CA1335388C - Anti-skid composition for use on cellulosic fibrous materials - Google Patents

Abstract

The invention provides an improved anti-skid composition for use on cellulosic fibrous materials, which composition comprises water, colloidal silica, a water soluble acrylamide polymer and an effective amount of a compatible amphoteric, anionic or nonionic surfactant. The invention is particularly valuable with linerboard prepared from reprocessed or recycled papers.

Description

The present invention relates to anti-skid compositions for use on cellulosic fiber materials, to a method of imparting anti-skid characteristics to cellulosic fiber materials and to the treated cellulosic fiber materials having anti-skid character-istics. The invention is particularly concerned with imparting anti-skid properties to linerboard prepared from reprocessed or recycled paper.
Various articles such as bags, cartons and other containers fabricated from Kraft paper, cardboard and other types of cellulosic fiber material used for the packaging of foodstuffs, chemicals and the like possess the inherent disadvantage of slipp-ing and sliding against each other. This tendency of the cellulo-sic fiber material to slip or slide is undesirable and in many cases harmful. Attempts have been made to overcome this diffi-culty. For example, containers fabricated from crepe paper or containers treated with a form of an adhesive have been employed.
Such containers have not been entirely satisfactory for reasons including economy, poor printing characteristics, insufficient slip resistance, unpleasant or uncomfortable handling characteris-tics, cleanability factors and the excessive amount of material required.
The problems of slipping and sliding are exacerbated when recycled fiber is used in the cellulosic material. As a consequence of extra processing, when compared with virgin fiber, the fiber length of the recycled material is less than that of the virgin fiber. The tendency to slipping and sliding increases as the amount of recycled fiber increases. In recent years there has 1 33~388 been a tendency to increase the proportion of recycled fiber in cellulosic material, so that the problem of slipping and sliding is increased.
It is possible to coat cellulosic materials with col-loidal silica sols to impart anti-skidding properties to the coated cellulosic materials. The use of colloidal silica sols to coat paper in order to provide slip resistance is disclosed in United States Patents Nos. 2,643,048 and 2,872,094. Colloidal silica sols have also been employed to impart stiffness to paper and generally for the treatment of paper as disclosed in United States Patent Nos. 2,833,661; 2,801,938 and 2,980,558.
Other patents disclosing the use of various silica sols for the frictionizing, or to provide anti-skidding properties to cellulose materials, include United States Patents Nos. 3,689,431; 3,711,416; 3,754,984; 3,860,431; 3,836,391; and 3,901,987.
A problem associated with the treatment of cellulose articles with colloidal silica sols has been the capacity of these colloidal silica sols to adhere strongly to machinery, application equipment, floor surfaces, etc. when overspray occurs. Recently, commercial colloidal silica sol products containing urea have appeared on the market. Those materials tend to eliminate this adherence problem in the formation of a water washable material.
The problem of overspray has been recognized in the art as seen in United States 3,901,987, and accordingly, it would be an advance if a product could be found which could be easily removed from machinery, floors, etc. when overspray of colloidal silica sols t 335388 occurs.
Two important characteristics of an anti-skid composi-tion are the attainable slide angle and washability of the compo-sition, i.e. the ease with which excess, oversprayed material is removed by water washing. The slide angle is measured by observ-ing the angle from the horizontal to which sheets of cellulosic material in contact with each other can be tipped before sheets slide apart. Typical required slide angles are 20 to 28, but there is a tendency to require higher slide angles; and slide angles of at least 22 are preferred.
Although ability to impart a high slide angle and washa-bility are important, there are other desirable characteristics of an anti-skid composition. The composition should be stable over a period of at least 6 months. The anti-skid coating should not create dusting. The magnitude of any dusting problem depends to some extent on the speed at which machinery handling the anti-skid treated cellulosic material operates; the faster the machine operates the greater its tendency to throw dust in the air.
Hence, as machine speeds increase this problem also increases.
Desirably the anti-skid composition should not adversely affect sizing, i.e. it should not lead to increased Cobb values, or if it does lead to increased Cobb values the increase should be limited.
The anti-skid composition should produce a colour with an indicator spray, so that a proper application pattern can be observed. The anti-skid composition should not adversely affect the sizing of the paper product as measured, for instance, by the Cobb test. 1 3353~8 Canadian Patent No. 1,156,803 discloses a composition for increasing the coefficient of friction of a surface to wllic11 it i8 applied, which composition is an aqueous solution of colloi-dal silica and urea.
We have now di~covered anti-skid compositions which are as good as, or superior to, those disclosed in C~nadian Patent No. 1,156,803 at the same application rates and are urea-free.
The present invention provides an anti-skid composition for use on cellulosic fibrous material which comprises water, colloidal silica having a particle size in the range 10 to 150 nm, a water soluble acrylamide polymer and an effective amount of a compatible anionic, amphoteric or nonionic surfactant.
The silica particles have a slze in the range 15 to 150 nm, preferably 25 to 150 nm, with a size in the range 85 to 130 nm being particularly preferred. It is sometimes de~lrable to use particles of two different sizes. Smaller particles may en-hance the colour effect with an indicator, 80 that it can be more readily observed whether tha anti-~kld composition ha~ been applied, or applied evenly.
Because too low a pH may cause coagulation of the colloidal 80-, the pH should not be allowed to drop below about 7.5 or 8. D~fferent 8018 coagulate at different pH values, 80 it is not possible to be absolutely precise about the pH at which coagulation will occur. Furthermore, stability of the colloidal silica 8018 is somewhat temperature dependant and lower pH values can be tolerated at higher temperatures.

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One colloidal silica sol suitable for use in the inven-tion is available from Nalco Chemical Company under the trade mark NALCOAG 7604-LF. It is a sol containing 40% by weight of parti-cles of minimum size 85 nm. The sol has a relative density at 25C of 1.290 to 1.310, a pH at 25C of about 8.3 to 8.5, a maxi-mum viscosity at 25C of 25 mPa and a maximum of 0.5% sediment.
The composition of the invention contains a surfactant which is amphoteric, nonionic or anionic, of which nonionic surfactants are preferred. Mention is made of nonionic polyoxy-alkylene polymers, particularly polyoxyethylene-polyoxypropylene block copolymers. One preferred surfactant is a polyoxyethylene-polyoxypropylene block copolymer having a molecular weight of about 1,100, a polyoxyethylene content of about 10%, and an HLB
valve at 25C of about 4 to 4.5, available from BASF under the trade mark Pluronic L31. Similar and suitable surfactants are available under the trade marks Synperonic T304 and Tetronic T304.
Other suitable surfactants include olefin sulfonates, ethoxylated alkylphenols and sulfosuccinate ester amides, such as that available under the trade mark Aerosol 18.
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~ 335388 By a compatible nonionic or anionic surfactant we mean a surfactant which can be used in the formulation and produce a stable composition. Colloidal silica sols are fairly delicate and are easily destabilized upon the addition of other chemical additives. Stability was checked at room temperature over a number of days or weeks and a 50 ml sample at 50C was observed over a 1 - 2 week period. Evidence of separation, the formation of gel, or a heavy deposit indicating rapid settling, were all grounds for stability failure. The use of a temperature of 50C
accelarates any destabilising that may occur, one day at 50C
being considered to be approximately equivalent to about 20 days at normal room temperature. By a compatible surfactant we mean a surfactant which gives a composition which is stable over 20 days when subjected to this test.
The surfactant must be used in an effective amount, by which is meant an amount which is compatible and also an amount which does not have an unacceptable effect on sizing. A surfac-tant may be compatible at one amount and yet not compatible at another amount. Furthermore a surfactant at one amount may have a marked effect on sizing and at another amount may have no effect on sizing. For instance the surfactant Pluronic L-31 provides stable compositions when used in amounts of 2.0% and 0.5% by weight. When used at 2.0~ it has been observed to affect sizing markedly and adversely, whereas at 0.5~ it has no significant effect on si~ing. Hence with Pluronic L-31 it is preferred to use an amount of about 0.5% by weight. Other amounts may be appropriate with other surfactants. Furthermore, different users may have different requirements regarding both stability and siz-ing. Stability tests and Cobb tests to determine the effect on sizing can readily and routinely be carried out by means of the procedures described herein to determine effective amounts of surfactant. In general it is preferred to use surfactant in amounts of from about 0.1 to 10.0% by weight, more preferably 0.5 to 2.0~ by weight, but amounts outside these limits may be appropriate with particular surfactants in particular circums-tances.
The acrylamide polymer should be present in the composi-tion in an amount of from 0.1 to 15% by weight, preferably about 2 to 7% by weight and most preferably about 3% by weight. It can be non-crosslinked but it is preferred that it is crosslinked. The polymer is conveniently handled as an aqueous solution of about 25~ by weight solids. The solubility of the acrylamide polymer depends upon the degree of cross-linking, which should not be so great that a solution of about 25~ by weight solids cannot be obtained. The cross-linked acrylamide polymer suitably has a molecular weight in the range 1,000 to 100,000 preferably 12,000 to 50,000; a polymer of about 18,000 to 20,000 molecular weight is particularly preferred. Polymers of higher molecular weight, say up to about 500,000, can be used together with a viscosity reduc-ing additive. Suitable viscosity reducing additives include sodium phosphate and sodium sulphate.
The acrylamide polymer can be a homopolymer or a copoly-mer with an uncharged monomer, for example acrylonitrile, or with a charged monomer that imparts some anionic character to the poly-mer. Examples of monomers that impart anio~llc character includealkali metal acrylates and methacrylates, of which sodium acrylate is preferred, and 2-acrylamido-2-methylpropane sulphonic acid (AMPS), sodium salt. Sodium methacrylate is less preferred as it leads to a shorter shelf life for the composition. The amount of copolymerisable monomer is preferably not greater than about 15 mole% of the total polymerisable monomers, more preferably not greater than about 10 mole%.
Any known cross-linking agent for acrylamide polymers can be used: ~,N'-methylene-bis-acrylamide is mentioned as a preferred example. Other crosslinking agents include, for example ~,N'-methylene-bis-methacrylamide, other lower alkylidene bis-acrylamides, divinyl benzene sulfonate, ethylene glycol di-acrylate, ethylene glycol dimethacrylate, diallyl ethylene glycol ether, divinyl esters of polyethylene glycol (e.g. polyethylene glycol-600 diacrylate), divinyl ethers of polyethylene glycol and the like difunctional monomer containing two CH2=C groupings which are to some extent soluble in the aqueous phase. Mention is further made of adducts of glycerine and allyl glycidyl ether and adducts of allylamine and a copolymer of maleic anhydride and methyl vinyl ether with different mole ratios of allylamine to anhydride.
The acrylamide polymer can be made in known manner. One preferred polymer is prepared from the following components, by weight:

1 3~5388 Acrylamide solution 50% 50.00 Water 45.3243 N,N'-methylene-bis-acrylamide 0.0017 EDTA, tetrasodium salt - 50~ 0.0240 Ammonium persulphate 0.750 Water 1.400 Sodium bisulphate 0.750 Water 1.700 Biocide (Kathon WT) 0.050 100.000 The acrylamide solution, water, N,N'-methylene-bis-acrylamide crosslinking agent and the EDTA sodium salt are first mixed to form a solution. The ammonium persulphate, in solution in water, is then added to the monomer solution and mixed vigorously. Thereafter the sodium bisulphite solution is added so that redox initiation commences. The polymerization reaction proceeds adiabatically. With the exothermic reaction complete the temperature peaks at about 90-95C. After cooling the biocide is added. This preferred polymer was used in the examples, as described below.
The EDTA serves as a chelating agent to complex any polymerization inhibitors present in the acrylamide monomer, for instance copper compounds. Other chelating agents, for example trinitriloacetic acid, sodium salt, can be used and if no poly-merization inhibitor is present a chelating agent can be dispensed with. The ammonium persulfate and the sodium bisulfite act as polymerization initiators and catalysts. Other initiators and catalysts can of course be used.
The composition usually also contains a biocide. A
preferred biocide is Kathon 886, whose active ingredients are 5-chloro-2-methyl-4-isothiazolin-3-one, 1.15%, and 2-methyl-4-isothiazolin-3-one, 0.35%, which is available from Rohm and Haas.
Other suitable biocides include hexahydro-1,3,5-tris(2-hydroxy-ethyl)-s-triazine, available under the trade mark Grotan BK from Gray Products of Toronto, and Thiostat BM 2213, available from Uniroyal Chemical.
The composition of the invention can also contain an organic base, for example triethanolamine or a humectant, for example a polyol such as ethylene glycol, sorbitol or glycerol.
These and other additives may be used to enhance washability, dust control and print quality of treated paper.
One preferred composition in accordance with the inven-tion is composed of the following:
40% by wt colloidal silica of particle size between 85-130 nanometers partially cross-linked acrylamide Pluronic L31 surfactant 40% by wt colloidal silica of particle size about 25 nanometers Grotan biocide.
Another preferred composition is composed of the follow-ing:
96.5% by weight of a colloidal silica sol, of which 40% by weight is silica of particle size between 85 and 130 manometers and the balance water 0.5% by weight compatible surfactant 3.0% crosslinked acrylamide polymer 0.025% Kathon biocide.
If the surfactant is Pluronic L31 this tends to inter-fere with the indicator reaction. To enhance the indicator effect, when using Pluronic L31 a small amount of the colloidal silica sol, say about 5%, is replaced by a colloidal silica sol which contains silica of a smaller particle size suitably about 25 nanometers.
The anti-skid composition is applied to the cellulosic fiber material in known manner. For example, when applied to linerboard the composition may be added to water sprayed from a spray bar directly onto the sheet or onto a roll which is part of the machine on which the linerboard is formed. Alternatively the composition can be applied from a water box or starch box. The amount of the composition added to the water is usually about 5%
by volume. In a typical machine this may require supply of the anti-skid composition at a rate of about 135 to 140 ml/min. The quantity can of course be metered and varied in accordance with need.
This invention will be further illustrated with reference to the following Examples.
Example 1 In this example the following test procedures were used.
The test procedure for determining slide angle involves spraying a 1 m long, 30 cm wide strip of mill paperboard with approximately 2 gms of a 5% solution of formulated product. Thepaper strip is allowed to dry overnight. Samples of treated paper are mounted on the coefficient of friction tester and block weight with the paper grain oriented in one direction. Three samples are tested (right side, middle, left side) and three measurements taken of each sample. The important criterion is the level of angle achieved and the degree of change between the first and third measurement of any one sample. This test procedure is based on TAPPI Test T503 OM-84 or T542 OM-83.
Washability testing was carried out to determine how easily anti-skid overspray can be removed from mill equipment.
Small sections of steel plate were sprayed and dried 21 times over a several day period with neat (100%) anti-skid formulations. The panels were then held at a 45 angle under a stream of cold tap water flowing at about 4.3 L/minute. The amount of time taken to remove the product build-up, and the completeness of removal, are a measure of the degree of washability.
The Cobb test is a widely accepted procedure for measur-ing degree of sizing of paper surfaces, as well as sizing through-out internal plys in multiply board manufacture. It is performed according to Canadian Pulp and Paper Association Standard Test Method F.2 or TAPPI Test T441 OM-84. The Cobb test measures the number of grams of water absorbed per square meter of sample in a prescribed time. A 5" x 5" sample of paper is cut and heated in an oven at 50C until oven temperature is reached. Approximately one gram of anti-skid composition per square foot is applied as a 5% solution using an applicator sponge. The paper square is dried, tare weighed and put into a Cobb test apparatus. One 1 3353g8 hundred mL of water at room temperature is poured into the appara-tus and left for 45 seconds. The water is decanted, the paper square is blotted to remove excess water and reweighed. The weight of water absorbed is multiplied by 100 to give the Cobb value per square meter.
For a dusting test, a test strip of linerboard was sprayed with anti-skid composition at 50% product dilution and was rubbed anti-skid treated side over a fume hood edge to which an untreated piece of the same linerboard was attached. The test strip was rubbed 4 times, then brushed off 3 times, turned through 90 and rubbed 4 more times, brushed 3 strokes, tapped sharply on edge and reweighed. The value presented is the average of three trials and indicates the weight in grams of the anti-skid removed in the test. Best possible score is 0.00. It has been found that this laboratory test correlates well with performance under mill conditions.
Various compositions A to H in accordance with the invention were made up, using NALCOAG 7604-LF silica sol as the silica base, a polymer of acrylamide partially crosslinked with N,N'-methylene-bis-acrylamide, and various surfactants. The compositions are described in Table 1 below. The compositions were all applied at a rate of two samples of linerboard all cut from the same sheet, and the linerboard was then subjected to test for Cobb value, dust removal and slide angle as described above.
For comparison purposes one sample of linerboard cut from the same sheet was not treated with a composition in accordance with the invention but was tested for Cobb value. The average Cobb value of the untreated linerboard was approximately 25.

-FORMULA VARIATIONS WITH DIFFERENT SURFACTANTS
Sample Silica Base Acrylamide Surfactant ~ Polymer ~ % Type A- 96.5 3.0 0.5 nonionic polyoxy-ethylene-polyoxy-propylene block copolymer (Pluronic L-31) B- 95 3.0 2.0 fluorinated alkyl amphoteric mixture (Fluorad FC-100) C- 95 3.0 2.0 sodium methyl oleoyl taurate (Fenepon T-33) D- 95 3.0 2.0 sodium salt of alkylaryl polyether sulphate (Triton X-301) E- 95 3.0 2.0 sodium olefin sulphonate (Sterling AOS) F- 95 3.0 2.0 ammonium alkyl-phenoxyethoxy sulphate (Fenepon C0-436) G- 95 3.0 2.0 Disodium N-Octadecyl sulphosuccinate (Aerosol 18) H- 95 3.0 2.0 dioctyl ester of sodium sulpho-succinic acid (Aerosol GPG) I- 95 3.0 2.0 ester sulphates (Stantex 322) I
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Example 2 A mill was operatlng to produce linerboard. To impart anti-skid properties there was used a solution of urea and colloidal silica of size less than 60 nm, in accordance with Patent No. 1,156,803. The spray bar was directed onto the first roll rather than the linerboard. Pump rate was set at 50~ stroke with the water pressure at 24 psi. The flow rate of anti-skid composition was calibrated at 135-140 mL/min. The board speed was 570-575 ft/min. The grade of linerboard was 10 point caliper and represented the mill's smoothest, thinnest board. Target slide angle was 28 average of three slides. Cobb tests were conducted on top plies (T) and bottom plies (B) and were of 2 minutes dura-tion.
TimeAverage SlideFeed Rate Cobb (2 min.) Angle mL/min. T/B
1:20 28 135-140 09/20 2:25 27 135-140 10/22 3:30 27 135-140 11/23 4:20 27 135-140 08/19 5:10 27 135-140 30/31 6:08 29 135-140 26/26 7:08 30 135-140 24/28 8:09 30 135-140 28/27 9:12 30 135-140 15/19 10:30 30 135-140 29/28 At this time the anti-skid composition was changed to a composition in accordance with the present invention, applied at the same feed rate. The composition was as follows, by weight:
40% by weight colloidal solution 91.4 of silica whose particle size ranges from 85 to 130 nanometers Acrylamide polymer, crosslinked 3.0 with N,N'-methylene-bis-acrylamide Surfactant (Pluronic L31) 0.5 40% by weight colloidal solution 5.0 of silica whose particle size is about 25 nanometers Biocide (Grotan BK) 0.1 Time Average Slide Feed Rate Cobb (2 min.) Angle mL/min. T/B

11:01 28 135-140 27/28 12:01 31 135-140 26/27 13:20 29 135-140 25/26 14:25 29 135-140 27/27 15:25 28 130-135 27/26 16:35 27 130-135 26/27 17:40 30 130-135 27/26 18:51 30 130-135 29/29 19:55 31 130-135 27/27 21:05 32 130-135 29/29 22:12 30 130-135 26/26 23:12 32 130-135 30/30 00:25 29 130-135 19/22 1:25 28 125-130 19/20 2:30 28 135-130 10/18 3:37 30 125-130 16/16 4:40 28 125-130 13/18 5:55 30 125-130 09/17 7:00 29 125-130 13/20 8:08 30 125-130 22/23 9:18 30 125-130 26/27 10:24 31 125-130 24/26 11:30 27 125-130 22/24 As can be seen even when using a feed rate of 135-140 mL/min. with the prior art product a slide angle of 28 is not always achieved. In contrast with the composition of the inven-tion a slide angle in excess of 28 is always achieved at that application rate, and is often achieved at lower application rates.

Claims (13)

1. An anti-skid composition for use on cellulosic fibrous material, which composition comprises water, colloidal silica having a particle size in the range 25 to 150 nm, a water-soluble acrylamide polymer and an effective amount of a compatible amphoteric, anionic or nonionic surfactant.

2. A composition according to claim 1 which comprises a compatible anionic or nonionic surfactant.

3. A composition according to claim 1 wherein the acryl-amide polymer is a crosslinked homopolymer of acrylamide or a crosslinked copolymer of acrylamide and up to 15 mole % of an anionic monomer.

4. A composition according to claim 1, 2 or 3 wherein the acrylamide polymer has a molecular weight in the range from about 1,000 to about 100,000.

5. A composition according to claim 1, 2 or 3 wherein the acrylamide polymer is a copolymer of acrylamide and up to 15 mole%
of sodium acrylate.

6. A composition according to claim 1, 2 or 3 wherein the surfactant is a polyoxyethylene-polyoxypropylene block copolymer having a molecular weight of about 1100, a polyoxyethylene content of about 10% and an HLB value at 25°C of about 4 to 4.5.

7. A composition according to claim 1, 2 or 3 wherein the surfactant is disodium N-octadecyl sulphosuccinate.

8. A composition according to claim 1, 2 or 3 wherein the surfactant is the sodium salt of alkylaryl polyether sulphate.

9. A composition according to claim 1, 2 or 3 wherein the surfactant is sodium olefin sulphonate.

10. A composition according to claim 1, 2 or 3 which also comprises a humectant.

11. A process for improving the anti-skid properties of cellulosic fibrous material, as determined by the slide angle, which process comprises applying to the cellulosic fibrous material an anti-skid composition as claimed in claim 1, 2 or 3.

12. Cellulosic fibrous material whose anti-skid properties have been improved by the process of claim 11.

13. Cellulosic fibrous material as claimed in claim 12 in the form of linerboard.