CA2046215A1

CA2046215A1 - Precast concrete coated with copolymer films

Info

Publication number: CA2046215A1
Application number: CA002046215A
Authority: CA
Inventors: Bernhard Dotzauer; Eckehardt Wistuba; Manfred Schwartz; Rolf Petri; Bertold Bechert
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1990-07-05
Filing date: 1991-07-04
Publication date: 1992-01-06
Also published as: NO912625D0; ES2064813T3; EP0469295A3; JPH04231390A; EP0469295A2; DE59103764D1; NO912625L; FI913278A; EP0469295B1; DE4021502A1; NO303627B1; FI913278A0; DK0469295T3; JP3636369B2

Abstract

O.Z. 0050/41719 Abstract of the Disclosure: Precast concrete which is coated on at least one of its surfaces with a film, with or without fillers, of a copolymer of a) from 65 to 100% by weight of C1-C8-alkyl acry-lates, C1-C8-alkyl methacrylates and/or vinyl-aromatic monomers and b) from 0 to 35% by weight of other copolymerizable monomers with a glass transition temperature of from -25 to +30°C, where the film contains from 0.5 to 10% by weight, based on the copolymer, of a compound of the formula I

Description

2~4~2~5 o.z. 0050/41719 Precast concrete coated with copolvmer films The present invention relates to precast concrete which is coated on at least one of its surfaces with a film, with or without fillers, of a copolymer of S a) from 65 to 100% by weight of Cl-C3-alkyl acrylates, C~-Ca-alkyl methacrylates and/or vinylaromatic monomers and b) from 0 to 35% by weight of other copolymerizable monomers with a glas~ transition temperature of from -25 to +30C, where the film contains from 0.5 to 10% by weight, based on the copolymer, of a compound of the formula I
Rl R2 (I) SO3X So3~
where R1 and R2 are each hydrogen or C4-C24-alkyl but not more than one i8 hydrogen, and X and Y are each alkali metal ions or ammonium ions.
Precast concrete, especially concrete roofing tile~, is manufactured from mortar whose consistency makes the final molding possible. The shape of the roofi~g tile is retained even during hardening, which usually take~ place at from 40 to 100C. Concrete roofing tile~ are prone to efflorescence of lime; this is pro-duced by reactlon of calcium hydroxide on the surface of the tiles with the carbon dioxide from the air. Calcium hydroxide may reach the ~urface of the tiles during curing or else on weathering. The results are spotted, unsightly roofs.
Polymer dispersions are used a~ coatings (cf. DE-A 21 64 256). However, the results achieved with the copolymer coating~ to date are still unsatisfactory.
Moreover, the tiles become heavily soiled.
DE-A 39 01 073 describes a concrete roofLng tile which i8 coated with a copolymer which contains an 20~62~
- 2 - O.Z. 0050/41719 organotin compound as copolymerized unit. The emulsifier I is not mentioned in this publication.
German Patent Application P 40 03 909.9 and DE-A
38 27 975 disclose processe~ for preventing efflorescence on mineral substrates, in which copolymers with a glass tran~ition temperature of from -25 to +30C are used.
However, the process requires the addition of special substances, namely aromatic ketones and, as additional process step, irradiation of the coating with ultraviolet light.
It is an ob~ect of the present invention to find precast concrete which is coated in a straightforward manner, shows virtually no efflorescence and becomes soiled to only a small extent, especially at elevated temperature. Moreover, the coating should display its action as quickly as possible.
We have found that this ob~ect is achieved by the precast concrete defined in the first paragraph.
We have also found a process for producing preca~t concrete of this type.
Preferred embodiments of the invention are to be found in the ~ubclaims.
The copolymer i~ composed of a) from 65 to 100, preferably 80 to 100 and e~peclally 90 to 99, ~ by weight, based on the copolymer, of Cl-C~-alkyl acrylates, Cl-C~-alkyl methw rylates and/or vinylaromatic monomers.
At lea~t two monomer~ are preferably employed. The alkyl group~ ln the acrylate~ and methacrylates can be linear, branched or cyclic. They are, in general, methyl, ethyl, propyl, n~ o- and t-butyl, n-pentyl, n-hexyl, ethyl-hexyl, n-octyl, cyclohexyl and, preferably, methyl, n-butyl and ethylhexyl.
Vlnylarom~tic monomers with, norm~lly, up to 20 carbon atom~ are, in gener~l, styrenes which are sub~ti-tuted on the nucleus by C~-C~-~lkyl, chlorine or bromine, such as ~-methylstyrene, para-methylstyrene, p~ra-chloro-styrene or para-bromostyrene, especi~lly ~tyrene it~elf.

20~2ta - 3 - O.Z. 0050/41719 Other monomers b) which are copolymerizable with the abovementioned monomers are used in amounts of up to 35, preferably up to 20, especially from 1 to 10, % of the weight of the copolymer. Possible examples of these are: acrylonitrile, methacrylonitrile, ~-olefins such as ethylene, propene or isobutene, diene~ such as butadiene and isoprene, vinyl chloride, vinylidene chloride, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, amides of these acids, tetrahydrofur-furyl acrylate and methacrylate, alkoxyalkyl acrylatesand methacrylates with from 1 to 4 carbon atoms in the alkoxy andJor alkyl, such as 2- or 3-methoxy-n-butyl acrylate and methacrylate. Acrylic acid, methacrylic acid, the amide~ thereof, acrylonitrile and methacrylo-nitrile are preferred. In some cases, good results areachieved with copolymers which contain no monomers b.
It is essential to the in~ention that the copoly-mer has a glas~ tran~ition temperature of from -25 to +30C, in particular from -12 to +22C.
The glass transition temperature can be deter-mined by conventional methods, eg. by measurement of the modulus of ela~ticity a~ a func~ion of the temperature in a creep te~t or by differential thermal anslysis ~DTA) (see A. Zosel, P~rbe und Lack 82 (1976) 125-134)~
Typlcal comblnation~ of monomer~ a whose gla~s transltlon temperature i~ in the range according to the inventlon are, for example, (in % by weight)s - 65% 2-ethylhexyl acrylate, 35% styrene, - 55% 2-ethylhexyl acrylate, 45% styrene, - 60% 2-ethyl~exyl acrylate, 20% methyl methacrylate, 20% ~tyrene, - 55% 2-ethylhexyl acrylate, 35% n-butyl meth-acrylate, 10% ~tyrene, - 25% n-butyl acrylate, 25% 2-ethylhexyl acrylate, 50% styrene, - 60% n-butyl acrylate, 40% ~tyrene, 50% n-butyl acrylate, 50% ~tyrene, 2 0 ~

- 4 - O.Z. 0050/41719 - 30~ n-butyl acrylate, 30% 2-ethylhexyl acrylate, 20% styrene, 20% methyl methacrylate, - 35% n-butyl acrylate, 30% methyl methacrylate, 35% n-butyl methacrylate.
Additional incorporation of monomers b likewise has an effect on the glass transition temperatures of the copolymers. This iq why the ratios of the amounts of monomers a indicated above may need adjustment.
Compound I is preferably employed in amounts of from 0.5 to 4, in particular 0.5 to 3 and e~pecially 1 to 2, % of the weight of the copolymer.
In formula I, R1 and R2 are preferably linear or branched alkyls of from 6 to 18 carbon atoms or hydrogen, especially of 6, 12 or 16 carbon atoms, with R1 and R2 not both being hydrogen. X and Y are preferably ~odium, potas~ium or ammonium ion~ and especially sodium. It is particularly preferred for X and Y to be sodium, R1 to be a branched alkyl of 12 carbon atoms and R2 to be hydrogen or R1. Mixtures which contain from 50 to 90~ by weight of the monoalkylated product are often uset in industry, for example Dowfax 2A1 (proprietary name of Dow Chemical Company)~
These compounds are generally known as emulsi-fiers, for example from US-A 4 269 749 of the Dow Chemi-cal Company, and are commercially available.
The emulsifler I is preferably added to the copolymer during the preparation thereof. However, it can al~o be added in whole or in p rt to the copolymer after the polymerization. The copolymer can be prepared in a conventional manner by free radical copolymerization of monomers a and b in aqueous emulsion. It is possible to use batch processes or feed processes in which the initiator and/or monomer~, which may be emulsified in water, are added a little at a time or continuously during the polymerization (see, for example, Encyclopedia of Polymer Science and Engineering, Vol. 6 tl986) 1-52)~
The resulting aqueou~ polymer dispersions usually have a 20~6~

- 5 - o.z. 0050/41719 copolymer concentration of from 40 to 60% by weight. From 0.5 to 4, in particular 0.5 to 3 and especially 1 to 2, ~ by weight, based on the copolymer, of compound I are preferred as emulsifier. It i~ possible additionally to use conventional emulsifiers such as anionic and/or nonionic emulsifiers, for example sodium dialkyl sulfo-succinates, sodium salts of sulfated oils, sodium alkyl-sulfonates, sodium, potassium and ammonium alkyl sul-fates, alkali metal salts of sulfonic acids, alkoxylated Cl2-C24-fatty alcohols and alkoxylated alkylphenols, as well as ethoxylated fatty acids, fatty alcohols and/or fatty amides, ethoxylated alkylphenols, furthermore sodium salts of fatty acids such as sodium stearate and sodium oleate or fatty alcohol sulfate~ and fatty alcohol ethoxylates.
The aqueous copolymer di~persion~ form at room temperature films which are shiny, clear and tough but flexible and which absorb only little water, less than 10, usually le~s than 5, % by weight being measured after storage in water for 24 hours. They are generally free of plasticizers and of film-formers.
The coating compositlons are prepared in a conventional manner by incorporating inorganic fillers and colored pigments into the aqueou~ copolymer disper-sions and ad~usting to the required viscosity with water.
Examples of suitable inorganic fillers ares chalk, silica flour and/or barytes. The amount of pigments and/or fillers is generally from 50 to 450 parts by weight based on the copolymer as 100 parts by weight.
Exsmples of ~uitable precast concrete are shaped articles made of concrete ~nd expanded concrete, eg.
slabs, pipes and, especially, roofing tiles, it also being possible to apply the coating to uncured products of this type, e~pecia~ly roofing tiles, called green tiles. The precast concrete is produced in a conventional manner from ready-mixed concrete by an extrusion proce~s during which it is given it~ final shape. The coating 20~62~ ~

- 6 - o.z. 0050/41719 composition is applied in a conventional manner by spray, trowel, knife or by pouring, the amounts applied u~ually being from sO to 400, in particular 100 to 250, g/mZ~
measured in the dry state. It i9 of particular interest to apply such coatings to concrete roofing tile~ which have not set. The coating or coating~ can be dried in a conventional manner, at room temperature or at a ~lightly elevated temperature. For thi , the coated tile is generally placed in a chamber where the concrete sets in a process lasting from 6 to 12 hours at from 40 to 65C, and the copolymer in the coating composition form3 a film.
After this proce~s, the tile is preferably sprayed with the coating composition a second time. It is dried in a drying tunnel with air circulating at 100C.
The drying tunnel and the subsequent cooling section are designed so that complete film formation takes place.
The tiles are thus well protected against lime efflorescence. In addition, the surface of the coatings is not tacky even at elevated temperatures, so that the tiles pick up hardly any dirt.
Unle~s otherwise indicated, parts and percentages are by welght in the followlng Examples.
COMPARATIVE EXANPLE lC
An emulsion of 45 parts of styrene (S), 55 part~
of 2-ethylhexyl acrylste (EHA), 2.5 parts of acrylic acid (AA), 105 parts of water and 1.5 parts of the sodium salt of a sulfuric acid hemiester of an isononylphenol ethoxy-late with an average of 25 ethylene oxide units and 0.5 part of an isononylphenol ethoxylate with an average of 25 ethylene oxide units as emul~ifiers wa~ polymerized using 0.5 part of ~odium peroxodisulfate in a feed process at 90C.
EXAMP~E 1 ~he process of Comparative Example lC was carried out but with the difference that the emulslfier used was not the mixture from Comparative Example lC but 1.5 parts 2 ~

- 7 - o.Z. 0050/41719 of a technical mixture of abou~ 80% of a compound I where X and Y are sodium, R1 is a branched alkyl of 12 carbon atoms and R2 is hydrogen, and about 20% of a compound I
where X and Y are sodium and Rl and R2 are branched alkyls of 12 carbon atoms. The resulting copolymer dispersion had a copolymer content of 4g% measured in the conven-tional manner by evaporation of the water.
A3 a measure of the soilability, the energy to separate a sample specimen from a polymer film dried at room temperature for 2 weeks was measured at 70C by the method of A. Zosel, J. Adhesion 30 (1989) 135-139. The results in Table 1 clearly show the superiority of the claimed emulsifier. All the Examples and Comparative Experiments were tested in the same way.

An emulsion of 35 parts of n-butyl acrylate (BA), 35 parts of n-butyl methacrylate (BMA), 30 parts of methyl methacrylate (MMA), 2.5 part~ of acrylic acid, 105 parts of water and 1.5 parts of the sodium ~alt of a sulfuric acid hemiester of an isononylphenol ethoxylate with an average of 25 ethylene oxide units and 0.5 part of an isononylphenol ethoxylate with an average of 25 ethylene oxide units as emulsifiers was polymerized using 0.5 part of sodium peroxodisulfate in a feed process at 90C.

The process of Comparative Example 2C was carried out but with the difference that the emulsifier used was not the mixture from Comparative Example 2C but 1.5 parts ef a technical mixture of about 80% of a compound I where X and Y are sodium, Rl is a branch0d alkyl of 12 carbon atom~ and R2 is hydrogen, and about 20% of a compound I
where X and Y are sodium and Rl and R2 are branched alkyls of 12 carbon atoms.

An emulslon of 20 parts of methyl methacrylate, 60 parts of 2-ethylhexyl acrylate, 20 parts of styrene, - 2 0 ~

- 8 - O.Z. OOS0/41719 2.5 part3 of acrylic acid, 105 parts of water and 1.5 parts of the sodium ~alt of a sulfuric acid hemiester of an isononylphenolethoxylate with an average of 25 ethylene oxide unit4 and 0.5 part of an isononylphenol-ethoxylate with an average of 25 ethylene oxide units as emulsifier~ wa~ polymerized u~ing 0.5 part of sodium peroxodisulfate in a feed process at 90C.

The process of Comparative Example 3C was carried out but with the difference that the emulsifier used was not the mixture from Comparative Example 3C but 1~.5 parts of a technical mixture of about 80% of a compound I where X and Y are sodium, R1 i8 a branched alkyl of 12 carbon atoms and R2 i8 hydrogen, and about 20% of a compound I
where X and Y are ~odium and Rl and R2 are branched alkyls of 12 carbon atoms.

An emulsion of 35 part~ of n-butyl methacrylate, 10 parts of styrene, 55 part~ of 2-ethylhexyl acrylate, 2.5 parts of acrylic acid, 105 parts of water and 1.5 parts of the sodium salt of a sulfuric acid hemiester of an i~ononylphenolethoxylate with an average of 25 ethy-lene oxide units and 0.5 part of an isononylphenol ethoxylate with an average of 25 ethylene oxide units as emulsifiers wa~ polymerized using 0.5 part of sodium peroxodisulfate in a feed process at 90-C.

The process of Comparative Example 4C was carried out but with the difference that the emulsifier used was not the mixture from Comparative Example 4C but 1.5 parts of a technical mixture of about 80~ of a compound I where X and Y are sodium, Rl is a branched alkyl of 12 csrbon atoms and R2 is hydrogen, and bout 20~ of a compound I
where X and Y are sodium and R~ and R2 are branched alkyls of 12 carbon atoms.

2 0 ~

- 9 - O.Z. 0050/41719 ~ABLE 1 Monomers Separation energy [parts] in J/ma at 70C
. . _ . . .
lC 45 S 55 EHA 2.5 AA 4.6 1 45 S 55 EHA 2.5 AA 2.0 2C 35 ~A 35 BMA 30 MMA 2.5 AA 4.5 2 35 BA 35 BMA 30 MMA 2.5 AA 1.0 3C 60 EHA 20 MMA 20 S 2.5 A~ 8.3 3 60 EHA 20 MMA 20 S 2.5 AA 1.5 4C 55 EHA 35 BMA 10 S 2.5 AA 4.0 4 55 EHA 35 BM~ 10 S 2.5 AA 3.7

Claims

1. Precast concrete which is coated on at least one of its surfaces with a film, with or without fillers, of a copolymer of a) from 65 to 100% by weight of at least one mono-mer, selected from the group comprising C1-C8-alkyl acrylates, C1-C8-alkyl methacrylates and/or vinylaromatic monomers and b) from 0 to 35% by weight of other copolymerizable monomers with a glass transition temperature of from -25 to +30°C, where the film contains from 0.5 to 10% by weight, based on the copolymer, of a compound of the formula I

(I) where R1 and R2 are each hydrogen or C4-C24-alkyl but not more than one is hydrogen, and X and Y are each alkali metal ions or ammonium ions.

2. Precast concrete as claimed in claim 1, wherein R1 and R2 are linear or branched alkyls of from 6 to 18 carbon atoms or hydrogen, with R1 and R2 not both being hydrogen, and X and Y are sodium, potassium or ammonium ions.

3. Precast concrete as claimed in claim 1 or 2, wherein the film contains from 0.5 to 4% by weight, based on the copolymer, of the compound I.

4. Precast concrete as claimed in claim 1 or 2 or 3, wherein the copolymer 18 prepared by emulsion polymeriza-tion using compound I.

5. A process for producing precast concrete as claimed in claim 1 or 2 or 3 or 4 by applying to at least one surface of green precast concrete an aqueous composi-tion which contains an aqueous dispersion of a copolymer of - 11 - O.Z. 0050/41719 a) from 65 to 100% by weight of at least one mono-mer, selected from the group comprising C1-C8-alkyl acrylates, C1-C8-alkyl methacrylate. and/or vinylaromatic monomers and b) from 0 to 35% by weight of other copolymerizable monomers with a glass transition temperature of from -25 to +30°C, wherein the aqueous composition contains from 0.5 to 10%
by weight, based on the copolymer, of a compound of the formula I
( I ) where R1 and R2 are each hydrogen or C4-C24-alkyl but not more than one is hydrogen, and X and Y are each alkali metal ions or ammonium ions.

6. A process as claimed in claim 5, wherein the composition is applied to the precast concrete in an amount such that the total amount applied is from 50 to 400 g/m2 when dry.