GB2099331A - Process for the surface treatment of manufactured articles based on chloro-vinyl polymers - Google Patents

Abstract

A process for incorporating one or more additives, such as pigment, dye, stabilizer, antioxidant, and hardener, into the surface of a manufactured article based on a chloro-vinyl polymer, in particular polyvinylchloride, by coating the surface of the manufactured article with at least one polymeric film containing the additive or additives dispersed or dissolved therein.

Description

SPECIFICATION Process for the surface treatment of manufactured articles based on chloro-vinyl polymers This invention relates to a process for the surface treatment of manufactured articles based on chloro-vinyl polymers. More particularly, the invention relates to a process for incorporating into the surface of articles manufactured from polyvinylchloride, additives such as pigments, dyes, stabilizers, antioxidants and hardeners.

As is known, articles manufactured from polyvinylchloride exhibit some limitations in use due to the non-stability of the polymer to surface aggressive agents such as oxygen, actinic radiation, mildew, bacteria, etc. This drawback is particularly marked in the case of manufactured articles based on plasticized polyvinylchloride, since the plasticizer, in consequence of its migration towards the article surface, combines with the air dust, thus forming an environment favourable to biological aggression and to photo-oxidation.

To improve the stability of polyvinylchloride, as well as of any other polymer, it is known to add to the polymeric mass suitable stabilizers, pigments, U.V. screening agents, opacifiers, etc. However, only a low percentage (5 - 10%) of the added amount of additive is effective as regards protection from sunlight, i.e. the percentage of additive present on the exposed surface. As a consequence thereof, it is necessary to employ greater and greater amounts of additives in order to obtain results which not always are satisfactory. The use of considerable amounts of additives involves, as is known, problems connected with cost, processability of the mass and appearance of the article.

Furthermore, the addition of the additive to the polymeric mass does not permit the various and different problems of chemical aggression which may arise for example on two different surfaces of the manufactured article to be selectively overcome.

Thus, for example, in the case of polyvinylchloride films intended for the waterproofing of dumps, it is necessary to provide protection against bacterial aggression on the film surface in contact with the ground, and protection against actinic attack on the other surface exposed to the light.

The above problems also arise in the case of articles manufactured from unplasticized polyvinlchloride. It is known that such articles, which are mass-dyed and pigmented, become discoloured and turn yellow-brown, and their mechanical strength decays very rapidly when they are exposed to ultraviolet rays.

For this reason manufactured articles based on unplasticized polyvinylchloride are hardly suitable for being used in very sunny areas because of their insufficient stability in use.

The present invention provides a process for incorporating one or more additives into the surface of a manufactured article based on a chloro-vinyl polymer, comprising coating the surface of the manufactured article with at least one polymeric film containing the additive or additives dispersed or dissolved therein.

By means of the process according to the invention there may be incorporated into manufactured articles based on chloro-vinyl polymers additives, such as pigments, dyes, stabilizers, antioxidants, and hardeners, while avoiding the above-mentioned drawbacks.

In particular, there may be incorporated into polyvinylchloride-based articles additives which need not be present in large amounts in order to obtain the necessary protection of the manufactured article.

The concentration of the additive or additives in the polymeric film is not critical and may vary over a wide range depending on the required properties. Generally, concentrations of from 0.1 to 10% by weight in respect of the film-forming polymer are employed.

Polymers suitable for the coating of the article are acrylic, methacrylic, and polyurethane resins, such as polymethyl-methacrylate, or mixtures thereof.

Depending on the intended use of the manufactured article, one or more polymeric films may be applied, and each of them may contain the same additive or different additives. The total thickness of the film or films is not critical and preferably ranges from 2 to 30 Rm.

The polymeric film containing the additive or additives is preferably applied onto the article surface in the form of a solution in a solvent of the polymer. Preferred suitable solvents are methyl-ethyi-ketone, acetone, toluene, isopropanol, n.butanol, and xylene. In practice, it is preferable to employ mixtures of these solvents.

The solution may be suitably applied onto the surface of the manufactured article by spraying or by means of a brush.

Depending on the shape of the manufactured article and on the use it is intended for, the polymeric film containing the additive or additives may be applied onto the entire surface or onto only a portion thereof, for example onto the faces or surfaces which will be subjected to the weather or chemical aggression.

The process according to the present invention permits the application of a polymeric film containing a different additive onto different faces of a manufactured article depending on the intended use thereof or on the type of attack to which each face is to be subjected during use.

In order to improve the adhesion between the chlorovinyl polymer forming the manufactured article and the polymeric coating film, it is advisable to remove lubricants employed during extrusion of the article, at least from the article surface to be coated. The removal may be accomplished by washing with an alkaline or acid inorganic solution, with a soap solution or with an organic solvent. The latter is especially preferred when the process is conducted continuously. The washed manufactured article is subjected to drying prior to the application of the additive-containing polymeric layer. In the case of a continuous process, drying is suitably carried out by means of an intense hot air circulation, at a temperature ranging from 40 to 80"C for a contact time of from 30 seconds to 3 minutes.

After application of the additive-containing polymeric layer, the manufactured article is preferably dried in a forced air stream, at a temperature ranging from 40 to 800C and for a time-period ranging from 3 to 10 minutes.

According to a preferred embodiment, the process of the present invention comprises the following steps conducted continuously: (a) washing the manufactured article; (b) drying the manufactured article by means of an air stream, at a temperature from 40 to 800C for a period of time of from 30 seconds to 3 minutes; (c) applying a surface layer or coating prepared from an acrylic, methacrylic, or polyurethane polymer or a mixture thereof containing the additive or additives to be applied dissolved or dispersed therein; and (d) drying the surface layer by means of an air stream, at a temperature from 40 to 80"C and for a period of time of from 3 to 10 minutes.

The process of the present invention can be applied not only to articles manufactured from polyvinylchloride, but to all chloro-vinyl polymers. The term "chloro-vinyl polymers" includes vinylchloride copolymers containing up to 50% by weight of at least one other ethylenically unsaturated monomer copolymerizable with vinyl chloride; blends of polymers based on polyvinylchloride, such as blends of polyvinylchloride with an ethylene/vinyl acetate copolymer or with an acrylic copolymer or with chlorinated polyethylene; and vinyl chloride polymers grafted with other polymers, such as chlorinated polyethylene.

The invention will be further described with reference to the following illustrative Example.

Example 100 parts by weight of polyvinylchloride, having a value of K 65, additioned with: 3.5 parts by weight of dibasic lead phosphate, 0.6 parts by weight of barium and cadmium laurate and bisphenol A, and 0.4 parts by weight of epoxidized soybean oil, as stabilizers; with: 1.4 parts by weight of dibasic lead stearate, and 0.4 parts by weight of stearic acid, as lubricants; and with 9 parts by weight of precipitated calcium carbonate, having an average diameter of the particles of about 1 Fm, as reinforcing agent; and containing 1.5 parts by weight of a pigment based on calcined iron oxides, were mixed in a quick mixer for 15 minutes up to a temperature of 12000.

The mixture was granulated at 16000 by means of a BAUSANO two-screw extruder, and the granules were extruded by means of a BANDERA 100 single-screw extruder, at a temperature of about 160"-190"C, so as to obtain a gutter with a head having a U-section, provided with a hollow space.

From the gutter there were obtained, in the longitudinal extrusion direction, strips having a width of about 2 cm and a length of about 20 cm.

Some of these strips were exposed to a Weather-Ometer and to Xenotest 1200 for different ageing times.

On a drawn sample (sample A) the following were determined: - stability of the dye, before and after ageing; - dehydrochlorination time, before and after ageing; and - breaking energy in an impact tensile test, before and after ageing.

The stability of the dye was determined according to ISO R 879.

For measuring the dehydrochlorination time, the PVC strip was cut into small pieces which were introduced into a cell thermoregulated at 200"C. Hot nitrogen was made to flow through the product and made to bubble in a solution having a pH of 6. The nitrogen entrained the hydrochloric acid released as a result of the polyvinylchloride decomposition. The time required to bring the pH of 180 ml of an aqeuous 0.1 M NaCI solution from 6 to 3.8 was measured. Such time is defined as dehydrochlorination time.

The breaking energy was determined according to DIN 53448 standard, employing a width of the useful section, or portion, equal to 5 mm, a pendulum with an impact speed of 3.8 m/sec. and interchangeable rams of 75, 150 and 250 kg/cm2.

The results of the tests are given in the Table below.

The same gutter, leaving the extruder, was subjected, continuously and in line with the extrusion, to the following treatments: -washing with acetone; - drying in a hot air stream, at 60"C; - application, by means of a set of nozzles, of a film, having a thickness of 10 m, of a solution consisting of 34% by weight of polymethylmethacrylate, 65% by weight of a mixture composed of acetone, methyl-ethyl-ketone, toluene, isopropanol, n.butanol and xylene, and 1% by weight of a pigment based on calcined iron oxides; and - drying of the coated manufactured article by means of a hot air stream at 60"C.

On the product so obtained (sample B) were carried out the same determinations as were carried out on the uncoated product.

The results obtained are given in the Table below. TABLE SAMPLE A SAMPLE B After ex- After ex- After ex- After ex Before posure to posure to Before posure to posure to ex- Weather- Xenotest ex- Weather- xenotest posure Ometer for 1200 for posure Ometer for 1200 for 1500 h 500 h 1200 h 1500 h 500 h 1200 h Stability of the dye 5 2-3 4-3 1 5 5 5-4 5-4 dehydrochlorination 106 70 60 50 101 90 96 90 time in minutes Breaking energy in 608 270 450 150 640 450 600 590 kg cm/cm It is thus apparent from the results given in the Table that the Sample B treated in accordance with the process according to the invention substantially maintains the values in respect of stability of the dye, dehydrochlorination time, and breaking energy, as compared with the corresponding values of the untreated Sample A.

Claims (9)

1. A process for incorporating one or more additives into the surface of a manufactured article based on a chlorovinyl polymer, comprising coating the surface of the manufactured article with at least one polymeric film containing the additive or additives dispersed or dissolved therein.

2. A process as claimed in Claim 1, in which the concentration of the additive or additives in the polymeric film is from 0.1 to 10% by weight referred to the filmforming polymer.

3. A process as claimed in Claim 1 or 2, in which the thickness of the polymeric film is from 2 to 30 yam.

4. A process as claimed in any of Claims 1 to 3, in which the polymer of the polymeric film is selected from acrylic resins, methacrylic resins, polyurethane resins, and mixtures thereof.

5. A process as claimed in any of Claims 1 to 4, in which the chloro-vinyl polymer is polyvinylchloride.

6. A process as claimed in any of Claims 1 to 5, in which the polymer of the polymeric film is applied onto the manufactured article surface in the form of a solution in a solvent of the polymer.

7. A process as claimed in Claim 6, in which the solvent is selected from methyl-ethyl-ketone, acetone, toluene, isopropanol, n.butanol, xylene and mixtures thereof.

8. A process as claimed in any of Claims 1 to 7, which comprises the following steps: (a) washing the manufactured article; (b) drying the washed manufactured article by means of an air stream, at a temperature from 40 to 80C and for a time period of from 30 seconds to 3 minutes; (c) applying a surface layer of an acrylic, methacrylic, or polyurethane polymer or a mixture thereof containing the additive or additives to be applied dissolved or dispersed therein; and (d) drying the surface layer by means of an air stream, at a temperature from 40 to 80 and for a time period of from 3to 10 minutes.

9. A process according to Claim 1 for incorporating one or more additives into the surface of a manufactured article based on a chloro-vinyl polymer, substantially as herein described in the foregoing Example.