PLASTISOL COMPOSITION

Abstract: The present invention relates to a plastisol composition based upon polyvinyl chloride and comprising polyvinyl chloride, plas­ ticizers, and calcium carbonate, as main components, whereby the composition furthermore comprises a polyolefin oligomer having 2 to 4 carbon atoms in the monomer basic part, in an amount of 0.1 to 25 % by weight of the total composition.

Description: The present invention relates to a plastisol composition having improved thixotropic features and improved abrasive resistance. The object of the present invention is to obtain a polyvinyl based (PVC) plastisol having improved thixotropic features and an improved abrasive resistance. Further objects will be evident from the following. PVC-plastisols consist of a mixture of pulverulent PVC, calcium carbonate, plasticisers and other smaller additives, which in an unhardened state are to be regarded as emulsions of PVC and other components in the plasticiser. During hardening, which takes place at an elevated temperature, an irreversible change follows whereby it forms an emulsion of plasticizer in PVC, whereby the matrix formed embeds all other components. The feature of a PVC-plastisol are not only dependent on the type of PVC but also on the features of the other ingredients used. It is hereby important that one knows the impact of PVC-type as well as of the additives, such as plasticisers, stabilizers, fillers, pigments and others on the plastisol in order to be able to produce a paste for a predetermined area of use. Within the scope of the ambitions of the automobile industry to save fuel and generally reduce costs, such as to reduce the amount of underbody protective coating mass in the form of PVC plastisol demands have been brought forward for a lower density and a greater resistance to abrasion. The former gives a direct lowering of the weight, the latter furthermore allows a considerable reduction of the amount of plastisol being applied at equal mechanical properties. FR-A-985,327 discloses a composition comprising a polymer of polyvinylchloride or a copolymer of polyvinyl chloride, a compound containing an ethylenic linkage having a molecular weight of from 2000 to 15.000, plastifiers, and fillers. US-A-3,755,238 discloses a latex based coating composition consisting of plasticized polyvinyl chloride copolymerized with an acrylate, a filler, and polyolefin particles dispersed therein having a molecular weight of from 10.000 to 15.000 and a particle size of from 8 to 30 µm. The mean densities of the main components present in a PVC-plastisol are Calcium carbonate 2.65 PVC 1.40 Plasticisers 1.00 Thereby a drastic reduction of the content of calcium carbonate with a simultaneous increase of the contents of the PVC seems to be unavoidable, as an increase of the part of plasticizers is impossible due to the appearing exudation of this latter. However, the content of calcium carbonate is already today heavily reduced, and is normally about 15 % by weight and can hardly be further reduced without considerably deteriorate the rheological properties. Trials to reduce the density of the final plastisol to about 1.2 have been made by using other fillers. Thus microspheres of glass, or hollow bodies of silicate have been tested, but due to a following considerably increased worning out of the spraying equipment used this turned out not to be a feasible way. It has been proposed, JP-A-78140334, to add a powder of a polyolefin to a paint based upon polyvinyl chloride and containing solvents (ketones and cellosolve) to a 20% dry matter contents. The paint is dried at 205°C during loss of the solvents. Such paints are not and can not be used as a PVC-plastisol, which latter is essentially solvent-free. It has now surprisingly been shown possible to be able to solve this problem of replacing heavy components in such a plastisol in accordance with the present invention, which is characterized in that the composition further-more comprises one or more polyolefin oligomers having 2 to 4 carbon atoms in the monomer basic part, in an amount of 0.1 to 25 % by weight of the total composition, and whereby the polyolefin present has a particle size distribution of 0.5 to 100 µm, preferably 2 to 50 µm, more preferably 5 to 20 µm, and a molecular weight of 4,000 to 50,000, preferably 4,000 to 25,000. According to a preferred embodiment of the invention the polyolefin, which is an oligomer, consists of pulverulent low molecular weight polyethylene. By means of the present invention it has not only been shown possible to lower the density but this addition of polymer has a mainly positive influence on the PVC plastisol thus produced. Thus the amount of filler can be varied to a greater extent. It has also turned out that the thixotropy of the plastisol can be considerably improved using a polyolefin, such as polyethylene, having a particle size of the particle size distribution given. The modified plastisols obtained thus show a considerably improved brushability, as well, when one applies the demands of the automobile industry. The commonly appearing thin strikes fail to turn up completely. The common lining of this phenomena using suitable pigments is thus not necessary due to the presence of a necessary amount of material. The invention thus relates to compositions based upon PVC plastisols according to the prior art which plastisols comprises plasticizers of different types, calcium carbonate of different types (ground, precipitated, coated, uncoated) and PVC powder having different particles sizes, as main components, as well as different additives and stabilizers, the kind and amount of which is determined by the exact area of use. The invention will be described more in detail in the following with reference to some Examples which relate to PVC plastisols for the protection of car under bodies. The organic fillers according to the present invention relates to a group of polyolefins with accompanying monomers of the general formula CH₂=CHR wherein Compound R I ethylene -H II propylene -CH₃ III isobutylene -(CH₃)₂ IV butadiene-1,3 -CH=CH₂ The polymers used herein are polyolefin oligomers (waxes) and have a molecular weight of from 4,000 to 50,000, preferably 4,000 to 25,000. All these are the fillers according to the present invention. Due to its inert properties vis-a-vis the plasticizer, present polyethylene (I) and polypropylene (II) are particularly preferred, which, however, does not exclude the use of polyisobutylene (III) and polybutadiene-1,3 (IV). The amount of polyethylene used is 0.1 to 25 % by weight, preferably 0.3 to 10 % by weight, and more preferably 0.5 to 2 % by weight. Other polyolefins are used in amounts relative hereto. The particle size and the particle size distribution have a considerable importance to the properties of a plastisol, whereby the particle size distribution in the present case is between 0.5 to 100 µm, preferably 2 to 50 µm, more preferably 5 to 20 µm. At the preparation of the present pasty emulsions the organic filler is added preferably simultaneously with the PVC powder. Thereby it is achieved that the material becomes completely dispersed in and absorbed by the composition. The rheological properties will thereby be fully exposed. Example 1 (basic). In a rapidly rotating mixer having a peripheral speed of 25 m/s the liquid components given below were first added, and then the solid components were stirred into it. After having reached a homogeneous paste the stirring was continued under vacuo to eliminate air incorporated therein. The basic plastisol thus prepared was used to the tests required. Component % Phthalate plasticizer 40 Secondary plasticizer 2 Polyamino amide 1.5 PVC 40 Calcium carbonate 15 Stabilizers 1.5 Rheological data obtained in a Physica Rotation Viscosimeter according to DIN 53019 are evident from FIG. 1 (shearing stress) and from FIG. 2 (viscosity course). Examples 2 to 4 In the same way as in Ex. 1 above, plastisols were prepared in accordance with the below table and comprising polyethylene, whereby the amount of PVC was replaced by polyethylene. The density of the polyethylene is typically 0.93. Compound Example 1 2 3 4 PVC (%) 40 38.5 33 33 Polyethylene (%) - 1.5 7 7 (Polyethylene per 1000 parts) - (15) (70) (70) The quality of the polyethylene used in Examples 2 to 3 had a molecular weight of 12,000 and a mean particle size of 5 µm, while the quality of the polyethylene used in Example 4 had a molecular weight of 5,000,000 (outside the scope of this invention, and used as a comparative example herein) and a mean particle size of 40 µm. The rheological properties compared with the same properties of the basic plastisol according to the prior art are evident from FIG. 1 and FIG. 2. The difference between the up-going curves and the down-going curves (FIG. 1) is a direct measure of the thixotropy and in combination with the yield point they are direct responsible for the stability of the plastisol. A comparison of the curves shows clearly that the stability has increased by influence of the additives added. The thixotropy corresponds to the area between the up-going and the down-going curves in FIG. 1 and can be calculated to the following for the Examples given: Thixotropy area (Pa/s/cm²) Example 1 166 Example 2 312 Example 3 360 Example 4 280 As evident from the data given the thixotropy area is considerably reduced between the plastisol of Ex. 3 and Ex. 4. In an abrasive test the plastisols according to the invention showed a 50% increased abrasive resistance. Example 5 Plastisol compositions according to Ex. 1 and Ex. 2 were simultaneously applied in a simulated serial underbody protective treatment by means of airless spraying on a smooth, non-absorbing body using a varying thickness of the layer between 0.5 and 1.0 cm, using one or more uncoated zones. Using an angled brush the thickly applied plastisol was brushed onto the uncoated zones, in order to obtain an equal coating to such a great extent as possible, and in order to obtain a simulation of the improvements made on a moving band using a brush. Hereby it turned out that the reference material of Ex. 1 was relatively easy to brush out, as it generally is, whereby, however, a very great thinning of the material occurred. In order to optically line this thinning a colouring pigment was added which, however, did not weakened the resulting layer of plastisol when hardened. The plastisol according to Ex. 2 showed on the contrary during the same brushing conditions a very equal distribution of material. The one skilled in the art immediately felt the "butter-like gliding" of the brush on the plastisol and equally the distribution of the material on the uncoated zones. An measurement afterwards of the thickness of the layers after hardening, showed that the thinning of the material, such as when using a plastisol of Ex. 1, did not occur. In all cases a protective layer thick enough was obtained. Determination of the thickness using an electronic Mitutoyo layer thickness meter gave the following values at comparable starting values. Brushing thickness Ex. 1 50 to 300 µm Ex. 2 300 to 600 µm The resistance to abrasion mentioned above was tested and surprisingly very pronounced when using a low molecular weight pulverulent polyethylene (polyethylene oligomer) and when added in amounts from 0.5 % by weight. The determination of the resistance to abrasion was made on coated steel plates. The PVC-plastisol was applied in layer of the thickness of 600 µm and was dried for 1 hr at 150°C in a warm air oven. The determination of the resistance to abrasion was compared with a plastisol containing no low molecular weight polyolefin, and with a plastisol containing a high molecular weight polyolefin. A standardized spraying liquid hereby fell from a given height down onto an inclined steel plate coated with the plastisol. The amount of liquid to cut through the coating was determined, and the resistance to abrasion can be expressed as ml of abrasive material µm of coating layer. In FIG. 3 attached the resistance to abrasion is given vis-a-vis the increased concentration of polyolefin (A) is a low molecular weight polyethylene of the invention; (B) is a high molecular weight polyethylene (M w =5,000,000); (C) is a PVC-plastisol without polyethylene (Ex. 1). The resistance to abrasion of (C) was given as 1, and the other data are expressed relative hereto. A PVC plastisol composition can thus be varied within the scope of the present invention with reference to its content in accordance with the following general compositions: PVC 15 -40 % by weight Polyolefin 0.1-25 "- Calcium carbonate 13.5-20 "- Plasticisers and other Components 40 -46.5 "- or more preferably PVC 30 -40 % by weight Polyolefin 0.5-10 "- Calcium carbonate 13.5-18 "- Plasticisers and other Components 42 -46.5 "-

Claims: A plastisol composition for coating of car underbodies based upon polyvinyl chloride and comprising plasticizers, and calcium carbonate, besides polyvinyl chloride, as main components, characterized in that the composition furthermore comprises one or more polyolefin oligomers having 2 to 4 carbon atoms in the monomer basic part, in an amount of 0.1 to 25 % by weight of the total composition, and whereby the polyolefin present has a particle size distribution of 0.5 to 100 µm, preferably 2 to 50 µm, more preferably 5 to 20 µm, and a molecular weight of 4,000 to 50,000, preferably 4,000 to 25,0000. A plastisol according to claims 1, characterized in that the polyolefin present is present in an amount of 0.5 to 10 % by weight. A plastisol according to claims 1-2, characterized in that the polyolefin present is based upon an olefin of the general formula CH₂=CHR wherein R is -H, -CH₃, -(CH₃)₂, and/or -CH=CH₂.

Inventors: PERLIK, HELMUTH, TOMASCHEK, HEINZ A.
Applicants: DINOL INTERNATIONAL AKTIEBOLAG
Application year: 1988
Main classification: C08L27
IPC codes: C08L27, C08L23, C08K3