1. Field of the Invention
This invention pertains to handling sheets of paper, and more particularly to apparatus and methods for sealing a folded sheet of paper to itself.
2. Description of the Prior Art
Numerous types of business forms have been developed over the years. Many kinds of business forms are used as mailers. An example of a multi-page mailer type business form may be seen in U.S. Pat. No. 5,167,739.
Business forms are usually constructed as sheets of paper having patterns of pressure sensitive adhesive applied to one surface. The sheets are folded in a desired manner by a folding machine such that certain portions of the sheet come into facing contact with the adhesive. The folded sheets are then pressed together, which causes them to adhere to each other along the patterns of adhesive.
Prior equipment for pressing folded sheets together include the reversing machines of U.S. Pat. Nos. 5,133,828; 5,290,385; and 5,300,177. In those machines, a force biases one or more rollers into contact with mating rollers. A folded sheet is fed in a first direction into a roller nip until the sheet has almost completely passed through the nip. Then the rollers are reversed to drive the sheet through the nip again in the opposite direction. The biasing force is strong enough to activate the adhesive and thus create a finished business form.
A primary disadvantage of the machines of the foregoing patents is the noise produced by the contacting rollers when no folded sheets are in the nips. Another disadvantage is that the finished forms leave the machines at the same locations that they entered the machines. Consequently, second folded sheets cannot be fed to the nips until the previous forms have been discharged and removed from the nips.
U.S. Pat. No. 5,169,489 shows a pressure sealer system having four nips, two at one level and two at a higher level. The rollers of each nip are pressed together by spring biasing devices. Folded sheets are fed in a first direction between the two lower nips. Thereafter, the folded sheets pass to a higher elevation and reverse direction to pass through the two higher nips. Because of the four nip and reversing construction, the machine of the U.S. Pat. No. 5,169,489 patent is quite complicated as well as undesirably noisy. In addition, the reversing direction of the folded sheets complicates both the feeding of the folded sheets into the machine and the removal of the completed business forms from the machine.
U.S. Pat. No. 5,183,527 describes a seal module in which one roller of a nip is spring biased to be non-parallel to another roller when no form is present. When a form is a-fed to the nip, the form forces the rollers against the force of the spring into a parallel relationship. The forms travel in one direction in the downstream direction through the seal module. There is no adjustment for the linear distance between the rollers, thus limiting the versatility of the seal module. In addition, initial setup of the seal module can be rather tricky.
U.S. Pat. No. 5,397,427 discloses a pressure seal system in which two rollers of a nip are pressed into contact with each other by a biasing force. Forms passing through the nip are acted on by the biasing force but spread the rollers apart as they pass through the nip. The forms pass in one direction through the pressure sealer. The amount of noise as well as the wear on the rollers are important disadvantages of the seal system of the U.S. Pat. No. 5,397,427 patent.
Thus, a need exists for improvements in machines that seal folded business forms.