Method for stretching a gauze for use in screen printing

Abstract

 The invention relates to a method and a stretching device for stretching a gauze (10) for use in screen printing, wherein the gauze comprises a first pair (11) and a second pair (12) of opposed sides, which define an inner area (13) of the gauze. The first pair and the second pair of sides of the gauze are tensioned before the inner area is tensioned. Consequently, the warp and weft threads of the gauze (10) are oriented substantially at right angles relative to each other in said inner area (13).

Description

[0001] The invention relates to a method for stretching, i.e. tensioning, a gauze. The invention in particular relates to a method for stretching a gauze for use in screen printing, wherein the gauze comprises a first pair and a second pair of opposed sides, which define an inner area of the gauze. The invention also relates to a stretching device for stretching a gauze for screen printing.

[0002] In screen printing, a gauze of e.g. plastic material or steel is stretched in a steel or aluminium frame. Said gauze is the carrier of a stencil, which may have been provided in various ways. The stencil covers those parts of the gauze through which no printing ink must pass. The open parts in the template do allow the ink to pass therethrough, so that a print can be formed on the substrate. There are various kinds of printing ink for screen printing, such as glass ink, paper/cardboard ink, ink for plastics and metal ink. The ink is spread over the gauze with a first squeegee, as a result of which the meshes of the gauze are filled. Then the ink is pressed onto the substrate by means of a pressure squeegee.

[0003] To obtain a good print, it is important that the gauze be stretched in a suitable manner. Fig. 1 schematically shows a stretching table 100 comprising a frame 101 in which a gauze 110 is stretched. The gauze 110 comprises a first pair of opposed sides 112, which define an inner area 113. The central printing area is indicated at 114. The gauze 110 is fixed in lateral clamps 102, which are disposed near the sides 111, 112 of the gauze 110. Then the gauze 110 is tensioned from the lateral clamps 102 by applying a tension force T in directions away from the gauze 110 as indicated by the arrows.

[0004] It has been observed that when such a method for stretching the gauze is used, the orientation of the threads 115 (the warp threads and the weft threads; indicated by the dotted lines) of the gauze 110 increasingly deviates from a right-angled orientation towards the outer side. Such an orientation is disadvantageous for the screen printing process.

[0005] It is an object of the invention to provide an improved method and stretching device for stretching a gauze.

[0006] This object is accomplished by providing a method for stretching a gauze for use in screen printing, wherein the gauze comprises a first pair and a second pair of opposed sides, which sides define an inner area of the gauze, wherein said first pair and said second pair of sides of the gauze are stretched before the inner area is tensioned. Preferably, the method comprises the steps of:

a) stretching the first pair of sides of the gauze in a first direction substantially parallel to the sides of said first pair;

b) stretching the second thereof sides of the gauze in a second direction substantially parallel to the sides of said second pair; and

c) stretching the inner area of the gauze following steps a) and b) from the sides of the first pair and the second pair in the second direction and the first direction, respectively.

[0007] The above object is also accomplished by providing a stretching device adapted for stretching a gauze for use in screen printing, wherein the gauze comprises a first pair and a second pair of opposed sides, which sides define an inner area of the gauze, which stretching device comprises stretching means for stretching the first pair and the second pair of sides of the gauze before the inner area is tensioned. The stretching device preferably comprises:

a) first stretching means for stretching the first pair of sides of the gauze in a direction substantially parallel to the sides of the first pair;

b) second stretching means for stretching the second pair of sides of the goals in a second direction substantially parallel to the sides of the second pair; and

c) third stretching means for stretching the inner area of the gauze from the sides of the first pair and the second pair in the second direction and the first direction, respectively,

wherein the first, the second and/or the third stretching means are adapted for stretching the inner area of the gauze from the sides after the first pair and the second pair of sides have been tensioned by the first and the second stretching means.

[0008] The non-straight orientation of the threads near the corners of the gauze (which orientation also affects the inner area of the gauze) obtained with the conventional stretching device is caused by the fact that the distance between the clamps 102 is greatest near the corners of the gauze, so that the highest tension is reached at these locations. It has become apparent that when the sides of the gauze are first tensioned before the inner area of the gauze is tensioned, the wall and weft threads will be oriented at right angles relative to each other over substantially the entire inner area in the tensioned condition of the gauze. This effect can be ascribed to the fact that space for stretching the inner area of the gauze is created near the corners of the gauze by first stretching the first and second sides at the corners of the gauze. The present method makes it possible to stretch or tension the gauze from the centre.

[0009] In a preferred embodiment of the invention, the method comprises the steps of stretching the first pair of sides and the second pair of sides with different tension forces, and the stretching device is adapted for stretching the sides of the first pair and the second pair with different tension forces. Such an embodiment makes it possible to compensate at least in part for differences between rolls of gauze as regards the number of warp threads and weft threads.

[0010] Further advantageous embodiments are defined in the subclaims and will be discussed in detail in the description of the figures. It will be apparent that the invention is by no means limited to such preferred embodiments.

[0011] In the Figures:

Fig. 1 shows a prior art stretching device for stretching a gauze for use in screen printing;

Figs. 2A and 2B show a stretching device for stretching a gauze for use in screen printing according to a first embodiment of the invention during a first phase, a second phase and a third phase of the method; and

Fig. 3 shows a stretching device for stretching a gauze for use in screen printing according to a second embodiment of the invention.

[0012] Figs. 2A and 2B show a stretching device 1 comprising a frame 2 for stretching a gauze 10. The gauze 10 comprises a first pair of opposed sides 11 and a second pair of opposed sides 12, which define an inner area 13 of the gauze 10. Typically the gauze 10 is rectangular in shape. The dimension of the gauze 10 is 100 cm by 100 cm, for example.

[0013] The stretching device 1 comprises corner clamps 3, 4 disposed at or near the corners of the gauze 10, which corners are defined by the point of intersection of a side 11 of the first pair and a side 12 of the second pair. The corner clamps 3 can be moved in a first direction I for stretching the sides 11. The corner clamps 4 can be moved in a second direction II for stretching the sides 12 of the gauze 10. The corner clamps 3, 4 are preferably moved by pneumatic, mechanical or hydraulic means. The stretching device 1 furthermore comprises lateral clamps 5 provided near the sides 11, 12 of the gauze 10.

[0014] It is noted that in addition to or instead of making use of movable corner clamps 3, 4, other ways of stretching the sides 11, 12 of the gauze 10 are possible, such as moving only a part or means of the corner clamps 3, 4. Think in this connection of a clamp provided with a clamping element (not shown) that can be moved towards the corners of the gauze 10 for stretching the sides 11, 12. Following that, the entire clamp or the clamping element can be moved for stretching the inner area 13 of the gauze 10. The dimensions of the clamping element, at least the part thereof that clamps down the gauze 10, are preferably smaller than or equal to the width of the elements that form the frame 2. Another possibility is shown in Fig. 3, which will be discussed in more detail below.

[0015] In a method according to an embodiment of the invention as shown in Figs. 2A and 2B the gauze 10 is placed in the corner clamps 3, 4 during a first phase. The gauze 10 is not clamped down at the lateral clamps 5 yet so as to make it possible to realise an optimum stretching of the sides 11, 12 by means of the corner clamps 3, 4. It is furthermore advantageous in this connection if the corner clamps 3, 4 clamp down as small a portion of the sides 11, 12 as possible for stretching as large a portion of the sides 11, 12 as possible. Preferably, the corner clamps 3, 4 clamp down a portion of the sides 11, 12 smaller than or equal to the width of the elements of the frame 10.

[0016] The stretching of the sides 11, 12 takes place during a second phase, schematically indicated by the inner ring of clamps 3, 4, 5 in Fig. 2B, by moving the corner clamps 3, 4 over a distance of e.g. 4 cm in the directions I and II, respectively. This causes the sides 11, 12 of the gauze 10 to be stretched.

[0017] During a third phase, schematically indicated by the outer ring of clamps 3, 4, 5, the sides 11, 12 of the gauze 10 are subsequently placed or clamped in the lateral clamps 5 at the sides 11, 12, and the inner area 13 of the gauze is tensioned by stretching the gauze by means of the corner clamps 3, 4 and the lateral clamps 5 (see the arrows). Consequently, the warp and weft threads of the gauze 10 are oriented substantially at right angles relative to each other over a larger area of the gauze end than is the case with the conventional stretching method as shown in Fig. 1.

[0018] The stretching of the gauze is preferably carried out in such a manner that a stretch percentage in the range of 2-10% of the original thread length, e.g. 8%, is obtained. The stretch percentage depends on factors such as the number of threads per unit length, the thickness of the threads and the kind of gauze. In the case of a gauze having threads of plastic material, the corner clamps 3, 4 are to that end moved in the direction I and II, respectively, during the second phase of the stretching process, in such a manner that the sides 11, 12 give 4% stretch at each respective corner clamp 3, 4. The corner clamps 3, 4 and the lateral clamps 5 are then used in such a manner during the third phase that the threads in the inner area, too, exhibit 8% stretch. The tension of the threads ranges between 10 and 40 Newton, e.g. 15, 20 or 25 Newton. This tension is substantially uniform over the entire inner area. This is advantageous, e.g. as regards the life of the gauze 10. The tension determines the number of threads per unit length. For a gauze 10 comprising threads of plastic material with a diameter of 31 µm, which counts 165 threads per cm in untensioned condition, a tension of 22 Newton will result in about 152 threads per cm in the tensioned condition of the gauze 10. According to the invention, tensioning can be carried out according to the stretch percentage to be obtained within a tolerance of three threads per cm.

[0019] The method according to the invention has a large number of advantages. The substantially right-angled orientation of the warp and weft threads of the gauze 10 renders the gauze suitable for screen printing without the Moiré effect described in the non-prepublished European patent application EP 05101383, which is considered to be incorporated in the present application by reference. The right-angled orientation of the warp and weft threads of the results in uniform mesh dimensions of the gauze 10 over substantially the entire inner area 13. Consequently, the ink volume per mesh is substantially uniform over the inner area 13, making it possible to realise a reduced ink consumption. Furthermore it is possible to set up a greater tension in the gauze, which has a positive effect as regards the resolution of the screen printed image.

[0020] A very advantageous embodiment concerns the possibility to compensate for deviations in the gauze 10. To that end it is possible to use a higher tension at the sides 11 than at the sides 12, which can be done by stretching said sides separately. Consequently, a gauze which has e.g. 167 warp threads per cm and 163 weft threads per cm in unstretched condition can have substantially the same number of warp and weft threads in stretched condition. A stretch percentage of 9.2% is selected for the warp threads, for example, whilst a stretch percentage of 7% is selected for the weft threads, so that the number of threads will be 152 in both directions in the stretched condition.

[0021] It will be apparent to those skilled in the art that different methods may be used for stretching the gauze 10 on the one hand and the sides 11, 12 thereof on the other hand. The moving of the corner clamps 3, 4 in the directions I and II, respectively, is only described by way of example. It is also possible, for example, to provide a stretching device 20 for the gauze 10, which stretching device 20 is provided with an element 21 that is flexible in a direction parallel to the sides 11, 12 of the gauze 10 as shown in Fig. 3. The flexible element 21 is a rubber strip, for example, with clamps (not shown) provided thereon. When such a stretching device 20 is used, the sides 11, 12 of the gauze 10 can be completely fixed to the elements 21 during the first and the second phase and be tensioned in the directions I, II. The elements can then move in the directions II and I, respectively, during the third phase for stretching the inner area 13 of the gauze 10.

Claims

1. A method for stretching a gauze (10) for use in screen printing, wherein the gauze comprises a first pair (11) and a second pair (12) of opposed sides, which define an inner area (13) of the gauze, wherein said first pair and said second pair of sides of the gauze are stretched before the inner area is stretched.

2. The method according to claim 1, comprising the steps of:

a) stretching the first pair of sides (11) of the gauze (10) in a first direction (I) substantially parallel to the sides of said first pair;

b) stretching the second pair of sides (12) of the gauze (10) in a second direction (II) substantially parallel to the sides of said second pair; and

c) stretching the inner area (13) of the gauze (10) following steps a) and b) from the sides of the first pair (11) and the second pair (12) in the second direction (II) and the first direction (I), respectively.

3. The method according to claim 1 or 2, wherein the gauze (10) comprises corner points, where a side of said first pair (11) and a side of said second pair (11) intersect, and wherein the stretching of the first pair of sides and the second pair of sides takes place from said corner points.

4. The method according to claim 3, wherein a stretching device (1) is used which comprises a first corner clamp (3) and a second corner clamp (3) at or near each of the corner points of the gauze (10) and one or more lateral clamps (5) disposed at the sides (11, 12) between the first corner clamps (3), for stretching the first pair of sides (11) and the second corner clamps (4), respectively, for stretching the second pair of sides (12), and wherein the first corner clamps (3) tension the gauze (10) in a first direction (I) and the second corner clamps (4) tension the gauze (10) in a second direction (II) for stretching the first pair of sides (11) and the second pair of sides (12), respectively, and wherein the corner clamps (3, 4) and the lateral clamps (5) are subsequently used for stretching the inner area (13) (13) of the gauze (10) (10).

5. A method according to one or more of the preceding claims, wherein the sides of the first pair (11) and the second pair (12) are stretched with different tension forces.

6. A stretching device (1;20) adapted for stretching a gauze (10) for use in screen printing, wherein the gauze comprises a first pair (11) and a second pair (12) of opposed sides, which sides define an inner area (13) of the gauze, which stretching device comprises stretching means (3, 4) for stretching the first pair and the second pair of sides of the gauze (10) before the inner area is tensioned.

7. The stretching device (1; 20) according to claim 6, comprising:

a) first stretching means (3;21) arranged for stretching the first pair of sides of the gauze (10) in a direction substantially parallel to the sides of the first pair;

b) second stretching means (4;21) arranged for stretching the second pair of sides of the goals in a second direction substantially parallel to the sides of the second pair; and

c) third stretching means (5;21) arranged for stretching the inner area (13) of the gauze (10) from the sides of the first pair and the second pair in the second direction and the first direction, respectively,

wherein the first, the second and/or the third stretching means are adapted for stretching the inner area of the gauze from the sides after the first pair and the second pair of sides have been tensioned by the first and the second stretching means.

8. The stretching device (1) according to claim 6 or 7, wherein the gauze (10) comprises corner points, where a side of said first pair and a side of said second pair intersect, comprising first and second stretching means for stretching the first pair of sides and the second pair of sides from the corner points.

9. The stretching device (1) according to claim 8, comprising a first corner clamp (3) and a second corner clamp (3) disposed for engaging at or near each of the corner points of the gauze (10) and one or more lateral clamps (5) disposed between the first corner clamps (3), for stretching the sides of the first pair (11), and the second corner clamps (4), respectively, for stretching the sides of the second pair (12), wherein the first corner clamps (3), in use, tension the gauze (10) in a first direction (I) and the second corner clamps (4), in use, tension the gauze (10) in a second direction (II), and wherein the first corner clamps (3) and the lateral clamps (5), which are disposed between the first corner clamps (3), and the second corner clamps (4) and the lateral clamps (5), which are disposed between the second corner clamps (4), are arranged for subsequently stretching the inner area (13) of the gauze (10) in the second direction (II) and the first direction (I), respectively.

10. The stretching device (1) according to any one or more of the claims 6-9, wherein the stretching device can be adjusted for stretching the sides of the first pair and the second pair with different tension forces.

Drawing