WO1990014950A1

WO1990014950A1 - Method and apparatus of applying hot melt adhesive to paper products

Info

Publication number: WO1990014950A1
Application number: PCT/US1990/003191
Authority: WO
Inventors: Tadashi Taketani; Masaaki Toda
Original assignee: Nordson Corporation
Priority date: 1989-06-09
Filing date: 1990-06-06
Publication date: 1990-12-13
Also published as: AU5928490A; JPH0312267A

Abstract

A method and apparatus for applying a pattern of hot melt adhesive onto a moving paper substrate (0) comprises an applicator (9) which delivers molten hot melt adhesive to a pan (13) within which an intaglio roll (1) having a peripheral mesh pattern is partially submerged. The intaglio roll (1) transmits adhesive from the pan (3) onto the facing surface of the substrate such that a pattern of substantially uniformly spaced, circular-shaped spots or dots of adhesive are applied onto the substrate. The substrate is then transferred past a heater (5) which increases the temperature of the adhesive dots to lower their viscosity. The substrate then travels between a pair of rollers (7, 8) where a second substrate such as a release paper (R) is combined therewith. In the course of passage, the adhesive pattern forms an essentially continuous layer between the substrates.

Description

METHOD AND APPARATUS OF APPLYING HOT MELT ADHESIVE TO PAPER PRODUCTS

Field of the Invention

This invention relates to the application of adhesive, and, more particularly, to a method and apparatus for applying a pattern of hot melt adhesive onto a surface of a paper product such as adhesive tape.

Background of the Invention

A wide variety . of adhesively backed paper products are currently being manufactured such as adhesive tape, labels adhered to pattern release paper, office label paper, delivery slips, wall material fixing adhesive paper and many other prod¬ ucts. Historically, the adhesive backing for these types of paper products has either been a solution- type adhesive such as water-soluble or solvent-type solution adhesives, or hot melt thermoplastic adhe- sives. In many applications, these adhesives are applied by spreading them uniformly across the entire length and width of the paper substrate, such as by a roller, to produce an essentially continuous layer of adhesive on the substrate. Problems have been encoun¬ tered both with the types of adhesives employed, and with the methods of application of such adhesives to paper substrates. With respect to the two types of adhesives commonly used in adhesive paper products, the solu¬ tion-type adhesives present the most problems. While the viscosity of solution adhesives can be easily adjusted to facilitate their application, the water or solvent portion of such adhesives is allowed to evaporate after application which wastes a great deal of material. Such water or solvent must be dried after application which adds cost to the production line. Solution adhesives containing organic solvents can create environmental problems as the solvents evaporate to atmosphere. Additionally, solution adhesives are difficult to handle in production, i.e., control of the degree of dilution and adjustment of the concentration is difficult; the humidity in the application area must be controlled to prevent the coating material from curling, especially for water- soluble adhesives; and, it is difficult to maintain the appropriate application temperature for solution adhesives whose viscosity changes with the seasons. Hot melt thermoplastic adhesives solve many of these problems, but the viscosity of hot melt adhesives is not freely adjusted because such adhesives must be heated within a certain range to become flowable without creating charring or other heat damage.

With respect to the method of applying solution adhesives or hot melt thermoplastic adhesives to paper products, the method of applying a continuous coating of adhesive across the entire width and length of paper substrates has steadily given way to methods and apparatus in which a pattern of adhesive is applied to the paper. "Pattern coating" is a method of applying an adhesive onto a substrate in a prede¬ termined pattern, such as those shown in Figs. 10A, 10B and IOC, wherein the adhesive is deposited in discrete locations on a paper product. The "mountain pattern" illustrated in Fig. 10B, for example, is applied to the flaps of envelopes and similar applica¬ tions.

Experiments have been conducted employing conventional methods and apparatus for applying a pattern coating of adhesive onto paper substrates using both solution-type and hot melt thermoplastic adhesives. With reference to Figs. 5-7, a vinyl acetate, emulsion-based solution-type adhesive is directed into a tank 13 within which a dipping roll 11 is partially submerged. The dipping roll 11 is rotatable to transfer adhesive from the tank 13 onto a relief roll 12 which is spaced from a press drum roll 14. A substrate is transferred between the relief roll 12 and press drum roll 14 to receive a pattern of adhesive illustrated schematically in Figs. 5 and 6. This relief pattern of adhesive is in the form of rec¬ tangles having a width of about 56 millimeters and a length of about 182.4 millimeters. A pattern release paper R is then adhered to the layer of adhesive on the substrate 0 c₌L in the course of passage of the release paper R cL and substrate 0 S₌i between a pair of press rolls 16 and 17. Under these experimental conditions, it was found that the outline of the applied pattern of adhesive on the substrate 0a is irregular, producing a coating thickness which is non-uniform. See Fig. 7. In particular, the coating was found to be too thick, especially at the edges of the pattern, and the thickness varies in proportion to the speed of appli¬ cation of the adhesive onto the substrate 0a. Addi- tionally, it is difficult to properly adjust the gap between the dipping roll 11 and relief roll 12 so as to obtain a coating of adhesive on the substrate Oa which is stable and uniform in thickness. This results in an uneven density or quantity of adhesive between the pattern release paper R and substrate 0 in many areas therealong after they are brought into contact with one another between the press rolls 16 and 17. The same experimental conditions set forth above and illustrated in Figs. 5-7 were also attempted with a thermoplastic hot adhesive in which a hot melt applicator 19 introduces a quantity of hot melt adhesive into a thermally insulated tank 13a, both of which are illustrated in phantom in Fig. 5. The dipping roll 11 is partially submerged within this insulated tank 13a and transfers the hot melt adhesive to the relief roll 12 in the same manner described above. While the experiments conducted with such apparatus using hot melt adhesive produced results superior to those with solution-type adhesive, many of the problems mentioned above are still present and the degree of improvement over solution-type adhesives is only slightly better.

Another type of method and apparatus for applying a pattern coating of adhesive onto paper substrates involves the use of intaglio roll transfer equipment which is similar to that illustrated in Fig. 5 except the relief roll 12 is replaced with an intaglio roll 22 of the type shown in Fig. 8. An intaglio roll includes peripheral recesses 24 which receive adhesive from pan 13, and a scraper 23 is employed to scrape excess material away from the recesses 24. When the paper substrate O comes into contact with the intaglio roll 22, the adhesive is drawn ^• out of the recesses 24 and attaches to the substrate O .

Experiments have been conducted with intag¬ lio rolls incorporated in apparatus of the type illustrated in Fig. 5, wherein both solution-type and hot melt thermoplastic adhesives are used to obtain a pattern of adhesive on a paper substrate. While these experiments have demonstrated that intaglio rolls produce a generally improved result compared to relief rolls 12 of the type described above, problems never¬ theless remain particularly with solution-type adhe¬ sives. It has been found that with solution-type adhesives, intaglio rolls apply a pattern which is irregular and uneven upon the substrate, resulting in an uneven adhesive layer between the paper substrate and pattern release paper. Improved results are obtained with intaglio rolls of the type shown in Fig. 8 employing hot melt adhesive, wherein a relatively even and uniform coating can be obtained on the paper substrate, but there is still a need for improvement to produce an adhesive pattern on the paper substrate having the precise thickness, uniformity and density desired. Summary of the Invention It is therefore among the objectives of this invention to provide a method and apparatus for the application of an adhesive pattern onto a work material such as a paper substrate which is uniform in thickness and which is uniform in density when the paper substrate is adhered to a second substrate such as pattern release paper. These objectives are accomplished in a method and apparatus for applying a pattern of hot melt adhesive onto a moving paper substrate comprising an adhesive applicator which delivers molten hot melt thermoplastic adhesive to a pan within which an intaglio roll having a peripheral mesh pattern is partially submerged. The intaglio roll is operative to transmit adhesive from the pan onto the facing surface of a paper substrate such that a pattern of substantially uniformly spaced, circular-shaped spots or dots of adhesive are applied onto the substrate. The substrate is then transferred past a heater, such as a hot air heater, which increases the temperature of the adhesive dots to lower their viscosity forming at least partially flattened adhesive plates on the substrate. The substrate then travels between a pair of press rollers where a second substrate such as pattern release paper is combined with the paper substrate. In the course of passage between the press rollers, the adhesive plates are compressed to form an essentially continuous coating of adhesive between the paper substrate and pattern release paper which has a substantially uniform thickness. This invention is therefore predicated upon the concept of first applying a pattern of discrete, regularly spaced circular-shaped dots or spots of adhesive onto the paper substrate, and, prior to combination with a second substrate such as pattern release paper, heating the dots while on the paper substrate with a heater such as an air blower. The air blower is effective to lower the viscosity of the adhesive dots to form larger and more closely spaced adhesive plates prior to combination of the paper substrate with the pattern release paper. With the adhesive plates suitably heated by the air heater, the paper substrate is then transferred between press rollers where the pattern release paper is combined therewith such that the adhesive plates are compressed to form an essentially continuous, even adhesive coating of uniform thickness between the two sub¬ strates. Description of the Drawings The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a schematic illustration of the apparatus of this invention; Fig. 2A is an enlargement of the section "A" shown in Fig. 1;

Fig. 2B is a view in the direction "D" of Fig. 2A; Fig. 3A is an enlargement of the section "B" in Fig. 1;

Fig. 3B is a view in the direction "E" of Fig. 3A;

Fig. 4A is an enlargement of the section "C" in Fig. 1;

Fig. 4B is a view in the direction "F" of Fig. 4A;

Fig. 5 is a schematic view of a conven¬ tional, prior art relief roll coating apparatus; Fig. 6 is an enlarged, elevational view of a portion of the relief roll of Fig. 5;

Fig. 7 is a schematic view of the adhesive layer applied on a substrate by the relief roll of Figs. 5 and 6; Fig. 8 is an elevational view of a portion of a prior art intaglio roll;

Fig. 9 is a schematic view of the pattern of adhesive applied to a substrate by the intaglio roll of Fig. 8; and Figs. 10A, 10B and IOC are examples of various adhesive patterns obtained with prior art adhesive application apparatus. Detailed Description of the Invention

Referring now to Figs. 1-4B, an apparatus is illustrated for applying a pattern of hot melt adhe¬ sive onto one surface of a moving work material 0 such as a paper substrate. The apparatus comprises a hot melt adhesive applicator 9 of any conventional type which discharges molten hot melt thermoplastic adhe¬ sive into the bottom of a pan 3. An intaglio roll 1 having a mesh pattern on its circumference is at least partially submerged within the pan 3 and rotatable therein in the direction of the arrow shown in Fig. 1. The intaglio roll 1 is effective to pick up adhesive HM within the mesh pattern along its circumference in the course of movement through the pan 3, and carry this adhesive HM to the work material 0 as it passes over a roller 4. Preferably, a scraper 2 is located upstream from the work material 0 and roller 4 in a position relative to the intaglio roll 1 to scrape excess adhesive HM from the mesh pattern surface of the intaglio roll 1.

As viewed in Figs. 1-2B, the intaglio roll 1 contacts the surface of work material 0 and transfers a pattern of circular-shaped spots or dots HM onto such surface. As shown in Figs. 2A and 2B, these adhesive spots or dots are substantially the same diameter, extend outwardly from the work material 0 to the same height and are regularly spaced from one another on the work material 0. For each rotation of the intaglio roll 1, a pattern of adhesive dots HM is applied onto the work material 0 which is equal in length to the circumference of the intaglio roll 1, and in width to the length of the intaglio roll 1. The "length" of such roll 1 is the dimension of the roll 1 measured perpendicular to the plane of the sheet of Fig. 1.

In the presently preferred embodiment, a heater 5, such as a fan-operated hot air heater, is located downstream from the intaglio roll 1 in a position facing the work material 0. The heater 5 is effective to blow hot air onto the adhesive dots HM carried by the work material 0 which heats the dots HM and lowers their viscosity. Preferably, the temperature of the heated air is greater than the temperature of the hot melt adhesive within the pan 3. As shown in Figs. 3A and 3B, heating of the dots HM by the blower 5 produces adhesive plates HM_ which are at least partially flattened or leveled relative to the work material 0. The adhesive plates HM do not project to the same height from the work material 0 as dots HM., the plates HM_? have a larger diameter than dots HM and the plates HM_ are closer together than dots HM.. See Figs. 2B and 3B.

The work material 0 with partially flattened adhesive plates HM_ is then transmitted from the heater 5 to the nip formed between a pair of press rolls 7 and 8. Pattern release paper R is introduced within the nip between press rolls 7 and 8 for com¬ bination with the work material 0. The press rolls 7 and 8 are effective to press the work material 0 and pattern release paper R together, as shown in Fig. 4A, such that the adhesive plates HM, are compressed to produce an essentially continuous coating of adhesive HM_ between the work material 0 and pattern release paper R. See Fig. 4B. EXAMPLE

The apparatus illustrated in Fig. 1 is operative to provide the desired adhesive coating between the work material 0 and pattern release paper R with the construction and operating conditions given below.

Intaglio Roll (1)

Roll Type: mesh pattern etching intaglio

Dot Size of Intaglio Mesh: 0.5 mm diameter

0.13 mm depth

0.6 mm dot internal

Intaglio Adhesive Pattern Size: 182.4 mm length

56 mm width

2 mm pattern interval

Adhesive (HM)

Adhesive Type: JHL-103-85C

Nippon Fuller Co., Ltd.

Melt Viscosity: 22,000 cps at 160°C Softening Point: 109°C Adhesive Volume in Pan (3) : 70 cc

Adhesive Temperature in Pan (3) : 185°C

Size of Adhesive Dots HM. : 0.4 mm diameter 60 microns height

Paper (O) , (R)

Web Thickness of Work Material (0) : 80 g/m

Web Thickness of Pattern-Release Paper (R) : 80 g/m

Feed Speed of Work Material (0) and Pattern- Release Paper (R) : 50 m/min.

Blower (5)

Air Flow Rate: 500 L/min.

Air Speed: 9.3 m/sec.

Air Temperature: 200^βC

Press Rolls (7,8)

Press Roll Force: 10 Kg/cm²

Press Roll Temperature: 80°C

Thickness of Adhesive Coating (HM,)

At Center of Roll: 22 microns

At Sides of Roll: 23 microns

In the presently preferred embodiment, the equipment in the example set forth above is operated so that the adhesive discharged from hot melt adhesive applicator 9 maintains a relatively small volume of adhesive HM within the pan 3. It has been found that such supply should be in the range of about one to three minutes of production, depending upon the coating speed, to prevent changes in the physical properties of the adhesive. Under the conditions and with the structural elements listed above, an adhesive coating is obtained between the work material 0 and pattern release paper R having a uniform thickness in the range of about 10 to 30 microns. While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inven¬ tion without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

I claim:

Claims

1. A method of applying a coating of adhesive, comprising: applying a pattern of spaced adhesive dots onto a surface of a moving first substrate; heating the adhesive dots on the first substrate; pressing a second moving substrate against the surface of the first moving substrate to form an essentially continuous, uniform adhesive coating therebetween and to adhere the first and second substrates together.

2. The method of claim 1 in which said step of applying a pattern of spaced adhesive dots comprises moving a mesh pattern intaglio roll through an adhe¬ sive container to pick up adhesive, and then contact- ing the moving first substrate with the intaglio roll to apply said pattern of spaced adhesive dots thereto.

3. The method of claim 1 in which said step of applying a pattern of adhesive dots comprises applying a pattern of hot melt thermoplastic adhesive dots.

4. The method of claim 1 in which said step of heating the adhesive dots comprises blowing heated air onto the adhesive dots on the surface of the moving first substrate.

5. The method of claim 4 in which said step of blowing heated air comprises blowing heated air having a temperature greater than the temperature of the adhesive dots on the surface of the first substrate.

6. A method of applying a coating of adhesive, comprising: applying a pattern of adhesive dots onto a surface of a moving first substrate, said adhesive dots each having a diameter, a height relative to the moving first substrate and being spaced from one another; heating the adhesive dots on the moving first substrate to form adhesive plates thereon having a larger diameter than said adhesive dots, a lesser height than said adhesive dots and which are spaced closer together than said adhesive dots; compressing the adhesive plates between a second moving substrate and the first moving substrate to form an essentially continuous, uniform adhesive coating therebetween and to adhere the first and second substrates together.

7. The method of claim 6 in which said step of heating the adhesive dots comprises blowing heated air onto the adhesive dots to lower their viscosity to form the adhesive plates.

8. The method of claim 6 in which said step of applying a pattern of adhesive dots comprises applying a pattern of hot melt thermoplastic adhesive dots.

9. A method of applying a coating of adhesive, comprising: moving a mesh pattern intaglio roll through an adhesive container to pick up adhesive; contacting a moving first substrate with the intaglio roll to apply a pattern of spaced adhesive dots on the first substrate; blowing heated air onto the adhesive dots on the first substrate to form adhesive plates thereon; compressing the adhesive plates between a second moving substrate and the first moving substrate to form an essentially continuous, uniform adhesive coating between the first and second substrates and to adhere the first and second substrates together.

10. Apparatus for applying a coating of adhe¬ sive, comprising: means for applying a pattern of spaced adhesive dots onto a surface of a moving first sub- strate; means for heating the adhesive dots on the first substrate; means for pressing a second moving substrate against said surface of the first moving substrate to form an essentially continuous, uniform adhesive coating therebetween and to adhere the first and second substrates together.

11. Apparatus for applying a coating of adhe¬ sive, comprising: means for applying a pattern of adhesive dots onto a surface of a moving first substrate, said adhesive dots each having a diameter, a height rela¬ tive to the moving first substrate and being spaced from one another; means for heating the adhesive dots on the moving first substrate to form adhesive plates thereon having a larger diameter than said adhesive dots, a lesser height than said adhesive dots and which are spaced closer together than said adhesive dots; means for compressing the adhesive plates between a second moving substrate and the first moving substrate to form an essentially continuous, uniform adhesive coating between the first and second sub¬ strates and to adhere the first and second substrates together.

12. The method of claim 11 in which said means for heating the adhesive dots comprises a hot air blower which directs heated air onto the adhesive dots to lower their viscosity to form the adhesive plates.

13. Apparatus for applying a coating of hot melt adhesive, comprising: container means for receiving molten hot melt adhesive; a mesh pattern intaglio roll movable within said container means, said intaglio roll being effec¬ tive to pick up adhesive from said container means and to apply the adhesive in a pattern of spaced adhesive dots onto a surface of a moving, first substrate; heating means located downstream from said intaglio roll for heating the adhesive dots on the moving substrate to form adhesive plates; means for pressing the surface of the first substrate against a second substrate so that the adhesive plates are compressed to form an essentially continuous, uniform adhesive coating between the first and second substrates and to adhere the first and second substrates together.

14. The apparatus of claim 13 in which said heating means is a hot air blower which directs heated air onto the adhesive dots on the first substrate to lower their viscosity and to at least partially flatten the adhesive dots to form said adhesive plates.