Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/359—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using near infrared light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/34—Paper
  • G01N33/346—Paper sheets
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/34—Paper
  • G01N33/343—Paper pulp

Definitions

• the present invention is directed to a method for the quantifi ⁇ cation of the physical properties of pulp and paper treated with paper chemicals and more particularly to a method for quantifying the properties of paper containing, e.g. wet and dry strength agents, starches and retention agents; hydrophobic (sizing) agents, such as alkyl ketene dimer (AKD), alkylene succinic anhydride (ASA), carbamoylchloride and rosin; and debonding agents (fluff chemicals) such as e.g. quaternary fatty amines and fatty amine oxides. Properties to be determined are e.g. dry tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability.
• hydrophobic (sizing) agents such as alkyl ketene dimer (AKD), alkylene succinic anhydride (ASA), carbamoylchloride and rosin
• debonding agents fluff chemicals
• Properties to be determined are
• the resistance of a given paper or board to the sorption of water is e.g. a function not only of the surface charac ⁇ teristics of the fibres achieved by the presence of a sizing agent, but is also dependent on the structure of the web (i.e. the size of pores, its density, the surface treatments to which it has been subjected, etc.). (Cf. J.C.Roberts, Paper chemistry, Blackie Academic & Professional, Glasgow, 1992, p 97).
• TAPPI Technical Association of Pulp and Paper Industries
• SCAN Scandinavian Pulp, Paper and Board Testing Committee
• the present invention has for object to offer a solution to said problem, by providing a method that allows the quantifying of said properties of the paper and pulp during the production process. This object is attained by the combined use of spectrometric and chemometric techniques.
• the paper or the pulp in or off the production line is submitted to spectrometric analysis.
• the pulp as well as the paper represents a multi-component system or a system having a high degree of background interferences which increases the problem of spectrometric analysis.
• Brown et al in the US patent 5 121 337 (1990) disclose a method, based on multivariate data analysis, for correcting spect ⁇ ral data for data due to the spectral measurement process itself and estimating unknown property and/or composition data of a sample using such method.
• Richardson et al in US 5 242 602 disclose a method for simultaneously measuring the concentration of multiple chemical components, which they call performance indicators, in an aqueous system, by the analysis of the spectrum of the aqueous system in the wavelength range 200 to 2500 nm and by applying chemometric algorithms to the spectrum to simultaneously determine the concentrations of the different performance indicators.
• U.S. 5 104 485 discloses a method for measuring extremely low concentrations of non-aqueous constituents or chemicals in a water/matrix, including differentiating between pulp fines and extremely low concentrations of individual chemicals in a water/ cellulose matrix such as occur in papermaking.
• the water/matrix is exposed to the near-infrared spectrum from 1000 to 2500 nm to produce a record voltage that is directly proportional to the absorption by the non-aqueous constituent.
• the amount non-aqueous constituent is determined from voltage values of incremental additions of the non-aqueous constituent.
• Radiation from a near infrared sourse is allowed to impinge upon the paper sheet, and after interaction of the radiation with the chemical consti ⁇ tuents in the sheet, the reflected radiation is collected and stored.
• the chemical composition is calculated from the stored data after mathematical treatments are applied.
• the measurement system is calibrated via samples of known composition. Use of the full near infrared spectrum from 1100 to 2500 nanometers permits the analysis of several constitents simultaneously, especially when derivatives are employed as part of the mathematical treatment. This analysis aids in determining the extent of retention of the chemical additives and fillers.
• the first step is recording the simultaneously determination of the emission, transmittance or reflectance values from a huge number of wave lengths (e.g. 300 to 600 numbers of wave length is not uncommon).
• the second step is a pre-treatment of the spectral data, which is essential in the NIR region (800- 2400 nm).
• the third step is transformation of data, usually by centring, normalisation or autoscaling the data.
• the forth step is to find the mathematical expression for the calibration function.
• the spectral information is often highly correlated which seriously affect the success for quantification. If the spectral information is transferred into latent variables by principal component analysis a higher degree of orthogonalisation is obtained which can be a crucial factor for success.
• the object of the invention thus is to provide a method of deter ⁇ mination of the above-mentioned properties of pulp and paper treated with performance chemicals in real time without the use of the traditional lengthy mechanical measurements and analytical methods.
• the invention relates to the determination of properties in paper, specifically tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability.
• Pulp and paper Obtain strength from the interfibrillar hydrogen bonds which are created when the cellulose fibres are drawn together by surface tension during the drying process. Certain chemical additives, such as starch, improve the dry strength of a paper by creating a large contact area between the fibers in the paper.
• Dry defibration of cellulose pulp gives a cotton like soft material, fluff, used in absorbing sanitary products such as diapers etc.
• the pulp product intended for use for dry defibration has to be treated with debonding agents in some cases containing both hydrophobic and hydrophilic groups.
• the hydrophilic group will increase the absorption speed and capacity in the final product and counteract the hydrophobicity rendered by the hydrophobic groups.
• the interfibrillar hydrogen bonds should be as few as possible in the pulp intended for fluff.
• the most common debonding agents are quaternary fatty amines.
• the big hydrophobic groups interfere with and prevent the formation of hydrogen bonds.
• the fluff pulp is produced on a paper machine as a thick paper and the debonding agents are added to the stock as ordinary paper chemicals. There has to be no destruction of the fibres during the defibration process and the energy needed to defibrate the fibres in a fluff pulp should be as low as possible.
• the bursting strength is a good measurement of the debonding energy needed for good defibration of the pulp/paper.
• bursting strength is: the highest pressure applied on paper without any breakage in the paper.
• Pa kPa
• This property can also be given as burst index: Bursting strength divided by the grammage weight with the unit kPa*m 2 /g.
• Testing of bursting strength and burst index is today performed according to SCAN P 24:77 Scandinavian Pulp, Paper and Board Testing Committee as follows: The paper sample is placed and fixed on a circular rubber membrane. Underneath this membrane a fluid is pumped until the paper bursts. The pressure of the liquid when the burst occur is the bursting pressure.
• test procedure is as follows: A specific sample of fluff is prepared according to standard in the shape of a cylinder of 3 gram with the diameter of 50 mm. This sample is then placed vertically on a net in a low beaker and a weight of 500 gram is placed on top of the sample. Water is added to the beaker and the sample absorbs water from below, the time needed for the penetra ⁇ tion of water to the upper surface of the sample is measured and is reported as absorption time.
• sizing Yet another property important for paper or board is hydrophobi ⁇ city commonly achieved by sizing.
• Internal sizing is the process of imparting hydrophobicity to the paper by adding the chemicals at the wet end. Said process is carried out to produce paper or board that has an enhanced resistance to penetration by liquids such as water and printing inks.
• liquids such as water and printing inks.
• the meaning of the term sizing depends on whether or not one is referring to the resistance of the sheet of paper or board to the sorption of water, or to the water resistance of the cellulose fibres.
• the resistance of a given paper to the sorption of water is a function not only of the surface characteristics of the fibres achieved by the presence of a sizing agent but it is also dependent on the structure of the web, i.e. the size of the pores, its density, the surface treatments to which it has been subjected, etc. It also depends on the properties of the test fluid being used to measure sizing and the test procedure itself.
• sizing is achieved by different mechanisms and by a variety of chemicals. Rosin in different formulations is the most commonly used internal sizing agent. There are different ways to produce the rosin acids from softwood. Current economics favour tall oil as a source. Tall oil rosin is obtained by distillation of acidi ⁇ fied black liquor from the kraft pulping of soft wood. The main components are the so called rosin acids, all tricyclic acids. Abietic acid and levo pimaric acid are very important and have one carboxyl group each.
• the carboxyl group plays an important role for the development of sizing with rosin as they form ionic bonds with cationic aluminium ions (stemming from aluminium sulphate, paper makers alum). Good hydrophobicity is not achieved by the rosin itself but by the aluminium rosinates.
• the rosin particles have a size from 0,05 to 1 ⁇ m depending on the formulation. They are retained on the fines or fibres by ionic bonds.
• the levo pimaric acid is modified with a maleic anhydride or fumaric acid which gives a reaction product with three carboxyl groups the so called fortified rosin.
• the second mechanism for sizing is the chemical anchoring of single molecules containing fatty alkyl groups on the cellulose surface.
• the most common cellulose reactive product is the alkyl ketene dimer, the AKD, added to the stock as dispersions and retained by heterocoagulation of the cationic size particle and the negatively charged surface of the fines or the coarse fibres.
• the dispersed droplets break in the drying section of the paper machine and AKD is more or less spread over the surface and can react with the hydroxyl groups. They form a direct covalent link ⁇ age with cellulose via ⁇ -keto ester. Those esterbonds are less sensitive to acidic conditions than rosin and AKD is used in liquid boards exposed to milk,juice etc.
• the bonds can be destroy ⁇ ed by fresh precipitated calcium carbonate (PCC) containing hydroxyl ions used as fillers in many paper qualities. This destruction of the ester bonds can be a rather slow process.
• PCC precipitated calcium carbonate
• the sizing is fugitive and the hydrophobicity will decrease.
• the alkenyl succinic acid anhydride (ASA), the alkyl carbamoyl chloride (DACC) and the alkyl isocyanate (SIC) are like AKD able to undergo reaction with the cellulose.
• the third mechanism is achieved by different wax sizes.
• the paraffin melts and covers the surface and the paper or board gets a hydrophobic surface.
• the wax emulsions are stabilized in differ ⁇ ent ways.
• the soap stabilized emulsions are often alum precipi ⁇ tated and the soaps (the wax droplets) will be anchored to the surface as rosin and the wax itself is physically adsorbed.
• the hydrophobicity "sizing" of the paper is tested according to the Cobb test designed to estimate resistance to absorption of water and further described in SCAN-P 12:64 (1964).
• the Cobb number indicates the quantity water taken up by one m of paper during a certain time period.
• Hercules Sizing Tester HST is widely used for quality control and measures the change in reflectance of paper as ink or a coloured solution penetrates from the other side.
• HST test the liquid is contained in a ring on top of the paper, and the change in reflectance is measured photoelectrically from the bottom.
• a convenient end point is chosen, for example, a reduction in reflected light of 20%.
• Printability of ink-jet print refers to the quality of the image produced. Important parameters measured are the black text optical density, the wicking of black ink into the fibres, the optical density of composite black print composed of the three primary colours, and the bleed of composite black print into a coloured printed background. Colour bleed is further separated into line growth which is a measure of overall increase in the width of the line, an edge roughness which considers protrusions out of the main body of the line into the adjacent background colour.
• Optical density is measured using a reflective optical densitometer in which the density depends on the thickness of the ink layer.
• Black wicking and colour bleed are measured using image analysis by grabbing the image and measuring the area of a defined part of the text or the printed pattern. An increase in area indicates an increase in wicking or bleeding.
• the above objects of the invention are obtained by a method of determination of one or several of the physical properties selected from dry tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability in paper by analysing the visible, near-infrared and/or infrared spectrum of the paper/pulp in the process line in a wavelength range within 200 nm to 400 ⁇ m, preferably 800 nm to 2500 nm and applying chemometric evaluation of the spectrum to calculate the physical properties of the paper.
• pulp and/or paper refers not only to bleached pulp and/or paper, but also to unbleached or partially bleached pulp and/or paper as well as filled or unfilled quali ⁇ ties. This includes sac paper, liner, liquid board, printing paper and the like as well as creped paper qualities.
• the spectrometric analysis can be performed by on ⁇ line, in-line, at-line or off-line measurement and can be carried out as a monitoring, by use of an on-line, in-line or at-line probe, or by taking individual samples for separate analysis (off ⁇ line).
• the emission, transmittance or reflectance spectra are subject to further data treatment using values from several discrete wavelengths from each particular spectrum.
• An example of such a technique is the use of a device, placed at a distance from the process, containing a light source, detector, electronic components and other necessary components to transmit a signal through an optical fibre to the sample, where the light is transmitted through or reflected on or partly through the sample.
• the resulting signals are returned to the detector in an accom ⁇ panying optical fibre cable, and recorded.
• the light is converted into an electric signal which is then conveyed to a computer where the spectrum of a previously stored reference scan can be related to, e.g. subtracted from, the sample spectrum and a reference corrected spectrum is calculated.
• a computer where the spectrum of a previously stored reference scan can be related to, e.g. subtracted from, the sample spectrum and a reference corrected spectrum is calculated.
• Another example is by manually or automatically taking samples at relevant time intervals and submitting the samples to analysis in an analytical instrument, containing the light source, detector, electronic components and other necessary components.
• the emission, transmittance or reflectance spectra are then subjected to further data treatment, using values from several discrete wavelengths from each particular spectrum.
• the detection is performed in the UV-VIS-NIR wavelength range of 200 nm to 2500 nm, preferably 800 nm to 2500 nm and/or the IR wavelength range of 2500 nm to 400 ⁇ m.
• This can be accomplished by the use of a scanning instrument, a diode array instrument, a Fourier transform instrument or any other similar equipment, known to the man skilled in the art.
• the detector have a measuring interval of at least 10 nm, preferably 2 nm, and most preferably 1 nm or less.
• the determination and control of the physical properties as defined above in pulp and/or paper by use of the spectrometric measurements comprise three main sequences, the first main sequence being the development of a calibration model, involving the sequence of development of learning sets; data processing; and data analysis, by use of pulp and/or paper samples of known properties; and the second main sequence being that of the spectrometric analysis of the sample of the unknown properties of spectral data processing, optionally followed by data analysis; and application of the calibration model, developed in the first main sequence, to the thereby obtained data.
• the desired properties are measured in the traditional way (according to TAPPI and SCAN) for a number of pulp and/or paper samples. These samples, characterized by traditionally measured property values then are used in the development of a calibration model wherein the three sequences mentioned above are applied to the registered absorption, reflectance or emission spectra of said samples.
• Model learning sets consist of a large number of absorption, reflectance or emission spectra from the samples with known property characteristics, which samples preferably should be representative of the production line.
• the learning sets are used in the chemometric algorithms to calculate the resulting model parameters.
• the spectral raw data should be processed. This processing may also reveal hidden information, such as identity of apparently dissimilar spectra or non-identity of apparently very similar spectra.
• R ik is the apparent absorbance at the wavelength k
• a ik is the transformed absorbance at the wavelength k
• the index i represents the sample spectra available.
• a ik , R ⁇ , i and k have the same meanings as above, a i is the least squares estimation of the intercept parameter, and b ⁇ is the least squares estimation of the slope parameter.
• chemometric techniques Data analysis using chemometric techniques then allows the calibration model to be developed.
• chemometric techniques which can be used, such as Principal Component Analysis (PCA), Partial Least Squares Regression (PLS) , Principal Compo ⁇ nents Regression (PCR), Multilinear Regression Analysis (MLR) and Discriminant Analysis.
• PCA Principal Component Analysis
• PLS Partial Least Squares Regression
• PCR Principal Compo ⁇ nents Regression
• MLR Multilinear Regression Analysis
• Discriminant Analysis Discriminant Analysis.
• the preferred chemometric technique accord ⁇ ing to the invention is the PLS method.
• This transformation consists of a rotation of the coordinate system, resulting in the alignment of information on a fewer number of axes than in the original arrangement.
• the variables that are highly correlated with one another will be treated as a single entity.
• PCA it thus will be possible to obtain a small set of uncorrelated variables still representing most of the information which was present in the original set of variables, but being far easier to use in models.
• PLS is a modelling and computational method by which quantitative relations can be established between blocks of variables, e.g. a block of descriptor data (spectrum) for a series of samples and a block of response data measured on these samples.
• spectrum descriptor data
• By the quanti ⁇ tative relation between the blocks it is possible to enter spect ⁇ ral data for a new sample to the descriptor block and make pre ⁇ dictions of the expected responses.
• One great advantage of the method is that the results can be evaluated graphically, by different plots. In most cases, visual interpretations of the plot are sufficient to obtain a good understanding of different rela ⁇ tions between the variables.
• the method is based upon projections, similar to PCA.
• the PLS method is detailedly disclosed in Carlsson R.
• PCR is closely related to PCA and PLS.
• PLS each object in the descriptor block is projected onto a lower dimensional space yielding in scores and loadings.
• the scores are then regressed against the response block in a least squares procedure leading to a regression model which can be used to predict unknown samples.
• the same model statistics as in PLS and PCA can be used to vali ⁇ date the model.
• MLR Multilinear Regression Analysis
• This technique is generally limited to relatively 'clean' systems where there is not a significant amount of matrix interference and, in contrast to PLS, it requires more objects than variables.
• a sample of unknown property value then can be matched to a cluster, and the property can be assigned a value, e.g. the average value of the cluster.
• the determination of the unknown property can be performed by registering the absorp ⁇ tion, reflectance or emission spectrum, in correspondence to (I.a).
• NIRR near-infrared spectrometry
• the samples were scanned by NIRR and models developed.
• Drying section 60/80/95/110°C
• Paper samples sized with rosin were produced at an experimental paper machine with the following experimental parameters.
• Chemicals Rosin dispersion added amount 0 to 1,0 % dry weight on dry fibre
• Drying section 60/80/95/110
• Paper samples (45) of bleached sulphate intended for printing with ink-yet were tested for monochrome % area and colour % area, resp. and models were developed. (See Fig. 5 and 6. )
• the NIRR measurements were obtained using a NIR Systems® 6500 spectrometer, from NIR systems, U.S., equipped with a High fat/moisture cell with a scan surface of up to 60 cm , with a spectral operating range between 400 nm and 2500 nm, in even intervals of 2 nm, yielding 1050 measurements at different wavelengths. Diffuse reflectance data were obtained as apparent absorbance, and transferred to a Macintosh® Quadra 700 computer.
• the spectral data matrix was reduced to the NIR region (1100-2500 nm) for greater modelling speed.
• the spectra were reduced by a factor of 8 (every eighth wavelength was kept), which resulted in 175 spectral points for modelling.
• MSEP Mean Squared Error Prediction
• n is the number of samples
• c i is the modelled descriptor value
• c - is the traditionally measured descriptor value.
• the index i is the descriptor of the sample i.
• MSEP Standard Error Prediction
• RMSEP Root Mean Squared Error Prediction
• the MATLAB software V 3.5 was used for numerical calculations.
• the PLS-algorithm used for modelling the relationships between the spectra and descriptors is a customised function in the commer ⁇ cially available 'Chemometrics Toolbox' based on the NIPALS algorithm (H.Wold, P. Krishnaiah, Multivariate Analysis, 391 (1966)).
• the convergence criteria for the algorithm were 1x10 ° or 100 iterations.
• the method of establishing the significant number of PLS-components was crossvalidation (S. Wold, Techno- metrics 20, 397-405 (1978)) (Jack-knifing) with one sample left out. This number here was found to be 15 for both the bleached and the unbleached paper samples.
• the values of the properties as defined above were mean-centered and scaled to unit variance prior to modelling (autoscaling or z-transform) and rescaled prior to model evaluation.
• fig. 1 represents the measured vs. predicted values of wettability in seconds of 60 samples of paper.
• Fig. 2 represents the measured vs. predicted values of bursting strength as burst index in kPa*m-Vg of 60 samples of paper;
• Fig. 3 represents the measured vs. predicted values of debonding energy in kgJoule/kg of 60 samples of paper.
• Fig. 4 represents the measured vs. predicted hydrophobicity according to Cobb off machine by measuring 49 samples of bleached paper
• Fig. 5 represents the measured monochrome % area of 45 samples of bleached sulphate paper
• Fig. 6 represents the measured colour % area of 45 samples of bleached sulphate paper
• r and k should be as close to 1 as possible; while SEP, RMSEP, MSEP, and the intercept should be as close to 0 as posssible. In view of the values obtained, it will be possible to realize the very good validity and preciseness of the model.
• the total number of samples used for modelling The total number of samples used for modelling.
• SUBSTITUTE SHEET SEP is a characterisation of the variance attributable to random unexplainable error.
• MSEP is the average squared differences between actual and predicted values, i.e. for a set of objects not present in the calibration. In the literature MSEP is also referred to as PRESS (Predicted Residual Error Sum of Squares)
• the advantage of the novel method of determining one or several of the physical properties tensile strength, hydrophobicity, debonding energy, bursting strength, wettability and printability in pulp and paper using chemometrics thus should be readily apparent. Indeed, a wide variety of properties may be analysed using the same calibration set.
• the invention thus provides a method whereby the quantifying of the properties of pulp and paper during production process can be performed in a very rapid and precise way on any type of pulp and paper.

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