WO2010066142A1

WO2010066142A1 - Anti-counterfeit fiber and anti-counterfeit paper containing the same

Info

Publication number: WO2010066142A1
Application number: PCT/CN2009/073607
Authority: WO
Inventors: 孙显林
Original assignee: Sun Xianlin
Priority date: 2008-12-09
Filing date: 2009-08-28
Publication date: 2010-06-17
Also published as: EP2360315A1; EA201170723A1; EP2360315A4

Abstract

An anti-counterfeit fiber and an anti-counterfeit paper containing the same are provided. The fiber includes at least a first material part and a second material part which run parallel along the fiber length direction without being twisted. The first material part contains luminescent material A and the second material part contains luminescent material B with the luminescent colors visually different under excited light. When the anti-counterfeit fiber freely falls on a plane, one surface of two material parts is upward, and the other is adown. The thermal shrinkage rates of two material parts are the same so that the surface of the first material part can be oriented towards one side of anti-counterfeit paper and the surface of the second material part can be oriented towards the other side of anti-counterfeit paper after the anti-counterfeit fiber is added to paper pulps to produce the anti-counterfeit paper. Thus when the two sides of anti-counterfeit paper are irradiated by excited light respectively, the luminescent colors of the anti-counterfeit fiber are apparently changed.

Description

Anti-counterfeiting fiber and anti-counterfeiting paper containing anti-counterfeit fiber

A security fiber, in particular, a fluorescent anti-counterfeit fiber that changes color as the angle of excitation light changes. Background technique

The inventor's application No. 200710146239.X, the Chinese Patent Application entitled "Fluorescent Anti-Counterfeiting Fiber and Anti-Counterfeiting Material for Inducing Changes in Visual Angle Changes in Visual Angle" discloses a single anti-counterfeiting fiber having a flat shape in the lateral direction, It has at least two material portions distributed in cross section and extending in parallel along the length of the fiber, and the two material portions contain different luminescent materials, which are respectively distributed on the upper and lower surfaces of the flat surface of the security fiber. After the anti-counterfeiting fiber is added to the anti-counterfeit material, the upper and lower surfaces of the flat surface are nearly parallel to the surface of the anti-counterfeit material, and the excitation light is obviously changed when the excitation light is respectively irradiated from the two surfaces of the anti-counterfeit material. The inventors found that after the anti-counterfeiting fiber was copied into the paper, after the anti-counterfeit fiber was added to the paper, the change of the front-reverse surface illuminating color was not obvious. According to analysis, this is because the anti-counterfeiting fiber is added to the anti-counterfeiting material such as paper. At the same time, it is always intended to be distributed in the anti-counterfeiting material in the lowest energy state, and the two material portions having different luminescent materials are often different materials in addition to the luminescent materials, and therefore, the luminescent materials will have different luminescent materials. After the two materials are prepared into the anti-counterfeit fiber, the thermal shrinkage of the two materials is different, which causes the anti-counterfeit fiber to be distorted or does not contribute to the bending phenomenon of the anti-counterfeit fiber light-emitting surface, so that the upper and lower surfaces of the flat surface cannot be combined with the surface of the anti-counterfeit material. Nearly parallel, it is impossible to achieve a significant change in the luminescent color of the anti-counterfeit fiber when the excitation light is separately irradiated from the two surfaces of the anti-counterfeit material. Summary of the invention

The invention solves the problem that in the prior art, when the fluorescent anti-counterfeit fiber having different luminescent materials on the upper and lower surfaces is added to the sheet-shaped anti-counterfeit material such as paper or plastic film, the anti-counterfeiting visual characteristics cannot be realized due to the occurrence of distortion or non-target bending phenomenon. The technical defect enables the two surfaces of different anti-counterfeit materials to be respectively applied to the two surfaces of the anti-counterfeit material after the fluorescent anti-counterfeit fibers are added to the paper, thereby realizing the illuminating color of the anti-counterfeiting fibers when the excitation light is respectively irradiated from the two surfaces of the anti-counterfeit material. Significant change.

The invention also relates to a security paper in which the security fiber is distributed. The security paper refers to a sheet-like anti-counterfeiting material such as paper or plastic film to which the security fiber is added. The technical problem of the present invention is solved as follows:

A security fiber having at least a first material portion and a second material portion extending non-twisted in parallel along a length direction of the security fiber, the first material portion containing a first material portion surface and the second material portion containing a second material portion surface The first material portion and the second material portion respectively contain the luminescent material A and the luminescent material B. Under the action of the excitation light, the luminescent color of the luminescent material A and the luminescent color of the luminescent material B have obvious visual differences, and the characteristics thereof When the security fiber is free to fall to the horizontal plane, one of the first material portion surface and the second material portion surface faces upward, one surface faces downward, and the first material portion and the second material portion have the same heat shrinkage ratio, Ensuring that the anti-counterfeit fiber is added to the pulp to make the anti-counterfeit paper, the surface of the first material portion faces one side of the anti-counterfeit paper, and the surface of the second material portion faces the other side of the anti-counterfeit paper, so that the excitation light is respectively on the two surfaces of the security paper When irradiated, the luminescent color of the anti-counterfeit fiber changes significantly.

The same heat shrinkage rate means that when the first material portion 1 and the second material portion 2 are selected, the anti-counterfeit fibers that are spun out are not bent at normal temperature (for example, below 35 ° C) without the interface 3 of the two material portions. Bending, in order to further ensure the orientation of the security fibers after they are copied into the paper.

Also included is a third portion of material adjacent the same side of the first and second portions of material and extending non-twisted in parallel along the length of the security fiber, the third portion of material being colorless or colored.

In the longitudinal direction of the security fiber, the security fiber is bent along the bending of the joint faces of the first and second material portions and the third material portion.

The anti-counterfeit fiber has a circular cross section.

Also included is a fourth material portion that is adjacent to another identical side of the first and second material portions and along the first, second, and third material portions along the security fiber The length direction is non-twisted and extends in parallel, and the fourth material portion is colorless or colored.

Also including at least a fifth material portion that extends non-twisted parallel along the length of the security fiber along with the first to fourth material portions, the fifth material portion being located intermediate the security fiber, and the first material The portion and the second material portion are equally divided along the length direction of the security fiber to form a first material portion of the left segment and a first material portion of the right segment, and a second material portion of the left segment and a second material portion of the right segment; The material is partially colorless or colored.

The left material first material portion and the right segment first material portion may contain different luminescent materials, and/or the left segment second material portion and the right segment second material portion may contain different luminescent materials. The security fiber further includes a first and second material portions spaced apart between the first and second material portions and non-twisted parallel to the length of the security fiber along with the first and second material portions An extended intermediate material portion, the intermediate material portion being an excitation light blocking material.

Between the first and second material portions, an intermediate material portion separating the first and second material portions and extending non-twisted in parallel with the first and second material portions along the longitudinal direction of the security fiber is further disposed The intermediate material portion is an excitation light blocking material.

The security fiber contains at least one dyed segment and one non-stained segment in the length direction.

The security fiber has a dyeing section in the entire length direction.

An anti-counterfeit paper having the anti-counterfeit fiber distributed thereon, and a surface of the first material portion of the first material portion of the anti-counterfeit fiber and a surface of the second material portion of the second material portion are respectively presented on the front and back of the security paper On the surface, when the excitation light is separately irradiated on the two surfaces of the security paper, the luminescent color of the security fiber is significantly changed. The anti-counterfeit paper of the anti-counterfeit fiber is characterized in that the anti-counterfeit fiber in the anti-counterfeit paper is completely or partially transparent when viewed by light. Technical Effects: Since the security fiber of the present invention is free to fall to the horizontal plane, one of the surface of the first material portion and the surface of the second material portion faces upward, one surface faces downward, and the heat shrinkage rate of the first material portion and the second material portion are the same It can be ensured that the anti-counterfeit fiber is added to the pulp to make the anti-counterfeit paper, the surface of the first material part faces the side of the anti-counterfeit paper, and the surface of the second material part faces the other side of the anti-counterfeit paper, so that the anti-counterfeit fiber is twisted or not It helps the bending phenomenon of the light-emitting surface of the anti-counterfeit fiber, thereby realizing the significant change of the illuminating color of the anti-counterfeit fiber when the excitation light is respectively irradiated from the two surfaces of the security paper.

The third material portion and the fourth material portion and the first material portion and the second material portion are non-twisted and extend in parallel along the longitudinal direction of the fiber, respectively, and are adjacent to both sides of the two portions, and the anti-counterfeit fiber can also be realized after the anti-counterfeiting paper is added. The orientation of the first material portion and the second material portion greatly increases the difficulty of copying due to the spinning of the three or four components. In particular, when the third material portion and the fourth material portion are different from the first material portion and the second material portion in heat shrinkage, the points of the security fiber are maintained at a relative distance from the upper and lower surfaces of the security paper. Directional bending in the paper, the directional bending further guarantees the first The orientation of a material portion and a second material portion.

The third material part and the fourth material part are colorless and are transparent under the condition of transmitted light after being pressed in the paper, so that the anti-counterfeit fiber in the paper can be found transparent when viewed through light, and further the excitation light is used. The fiber was irradiated from the front and back sides of the security paper to observe changes in its luminescent color. When the third material portion and the fourth material portion are colored, the same can be used to guide and identify the anti-counterfeit fiber, and then the front and back surface of the paper are irradiated with light to confirm the significant change of the luminescent color of the front and back sides. Since the existing textile industry basically has no three-component spinning equipment in production, let alone four components, it must be manufactured separately, and the cost is greatly increased. Therefore, this structure satisfies the independent rule of anti-counterfeiting effect, that is, when the counterfeiter wants When he copied the anti-counterfeiting fiber, he found that he could not find any spinning company with equipment to produce it, which greatly improved the difficulty of fraud. The anti-counterfeiting fiber is further provided with a fifth material portion and other material portions which are equally divided by the interface and extend in the longitudinal direction of the fiber along the longitudinal non-twist of the first and second material portions, and the material portions will be first and The two materials are cut off from the cross section and are colorless or colored. They can also serve to guide the identification of anti-counterfeiting fibers with fluorescent color on the front and back of the paper, and provide various kinds of fluorescent fibers for different applications under different conditions. Applications. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view of a security fiber composed of a first material portion and a second material portion of the present invention;

Figure 2 is a cross-sectional view of the security fiber of Figure 1 added to the paper;

3-1 and 3-2 are a schematic cross-sectional view and a perspective view of the anti-counterfeit fiber of the first material portion and the second material portion of the second material portion adjacent to each other;

Figure 4 is a schematic cross-sectional view showing the anti-counterfeit fiber of the first material portion and the second material portion of the second material portion of the second material portion of the present invention;

Figure 5 is a schematic cross-sectional view of a security fiber having a fifth material portion equally divided by the interface 3; Figure 6 is a cross-sectional schematic view showing an intermediate material portion disposed between the first material portion and the second material portion;

Figure 7 is a first material portion, a second material portion, and an intermediate material portion of the present invention are adjacent to each other A schematic cross-sectional view of the security material of the three material portions;

Figure 8 is a schematic cross-sectional view showing the first material portion, the second material portion, and the other material side of the intermediate material portion adjacent to the fourth material portion;

Figure 9 is a perspective view of a dyed section in the longitudinal direction. detailed description:

Referring to Fig. 1, there is shown a cross section of the security fiber of the present invention, wherein the first material portion 1 and the second material portion 2 respectively present on the upper surface and the lower surface of the security fiber extend non-twisted in parallel along the longitudinal direction of the security fiber, The anti-counterfeit fiber of the present embodiment is composed of only the first material portion 1 and the second material portion 2, which respectively contain the luminescent material A and the luminescent material B, in the cross section, under the action of the excitation light, the luminescent material The illuminating color of A and the illuminating color of luminescent material B have obvious visual differences. In this embodiment, interface 3 is the largest bisector of the anti-counterfeit fiber. Of course, interface 3 may not be the largest bisector of anti-counterfeit fiber, but it must be ensured. The surface of the first material portion 1 when the security fiber is free to fall into the horizontal plane: the surface of the first material portion and the surface of the second material portion 2: the second material portion surface 2', the two surfaces, one surface facing upward, one surface Down. In order to ensure that the anti-counterfeit fiber of the present invention is added to the security paper, the surface of the first material portion is facing the side of the security paper, and the surface 2' of the second material portion is facing the other side of the security paper so that the excitation light is on the security paper. When the upper and lower surfaces of 8 are respectively irradiated, the illuminating color of the anti-counterfeit fiber is significantly changed, and then the first material portion 1 and the second material portion 2 are required to be materials having the same heat shrinkage rate.

2 is a schematic cross-sectional view of the anti-counterfeit fiber shown in FIG. 1 after the security paper 8 is added during the papermaking process. Since the anti-counterfeit fibers will be distributed in the security paper according to the state of the lowest energy state during the papermaking process, the surface of the first material portion and the surface of the second material portion 2' of the anti-counterfeiting fiber are free to fall to the horizontal plane, one upward, one Downward, it is equivalent to the lowest energy state; at the same time, the first material part 1 and the second material part 2 have the same heat shrinkage rate, and therefore, the first material part 1 is necessarily in the upper part of the security paper in the horizontally placed security paper, Close to the upper surface of the security paper 8, the second material portion 2 is necessarily in the lower portion of the security fiber, close to the lower surface of the security paper 8, such that when the excitation light is directed downward from the upper surface of the security paper 8, such as arrow A When the anti-counterfeit fiber is irradiated, the luminescent material A emits light; when the excitation light illuminates the anti-counterfeit fiber from below the lower surface of the anti-counterfeit paper 8 (as indicated by the arrow B), the luminescent material B emits a luminescent color A There is a significant difference in light to achieve anti-counterfeiting. Since the heat shrinkage rates of the first material portion 1 and the second material portion 2 are the same, the security fibers in Figs. 1 and 2 are straight in the longitudinal direction, and are also straight into the security paper. Therefore, the security fibers of Figures 1 and 2 must be flat fibers, and preferably the first material portion 1 and the second material portion 2 correspond to the equally divided upper half fibers and the lower half of the flat surfaces of the flat fibers, respectively. The fiber, the interface 3 of the first material portion 1 and the second material portion 2 is parallel to the horizontal plane after the security fiber is free to fall to the horizontal plane.

The security fibers of Figures 3-1 and 3-2 adjoin the third material portion 4 on the same side of the first material portion 1 and the second material portion 2, and together extend non-twisted parallel along the length of the security fiber, The interface 3 of the embodiment bisects the first material portion 1 and the second material portion 2, and the interface 3 of the embodiment further bisects the third material portion 4 up and down, the third material portion 4 and the first material portion 1 and the second portion The material portion 2 is small compared to the proportion, and it is not necessarily required to bisect the third material portion 4, provided that the orientation of the first material portion surface Γ and the second material portion surface 2' at the free fall to the horizontal plane is not affected. The third material portion 4 is colorless or colored, and when the color is colorless, the security paper is subjected to pressure treatment in the paper after the security paper 8 is added, so that it is transparent under transmitted light. Preferably, the third material portion 4 is different from the first material portion 1 and the second material portion 2 in heat shrinkage, such that the security fibers in Figure 3-1 follow the first material portion 1 and the second material portion. 2 is bent with the connecting surface 9 of the third material portion 4 to form a curved fiber, as shown in Fig. 3-2. Thus, even if the security fiber in Fig. 3 is not a flat fiber, the surface of the first material portion can be Γ The surface of the second material portion 2' is freely falling from the anti-counterfeiting fiber to a horizontal surface with a surface facing upward, and correspondingly, the anti-counterfeiting fiber, such as being added to the security paper, causes the surface of the first material portion to face toward the security paper. The surface, the second material portion surface 2' faces the lower surface of the security paper, and the excitation light exhibits different luminescent colors when illuminated on both the front and back sides of the security paper. The third material portion 4 is colorless transparent or colored and also helps to find the security fiber from the security paper prior to the identification of the excitation light.

The security fiber of FIG. 4 further includes a fourth material portion 5 on the basis of the three material portions of the security fiber of FIG. 3, and the fourth material portion 5 is located on the other same side of the first material portion 1 and the second material portion 2, preferably The interface divides the fourth material portion equally up and down, and together with the first, second and third material portions (1, 2, 4), non-twisted parallel along the length direction of the security fiber, the fourth material The portion 5 is colorless or colored, and when the color is colorless, the anti-counterfeit fiber is subjected to pressure treatment in the paper after the security paper is added, and the colorless transparent or colored effect and the third material portion 4 of FIG. the same. It is of course preferred that the fourth material portion 5 differs from the first material portion 1 and the second material portion 2 in heat shrinkage to form a specific first material portion surface Γ and a second material portion surface 2' The required bend mentioned earlier Curved fiber.

The security fiber of Figure 5 includes a fifth material portion (6) in addition to the third, fourth material portions of Figure 4, and of course may also include other material portions along with the first to fourth material portions. The length direction of the security fiber is non-twisted and parallel extending, and preferably the interface 3 divides all the material parts except the first and second material parts up and down respectively, and these material parts are located in the middle of the security fiber and are respectively The longitudinal parallel extension of the security fibers breaks the first and second material portions (1, 2) laterally, that is, the first material portion and the second material portion are equally split along the length of the security fiber, for the fifth material portion (6) The first and second material portions 1, 2 which are split apart, respectively form a left first material portion 11 and a right first material portion 12, and a left second material portion 21 and a right second material portion 22; the left segment first material portion 11 and the right segment first material portion 12 may contain different luminescent materials, and/or the left segment second material portion 21 and the right segment second material portion 21 may To contain different luminescent materials. Of course, the security fiber of Fig. 5, the fifth material part (6) or other material part is a colorless fiber or a colored fiber, and when it is a colorless fiber, the anti-counterfeit paper is pressed in the paper after the security paper (8) is added. , making it transparent under transmitted light, colorless transparent and colored, the same as before, but also of material different from the first and second material parts (1, 2) to form specific curved fibers .

The security fiber of Figure 6 includes a portion between the first and second portions of material (1, 2) that separates the two portions of material and is non-twisted along the length of the security fiber along with the first and second portions of material. Extending intermediate material portion 7. Preferably, the interface 3 divides the intermediate material portion 7 up and down, and the first and second material portions are symmetric with the interface 3, and the intermediate material portion 7 is an excitation light blocking material capable of blocking the excitation light transmitted through the first material portion 1. The excitation light that is irradiated onto the second material portion 2 and blocked through the second material portion 2 is irradiated onto the first material portion 1. Of course, the security fibers of Figure 6 must be flat fibers such that the first and second material portions (1, 2) are respectively oriented toward the upper and lower surfaces of the security paper after the security paper is added.

7 and 8 are a third material portion 4 and a fourth material portion 5 respectively adjoining the first and second material portions (1, 2) and the intermediate material portion in a non-twisted manner in the fiber length direction, this embodiment The third material portion 4 and the fourth material portion 5 are equally divided by the interface 3, the two material portions are colorless or colored, and when the color is colorless, the security fiber is subjected to the security paper after adding the security paper. The paper is pressed to make it transparent under transmitted light. If the third material portion 4 and the fourth material portion 5 are the same as the first and second material portions (1, 2), the security fibers must be flat. If the heat shrinkage rate is different, the security fiber is a specific curved fiber. Of course, there may be a fifth material portion and/or other material portions on the basis of FIG. 8, which together with the first to fourth material portions extend non-twisted in parallel along the length direction of the security fiber, and the interface 3 will be removed. All of the material portions other than the first and second material portions are equally divided up and down, the material portions being located intermediate the security fibers and the first and second material portions being extended in parallel along the longitudinal direction of the security fibers, respectively (1) 2) In the transverse direction, the materials are partially colored or colorless. When colorless, paper is applied to the security paper after the security paper is added to make it transparent under transmitted light.

Preferably, the security fibers described in the above figures are flat fibers whose upper and lower surfaces are nearly parallel to the interface (3). For very flat flat fibers, it is not necessary for the first and second portions of the material to be symmetrical to the boundary and the intermediate material portions, the third, fourth, fifth material portions, and other material portions to be equally divided by the interface 3.

The first and second material portions (1, 2) may be colorless, and the anti-counterfeiting fiber is subjected to pressure treatment in the paper after the security paper is added to form an overall transparent (under transmitted light) but front and back The color of the excitation light is changed.

Of course, the anti-counterfeiting fiber is a dyeing section in one or all of the length direction. The security fiber described in Fig. 9 contains at least one dyeing section 10 and one section of non-dyeing section 11 in the longitudinal direction. The security fiber may also be dyed in the entire length of the length. The dyeing section has the function of easily identifying the anti-counterfeit fiber in the security paper, so as to further detect the discoloration of the excitation light by the front and back of the anti-counterfeit paper.

Claims

Rights request

What is claimed is: 1. A security fiber having at least a first material portion (1) and a second material portion (2) extending non-twisted in parallel along a length direction of the security fiber, the first material portion (1) comprising a surface of the first material portion (1'), the second material portion (2) contains a second material portion surface (2'), the first material portion

(1) and the second material portion (2) respectively contain the luminescent material A and the luminescent material B, and under the action of the excitation light, the luminescent color of the luminescent material A and the luminescent color of the luminescent material B have obvious visual differences, which are characterized in that When the anti-counterfeit fiber is free to fall into a horizontal plane, one surface of the first material portion surface (Γ) and the second material portion surface (2') face upward, one surface faces downward, the first material portion (1) and the first The second material portion (2) has the same heat shrinkage rate to ensure that the surface of the first material portion (Γ) faces the side of the security paper after the security fiber is added into the pulp to form the security paper, and the surface (2') of the second material portion faces The other side of the security paper is such that when the excitation light is separately irradiated on the two surfaces of the security paper (8), the luminescent color of the security fiber is significantly changed.

2. The security fiber of claim 1 further comprising an adjacent side of said first and second material portions (1, 2) and non-twisted along said length of said security fiber A third material portion (4) extending in parallel, the third material portion (4) being colorless or colored.

3. The security fiber according to claim 2, wherein in the longitudinal direction of the security fiber, the security fiber is along the first and second material portions (1, 2) and the third material portion ( 4) The connecting surface (9) is bent and bent.

The security fiber according to claim 3, characterized in that the anti-counterfeit fiber has a circular cross section.

The security fiber according to claim 2, further comprising a fourth material portion (5), said fourth material portion (5) and said first and second material portions (1, 2) Another identical side is adjacently connected, and together with the first, second and third material portions (1, 2, 4), non-twisted parallel along the length direction of the security fiber, the fourth material portion (5) being Colorless or colored.

6. The security fiber according to claim 5, further comprising at least a fifth material portion (6), the fifth material portion (6) together with the first to fourth material portions along the length of the security fiber The twisted parallel extension, the fifth material portion (6) is located in the middle of the security fiber, and the first material portion (1) and the second material portion (2) are equally divided along the length direction of the security fiber to form a left segment a material portion (11) and a right first material portion (12), and a left second material portion (21) and The second material portion (22) of the right segment; the fifth material portion (6) is colorless or colored.

7. The security fiber according to claim 6, wherein the left first material portion (11) and the right first material portion (12) contain different luminescent materials, and/or the second segment of the second material portion ( 21) and the second material portion (22) of the right segment contain different luminescent materials.

8. The security fiber of claim 1 wherein said security fiber further comprises between said first and second material portions (1, 2) and said first and second material portions (1, 2) An intermediate material portion that is spaced apart and that extends non-twisted parallel along the length of the security fiber along with the first and second material portions

(7) The intermediate material portion (7) is an excitation light blocking material.

The security fiber according to claim 2, characterized in that the first and second material portions (1, 2) are further provided with a partition between the first and second material portions (1, 2), And an intermediate material portion (7) extending in parallel with the first and second material portions (1, 2) in a non-twisting direction along the longitudinal direction of the security fiber, wherein the intermediate material portion (7) is an excitation light blocking material.

10. The security fiber according to claim 5, characterized in that the first and second material portions (1, 2) are further provided with a partition between the first and second material portions (1, 2), And an intermediate material portion (7) extending in parallel with the first and second material portions (1, 2) in a non-twisting direction along the longitudinal direction of the security fiber, wherein the intermediate material portion (7) is an excitation light blocking material.

The security fiber according to claim 1, characterized in that said security fiber contains at least one dyeing section (10) and a length of non-dyeing section (11) in the longitudinal direction.

The security fiber according to claim 1, wherein said security fiber has a dyeing section in the longitudinal direction.

13. The security paper having the security fiber according to any one of claims 1 to 12, and the first material portion surface (Γ) and the second material portion of the first material portion (1) of the security fiber in the security paper The second material portion surface (2') of (2) is respectively present on the front and back surfaces of the security paper so that the excitation light is illuminated when the two surfaces of the security paper (8) are respectively irradiated The color will change significantly.

The security paper for anti-counterfeiting fibers according to claim 13, wherein the anti-counterfeit fibers in the security paper are all or partially transparent when viewed in light.