1. Field of the Invention
This invention pertains to manufacturing products from flexible materials, and more particularly to apparatus that seals articles between two continuously moving webs.
2. Description of the Prior Art
It is well known to encapsulate articles inside protective wrappers. Some articles lend themselves to being captured between two sheets of wrapping material that overlie opposite sides of the article. The sheets usually have margins that project beyond the article in all directions. The sheet margins are joined to each other, thus capturing the article between them. Depending on the materials of the articles and the sheets, the sheets may be joined to each other by adhesives, heat sealing, or other means. U.S. Pat. Nos. 4,369,613; 4,720,321; and 6,182,420 show articles captured between sheets that are joined to each other by adhesives.
U.S. Pat. No. 5,441,345 shows a heat sealed pouch for a flowable product. Other equipment for packaging non-rigid articles is described in U.S. Pat. Nos. 4,598,441; 5,628,165; and 6,185,908.
Again depending on the particular article and sheet materials, the sheets may be cut from continuously moving webs. In that case, the articles are inserted at spaced intervals between the webs, and the webs are joined to each other, on a more or less continuous basis. The webs are cut at proper locations to make the final products. U.S. Pat. No. 6,115,999 teaches press rolls for sealing the longitudinal margins of continuously moving webs.
To seal webs transversely to the downstream motion of the webs and articles, it is known to employ reciprocating mechanisms. In those designs, the webs and articles advance in the downstream direction to a sealing station, where they halt momentarily. A sealing mechanism, which may be hot irons, reciprocates in directions perpendicular to the downstream direction of the webs and articles to join the webs to each other along transverse lines. Then the composite web and articles resume downstream travel until the following article is at the sealing station. Examples of reciprocating equipment that heat seals webs to each other are disclosed in U.S. Pat. Nos. 4,299,075; 4,601,157; 4,864,802; 5,803,888; and 6,115,999. U.S. Pat. No. 5,875,614 discloses a machine that uses reciprocable ultrasonic welding to join two webs to each other. The packaging machine of U.S. Pat. No. 5,044,145 uses hot air to heat the webs for joining them together. Using intermittently moving webs and reciprocating mechanisms to transversely seal webs produces undesirable vibrations. In addition, that type of sealing equipment has the disadvantages of undesirable complexity and reduced production.
To overcome the deficiencies of intermittently moving webs and reciprocating mechanisms for producing transverse seals on the webs, continuously operating rotary heat sealing equipment has been developed. In such equipment, a heating element is part of a roller that contacts a continuously moving web. The heated roller rotates and contacts the web in proper timing to the web downstream motion to produce the transverse seals. U.S. Pat. Nos. 4,244,158; 5,357,731; and 6,122,898 are representative of continuously rotating heat sealing mechanisms. U.S. Pat. No. 6,030,329 shows a rotary machine that uses ultrasonics for transversely sealing webs to each other.
Despite the availability of prior equipment for sealing webs to each other in directions transverse to the direction of web movement, a need exists for further improvements.
In accordance with the present invention, a rotary heat sealing system is provided that seals two webs to each other around articles on a continuous basis. This is accomplished by apparatus that includes a heating die having circumferential rails and a heat sealing grid that forms a nip with an anvil.
The heating die and anvil are part of a sealing station of the heat sealing system. They are geared together and rotate continuously in opposite directions. The anvil is cylindrical in shape, having a uniform diameter along its nip with the heating die heat sealing grid. The anvil is rotatably mounted on a fixed axis of rotation in side plates of a machine that completely processes the articles and webs into finished products.
The heating die is generally cylindrical in shape, having opposed axially spaced journals. The rails are close to the journals, and the heat sealing grid is between the rails. The heat sealing grid is made to suit the particular article that is sealed between the webs. In all cases, the heat sealing grid has at least two axially spaced circumferential lands and at least one transverse land connecting the circumferential lands. The lands are arranged to define pockets having a depth that suits the particular article. In a particular embodiment of the invention, there are four circumferential lands and four transverse lands that make a pattern of 12 rectangular pockets. All the circumferential and transverse lands have the same diameter relative to the axial centerline of the heating die. The diameter of the circumferential and transverse lands is slightly less than the diameter of the rails.
The heating die has a long hole along its axial centerline. A heating element is inserted into the heating die hole. The heating element has a rotary connector outside of the heating die. Applying electrical power to the heating element causes the heating die to heat.
The heating die journals are received in respective die blocks. The die blocks are slidable within the machine side plates in directions toward and away from the anvil such that the center distance between the heating die and the anvil is variable.
A force mechanism is also part of the rotary heat sealing system. The force mechanism applies a force that keeps the heating die rails in contact with the anvil. For that purpose, the force mechanism is comprised of a bearing block in each side plate of the machine. A bearing bar extends between the bearing blocks. On the bearing bar are two bearings that contact the respective heating die rails. A pressure plate is fastened to each machine side plate. A long screw is threaded through each pressure plate and bears against a corresponding bearing block. By tightening the screws, the heating die rails are kept in firm contact with the anvil by means of the force that is transmitted from the screws through the bearing blocks, bearing bar, and bearings to the heating die rails. Removing the pressure plates and bearing blocks from the machine side plates enables different heating dies to be used for making different products.
When the heating die rails are in contact with the anvil, there is a fixed clearance between the heating die heat sealing grid and the anvil. The heat sealing grid and anvil cooperate to form the nip, which has a clearance through which the webs pass. The clearance at the nip is usually equal to about the combined thicknesses of the webs. The nip defines a nip plane that is tangent to the anvil and the heating die heat sealing grid.
The articles are inserted between the webs at an insert station in the upstream direction of the rotary heat sealing system. The articles are aligned and spaced between the webs in a pattern that matches the pattern of the pockets in the heating die. The articles are held in place between the webs only by friction. The articles enter the heating die pockets as the webs and articles pass through the sealing station. As the webs and articles pass through the sealing station, the webs are sealed to each other at areas corresponding to the heat sealing grid of the heating die. The web areas at the locations of the heating die pockets remain unsealed. The result is that the articles are permanently captured in individual spaces surrounded by sealed margins of the two webs. From the rotary heat sealing system, the composite webs and articles are propelled in the downstream direction for further processing into finished products.
Further in accordance with the present invention, the rotary heat sealing system comprises a tensioning station upstream of the sealing station. The tensioning station produces a tension in the webs and articles so as to hold the articles firmly in place as they enter the sealing station. The tension is produced by wrapping the articles and webs in a reverse bend. A first bend occurs at a guide rod, which may be at the downstream end of the machine insert station. The second bend occurs at a wrap roller between the guide rod and the sealing station. The diameters of the guide rod and wrap roller are preferably different, which contributes to producing proper tension in the webs and articles. The guide rod and wrap roller are so spaced in the direction of downstream motion as to enable a person to see the alignments and spacings of the articles as they enter the sealing station. At least the guide rod is adjustable in two directions to suit different articles and webs, and also to correct any misalignment of the articles as they enter the sealing station. In a preferred embodiment, the guide rod and wrap roller have respective lowermost lines that lie in the nip plane. The webs and articles pass over the guide rod opposite its lowermost line, and then pass under the wrap roller in contact with its lowermost line.
The method and apparatus of the invention, using a heating die with a heat sealing grid in combination with a uniformly cylindrical anvil, thus seals two webs around flexible articles on a continuous basis. The probability of misaligning the articles relative to the heating die heat sealing grid is remote, even though the articles are held only by friction between the webs as the webs and articles enter the sealing station.
Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention.