CS239799B1 - A process for continuous photochemical crosslinking of polyvinyl chloride based compositions - Google Patents

Abstract

Method of continuous photochemical crosslinking of products from mixtures based on polyvinyl chloride. The mixture containing a light-sensitive reactive component is heat-treated into the final shape of the product and this product is exposed to light radiation with a wavelength in the range of 200-800 nm immediately after the completion of shaping, at a product temperature of 50-200 °C. The light source is high-pressure or medium-pressure mercury, halide, xenon or sodium discharge lamps. The continuous method of photochemical crosslinking of products from polyvinyl chloride according to the invention is suitable for crosslinking products of a planar nature /deposits, foils/ and of a volumetric nature /pipes, profiles/.

Description

The invention relates to the continuous photochemical crosslinking of products from polyvinyl chloride based compositions.

Crosslinking is one of the widespread methods of modifying properties of polymeric materials, since the formation of a spatial network in the polymer structure results in a significant change in properties. It is about improving mechanical properties especially at higher temperatures, improving shape stability, chemical resistance and the like.

Spatial networks in the polymeric structure can be achieved by degradation crosslinking, chemical crosslinking, electron beam crosslinking and electromagnetic radiation.

Degradation crosslinking occurs at elevated temperature. Heating first results in dehydrochlorination and marked discoloration, and after some induction period the first insoluble fractions are formed. Thus, the crosslinking reaction competes with a degradation reaction. A disadvantage of this crosslinking method is also the considerable energy consumption.

In the chemical crosslinking process of polyvinyl chloride, the crosslinking reaction takes place under the effect of heat and a crosslinking agent. A known cross-linking agent is, for example, peroxides. However, as separate crosslinking agents, peroxides are not very effective for polyvinyl chloride and crosslinking is accompanied by darkening of the polymer.

Other known crosslinking agents are thiourea derivatives, amino compounds, sulfur, sulfur donors and others. The disadvantage of crosslinking with chemical agents is the difficult separation between processing and crosslinking, since both processing and crosslinking take place at elevated temperature. However, the crosslinking should only take place after the processing operation has been completed. This problem can be solved, for example, by using a crosslinking agent effective either at a temperature higher than the processing temperature or after a longer induction period. Networking is then more energy and time consuming.

Radiation crosslinking removes this deficiency, because the final shape of the product is exposed to the dose of energy radiation. However, this type of networking has its drawbacks, in particular. it is a necessity to purchase a demanding device - a radiator. All components of the mixture, including those where the reaction is undesirable, such as plasticizer 1a, are also attacked by high energy radiation.

The sieving reaction can also be triggered by the action of radiation of greater wavelength in the region of visible ultraviolet light. The polyvinyl chloride mixture contains a photosensitive reactive component whose molecules are activated by radiation and act as initiators of the desired chemical reaction.

For example, Japanese Patent Application 57-129 442 describes a process for producing lithographic printing plates based on polyvinyl chloride or chlorinated polyolefin and a multifunctional vinyl monomer by a photochemical method.

It is discontinuous production with relatively long light exposure times (minutes to tens of minutes), which is given by the thickness of the crosslinked polymer layer. The continuous method of photochemical cross-linking is described in Soviet certificate 883 098.

The mixture containing polyvinyl chloride, triethylene glycol dimethacrylate and photoinitiator is applied by means of a scanning roller to the surface of the synthetic leather and after irradiation with developer - a source of ultraviolet light with an input of 8-10 kw - the coating crosslinks in 0.5 s. However, this cross-linking method is only applicable to very thin layers.

These drawbacks are overcome by the process of photochemical crosslinking of products from polyvinyl chloride based compositions containing a photosensitive reactive component according to the invention. The essence of the invention is that the products immediately after the shaping of the product, i.e. immediately after heat treatment of the mixture to its final shape, at a product temperature of 50-200 ° C,

239799 'exposed to light radiation of wavelength in the range 200-800 nm. The wavelength of the electromagnetic radiation corresponds to the sensitivity of the photosensitive reactive component of the mixture.

Radiation in the range of 200-800 nm is particularly suitable for easy availability of a powerful light source. The energy of electromagnetic radiation is inversely proportional to its wavelength. Radiation with a wavelength lower than 200 nm is energy rich, but has limited ability to penetrate matter.

Radiation with a wavelength above 800 nm has good penetration capability, but is energy disadvantageous. Accordingly, depending on the type of light radiation (according to the type of lamp used), it is possible to crosslink the products to a depth given by the penetration of radiation.

The penetration depth is also influenced by the composition of the crosslinking composition, since the filled and pigmented layers penetrate the radiation to a lesser depth than the transparent layers. A product temperature of less than 50 ° C is not suitable for photochemical crosslinking in a continuous manner since the required exposure times necessary to achieve the desired crosslinking and hence to improve product properties are too long at this temperature and light exposure cannot be included as part of the processing equipment.

The continuous process of photochemical crosslinking of the polyvinyl chloride products according to the invention is suitable for crosslinking products of a flat nature (deposits, foil) and also of a bulk nature (tubes, profiles).

The following examples serve to illustrate the invention in more detail.

He did

The following mixture was prepared for sheathing of electric cables:

polyvinyl chloride powder i wt. 67.5 ester type plasticizer 15 Dec a tri-functional monomer acrylic ester 15 Dec stabilizer Ba / Cd 1.5 4-chlorothioxantone 0.5 triethanolamine 0.5

This mixture was melted in a screw extruder and used as a melt to sheath a 1.2 mm diameter wire. The insulation layer had a thickness of 0.8 mm so that the total diameter of the insulated conductor was 2.8 mm. .

A lighting device was incorporated into the production line to expose the sheathed cable as it exits the die head at an insulating layer temperature of 100-150 ° C. The lighting equipment consisted of three medium-pressure halide (InJ) lamps in a discharge tube with a maximum radiation intensity in the region of 400 nm. The distance between the wire and the lamp was 800 mm.

At a light intensity of 100 k / x and an insulation temperature of the exposed cable of 50 ° C, a light exposure time of 180 seconds is required to achieve a thermal resistance of 120 ° C, while a light exposure time of 0.5 s is sufficient at a cable insulation temperature of 150 ° C. then an extrusion speed that can reach 100 m / min.

The electric cable produced in this way is characterized by the resistance of the insulating layer against punching during the resistance test of insulation and sheath made of softened polyvinyl chloride against pressure at elevated temperature (ČSN 347010, test 61) up to 120 ° C against 50-60 ° C for the same cable .

39799

Example 2

The following mixture was prepared for coating on an endless substrate:

% wt. mixtures paste-forming polyvinyl chloride 50 ester type plasticizer 35 bifunctional methacrylate monomer 12.5 organotin stabilizer 2.0 diethoxy-phenyl-acetophenone 0.5

This mixture was applied to an endless separation pad on a coating apparatus and gelatinized in a tunnel dryer at 190 ° C. When leaving the tunnel drier, the deposit was illuminated by a high-pressure mercury lamp with a high radiation intensity in the 350 nm region at a deposit temperature of 150-170 ° C. The distance of the lamp from the deposition was 400 mm, the feed rate during painting was 10 m / min.

After cooling to normal temperature, the photochemically reticulated film has the following properties:

modulus at 100% deformation tensile strength elongation insoluble in tetrahydrofuran uncrosslinked foil 3.2 MPa

12.1 MPa 560%%

mesh film 8.8 MPa 17.9 MPa

330%%

The photochemically crosslinked film thus produced can be used as a covering layer of synthetic leather or flooring since it has better mechanical and chemical properties compared to the noncrosslinked film.

Claims (1)

SUBJECT OF THE INVENTION Process for the continuous photochemical crosslinking of products from mixtures based on polyvinyl chloride containing a photosensitive reactive component, characterized in that the products are immediately exposed to light wavelengths in the range of 200-800 immediately after heat treatment of the mixture to the final shape at a product temperature of 50-200 ° C. nm from a source of high- or medium-pressure mercury, metal halide, xenon or sodium lamps.