CN108648891B - A kind of preparation method of core-shell structure latent fingerprint revealing powder - Google Patents

Abstract

The invention relates to a preparation method of a core-shell structure latent fingerprint display powder, specifically, dissolving polyvinyl alcohol in ethanol, stirring to form a white suspension; adding graphene to the white suspension, and ultrasonically dispersing to obtain Solution A; age solution A, put it in a freeze dryer until freeze-dried, and obtain graphene and polyvinyl alcohol composite coating material B; mix composite coating material B and ferrite powder evenly, and put it into a ball mill Carry out ball milling, put the ball milled powder into a vibrating sieve to screen, select powder C with a particle size ≥ 200 mesh; mix powder C with coated iron powder evenly to obtain latent fingerprint display powder. In the present invention, the chemical method is combined with the trace substances contained in the fingerprint to realize the rapid display of the latent fingerprint, adding ferrite powder, adopting a ball milling process, and then coating the powder on the surface of the ferrite powder, and obtaining the magnetic powder through screening , Realize the recycling of fingerprint powder and avoid the appearance of dust clouds.

Description

A kind of preparation method of core-shell structure latent fingerprint revealing powder

technical field

The invention belongs to the technical field of detection, and in particular relates to a preparation method of a core-shell structure latent fingerprint revealing powder.

Background technique

Fingerprints have always been recognized as the "king of evidence" by the judiciary, because fingerprints have the following characteristics: fingerprints are unique symbols inherent in individuals, and are unique; The surface of the skin is covered with sweat and sebum, leaving traces of touch objects; the pattern of lines on the surface of the end of the fingers is neat and orderly. Therefore, fingerprints play an important evidential role in forensic science and criminal proceedings. However, as the means of committing crimes adopted by criminals become more and more concealed, the fingerprints appearing at the crime scene are often latent, and some special display methods are needed to make the lines appear.

Since 1887, French doctor Aubert applied silver nitrate solution on paper to reveal sweat gland fingerprints in the process of researching skin diseases and glandular secretions. After more than one hundred years of development, fingerprint display has developed into a comprehensive Applying the professional technology of physics, chemistry, biology and other subject knowledge, the fingerprint visualization methods currently used in the field mainly include: chemical visualization method, physical visualization method, optical visualization method, etc. At present, the most widely used method is the powder method. This method can realize large-scale detection and sampling on the spot. It is easy to operate and low in cost. However, many powders contain harmful components such as heavy metals such as Cd and Pb. The health of professional technicians is seriously endangered, and the sensitivity is not high enough. Therefore, it is a problem that researchers need to solve to be able to display latent fingerprints sensitively without harmful components.

The appearance of polyvinyl alcohol is a white powder. It is a water-soluble polymer with a wide range of uses. Because of the presence of hydrogen bonds, it has unique properties such as strong adhesion and film flexibility. Some residues in the fingerprint, such as fatty acids and amino acids, also have hydrogen bonds, which can be developed by hydrogen bonds with polyvinyl alcohol. However, the hydrogen bond between PVA powder and potential fingerprint residues may be quite weak, which makes it difficult to bond between them, and in order to enhance the bonding force, PVA particles need to be modified.

Graphene is a two-dimensional material with a hexagonal honeycomb lattice composed of carbon atoms in sp2 hybridized orbitals, and a thickness of only one carbon atom. Both graphene and its precursor graphene oxide have a very high specific surface area, which can increase the contact area with fingerprints. The connection between each carbon atom in graphene is very flexible. When an external mechanical force is applied, the carbon The atomic surface is bent and deformed, so that the carbon atoms do not have to rearrange to adapt to the external force, so that the graphene has good lubricity. Graphene has good lipophilicity, and as a modifier, it can improve the bonding ability of vinyl alcohol polymers and fingerprints.

The present application is mainly to design a latent fingerprint revealing powder with a core-shell structure using graphene-modified polyvinyl alcohol for the above-mentioned problems.

Contents of the invention

The object of the present invention is to provide a preparation method of a latent fingerprint revealing powder with a core-shell structure in order to solve the above problems.

The object of the present invention is achieved through the following technical solutions:

A preparation method for a core-shell structure latent fingerprint display powder, comprising the following steps:

(1) dissolving polyvinyl alcohol in ethanol, stirring to form a white suspension;

(2) Graphene is added in the white suspension liquid, carries out ultrasonic dispersion, obtains solution A;

(3) Aging the solution A, putting it into a freeze dryer until freeze-drying, and obtaining the composite coating material B of graphene and polyvinyl alcohol;

(4) Mix the composite coating material B and the ferrite powder evenly, put it into a ball mill for ball milling, put the ball-milled powder into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh;

(5) Mix the powder C and the coated iron powder evenly to obtain the latent fingerprint revealing powder.

Further, the temperature of ethanol in step (1) is 40° C., and the mass ratio of ethanol volume to polyvinyl alcohol is 15˜25 mL/g.

Further, the polyvinyl alcohol in step (1) adopts polyvinyl alcohol with a degree of polymerization of 1788-2688, and polyvinyl alcohol is used as the main component of the binder, which has unique properties such as strong adhesion and film flexibility, The hydrogen bonds on it can make strong bonds with some residues in fingerprints such as fatty acids and amino acids.

Further, the mass ratio of graphene and polyvinyl alcohol described in step (2) is 1:16-20, and graphene itself has the characteristics of lubricity, skin affinity and large specific surface area. Through methods such as ultrasonication and aging, it can be Effective adhesion to the surface of polyvinyl alcohol, compared with graphite, can make the bonding of polyvinyl alcohol to fingerprint residue significantly enhanced.

Further, during step (2) ultrasonic dispersion, the ultrasonic frequency is 80-100HZ, and the time is 15-20min.

Further, the aging time in step (3) is 10-20 hours.

Further, when step (4) adopts a ball mill for ball milling, the ball-to-material ratio is 200:1, the ball milling time is 20-30 min, and the rotation speed is 150-180 rap/min.

Further, the ferrite powder in step (4) is AlNiCo, MnZn ferrite or barium strontium permanent magnet ferrite, with a particle size of 200-300 mesh, and the composite cladding material B and ferrite powder The mass ratio is 1:1.5-2. Compared with traditional iron powder, ferrite has a larger magnetic energy product (B _s ), and its comprehensive magnetic properties are more excellent. A uniformly coated core-shell structure can be formed by ball milling, which is faster The recovery of powder can effectively reduce the problem of slag falling in the process of brushing and displaying.

Further, the mass ratio of the powder C to the coated iron powder in step (5) is 1:5, and the particle size of the coated iron powder is 80 mesh, because there will still be unformed Core-shell structure and material B that exists alone, therefore, the iron powder is activated to change the polarity of its surface, and can be combined with the composite coating material B that exists alone, and compared with ordinary iron powder, the coating The iron-coated powder has low magnetic properties, which can play a role in adjusting the magnetic strength of the powder.

Further, the coated iron powder in step (5) is prepared by in-situ generation method: mix the iron powder with deionized water, put it into a muffle furnace, raise the temperature from room temperature to 270°C and keep it warm for 0.5h, and then cool naturally to room temperature to obtain coated iron powder.

The invention proposes a method for preparing a core-shell structure latent fingerprint revealing powder. The components mainly include graphene, polyvinyl alcohol, ferrite powder and coated iron powder, wherein the latent fingerprint revealing powder is prepared by ball milling and coating methods When displaying, use magnetic dry paint or fiber brush to realize the display of latent fingerprints on different objects. The present invention uses graphene and polyvinyl alcohol as raw materials, adopts a coating process to make powder, and can combine with trace substances contained in fingerprints through chemical methods to realize the rapid display of latent fingerprints; secondly, ferrite powder is added , using the ball milling process, and then coating the powder on the surface of the ferrite powder, after screening to obtain the magnetic powder, so as to realize the recycling of fingerprint powder and further avoid the appearance of dust clouds. The powder for revealing latent fingerprints prepared by the invention further solves the problem of slag dropping, has fast powdering speed, clear and continuous lines, no false features, strong binding force with fingerprints, wide application range, low raw material cost, and is convenient for industrialized production.

Compared with the prior art, it has the following beneficial effects:

(1) The present invention is easy to operate and can display latent fingerprints on various surfaces (glass plate, copper sheet, paper, aluminum foil, plastic, table or test bench surface).

(2) The powdering speed of the present invention is high, and the sensitivity is high, and the visible latent fingerprint can be identified by naked eye observation, and the obtained visible fingerprint can be directly photographed to obtain data under natural light.

(3) The present invention is easy to prepare and preserve, has low cost and can be used in large quantities.

(4) The fingerprint image displayed on the light-colored object of the present invention has a clear contrast with the substrate and has a long retention time.

(5) Regardless of the raw materials, product preparation process or final powder product obtained in the present invention, it does not contain any toxic components and is safe to use.

Description of drawings

Figure 1 is the brushing effect of fingerprint developer powder on the ceramic surface;

Figure 2 is the brushing effect of the fingerprint developer powder on the plastic surface;

Figure 3 is the brushing effect of fingerprint developer powder on the surface of copper foil;

Fig. 4 is the brushing effect of the fingerprint developing powder on the surface of the iron plate coated with blue paint;

Figure 5 is the brushing effect of the fingerprint developer powder on the surface of the white wood board;

Fig. 6 is the SEM image of the common magnetic fingerprint powder that adds graphite;

Figure 7 is a SEM image of graphene-modified magnetic fingerprint powder.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

A preparation method for a core-shell structure latent fingerprint display powder, comprising the following steps:

(1) Pour 150ml of alcohol into a beaker, and put the beaker into a constant temperature water bath at 40°C;

(2) Take 8g polyvinyl alcohol, polyvinyl alcohol powder adopts polyvinyl alcohol with a degree of polymerization of 2688, slowly dissolve in the alcohol solution, stir while adding, until a white suspension is formed;

(3) Weigh 0.5g graphene and add it to the suspension, put it into an ultrasonic instrument for ultrasonic dispersion, the ultrasonic frequency is 90HZ, and the time is 15 to 20 minutes to obtain solution A;

(4) Aging the solution A for 10h, putting it into a lyophilizer until lyophilized, and obtaining the composite coating material B of graphene and polyvinyl alcohol;

(5) Weigh 8.5g of coated powder B and 16g of ferrite powder and add them to a ball mill tank for mixing, stir evenly, add steel balls, put them into a ball mill for ball milling, the ball-to-material ratio is 200:1, and the ball milling time is 20min , the rotation speed is 150rap/min, the ferrite powder composition is barium strontium permanent magnet ferrite, and the particle size is 200 mesh;

(6) put the powder after ball milling into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh;

(7) Put the magnetic powder C with a mass ratio of 1:5 and the coated Fe powder into a mixer for stirring and mixing to obtain a latent fingerprint display powder, wherein the particle size of the coated Fe powder is 80 mesh, and the in-situ The production method is prepared by mixing iron powder with deionized water, putting it into a muffle furnace, raising the temperature from room temperature to 270°C and keeping it warm for 0.5h, and then naturally cooling to room temperature to obtain coated iron powder.

Example 2

A preparation method for a core-shell structure latent fingerprint display powder, comprising the following steps:

(1) Pour 150ml of alcohol into a beaker, and put the beaker into a constant temperature water bath at 40°C;

(2) Weigh 10g polyvinyl alcohol, polyvinyl alcohol powder adopts polyvinyl alcohol with a degree of polymerization of 1788, slowly dissolve in the alcohol solution, stir while adding, until a white suspension is formed;

(3) Weigh 0.5g graphene and add it to the suspension, put it into an ultrasonic instrument for ultrasonic dispersion, the ultrasonic frequency is 90HZ, and the time is 15 to 20 minutes to obtain solution A;

(4) Aging the solution A for 20h, putting it into a lyophilizer until lyophilized, obtaining graphene and polyvinyl alcohol composite coating material B;

(5) Weigh 8g of coated powder B and 16g of ferrite powder and add them to a ball mill tank for mixing, stir evenly, add steel balls, put them into a ball mill for ball milling, the ball-to-material ratio is 200:1, and the ball milling time is 20min. The rotation speed is 150rap/min, the ferrite powder composition is barium strontium permanent magnet ferrite, and the particle size is 200 mesh;

(6) put the powder after ball milling into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh;

(7) Put the magnetic powder C with a mass ratio of 1:5 and the coated Fe powder into a mixer for stirring and mixing to obtain a latent fingerprint display powder, wherein the particle size of the coated Fe powder is 80 mesh, and the in-situ The production method is prepared by mixing iron powder with deionized water, putting it into a muffle furnace, raising the temperature from room temperature to 270°C and keeping it warm for 0.5h, and then naturally cooling to room temperature to obtain coated iron powder.

Example 3:

A preparation method for a core-shell structure latent fingerprint display powder, comprising the following steps:

(1) Pour 150ml of alcohol into a beaker, and put the beaker into a constant temperature water bath at 40°C;

(2) Take 8g polyvinyl alcohol, polyvinyl alcohol powder adopts polyvinyl alcohol with a degree of polymerization of 2488, slowly dissolve in the alcohol solution, stir while adding, until a white suspension is formed;

(3) Weigh 1g of graphene and add it to the suspension, put it into an ultrasonic instrument for ultrasonic dispersion, the ultrasonic frequency is 90HZ, and the time is 15 to 20 minutes to obtain solution A;

(4) Aging the solution A for 10h, putting it into a lyophilizer until lyophilized, and obtaining the composite coating material B of graphene and polyvinyl alcohol;

(5) Weigh 8g of coated powder B and 14g of ferrite powder and add them to a ball mill tank for mixing, stir evenly, add steel balls, put them into a ball mill for ball milling, the ball-to-material ratio is 200:1, and the ball milling time is 30min. The rotation speed is 200rap/min, the ferrite powder composition is manganese zinc ferrite, and the particle size is 200 mesh;

(6) put the powder after ball milling into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh;

(7) Put the magnetic powder C with a mass ratio of 1:5 and the coated Fe powder into a mixer for stirring and mixing to obtain a latent fingerprint display powder, wherein the particle size of the coated Fe powder is 80 mesh, and the in-situ The production method is prepared by mixing iron powder with deionized water, putting it into a muffle furnace, raising the temperature from room temperature to 270°C and keeping it warm for 0.5h, and then naturally cooling to room temperature to obtain coated iron powder.

comparative example

A kind of preparation method of common core-shell structure latent fingerprint revealing powder, comprises the following steps:

(1) Weigh 8g polyvinyl alcohol, the polyvinyl alcohol powder is polyvinyl alcohol with a polymerization degree of 2688, then weigh 0.5g graphite and 16g ferrite powder and add them to the ball mill jar for mixing, stir evenly, add steel balls, put Put it into a ball mill for ball milling, the ball-to-material ratio is 200:1, the ball milling time is 20min, the rotation speed is 150rap/min, the ferrite powder composition is barium strontium permanent magnet ferrite, and the particle size is 200 mesh;

(2) put the powder after ball milling into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh;

(3) Put the magnetic powder C with a mass ratio of 1:5 and the coated Fe powder into a mixer for stirring and mixing to obtain the latent fingerprint display powder, wherein the particle size of the coated Fe powder is 80 mesh, and the in-situ The production method is prepared by mixing iron powder with deionized water, putting it into a muffle furnace, raising the temperature from room temperature to 270°C and keeping it warm for 0.5h, and then naturally cooling to room temperature to obtain coated iron powder.

Figure 1-5 shows the brushing effect of fingerprint developer powder on the surface of different objects (ceramic, plastic, copper foil, iron plate coated with blue paint, white wood board). Latent fingerprints can be accurately and completely displayed on ceramics or rough white wood boards, and the fingerprint lines are clear, there are no redundant impurities between the lines, and there are no false features. The detailed features of the fingerprints are obvious, which can effectively reduce the technical Personnel identify interference.

Fig. 6, 7 are the scanning electron microscope images of comparative example common magnetic fingerprint powder and graphene modified magnetic fingerprint powder of the present invention respectively, Fig. 6 can find out that the common magnetic fingerprint powder fingerprint ridge line that adds graphite is incoherent, appears on the ridge line There are many gaps, and there are a large number of black spots in the area between the lines, which are fingerprint powder residues. It can be seen in Figure 7 that each line is coherent and clear, and the details of the lines are clearly displayed, and there is nothing between the lines. Residue, there will not be any spurious features.

Claims (10)

1. a preparation method of core-shell structure latent fingerprint display powder, is characterized in that, comprises the following steps: (1) dissolving polyvinyl alcohol in ethanol, stirring to form a white suspension; (2) Graphene is added in the white suspension liquid, carries out ultrasonic dispersion, obtains solution A; (3) Aging the solution A, putting it into a freeze dryer until freeze-drying, and obtaining the composite coating material B of graphene and polyvinyl alcohol; (4) Mix the composite coating material B and the ferrite powder evenly, put it into a ball mill for ball milling, put the ball-milled powder into a vibrating sieve for screening, and select powder C with a particle size ≥ 200 mesh; (5) Mix powder C and coated iron powder evenly to obtain latent fingerprint display powder, The coated iron powder is prepared by an in-situ generation method: the iron powder is mixed with deionized water, put into a muffle furnace, heated from room temperature and kept warm, and then naturally cooled to room temperature to obtain the coated iron powder. 2. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, is characterized in that, the temperature of step (1) ethanol is 40 ℃, and the mass ratio of ethanol volume and polyvinyl alcohol is 15～25mL /g. 3. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, is characterized in that, the polyvinyl alcohol described in step (1) adopts the polyvinyl alcohol that polymerization degree is 1788-2688. 4. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, is characterized in that, the mass ratio of step (2) described graphene and polyvinyl alcohol is 1:16-20. 5. The preparation method of a core-shell structure latent fingerprint revealing powder according to claim 1, characterized in that, during step (2) ultrasonic dispersion, the ultrasonic frequency is 80-100HZ, and the time is 15-20min. 6. The preparation method of a core-shell structure latent fingerprint revealing powder according to claim 1, characterized in that the aging time in step (3) is 10-20 hours. 7. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, it is characterized in that, when step (4) adopts ball mill ball mill, ball material ratio is 200:1, and ball milling time is 20～30min, The speed is 150-180 rap/min. 8. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1 is characterized in that, the ferrite powder described in step (4) is manganese zinc ferrite or barium strontium permanent magnet ferrite, The particle size is 200-300 mesh, and the mass ratio of composite coating material B to ferrite powder is 1:1.5-2. 9. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, it is characterized in that, the mass ratio of step (5) described powder C and coated iron powder is 1:5, coated iron The particle size of the powder is 80 mesh. 10. the preparation method of a kind of core-shell structure latent fingerprint revealing powder according to claim 1, is characterized in that, step (5) described coated iron powder is prepared by in-situ generation method: iron powder and deionized Mix it with water, put it into a muffle furnace, raise the temperature from room temperature to 270°C and keep it warm for 0.5h, then cool it down to room temperature naturally to obtain coated iron powder.