as those of the DGEBA type. The higher gel content and lower strain compared to when DGEBA resin is used may be due to the cycloaliphatic epoxy resin not competing as well with the polymer-based epoxy groups for (I).

In examples 3-5, the addition of low molecular weight epoxy resin has produced a lighter or whiter material at the expense of somewhat poorer cross-linking. In all these experiments, the epoxy resin has been difunctional and the mercaptosilane has been tetra-functional. This has obviously not been sufficient to make an overall positive contribution to the mechanical durability of the network, based on an assessment of the hot-set values.

EXAMPLE 6:

Three different formulations were prepared according to table 11.

The formulations were mixed/hot mixed up to 100° C. They were then rolled at 170° C for 5 min. The cross-linking was then carried out in an autoclave at 110° C. for 2 hours. The same analyzes as in example 1 were carried out. The result appears in 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 small additions. The fact that the material became light yellow is probably due to Araldite 0163 itself being intense yellow. That the gel content was lower than in example 3 can be explained by the fact that the epoxy content is higher per unit weight in the tetrafunctional resin than for DGEBA resin.

In all examples where white material has appeared, it has only happened after autoclaving. Before autoclaving, the material had a light yellow hue. Material that does not contain low molecular weight epoxy, on the other hand, shows a tendency to give a stronger yellow color after autoclaving.

With the present invention, a method has been arrived at for producing white or light-coloured cross-linked material using halogen-containing polymers, mercaptosilanes, lead stabilizers and a low molecular weight epoxy resin. In certain formulations, especially when tetrafunctional epoxy resin is used, a positive contribution to the network's mechanical properties can be maintained.

Claims (6)

1. White or light colored crosslinked polymer material, which is formed from 30-98 wt% halogenated polymer, 0-60 wt% plasticizer, 0.05-10 wt% hydrolyzable silane, 0.1-10 wt% lead stabilizer, 0-4 wt% lubricant and 0.1-10% by weight of a further component, characterized in that the further component is an epoxy resin and that the silane is a mercaptosilane. 2. Halogen-containing polymer material according to claim 1, characterized in that the epoxy resin is a low molecular weight mono- to tetra-functional compound of the glycidyl ether, glycidyl ester, glycidylamine or linear or cycloaliphatic type. 3. Polymer material according to claim 1, characterized in that the halogen-containing polymer is PVC homopolymer. 4. Polymer material according to claim 1, characterized in that the halogen-containing polymer is a copolymer between a halogen-containing monomer and a glycidyl-containing acrylate. 5. Polymer material according to claim 4, characterized in that the content of glycidyl-containing acrylate in the copolymer is 0.05-10% by weight. 6. Process for the production of white or light cross-linked halogen-containing polymer material according to claims 1-5, where a mercaptosilane of the type is used: where: R' = a -CH2~ -C2H4- up to - C<q>H^^ or other non-functional group. R''= a freely chosen (non-hydrolyzable group). Y = one or more hydrolyzable groups which e.g. -OCH3, -OC2H5, -OC3H7, -OC4H9 n = 0.1 or 2 as a cross-linker and where the cross-linking is carried out in the presence of moisture after processing the polymer, characterized in that a low molecular weight epoxy resin is added to the mixture.