U.S. patent application number 09/775114 was filed with the patent office on 2002-08-01 for x-ray measurement of resin distribution in a cellulosic material.
Invention is credited to Feng, Martin W..
Application Number | 20020101957 09/775114 |
Document ID | / |
Family ID | 25103365 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020101957 |
Kind Code |
A1 |
Feng, Martin W. |
August 1, 2002 |
X-ray measurement of resin distribution in a cellulosic
material
Abstract
A method for measuring bonding agent content and distribution in
a composite product that includes bonding agent and cellulosic
material. The method involves using a bonding agent that includes
electronegative functional groups and an X-ray active cationic
label bonded with the functional groups in the manufacture of the
composite product. The cellulosic material is exposed to X-rays to
generate a characteristic fluorescence signal from the label. The
X-ray fluorescence of the label is measured to determine the amount
and distribution of the label in the cellulosic material and
thereby the amount and distribution of the bonding agent in the
composite product. The present invention also provides a bonding
agent composition useful for determining the distribution of the
bonding agent in a composite product comprising a bonding agent
containing electronegative functional groups and a label compound
that includes positively charged ions to emit characteristic
fluorescence when exposed to X-rays. The bonding agent and the
label compound are homogeneously mixed.
Inventors: |
Feng, Martin W.; (Vancouver,
CA) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
350 WEST COLORADO BOULEVARD
SUITE 500
PASADENA
CA
91105
US
|
Family ID: |
25103365 |
Appl. No.: |
09/775114 |
Filed: |
February 1, 2001 |
Current U.S.
Class: |
378/45 ; 378/44;
378/47 |
Current CPC
Class: |
G01N 2223/076 20130101;
G01N 23/223 20130101 |
Class at
Publication: |
378/45 ; 378/47;
378/44 |
International
Class: |
G01T 001/36; G01N
023/223 |
Claims
I claim:
1. A method for measuring bonding agent content and distribution in
a cellulosic material mixed with the bonding agent comprising the
steps of: using a bonding agent that includes electronegative
functional groups and an X-ray active cationic label bonded with
the functional groups; exposing the cellulosic material to X-rays
to generate a characteristic fluorescence signal from the label;
and measuring the X-ray fluorescence of the label to determine the
amount and distribution of the label in the cellulosic material and
thereby the amount and distribution of the bonding agent in the
cellulosic material.
2. A method as claimed in claim 1 including the step of converting
the amount of the label in the cellulosic material to the amount of
bonding agent using a calibration curve.
3. A method as claimed in claim 1 in which the bonding agent is a
resin having electronegative functional groups and the label is
metallic cations.
4. A method as claimed in claim 3 in which the label is Cu(II+)
ions.
5. A method as claimed in claim 4 in which the Cu(II+) ions are
provided by a source selected from the group consisting of an
aqueous solution of cupric sulphate, cupric chloride and cupric
nitrate.
6. A method as claimed in claim 3 in which the label is Ba(II+)
ions.
7. A method as claimed in claim 3 in which the label is Na(I+)
ions.
8. A method as claimed in claim 3 in which the label is K(I+)
ions.
9. A method as claimed in claim 3 in which the cellulosic material
is selected from the group consisting of wood, straw, bamboo and
hemp.
10. A method as claimed in claim 1 in which the cellulosic material
is formed into a composite product.
11. A method as claimed in claim 1 in which the cellulosic material
is at an intermediate stage in the manufacture of a composite
product.
12. A method as claimed in claim 3 in which the bonding agent is a
resin selected from the group consisting of urea-formaldehyde,
melamine-urea-formaldehyde, melamine-formaldehyde and
phenol-formaldehyde resins.
13. A method as claimed in claim 1 in which the steps of exposing
the cellulosic material to X-rays and measuring the X-ray
fluorescence of the label are conducted on a continuous on-line
basis during the manufacture of a composite product.
14. A method as claimed in claim 1 in which the steps of exposing
the cellulosic material to X-rays and measuring the X-ray
fluorescence of the label are conducted on an off-line basis to
selected samples of the cellulosic material during the manufacture
of a composite product.
15. A method as claimed in claim 1 including the additional step of
adding the X-ray active cationic label to the bonding agent.
16. A method as claimed in claim 1 in which the X-ray active
cationic label is a natural constituent of the bonding agent.
17. A bonding agent composition useful for determining the
distribution of the bonding agent in a cellulosic material mixed
with the bonding agent comprising: a bonding agent containing
electronegative functional groups; and a label compound that
includes positively charged ions to emit characteristic x-ray
fluorescence when exposed to X-rays, the bonding agent and the
label compound being homogeneously mixed.
18. A bonding agent composition as claimed in claim 17 in which the
bonding agent is selected from the group consisting of
urea-formaldehyde resin and modified urea-formaldehyde resin.
19. A bonding agent composition as claimed in claim 17 in which the
bonding agent is selected from the group consisting of
melamine-urea-formaldehyde resin and modified
melamine-urea-formaldehyde resin.
20. A bonding agent composition as claimed in claim 17 in which the
bonding agent is selected from the group consisting of
melamine-formaldehyde resin and modified melamine-formaldehyde
resin.
21. A bonding agent composition as claimed in claim 17 in which the
bonding agent is selected from the group consisting of
phenol-formaldehyde resin or modified phenol-formaldehyde
resin.
22. A bonding agent composition as claimed in claim 17 in which the
label compound is mixed with the bonding agent in sufficient
quantity to create an ion concentration capable of emitting
detectable amounts of x-ray fluorescence.
23. A bonding agent composition as claimed in claim 17 in which the
label compound is a source of Cu(II+) ions.
24. A bonding agent composition as claimed in claim 23 in which the
source of Cu(II+) ions is selected from the group consisting of an
aqueous solution of cupric sulphate, cupric chloride and cupric
nitrate.
25. A bonding agent composition as claimed in claim 23 in which the
label compound is mixed with the bonding agent in sufficient
quantity to create a Cu(II+) ion concentration in the bonding agent
greater than about 0.1% based on the bonding agent solids
content.
26. A bonding agent composition as claimed in claim 17 in which the
label compound is a source of Ba(II+) ions.
27. A bonding agent composition as claimed in claim 17 in which the
label compound is a source of Na(I+) ions.
28. A bonding agent composition as claimed in claim 27 in which the
source of Na(I+) ions is the bonding agent itself.
29. A bonding agent composition as claimed in claim 17 in which the
label compound is a source of K(I+) ions.
30. A bonding agent composition as claimed in claim 29 in which the
source of K(I+) ions is the bonding agent itself.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a new system for improved quality
and process control in the wood products industry, and in
particular, to a system for determining resin distribution in
cellulosic material by using a novel labelled resin for detection
by x-ray spectrometry.
BACKGROUND OF THE INVENTION
[0002] Cellulosic composite products are generally manufactured by
organizing cellulosic material, such as particles of wood, straw,
bamboo, hemp or the like into a mat of material after coating by a
bonding agent, and exposing the resulting mat to pressure and heat
to create a finished product such as a board or panel. In the case
of wood, the particles can include chips, flakes, fibres or
strands. The bonding agent plays a crucial role in determining the
strength of the finished product. In the medium density fibreboard
and particleboard industry, urea-formaldehyde resins are preferably
used. Other resins include melamine-urea-formaldehy- de, melamine
formaldehyde, and phenol-formaldehyde resins.
[0003] The amount of resin added and the overall distribution of
the resin are key factors in determining the strength of the
finished product. Presently, it is standard practice to blend a
pre-determined amount of resin with the cellulosic material and
test samples of the resulting product to determine strength
properties. Depending on strength test results, the amount of resin
added is adjusted downwardly to lower the strength of the product
while reducing cost or adjusted upwardly to increase strength and
costs. Resin is among the costliest components of a composite
cellulosic product and being able to reduce the amount of resin
while ensuring that the final product meets quality control and
assurance guidelines is a sought after goal in the industry.
[0004] Using less resin requires that the resin be distributed as
efficiently as possible in the finished product. Reliable
measurement of resin distribution has been a long standing problem
for the industry particularly with respect to composite wood
products which represent the majority of products produced. The
problem has been particularly difficult for the medium density
fibreboard and particleboard industry which use urea-formaldehyde
resins. No reliable and effective nondestructive test method for
the detection and measurement of the resin is currently known.
Urea-formaldehyde resin is nearly colourless when viewed in white
light. Phenolformaldehyde resin has a distinctive red-brown colour,
but when it appears in a thin layer, it is also difficult to detect
against a brown coloured wood background. Visual inspection systems
are therefore not appropriate for determining resin
distribution.
[0005] Work has been conducted to discover reliable methods for
determining resin distribution. For example, Kasper & Chow
(1980) in their paper entitled Determination of Resin Distribution
in Flakeboard Using X-Ray Spectrometry, Forest Products Journal
30(7):37-40, examined phenol-formaldehyde resin distribution in
wood flakes using bromide as a label and X-ray spectrometry as a
detection tool. Using bromide as a label for resins has some
fundamental limitations for detection and measurement of resin
distribution. In particular, bromide is negatively charged and is
therefore, not strongly attracted to the resin molecules which have
many highly electronegative functional groups. Therefore, bromide
will tend not to stay with the resin molecules throughout the board
manufacturing process. In addition, bromide is highly water soluble
and will tend to migrate through the wood flakes along with water.
The factors impose serious limitations on bromide as a resin
label.
[0006] Johansson et al. (1991) in a paper entitled A Method for the
Analysis of the Glue Efficiency in Particleboards Trtek, Rapport I
9112076, Stockholm describe how they developed a method for the
analysis of resin efficiency in particleboard using copper sulphate
and rubeanic acid. The test method is destructive in that it turns
the resinated material black to indicate the presence of resin.
Such a method has great limitations for developing into a practical
test method for both on-line and off-line measurement of resin
distribution in the composite wood product industry.
[0007] The most current work to develop an effective and reliable
method of detecting urea-formaldehyde resin distribution has been
undertaken by Kamke. In a paper presented at the Wood Adhesives
2000 meeting, Kamke discussed using fluorescent dyes to track resin
distribution, however, the results of initial test were
inconclusive.
SUMMARY OF THE INVENTION
[0008] Good resin distribution is key to the manufacture of high
quality cellulosic products, and, in particular, composite wood
products at reasonable cost. There is a need for a reliable method
of monitoring resin distribution in order that the distribution can
be optimized during the resin blending and application process.
[0009] The present invention addresses the problem of
[0010] measuring resin distribution by providing a nondestructive
method of determining resin content and distribution. Accordingly,
the present invention provides a method for measuring bonding agent
content and distribution in a cellulosic material mixed with the
bonding agent comprising the steps of:
[0011] using a bonding agent that includes electronegative
functional groups and an X-ray active cationic label bonded with
the functional groups;
[0012] exposing the cellulosic material to X-rays to generate a
characteristic fluorescence signal from the label; and
[0013] measuring the X-ray fluorescence of the label to determine
the amount and distribution of the label in the cellulosic material
and thereby the amount and distribution of the bonding agent in the
cellulosic material.
[0014] In a further aspect, the present invention provides a
bonding agent composition useful for determining the distribution
of the bonding agent in a cellulosic material mixed with the
bonding agent comprising:
[0015] a bonding agent containing electronegative functional
groups; and
[0016] a label compound that includes positively charged ions to
emit characteristic x-ray fluorescence when exposed to X-rays, the
bonding agent and the label compound being homogeneously mixed.
[0017] Preferably, the bonding agent will be a water based resin
that contains electronegative functional groups and the label
compound will contain an X-ray active metallic ion. To trace
bonding agent distribution successfully, it is essential that the
label stays with the bonding agent at all times during and after
the manufacturing process. The metallic ions are positively charged
and form strong bonds with the highly electronegative functional
groups of the resin molecules to move with the resin as the resin
is distributed during the manufacturing process. Subsequently, the
metallic ions can be located and measured by X-ray fluorescence and
converted to resin content by a standard calibration curve.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Aspects of the present invention are illustrated, merely by
way of example, in the accompanying drawings in which:
[0019] FIG. 1 is a schematic view of a production line for
manufacturing a composite wood product according to the method of
the present invention;
[0020] FIG. 2 is a schematic view of the X-ray scanning and
detecting apparatus for use in scanning samples according to the
present invention; and
[0021] FIG. 3 is a sample calibration curve showing the
relationship between measured copper concentration and resin
content.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The method of the present invention finds general
application in measuring bonding agent distribution when the agent
is mixed with cellulosic material. Such cellulosic material
includes, but is not limited to, particles of wood, straw, bamboo
and hemp which are used to make composite products such as panels
and boards. The description and examples below relate generally to
measuring resin distribution in composite wood products formed from
wood particles such as chips, flakes, strands, fibres or the like.
It will be apparent to those skilled in the art that the method and
bonding agent composition of the present invention can be used in
the manufacture of any composite products made by mixing cellulosic
material and a bonding agent which includes highly electronegative
functional groups.
[0023] Referring to FIG. 1, there is shown schematically the
general process for manufacturing a finished composite wood product
2 from wood furnish and a bonding agent. Depending on the wood
product to be manufactured, the wood furnish will be in the form of
chips, flakes, strands, fibres or the like. Strands 4 are
illustrated for convenience in FIG. 1. The strands are supplied
from a source of wood furnish 8 that is replenished by cutting and
processing of raw logs.
[0024] The bonding agent is preferably a resin 10 selected for
having a chemical composition that includes electronegative
functional groups. This includes resins such as urea-formaldehyde,
melamine-urea-formaldehyd- e, melamine-formaldehyde and
phenol-formaldehyde which are commonly used in various cellulosic
products. Modified versions of these resins are also used. Modified
resins are generally commercial resins that have additives such as
ammonia, salt, sugar or molasses intended to improve some specific
properties of the resin. All these resins and modified versions
have strongly electronegative functional groups. Resin 10 is held
in a storage tank 12.
[0025] An X-ray active label selected to bond with the
electronegative functional groups of the resin can be added to the
resin. The X-ray active label is preferably a metallic ion that
generates a characteristic fluorescence signal when exposed to
X-rays. The metallic ion is positively charged and forms strong
bonds with the electronegative functional groups of the resin
molecules to move with the resin as the resin is distributed during
the manufacturing process. The cation is supplied in the form of a
water soluble compound that is added to the resin either during or
after the resin manufacturing process. Suitable cations include
Cu(II+), Ba(II+), Na(I+) and K(I+). The cations are mixed with the
bonding agent in sufficient quantity to create an ion concentration
in the resin capable of emitting detectable amounts of x-ray
fluorescence.
[0026] In some cases, the label cations are already present in the
resin. For example, Na(I+) cations exist in phenol-formaldehyde
resin (resol resin) and do not need to be added to the resin.
[0027] In FIG. 1, the cation is shown being added to resin 10 in
tank 12 from a cation supply tank 14 such that tank 12 acts as a
mixing vessel. The cation is homogeneously mixed with the resin
under agitation. The water soluble compound supplying the cation is
added to the resin in an amount not to cause sedimentation or
precipitation. The result is a novel homogeneous resin composition
containing an X-ray active label.
[0028] The resin composition is applied as a solution to the
cellulosic material in the form of wood furnish in the example of
FIG. 1. The resin solution 6 is applied to wood strands 4 by
sprayer 16. Alternatively, resin solution 6 can be applied by
immersing the strands in a bath. Other conventional methods of
applying resin to the wood furnish can also be used.
[0029] After applying the resin solution to the wood furnish in the
form of strands 4, the strands are conveyed to form an organized
mat 18 of stacked strands.
[0030] Mat 18 is then advanced in the direction of arrow 20 to hot
press 22. In press 22, heat and pressure are applied to the mat to
compress and bond the wood furnish together to create finished
composite wood product 2. Hot press 22 can be a continuous press or
a batch press. A batch press is shown in FIG. 1. In the event that
a continuous press is used, mat 18 is formed and conveyed to press
22 on a continuous basis.
[0031] At certain stages in the production of the composite
product, the cellulosic material is exposed to X-rays to generate
X-ray fluorescence signals from the label in the resin. These
signals are measured to determine the distribution of the label in
the product. Using calibration curves, the amount of label measured
by X-ray fluorescence can then be converted to resin content and
distribution.
[0032] FIG. 1 and 2 show exemplary X-ray generation and detection
units 30. Each unit includes an X-ray source 32 to direct X-rays to
the cellulosic material to cause the metallic ions to fluoresce and
an X-ray detector 34 to detect the fluorescence signals. The
generation and detection of X-rays is preferably controlled by a
central processing unit 35 running an appropriate control
programme. FIG. 3 illustrates an example calibration curve that can
be incorporated into the control programme as a look-up table to
convert measured metal ion concentrations into resin content. In
the example of FIG. 3, Cu (II+) ions as a CuO percent of the total
weight of the sample are plotted against resin solids content as a
percent total weight of the sample. Based on testing, it has been
determined that different calibration curves exist for different
solids contents of the same resin. Therefore, it is necessary to
monitor the solids content of the resin and input the resin and
solids content into the computer programme to ensure accurate
results.
[0033] Preferably, central processing unit 35 will display resin
distribution measurement results in an easy to read manner on a
video display unit. The metallic ion concentrations can be easily
converted to resin concentrations by a function button that applies
the calibration curve and displays the resin concentration
results.
[0034] The X-ray units 30 of FIG. 1 are positioned to operate on a
continuous on-line basis during the manufacture of the composite
wood product. The unit positioned at location 37, before the hot
press, operates to measure the resin content and distribution of
mat 18 on an on-line basis as the manufacturing process is on
going. Similarly, the unit positioned at location 38, after the hot
press, operates to measure the resin content and distribution of
the finished composite wood product as the product is
manufactured.
[0035] Resin distribution measurements can also be conducted using
the X-ray units on an off-line basis. Generally, this involves
selecting samples from the manufacturing line for testing. The
X-ray unit illustrated in FIG. 2 is specifically designed to handle
test samples. A sample holder 39 is provided to securely hold the
sample of material to be analyzed in place while X-ray scanning
occurs using X-ray source 32 and detector 34.
[0036] Off-line scanning of random samples of resinated cellulosic
material can be performed immediately after resin is applied to the
wood particles to check for resin content and the evenness of
distribution at an early stage in the manufacturing process. After
hot pressing, the finished composite wood product can be randomly
sampled and evaluated in an off-line X-ray unit to determine resin
content and distribution.
[0037] Some specific examples of the method of the present
invention using specific resin compositions will serve to further
clarify the present invention:
EXAMPLE 1
[0038] The method of the present invention can be used to study and
monitor the manufacture of medium density fibreboard (MDF) with
urea-formaldehyde resin, melamine-urea-formaldehyde resin or
phenol-formaldehyde resin. Monitoring of the resin content and
distribution can be conducted for both the resinated wood furnish
and the MDF panels on an on-line or off-line basis.
[0039] For example, in the manufacture of MDF using
urea-formaldehyde resin, a water solution of cupric sulphate is
added to the resin dilution tank with agitation so that the Cu(II+)
concentration in the resin is about 0.2% of the resin solids
content. The pH of the resulting homogeneous resin solution is
lowered due the addition of cupric sulphate. Alternatively, the
source of cations can be a solution of cupric chloride or cupric
nitrate. The resulting homogeneous resin solution is then blended
with the wood fibres in a conventional manner. The resinated fibres
are then sampled randomly, and the samples used to monitor resin
content and distribution based on scanning of the samples by an
off-line X-ray unit programmed with an appropriate calibration
curve. Alternatively, an on-line X-ray unit can be installed before
the hot press to measure the mat resin content continuously. After
hot pressing, the boards are sampled randomly, and the samples used
to monitor the resin content and distribution in the finished MDF
product based on scanning of the board samples by an off-line X-ray
unit. Alternatively, an on-line X-ray unit can be used after the
hot press to monitor the board resin content and distribution on a
continuous basis as the board is produced.
EXAMPLE 2
[0040] The method of the present invention can be used to study and
monitor the manufacture of particleboard with urea-formaldehyde
resin, melamine-urea-formaldehyde resin or phenol-formaldehyde
resin. Monitoring of the resin content and distribution can be
conducted for both the resinated wood furnish and the particleboard
panels on both an on-line or off-line basis.
[0041] For example, in the manufacture of particleboard using
urea-formaldehyde resin, a water solution of cupric sulphate is
added to the urea-formaldehyde resin dilution tank with agitation
so that the Cu(II+) concentration in the resin is about 0.4% of the
resin solids content. The pH of the resulting homogenous resin
solution is lowered due to the addition of cupric sulphate. The
resulting homogeneous resin solution is then applied to the wood
furnish in a conventional manner. The resinated furnish is then
sampled randomly, and the samples used to monitor resin content and
distribution based on scanning of the samples by an off-line X-ray
unit programmed with an appropriate calibration curve.
Alternatively, an on-line X-ray unit can be installed before the
hot press to measure the mat resin content continuously. After hot
pressing, the boards are sampled randomly, and the samples used to
monitor the resin content and distribution in the finished
particleboard product based on scanning of the board samples by an
off-line X-ray unit. Alternatively, an on-line X-ray unit can be
used after the hot press to monitor the board resin content and
distribution on a continuous basis as the board is produced.
EXAMPLE 3
[0042] The method of the present invention can be used to study and
monitor the manufacture of oriented strand board (OSB) with
phenol-formaldehyde resin (resol type in either liquid or powder
form). Monitoring of the resin content and distribution can be
conducted for both the resinated wood strands and the OSB panels on
both an online or off-line basis.
[0043] In this case, the label is the Na(I+) ion existing in the
resol resin. The resin solution is applied to the wood strands in a
conventional manner. The resinated strands are then sampled
randomly, and the samples used to monitor resin content and
distribution based on scanning of the samples by an off-line X-ray
unit programmed with an appropriate calibration curve.
Alternatively, an on-line X-ray unit can be installed before the
hot press to measure the mat resin content and distribution
continuously. After hot pressing, the boards are sampled randomly,
and the samples used to monitor the resin content and distribution
in the finished OSB product based on scanning of the board samples
by an off-line X-ray unit. Alternatively, an online X-ray unit can
be used after the hot press to monitor the board resin content and
distribution on a continuous basis as the board is produced.
[0044] Although the present invention has been described in some
detail by way of example for purposes of clarity and understanding,
it will be apparent that certain changes and modifications may be
practised within the scope of the appended claims.
* * * * *