Provided is a radio communication device which can surely prevent inter-code interference while maintaining the use efficiency of an upstream line control channel and suppress separation characteristic of a response signal. The device includes: a control unit (209) which controls a cyclic shift amount of a ZC sequence used for a primary diffusion in a diffusion unit (214) and a Walsh sequence used for secondary diffusion in a diffusion unit (217) according to a PUCCH number inputted from a judgment unit (208); the diffusion unit (214) which performs primary diffusion of the response signal by the ZC sequence set by the control unit (209); and the diffusion unit (217) which performs secondary diffusion of the response signal by the Walsh sequence set by the control unit (209). The diffusion unit (214) performs primary diffusion of the response signal by using the ZC sequence having such a cyclic shift amount that the guard interval at the both ends of the detection window section is maximum in the ZC sequences having different cyclic shift amounts.

In mobile communication, ARQ (Automatic Repeat Request) is applied to downlink data from a radio communication base station apparatus (hereinafter abbreviated to "base station") to radio communication mobile station apparatuses (hereinafter abbreviated to "mobile stations"). That is, mobile stations feed back response signals representing error detection results of downlink data, to the base station. Mobile stations perform a CRC (Cyclic Redundancy Check) of downlink data, and, if CRC=OK (no error), feed back an ACK (ACKnowledgement), or, if CRC=NG (error present), feed back a NACK (Negative ACKnowledgement), as a response signal to the base station. These response signals are transmitted to the base station using uplink control channels such as a PUCCH (Physical Uplink Control CHannel) and uplink L1/L2 CCH (L1/L2 Control CHannel).
Also, as shown in FIG. 1, studies are underway to perform code-multiplexing by spreading a plurality of response signals from a plurality of mobile stations using ZC (Zadoff-Chu) sequences and Walsh sequences (see Non-Patent Document 1). In FIG. 1, (W0, W1, W2, W3) represents a Walsh sequence having a sequence length of 4. As shown in FIG. 1, first, an ACK or NACK response signal from a mobile station is subject to first spreading in one symbol by a ZC sequence (having a sequence length of 12) on the frequency domain. Next, the response signal subjected to first spreading is subject to an IFFT (Inverse Fast Fourier Transform) in association with W0 to W3. The response signal spread on the frequency domain by a ZC sequence having a sequence length of 12 is transformed to a ZC sequence having a sequence length of 12 on the time domain by this IFFT. Then, the signal subjected to the IFFT is subject to second spreading using a Walsh sequence (having a sequence length of 4). That is, one response signal is allocated to four symbols S0 to S3 individually. Similarly, response signals of other mobile stations are spread using ZC sequences and Walsh sequences. Here, different mobile stations use ZC sequences of different cyclic shift values on the time domain, or different Walsh sequences. In this case, the sequence length of ZC sequence on the time domain is 12, so that it is possible to use twelve ZC sequences of the cyclic shift values "0" to "11," generated from the same ZC sequence. Also, the sequence length of Walsh sequence is 4, so that it is possible to use four different Walsh sequences. Therefore, in an ideal communication environment, it is possible to code-multiplex maximum 48 (12×4) response signals from mobile stations.
Here, there is no cross-correlation between ZC sequences of different cyclic shift values generated from the same ZC sequence. Therefore, in an ideal communication environment, a plurality of response signals subjected to spreading and code-multiplexing by ZC sequences of different cyclic shift values (0 to 11), can be demultiplexed on the time domain without inter-code interference, by correlation processing in the base station.
However, due to the influence of, for example, transmission timing difference in mobile stations, multipath delayed waves and frequency offsets, a plurality of response signals from a plurality of mobile stations do not always arrive at a base station at the same time. For example, if the transmission timing of a response signal spread by a ZC sequence of the cyclic shift value "0" is delayed from the correct transmission timing, the correlation peak of the ZC sequence of the cyclic shift value "0" may appear in the detection window for the ZC sequence of the cyclic shift value "1." Further, if a response signal spread by the ZC sequence of the cyclic shift value "0" has a delay wave, interference leakage due to the delayed wave may appear in the detection window for the ZC sequence of the cyclic shift value "1." That is, in these cases, the ZC sequence of the cyclic shift value "1" is interfered by the ZC sequence of the cyclic shift value "0." Therefore, in these cases, the separation performance degrades in a response signal spread by the ZC sequence of the cyclic shift value "0" and a response signal spread by the ZC sequence of the cyclic shift value "1." That is, if ZC sequences of adjacent cyclic shift values are used, the separation performance of response signals may degrade.
Therefore, up till now, if a plurality of response signals are code-multiplexed by spreading of ZC sequences, a cyclic shift interval is provided between the ZC sequences, in order to suppress inter-code interference between the ZC sequences. For example, when the cyclic shift interval between ZC sequences is 2, studies are underway to use only six ZC sequences of the cyclic shift values "0," "2" "4" "6," "8" and "10" in first spreading of response signals, amongst twelve ZC sequences of the cyclic shift values "0" to "11." Therefore, if Walsh sequences having a sequence length of 4 are used in second spreading of response signals, it is possible to code-multiplex maximum 24 (6×4) response signals from mobile stations.
Also, the base station transmits control information for reporting resource allocation results of downlink data, to the mobile stations. This control information is transmitted to the mobile stations using downlink control channels such as PDCCH (Physical Downlink Control CHannel), downlink L1/L2 CCH (L1/L2 Control CHannel) and DL grant (DownLink grant) provided on a per mobile station basis. Each PDCCH occupies one or a plurality of CCE's (Control Channel Elements). If one PDCCH occupies a plurality of CCE's, the plurality of CCE's occupied by the PDCCH are consecutive. Based on the number of CCE's required to notify control information, the base station allocates an arbitrary PDCCH among the plurality of PDCCH's to each mobile station, maps control information on the physical resources associated with the CCE's occupied by the allocated PDCCH's, and performs transmission.
Also, to use downlink communication resources efficiently without signaling to report PUCCH's used for transmitting response signals from the base station to the mobile stations, studies are underway to associate CCE's with PUCCH's on a one-to-one basis. According to this association, each mobile station can decide the PUCCH to use to transmit a response signal from that mobile station, from the CCE's associated with the physical resources on which control information for that mobile station is mapped. That is, each mobile station maps a response signal from that mobile station on physical resources, based on the CCE's associated with physical resources on which control information for that mobile station is mapped.
Here, the number of CCE's occupied by PDCCH varies according to the MCS (Modulation and Coding Scheme) of the PDCCH. If a mobile station is located far from a base station and has lower received signal quality, the base station reduces the modulation level or coding rate of PDCCH while increasing the number of CCE's. By contrast, if the mobile station is located near the base station and has higher received signal quality, the base station increases the modulation level or coding rate of PDCCH while decreasing the number of CCE's. That is, a PDCCH of a lower MCS level occupies a larger number of CCE's, and a PDCCH of a higher MCS level occupies a smaller number of CCE's. In other words, a mobile station to which a PDCCH of a low MCS level is allocated provides a large number of CCE's, and a mobile station to which a PDCCH of a high MCS level is allocated provides a small number of CCE's. For example, when the coding rate of a PDCCH is one of ⅔, ⅓ and ⅙, and a PDCCH of the coding rate ⅔ occupies one CCE, an PDCCH of the coding rate ⅓ occupies two CCE's, and a PDCCH of the coding rate ⅙ occupies four CCE's.
Also, as described above, studies are underway to allow a single mobile station to transmit a response signal using only the PUCCH associated with the CCE of the minimum number among a plurality of CCE's in the case of allocating these CCE's to the mobile station (see Non-Patent Document 2).    Non-Patent Document 1: Multiplexing capability of CQIs and ACK/NACKs form different UEs (ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1—49/Docs/R1-072315.zip)    Non-Patent Document 2: R1-072348, LG Electronics, "Allocation of UL ACK/NACK index", 3GPP TSG-RAN WG1 Meeting #49, Kobe, Japan, May 7-11, 2007

Radio communication device and response signal diffusion method


A multicasting conferencing system is described wherein permanently or temporarily assigned addressing may be used. When permanently assigned multicast addressing is used, several channel parameters are assigned to a multicast session, and any terminals desiring to “tune in” to the multicast session simply invoke those parameters from a storage location at which they have been previously stored.

Videoconferencing and streaming media systems for use over data networks are known in the art. A variety of techniques for implementing such a conference have been published and in use for at least a decade.
One "brute force" manner in which a videoconference may be implemented over a data network involves the broadcasting of packets in multiple copies to all other conferees. Specifically, each member of a videoconference that converts the information into the packets, may duplicate the packets and transmit them over to the data network, with each copy of the packet containing a separate one of the other conferee's addresses. In this manner, each packet produced is transmitted plural times, to different addresses.
An inefficiency with the foregoing is that much of the network bandwidth is wasted. The foregoing method does not take advantage of the fact that a single version of the packet could be sent partially through the network, where it may be split and sent to plural recipients. Additionally, processing power in each transmitting terminal is wasted, since each terminal must duplicate the same packet plural times.
A proposed solution to the foregoing system was developed during the 1990s by an Internet standards group and is termed "Multicast." In multicast technology, a single copy of the packet traverses the data network until the last possible point where it may be replicated and still reach plural recipients. The packet is then replicated at that point. An example, with respect to FIG. 1, will help clarify. Consider a multicast packet originating at node 106 which is destined for both node 102 and 101. Multicast technology might employ a routing algorithm that routes the packet from 106 to 110, and from 110 to 108. However, the routing algorithm at node 108 would recognize the packet as a multicast packet, duplicate it, and transmit copies to each of nodes 101 and 102. Thus, while the packet must be replicated, it is transported as one packet for as long as possible until being copied to produce two or more packets.
It will be recognized by those of skill in the art that the above technique requires a specialized set of addresses to perform multicast conferencing. More specifically, it can be appreciated that the network 100 needs to be capable of routing packets in a conventional fashion from one node to the next when multicast packets are not at issue. Thus, with respect to conventional packet switching, each of the nodes in network 100 must be capable of examining a packet, performing a table lookup to determine the next node to which such packet should be routed, and sending the packet. With respect to multicast technology, each node must be capable of recognizing the address as a multicast address and duplicating the packet in a manner such that copies of the packet get routed to the next node on their way to various conference participants.
Further complicating the situation is the fact that the conference participants in any conference change on a dynamic basis. Thus, a particular multicast address may be utilized to identify a first conference at a first time, and a second conference at a second time. Each multicast address represents all of the conference participants and the nodes are programmed such that any packet with the multicast address is appropriately treated, duplicated where necessary, and sent to plural recipients.
Another problem with the foregoing is the fact that the multicast addresses are dynamic. More specifically, typically a band of addresses are reserved for multicast conferences. When a conference is desired to be started, the originator of the conference would randomly pick one of the band of addresses reserved for multicast. This band of addresses is referred to as Class D addresses.
To initiate the conference once the address is picked, a specialized software tool called a session directory ("SDR") must announce to other network nodes that the session is to be on the particular random Class D address chosen. Users desirous of joining the conference must then attempt to configure in a manner to participate.
If a particular user's workstation is not turned on at the time that the announcement of the conference is made from the originating terminal's SDR, then the terminal, when later turned on, will have no information regarding the videoconference. Since the originating SDR would typically only repeat the conference information in 10-20 minute intervals, it could be a significant amount of time before a user knew what conferences were proceeding. Moreover, the entire process involves random dynamic addresses, software tools such as SDR, directories, and a variety of other complex software tools and files. In short, the system was complicated and cumbersome.
A slight improvement occurred in the late 1990s. A certain subset of the Class D addresses were declared to have special properties and were defined as being applicable in specified geographic areas. Since the specified geographic area may include, for example, a community of interest such as a particular corporation, or set of buildings, there is little chance of conflict among users competing for the same Class D addresses. Thus, it became possible to permanently assign certain administratively scoped addresses for specific multicast use.
The foregoing system does not take advantage of the full capability of such administratively scoped addresses. Accordingly, there exists a need in the art for a technique of performing multicast which permits flexibility and ease of use in multicast systems, and specifically, in the use of administratively scoped multicast systems.


In a control device for a vehicle AC generator, a voltage control includes target voltage adjusting means for adjusting a target voltage value in response to a target change command from an external control unit and a gradual excitation control circuit that controls an excitation duty to increase according to an excitation duty control characteristic when a vehicle load increases and when the target voltage adjusting means varies the target voltage value to a lower value. The gradual excitation control circuit includes duty characteristic varying means for varying the excitation duty control characteristic. The duty characteristic varying means varies a rate of increase of the excitation duty in a predetermined region of the excitation duty control characteristic in comparison with its other region.

Generally, a vehicle AC generator is provided with a voltage control unit and the voltage control unit controls an output voltage of the vehicle AC generator to take a target voltage value. In many cases, the voltage control unit is configured to control an output voltage of the vehicle AC generator to take a target voltage value by repetitively giving a control cycle to a power switch element that controls an exciting current flowing through a field coil of the vehicle AC generator and adjusting an excitation duty indicating an ON time ratio of the power switch element in each control cycle.
JP62-64299A discloses gradual excitation control by which an exciting current of a vehicle AC generator is increased gradually with time to suppress an abrupt increase of a drive torque of the vehicle AC generator when a vehicle load is newly activated. Also, JP7-194023A discloses external control by which a target change command for an output voltage of the vehicle AC generator is given to the voltage control unit from an external control unit thereof, so that the voltage control unit adjusts the target voltage value for an output voltage of the vehicle AC generator in response to this target change command with the aim of controlling an output voltage of the vehicle AC generator to take an appropriate value according to an operation state of the vehicle.


A grout plug assembly for use in forming a pipe pile system defining at least one pile assembly inner surface portion comprises a resiliently deformable plug body defining a plug outer surface, a plug inner surface, a first plug end surface, a second plug end surface. The plug inner surface defines a plug passageway. The plug outer surface is sized and dimensioned to engage the at least one pile assembly inner surface portion of the pipe pile system during formation of the pipe pile system.

Vibratory and rotary drivers are used for the installation of pipe piling. Pipe piles, as used in the installation of structural foundations or geothermal piles, are segments of pipe that must be connected and driven together from the surface to reach the desired depth. Consequently, whether used in connection with vibratory or rotary drivers, the connection between pipe pile segments is vitally important to maximizing the driving power and reducing the possibility of failure of the pipe segment connection points. The installation of pipe pilings may be improved in stability and/or strength when installed with grout or similar material along the exterior of the column.
The need exists for improved grout plug systems and methods for use when placing piles

Grout plug systems and methods for placing piles


Embodiments of the present disclosure are directed towards metallization of a fluorocarbon-based dielectric material for interconnect applications. In one embodiment, an apparatus includes a semiconductor substrate, a device layer disposed on the semiconductor substrate, the device layer including one or more transistor devices, and an interconnect layer disposed on the device layer, the interconnect layer comprising a fluorocarbon-based dielectric material, where x represents a stoichiometric quantity of fluorine relative to carbon in the dielectric material, and one or more interconnect structures configured to route electrical signals to or from the one or more transistor devices, the one or more interconnect structures comprising cobalt (Co), or ruthenium (Ru), or combinations thereof. Other embodiments may be described and/or claimed.

An integrated circuit (IC) device may include an interlayer dielectric (ILD) stack having interconnect structures formed in a dielectric material to route electrical signals of the IC device. Careful selection of materials used for the dielectric materials and interconnects of an ILD stack may facilitate formation and function of an IC device that includes such an ILD stack.

Metallization of fluorocarbon-based dielectric for interconnects


A gun can be powered by a cartridge of pressurized gas or by pressurized air. The gun includes a valve body which provides a pressure reservoir for storing pressurized gas or air. When the gun is fired, pressurized gas or air is discharged from the pressure reservoir and propels a projectile out of the barrel of the gun. An air pump is mounted on the gun for supplying pressurized air to the pressure reservoir. An adapter assembly is mounted on the gun for holding a cartridge of compressed gas. The adapter assembly includes an adapter housing and a plunger which is slidably mounted in the adapter housing. The plunger is movable between a sealing position in which the plunger sealingly engages the adapter housing and an exhaust position in which pressurized gas or air from the pressure reservoir can flow out of the adapter housing. The plunger is maintained in the sealing position by a gas cartridge or by a plug which can be screwed into the adapter housing. A check valve in the plunger permits pressurized gas to flow through the plunger into the pressure reservoir but prevents pressurized gas or air to flow from the pressure reservoir through the plunger.

This invention relates to guns, and, more particularly, to a gun which can be powered by pressurized gas, by pressurized air, or by both pressurized gas and pressurized air.
Guns which are powered either by pressurized gas or by pressurized air are well known. Guns which are powered by pressurized gas are commonly called CO.sub.2 guns and use a cartridge of pressurized CO.sub.2 gas. Guns which are powered by pressurized air are commonly called air guns. Both types of guns generally include a valve body which stores a charge of pressurized gas or air. A BB, pellet, or other projectile is loaded into the barrel of the gun, and when the gun is fired, the charge of pressurized gas or air is discharged from the valve body and propels the projectile out of the barrel.
Heretofore, a gun was usually either a CO.sub.2 gun or an air gun. A few guns have been provided which had the capability of being powered by either pressurized gas or pressurized air. However, those guns have usually required some modification of the gun, such as an exchange of parts, in order to adapt the gun to one mode or the other.

Gun powered by pressurized gas and/or pressurized air


A system and a method for assisting in the process of generating mailing communications and satisfying their requirements are provided. The system and the method allow customers or users to interact on a computer network, such as the internet, with a database to generate a communication with minimal time or effort expended such that the communication complies with requirements for delivery of mail by a special service. The system and method inform users of requirements of special mailing needs to effectuate delivery of, for example, a legal letter, allows users automatic delivery of a mailing requiring a special service and provides automatic transfer of fees associated with postage and services rendered.

The present invention generally relates to a system and a method for assisting in the process for generating and satisfying requirements for mailing communications such as, for example, a letter requiring delivery by a special service such as certified mail, registered mail, insured mail, return receipt for merchandise mail or the like. More specifically, the present invention relates to a system and a method from which customers may interact on a computer network, such as the internet, with a database to generate a communication that complies with requirements for delivery of mail by a special service.
It is, of course, generally known that individuals as well as businesses are using the internet as a resource for information. The use of the internet as a resource for information or other needed function has become widely accepted. Often individuals communicate, conduct research, shop, buy groceries, bank, and/or pay taxes via the internet. As the use of the internet becomes more pervasive, individuals become more dependent on the internet and turn to the internet to improve or conduct their personal and/or commercial business.
In a more relevant example, individuals as well as businesses at times are compelled to make communications of a legal nature. However, many individuals are not aware of special mailing requirements for certain legal letters. Moreover, individuals are often hesitant to consult attorneys for such information as the costs associated therewith are often prohibitive. Many businesses are required to staff individuals for the sole purpose of handling their mailing requirements. Managing special service mail, such as certified mail, is a costly and labor-intensive process. Using the internet to conduct a variety of business-related functions and as a less expensive alternative and/or resource has become a viable option for both individuals and businesses.
Currently, internet web sites offer legal forms, such as the website maintained by Badger Information Service. Further, web sites are known that offer services relating to preparation of mailpieces for delivery by a special service, such as the website maintained by USCertifiedLetters, LLC for sending one page certified letters or the website maintained by CertifiedMail.com for sending certified electronic mail. In addition, methods and systems are known for generating postage values for articles to be mailed including special fees applicable to the articles, such as certified mail. Such methods and systems are disclosed in U.S. Pat. Nos. 4,595,984; 4,325,440; and 4,286,325.
However, no systems or methods are known that inform users of requirements of special mailing needs to effectuate delivery of, for example, a legal letter. Moreover, no systems or methods are known that allow the user automatic delivery of a mailing requiring a special service and/or provides automatic transfer of fees associated with postage and services rendered.
A need, therefore, exists to provide a system and a method which addresses the problems associated with the preparation of communications, such as legal letters and their mailing requirements, via an easily accessible and widely used source, such as the internet.

System and a method for automating delivery of communication by a special service


A boring head of a boring tool for boring the ground includes a device for detecting inclination of the boring head therein. The device includes a roll angle sensor and a pitch angle sensor. The roll angle sensor detects an angular position of the boring head in a roll direction and outputs a roll angle detecting signal. The pitch angle sensor detects an angular position of the boring head in a pitch direction outputs a pitch angle detecting signal. A signal modulating circuit converts the roll angle detecting signal and the pitch angle detecting signal into a serial signal and modulates the serial signal. An output circuit receives the modulated serial signal and outputs a magnetic field which is receivable by a receiver located on the ground and which permits determination of the roll angle and the pitch angle of the boring head.

1. Field of the Invention
The present invention relates to a device for detecting inclination of a boring head of a boring tool which is used to install pipelines under the ground without digging a trench.
2. Description of the Prior Art
When the ground is bored by a boring tool to install pipelines under the ground without digging a trench, it requires to grasp both horizontal and vertical positions of a boring head during the boring operation so as to correct the deviation relative to a planned course.
U.S. Pat. No. 5,165,490 in the name of the same assignee of the present application has proposed a device for detecting an angular position in a circumferential direction of a boring head having a slant surface as a reference surface. With the device of this U.S. patent, a magnetic field is intermittently generated from the boring head when the slant surface is positioned out of a predetermined angular range, while the magnet field is continuously generated when the slant surface is positioned within the predetermined angular range. Such a magnetic field is received by a receiver on the ground, and the receiver displays as to whether the inclination of the boring head in the circumferential direction is proper or improper. If the receiver displays that the inclination is improper, the boring head is rotated to correct the position of the slant surface so as to coincide with a reference angle, and a further correction is performed to correct the direction so as to correspond to a planned course.
With this prior art detecting device, however, although it can be operated to detect as to whether the inclination in the circumferential direction of the boring head is within the proper range, it cannot be operated to detect the inclination itself or an exact inclination angle in a rolling direction. Further, the prior art device cannot be operated to detect the inclination angle in an axial direction of the boring head or an inclination angle in a pitch direction. Therefore, the device is not operable to reliably correct the inclination according to the planned course, and it requires troublesome operation for such a correction.

Device for detecting inclination of boring head of boring tool


The present invention relates to a thermoplastic, multi-layer, electrostatic discharging, laminate comprised of at least one outer layer that is permanent static dissipative and non-contaminating, and a core or base layer that is conductive. The outer layer has a surface resistivity of from about 1.0xc3x97105 to about 1.0xc3x971012 Ohm/sq, and the core layer has a surface resistivity of from about 1.0xc3x97101 to about 1.0xc3x971011 Ohm/sq.

The present invention relates to a thermoformable polymeric multi-layer article or laminate for dissipating electrostatic charges and comprises an electrostatic dissipating or discharging core layer and at least one overlayer. The overlayer is substantially free of particulation, and sloughing. Preferably, the core layer has better dissipative properties than the overlayer in order to drain electrostatic charges away from the surface of the laminate.
Most thermoplastics are electrical insulators. The accumulation and retention of static electrical charges on the surface of most plastics due to their low conductivity is well known. The accumulation of static charge on the surface of a plastic is undesirable for various reasons. Sometimes the static charge on these materials can discharge very quickly and damage sensitive components or articles which come in contact with the plastic. In addition, dust is typically attracted to and accumulates on materials carrying a static charge. Therefore, the electrostatic dissipative properties of plastic materials are of importance in various applications where static charge accumulation must be avoided.
Four major approaches have been used to alleviate the accumulation of static electrical charges in plastics: external chemical treatments, internal chemical additives, conductive fillers and polymeric additives. Each approach while effective in certain specific applications, suffers from deficiencies.
The external chemical treatments, hygroscopic surfactants that can be applied to the surface of the plastic article, suffer due to their reliance on high humidity for effectiveness. Generally, the relative humidity needs to be greater than 30%. Also, permanence is an issue since the external chemical treatment can be rubbed, wiped or washed off resulting in a loss of electrostatic discharge (xe2x80x9cESDxe2x80x9d) protection. These types of chemical treatments are particularly undesirable in sensitive electronic handling applications where contamination of the components is an issue. Examples of these chemical treatments include fatty acids and their amines or salts, quaternary ammonium salts, monoalkyl glycerides, alkyl phosphonates and sulfonamides.
Internal chemical additives rely upon additive migration to the surface of the plastics to provide ESD protection to the plastic. Internal chemical additives are generally low molecular weight non-polymeric, hygroscopic surfactants which are compounded into the plastic material itself. While this approach provides more permanence than the external chemical treatments, just like external chemical treatments it is also prone to be rubbed, wiped or washed away. Internal chemical additives migrate to the surface of the plastic because of their limited compatibility with the plastic. When the additive migrates to the surface, it can be wiped, abraded or washed off, leaving the surface without any ESD protection. A static charge can then build on the surface, since the material is not protected. This lack of permanence results in periods of ESD susceptibility in which the plastic cannot dissipate a charge until additional additives can bloom to the surface. In addition, the ESD additive can contaminate sensitive devices that come into contact with the plastic article. The internal chemical additives also depend upon high humidity to be effective.
The use of conductive fillers can also alter the electrical properties of plastics. Examples of conductive fillers include conductive carbon black, carbon fibers, metal-coated substrates, metallic fibers or fillers. Although the conductive fillers are neither humidity dependent or susceptible to being wiped, washed or rubbed away, they do have certain disadvantages. For example, conductive fillers tend to increase the melt viscosity for processing the blend. Also, conductive fillers tend to limit the colorability of the plastic materials. Generally, they also tend to decrease the physical properties of the blend such as impact resistance. Also, contamination concerns often preclude the use of plastics loaded with conductive fillers in environments such as cleanrooms.
Conductive fillers also tend to have steep loading curves. As the percentage of conductive filler in the insulative thermoplastic is increased from zero, the composite material""s bulk will remain insulative until a continuous network of the conductive filler is formed. At this point, often called percolation, the resistivity will drop sharply with increasing filler percentage. The steep slope of the loading curve once the network is formed demonstrates the high level of variability that can be inherent in the electrical properties in these heterogeneous materials, particularly after secondary processes such as thermoforming. On a microscopic scale, different domains or regions within the composite will have varying concentrations of filler and hence varying levels of resistivity. Regions with low levels of filler can be electrically insulative and retain voltages that can potentially damage sensitive microelectronic devices. Such regions or domains are commonly called xe2x80x9chot spots.xe2x80x9d Conductive regions within the material can discharge voltages too rapidly, releasing current densities that can damage devices. This deficiency is more of a concern as microelectronic devices become more and more sensitive.
Numerous examples of internal polymeric additives exist. An example of the addition of an electrostatic dissipative polymer being added to an insulative polymer can be found in U.S. Pat. No. 3,425,981 to Puletti. The patent to Puletti discloses an olefin polymer composition containing ethylene oxide based polymers and exhibiting enhanced antistatic properties. Additionally, U.S. Pat. No. 5,010,139 to Yu discloses an antistatic polymeric composition consisting of a blend of a polymeric material and antistatic additive which is an ethylene oxide based copolymer or terpolymer material. The polymeric material can be any thermoplastic, thermoplastic elastomer or elastomer including acrylonitrile butadiene styrene (ABS); copolymers of styrene and acrylonitrile modified with acrylic elastomers (ASA); polyamides; polybutylene terephthalate (PBT); polyethylene terephthalate (PET); polyethylene terephthalate glycol (PETG); polymethylmethacrylate (PMMA); polyurethane (TPU); polyvinyl chloride (PVC); chlorinated polyvinyl chloride (CPVC); polycarbonate (PC); polyoxymethylene (POM); polyphenylene oxide (PPO); copolymer of styrene and maleic anhydride SMA; and styrene acrylonitrile copolymer (SAN).
U.S. Pat. No. 5,159,053 discloses a thermoplastic polyurethane which has electrostatic dissipative properties. The thermoplastic polyurethane comprises the reaction product of an ethylene ether oligomer glycol reacted with a non-hindered diisocyanate and an extender glycol. The ethylene ether oligomer intermediate comprises a polyethylene glycol, having an average molecular weight from about 500 to about 5,000. Such materials are commonly called inherently dissipative polymer (IDP).
U.S. Pat. No. 6,140,405 discloses the modification of the aforementioned electrostatic dissipative thermoplastic polyurethane with salts, enhancing the rate of static dissipation in the neat form and when blended with a variety of base polymers.
U.S. Pat. No. 5,342,889 discloses electrostatic dissipative polymeric compositions which are blends of an effective amount of a chain extended polymer and a matrix polymer. The chain extended polymer is formed from low molecular weight polyethers which are reacted with a chain extender and a diisocyanate. The matrix polymers include PVC, CPVC, a terpolymer of styrene, acrylonitrile and diene rubber; a copolymer of styrene and acrylonitrile modified with acrylate elastomers; a copolymer of styrene and acrylonitrile modified with ethylene propylene diene monomer rubber; rubber modified impact polystyrene; thermoplastic polyesters including PBT, PET and polyether-ester block copolymer; polyphenylene oxide; polyacetal; polymethyl methacrylate or mixtures thereof.
The usage of polymeric additives to alleviate the accumulation of static electrical charges in plastics provides a balance of performance advantages not achieved by the other ESD approaches described above. The polymeric additives are generally permanent, non-contaminating, colorable, easy to process, uniform in properties and even recyclable. These blends are commonly referred to as IDP alloys.
U.S. Pat. No. 4,478,903 to Denki describes a composite plastic sheet having a conductive surface layer. The conductive layer(s) is a carbon black filled polystyrene or ABS. The core layer material is an unfilled polystyrene or ABS. Disadvantages of such structures include high volume resistivity due to the insulative core, a carbon sloughing surface, and a surface resistivity in the conductive range.
U.S. Pat. No. 5,914,191 discloses a multi-layer structure using an IDP alloy as the outer layer to provide electrostatic dissipative characteristics. However, the core compositions described in this patent are electrical insulators. This creates a structure with deficiencies in the electrical properties such as high volume resistivity that can retard the decay of electrical charges to ground. The high volume resistivity and the requisite, higher degree of charge transfer on the surface is problematic for applications such as the packaging of today""s complex and sensitive microelectronic devices.
The present invention comprises multi-layer structures containing a conductive, thermoplastic core and at least one static dissipative, thermoplastic outer layer. This invention creates a synergistic merger between inherently dissipative polymers and conductive filler technology through the use of multi-layer laminates.
The thermoformable multi-layer article or laminate contains a core layer comprising a conductive component, such as conductive carbon black, and a polymer having desirable properties such as stiffness, flexibility as well as strength for a desired end use application. An overlayer is preferably affixed or bonded to each core side and is generally a blend of an inherently electrostatic dissipating or dissipative polymer and a large amount of a host polymer which desirably is the same as the core polymer. The article or laminate provides an electrostatic dissipating article lacking the disadvantages of the prior art articles. When the core layer exhibits greater dissipative capacity than the overlayer, electrostatic charges accumulated can be drained or pulled away from the laminate surface to ground through the core layer. The laminate is essentially free of sloughing, particulation, and hot spots, further exhibiting low tribocharge and residual voltage.
The present invention relates to a thermoformable article or laminate containing a plurality of layers or sheets, generally including at least one core layer. Preferably an overlayer is bonded on each side of the core. Less preferably, two or more overlayer sheets or layers can independently be present on each side of the core layer. Additionally, tie layers can be utilized between the core and one or more of the overlayers depending on the desired end use application.
The core layer of the present invention laminate or article has conductive properties and contains a conductive component in an amount sufficient to impart to the core layer, measured independent of any other layer, a surface resistivity of generally from about 1.0xc3x97101 to about 1.0xc3x971011 Ohm/sq, desirably from about 1.0xc3x97102 to about 1.0xc3x97108 Ohm/sq, preferably from about 1.0xc3x97102 to about 1.0xc3x97106 Ohm/sq, and a volume resistivity generally of from about 1.0xc3x97101 to about 1.0xc3x971011 Ohm-cm, desirably from about 1.0xc3x97102 to about 1.0xc3x97108, and preferably from about 1.0xc3x97102 to about 1.0xc3x97106 Ohm-cm as measured by ASTM D-257 or ESD S11.11-93. The core layer also contains at least one core polymer (which generally has negligible or no electrostatic dissipating properties) having suitable flexible and stiffness properties as well as strength for an intended end use such as in the electronic industry for packaging, process tubes, tote bins, and the like. Such properties can generally vary greatly with a desirable flexible modulus being from about 150,000 psi to about 350,000 psi.
Examples of suitable core polymers include but are not limited to amorphous polyesters, polyamide, polycarbonate, polystyrene, high impact polystyrene, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, polyolefins such as polyethylene and polypropylene, polyacetal, polysulfone, polybutylene terephthalate, polyethylene terephthalate, polyethylene terephthalate glycol (PETG) which is an ester of terephthalic acid, ethylene glycol and cyclohexanedimethanol (CHDM), polyurethane, polyphenylene sulfide, polyethersulfone, polyphenylene ether, polymethylmethacrylate, polyetheretherketone, polyvinyl chloride and blends thereof. High impact polystyrene, polyethylene terephthalate glycol and polyvinyl chloride are preferred.
The core layer also includes a conductive component or material. The conductive component can be a single compound or combination of compounds which provide the core layer with dissipative or conductive properties. Suitable conductive components include, but are not limited to, carbon black, carbon fibers, carbon fibrils, metal shavings or powders, metal fillers, inherently conductive polymers (ICPS) and metal coated mineral substrates.
Inherently conductive polymer (ICP), often called xe2x80x9csynthetic metalsxe2x80x9d or xe2x80x9corganic metalsxe2x80x9d exhibit conductivity that falls within the range of metals. The mechanism of conductivity is electronic, as in metals. Their most common feature is the presence of conjugated double bonds. Examples of such polymers include, but are not limited to, polyaniline (PAni), polypyrrole (Ppy), polythiophene (PTh), polyacetylene (PAc), polyisothianaphthane (PITN), polyheteroarylene vinylene (ParV) in which the heteroarylene group can be thiophene, furan or pyrrole, poly-p-phenylene (PpP), polyphenylene sulfide (PPS), polyphthalocyanine (PPhC), and their derivatives, their copolymers and their physical mixtures.
The type of carbon black is generally not important so long as it adds conductive or electrostatic dissipating properties to the core polymer. According to ASTM D-1765, carbon black particles having a nitrogen adsorption value of from about 20 to about 150 square meters per gram and a DBP absorption of from about 50 to 160 cc per 100 grams can be utilized with generally smaller sized particles, i.e. higher values, being desired. Examples of common types of carbon black which can be utilized include XC-72R, N110, N220, N234, N326, N330, N339, N351, N550, N650, N660, N754, N762, and N774.
The amounts of the conductive component or material such as ICP in the core layer are dependent on factors such as type, shape, and particle size, etc. Accordingly, suitable amounts effective to impart a predetermined surface resistivity or volume resistivity to the core layer as defined above are utilized.
For example, when the conductive component is a conductive grade of carbon black, it is utilized in amounts generally from about 2 to about 30, and preferably from about 12 to about 20 parts by weight based on 100 parts by weight of core polymer present in the core layer. When the conductive material utilized is fibrils, the amount thereof is from about 0.1 to about 10 parts by weight per 100 parts by weight of core polymer present in the core layer. When the conductive material or component is a metal shaving, a metal powder, a metal filler, or metal coated mineral substrate, the amount thereof is generally from about 5 to about 70 parts by weight per 100 parts by weight of core polymer. The amount of conductive polymer, when used, is from about 5 to about 50 parts per 100 parts by weight of the core polymer.
An overlayer is melt bonded, adhered, or otherwise affixed to the core layer of the present invention, preferably through a coextrusion or lamination process. Desirably two overlayers are utilized so that the core layer is sandwiched therebetween.
The one or more overlayers comprises a blend of a) an electrostatic dissipating agent which is at least one inherently dissipative polymer and/or static dissipative additive with b) an overlayer polymer which is a host polymer, i.e., desirably is the same polymer as utilized in the core layer to ensure sufficient adhesion between the layers.
The inherently dissipative polymer (IDP) is preferably a polyethylene glycol-based polyurethane copolymer, a polyethylene glycol-based polyamide copolymer, polyethylene glycol methacrylate copolymer, poly(ethylene/propylene oxide) copolymer, polyethylene glycol based polyesteramide, polyethylene glycol based polyester elastomer, poly(epichlorohydrin/ethylene oxide) copolymer or polyesteramide derived from an ethylene oxide adduct of bisphenol with polyamid having a carboxyl group at both terminal ends, or a combination thereof.
Examples of inherently dissipative polymer (IDP) are: polyurethanes, available as Stat-Rite C-2300 and C-2400 from Noveon; polyether amides, under commercial name Pebax MV 1074 and Pebax 4011 MA from Elf Atochem, or Irgastat from Ciba; polyetheresters such as Hytrel 8099 or Hytrel 8206 from DuPont; polyetherester amides, described in U.S. Pat. No. 5,863,466 and U.S. Pat. No. 6,268,030; poly(epichlorohydrin) such as Hydrin 200 from Nippon Zeon.
The polyurethane based inherently dissipative polymer is generally derived from a hydroxyl-terminated polyether intermediate and which is also chain extended with a glycol. The polyether intermediate can be a homopolymer or a copolymer of two or more copolymerizable cyclic ether monomers. Such polyurethanes are known to the art and to the literature such as those set forth in U.S. Pat. Nos. 5,159,053; 5,342,889; 5,574,104, and 6,140,405 which are hereby fully incorporated by reference. Some of these polymers are generally available as Stat-Rite(copyright) C-2300 and Stat-Rite C-2400 from Noveon, Inc. of Cleveland, Ohio.
More specifically, as set forth in U.S. Pat. Nos. 5,342,889 and 5,574,104, the chain extended polymer having electrostatic dissipative properties comprises (A) a low molecular weight polyether oligomer having two reactive moieties and an average molecular weight from about 200 to about 10,000 wherein the oligomer is a homopolymer or a copolymer of two or more copolymerizable cyclic ether monomers having the formula:
wherein R1, R2, R3, R4, and R5 are independently hydrogen, unsubstituted or substituted alkyl, cycloalkyl, cycloalkenyl, aryl, aralkyl or alkaryl, and wherein the substituents which can be substituted within the foregoing are OR6, SR6, CN or halogens, R6 is hydrogen, alkyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, alkaryl, or carboxyl, and further wherein the reactive moieties are OH, NH2, or NHR6, and n is 0, 1, 2, or 4; (B) from about 0 moles to about 35 moles of a diol or triol for each mole of low molecular weight polyether and (C) a diisocyanate or diisocyanate type component; with the proviso that the number of moles of diisocyanate per mole of the sum of the number of moles of low molecular weight polyether oligomer plus the number of moles of diol or triol is from about 0.95 to about 1.06. The number of moles of diisocyanate per mole of the sum of the number of moles of low molecular weight polyether oligomer plus the number of moles of diol or triol is from about 0.97 to about 1.03. By low molecular weight oligomer, it is meant that the polyether will have an average molecular weight from about 200 to about 10,000 and preferably from about 500 to about 5000, as determined by end group analysis. The reaction of the low molecular weight oligomer with a diisocyanate will furnish a polymer having melt indices from 0.05 to 110 grams per ten minutes. The preferred melt index range of the polymer will be from about 1.0 to 65 grams/10 minutes. In general, the melt index is determined according to ASTM D-1238 Procedure A at a barrel temperature of 190xc2x0 C. and an 8700 gram piston load.
The low molecular weight oligomer employed is a polymer of cyclic ether monomers having the formula:
Alternatively, the low molecular weight oligomer employed is a polymer of cyclic ether monomers wherein R1, R2 and R3 are hydrogen and R4 is H, CH3, or CH2 X wherein X is a halogen, OR6, NR6 R7 or COOR6, and R6 and R7 are as defined hereinabove.
The most preferred cyclic ether is ethylene oxide.
In an alternative embodiment the low molecular weight polyether oligomer is end capped with ethylene oxide or ethylene imine thereby providing an oligomer which will have two primary moieties. The alkyl groups can have from 1 to 6 carbon atoms, be straight or branched chain and may be unsubstituted or substituted. The alkenyl groups can have from 1 to 6 carbon atoms, be straight or branched chain, have 1 or two double bonds and be unsubstituted or substituted.
The cycloalkyl and cycloalkenyl groups can have from 3 to 8 ring carbon atoms and from 1 to 3 rings. The cycloalkenyl groups can have 1 or 2 double bonds.
The aryl groups can have from 6 to 10 ring carbon atoms and one or two rings.
Useful polyether oligomers are linear polymers having the general formula:
wherein X+1 is the number of repeating ether units, each M is a reactive moiety, n is 0, 1, 2, or 4 and R1, R2, R3, R4 and R5 are as defined hereinabove. The most common M is the OH group. For the subject invention X+1 is at least 4 and between 4 and about 250. On a molecular weight basis, the useful range of polyether oligomers have an average molecular weight from about 200 to 10,000 and preferably from about 500 to 5000. A highly preferred oligomer is polyethylene glycol. Commercially available polyethylene glycols useful in this invention are typically designated as polyethylene glycol 600, polyethylene glycol 1450, and polyethylene glycol 4000.
The polyether oligomer can be a homopolymer or a copolymer of two or more copolymerizable monomers. Some examples of monomers are ethylene oxide, propylene oxide, 1,2-butylene oxide, epichlorohydrin, allyl glycidyl ether, n-butyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, 2-ethylhexyl glycidyl ether, tetrahydrofuran, or styrene oxide.
Another IDP polymer is a salt modified inherently dissipative polymer derived from a polyether intermediate and can be a thermoplastic polyurethane, a polyether amide block copolymer, a polyether-ester block copolymer, and the like. More specifically, a salt-modified electrostatic dissipated polymer is made from a low molecular weight polyether oligomers. Such compounds are set forth in U.S. Pat. No. 6,140,405 and the same is hereby fully incorporated by reference. Polymers made according to this patent are commercially available as Stat-Rite(copyright) C-2400 from Noveon, Inc. of Cleveland, Ohio.
More specifically, the salt-modified electrostatic dissipating polymers are made from low molecular weight polyether oligomers, wherein the polymers display relatively low surface and volume resistivities, yet generally are free of excessive levels of extractable anions. This low molecular weight polyether oligomer that is useful is described and prepared as follows.
The low molecular weight polyether oligomer can comprise a homopolymer of ethylene oxide having a number average molecular weight of from about 200 to about 5000. The low molecular weight polyether oligomer can also comprise a copolymer of two or more copolymerizable monomers wherein one of the monomers is ethylene oxide and has a number average molecular weight from about 200 to about 20,000.
Exemplary of the comonomers which can be copolymerized with ethylene oxide are: 1,2-epoxypropane(propylene oxide); 1,2-epoxybutane; 2,3-epoxybutane(cis and trans); 1,2-epoxypentane; 2,3-epoxypentane(cis and trans); 1,2-epoxyhextane; 2,3-epoxyhextane(cis and trans); 3,4-epoxyhextane(cis and trans); 1,2-epoxy heptane; 1,2-epoxydecane; 1,2-epoxydodecane; 1,2-epoxyoctadecane; 7-ethyl-2-methyl-1,2-epoxyundecane; 2,6,8-trimethyl-1,2-epoxynonane; styrene oxide.
Other comonomers which can be used as comonomers with the ethylene oxide are: cyclohexene oxide; 6-oxabicyclo[3,1,0]-hexane; 7-oxabicyclo[4,1,0]heptane; 3-chloro-1,2-epoxybutane; 3-chloro-2,3-epxybutane; 3,3-dichloro-1,2-epoxypropane; 3,3,3-trichloro-1,2-epoxypropane; 3-bromo-1-2-epoxybutane, 3-fluoro-1,2-epoxybutane; 3-iodo-1,2-epoxybutane; 1,1-dichloro-1-fluoro-2,3-epoxypropane; 1-chloro-1,1-dichloro-2,3-epoxypropane; and 1,1,1,2-pentachloro-3,4-epoxybutane.
Typical comonomers with at least one ether linkage useful as comomoners are exemplified by: ethyl glycidyl ether; n-butyl glycidyl ether; isobutyl glycidyl ether; t-butyl glycidyl ether; n-hexyl glycidyl ether; 2-ethylhexyl glycidyl ether; heptafluoroisopropyl glycidyl ether, phenyl glycidyl ether; 4-methyl phenyl glycidyl ether; benzyl glycidyl ether; 2-phenylethyl glycidyl ether; 1,2-dihydropentafluoroisopropyl glycidyl ether; 1,2-trihydrotetrafluoroisopropyl glycidyl ether; 1,1-dihydrotetrafluoropropyl glycidyl ether; 1,1-dihydranonafluoropentyl glycidyl ether; 1,1-dihydropentadecafluorooctyl glycidyl ether; 1,1-dihydropentadecafluorooctyl-.alpha.-methyl glycidyl ether; 1,1-dihydropentadecafluorooetyl-.beta.-methyl glycidyl ether; 1,1-dihydropentadecafluorooctyl-.alpha.-ethyl glycidyl ether; 2,2,2-trifluoro ethyl glycidyl ether.
Other comonomers with at least one ester linkage which are useful as comonomers to copolymerize with ethylene oxide are: glycidyl acetate; glycidyl chloroacetate; glycidyl butyrate; and glycidyl stearate; to name a few.
Typical unsaturated comonomers which can be polymerized with ethylene oxide are: allyl glycidyl ether; 4-vinylcyclohexyl glycidyl ether; .alpha.-terpinyl glycidyl ether; cyclohexenylmethyl glycidyl ether; p-vinylbenzyl glycidyl ether; allyphenyl glycidyl ether; vinyl glycidyl ether; 3,4-epoxy-1-pentene; 4,5-epoxy-2-pentene; 1,2-epoxy-5,9-cyclododeca diene; 3,4-epoxy-1-vinylchlohexene; 1,2-epoxy-5-cyclooctene; glycidyl acrylate; glycidyl methacrylate; glycidyl crotonate; glycidyl 4-hexenoate.
Other cyclic monomers suitable to copolymerize with ethylene oxide are cyclic ethers with four or more member-ring containing up to 25 carbon atoms except tetrahydropyran and its derivatives. Exemplary cyclic ethers with four or more member-ring are oxetane (1,3-epoxide), tetrahydrofuran (1,5-epoxide), and oxepane (1,6-epoxide) and their derivatives.
Other suitable cyclic monomers are cyclic acetals containing up to 25 carbon atoms. Exemplary cyclic acetals are trioxane, dioxolane, 1,3,6,9-tetraoxacycloundecane, trioxepane, troxocane, dioxepane and their derivatives.
Other suitable cyclic monomers are cyclic esters containing up to 25 carbon atoms. Exemplary cyclic esters are beta-valerolactone, epsilon-caprolactone, zeta-enantholactone, eta-caprylactone, butyrolactone and their derivatives. The low molecular weight polyether oligomer prepared by the method detailed immediately above then can be reacted with a variety of chain extenders and modified with a selected salt to form the electrostatic dissipative polymer additive or antistatic agent.
For example, the polyether oligomer described immediately above can be reacted to form an electrostatic dissipative agent comprising a copolyether-ester polymer comprising one or more polyester blocks as well as one or more low molecular weight polyether oligomer blocks. The polyester block is generally made from an aromatic containing dicarboxylic acid or diester such as terephthalic acid, dimethyl terephthalate, and the like, with a diol generally containing from about 2 to about 10 carbon atoms. The low molecular weight polyether oligomer is generally made as described above. The polyether-ester block copolymers can be represented by the following formula:
-(polyester-b-low molecular weight polyether oligomer)n.
The polyester-ether block copolymer comprises the reaction product of ethylene glycol, terephthalic acid or dimethyl terephthalate and polyethylene glycol. These and other examples of other polyester-ether copolymers which can be utilized are set forth in the Encyclopedia of Polymer Science and Engineering, Vol. 12, John Wiley and Sons, Inc., NY, N.Y., 1988, pages 49-52, which is hereby fully incorporated by reference as well as U.S. Pat. Nos. 2,623,031; 3,651,014; 3,763,109; and 3,896,078.
Alternatively, the low molecular weight polyether oligomer can be reacted to form an electrostatic dissipative agent comprising one or more polyamide blocks as well as one or more low molecular weight polyether oligomer blocks. Alternatively, the low molecular weight polyether oligomer may be reacted with the polyamide in the presence of a diacid to form a polyether ester amide having the recurring formula:
xe2x80x94(C(xe2x95x90O)xe2x80x94Axe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94Bxe2x80x94O)nxe2x80x94
where A is the polyamide and B is the low molecular weight polyether oligomer. Further information on this polymer can be found in U.S. Pat. No. 4,332,920, incorporated herein by reference.
The low molecular weight polyether oligomer can be reacted to form a polyurethane electrostatic dissipative agent, such as the Stat-Rite(copyright) C-2300 ESD agent available from Noveon, Inc. More specifically, the polyurethane electrostatic dissipative additive comprises the reaction of a hydroxyl terminated ethylene ether oligomer intermediate with a non-hindered diisocyanate and an extender glycol, where the oligomer can be a diethylene glycol-aliphatic polyester, or a polyethylene glycol.
Referring first to the polyester intermediate, a hydroxyl terminated, saturated polyester polymer is synthesized by reacting excess equivalents of diethylene glycol with considerably lesser equivalents of an aliphatic, preferably an alkyl, dicarboxylic acid having four to ten carbon atoms where the most preferred is adipic acid. Other useful dicarboxylic acids include succinic, glutaric, pimelic, suberic, azelaic and sebacic acids. The most preferred polyester intermediate is polydiethylene glycol adipate. In accordance with this aspect of the present invention, excess moles of diethylene glycol are reacted with lesser moles of dicarboxylic acid at levels from about 5 mole percent to about 50 mole percent excess of glycol to provide a hydroxyl terminated polyester oligomer chain having an average molecular weight between about 500 to 5000 and preferably between about 700 and 2500. The short chain polyester oligomer contains repeating diethylene ether structures and comprises on an equivalent basis from about 1.05 to 1.5 equivalents of diethylene glycol co-reacted with one equivalent of dicarboxylic acid to produce the low molecular weight polyester oligomer intermediate. The high excess equivalents of diethylene glycol controls the molecular weight of the polyester oligomer preferably below 2500 and further assures a hydroxyl terminated linear polyester oligomer. The polyester oligomers synthesized by reacting the diethylene glycol with lesser equivalents of dicarboxylic acid at temperatures of from about 300xc2x0 F. to 450xc2x0 F. in the absence or in the presence of an esterification catalyst such as stannous chloride for time sufficient to reduce the Acid No. to about zero.
The hydroxyl terminated polyester oligomer intermediate is further reacted with considerably excess equivalents of non-hindered diisocyanate along with extender glycol in a so-called one-shot or simultaneous coreaction of oligomer, diisocyanate, and extender glycol to produce the very high molecular weight linear polyurethane having an average molecular weight broadly from about 60,000 to about 500,000, preferably from about 80,000 to about 180,000, and most preferably from about 100,000 to about 180,000.
Alternatively, an ethylene ether oligomer glycol intermediate comprising a polyethylene glycol can be co-reacted with non-hindered diisocyanate and extender glycol to produce the high molecular weight, polyurethane polymer. Useful polyethylene glycols are linear polymers of the general formula Hxe2x80x94(OCH2CH2)xe2x80x94nOH where n is the number of repeating ethylene ether units and n is at least 11 and between 11 and about 115. On a molecular weight basis, the useful range of polyethylene glycols have an average molecular weight from about 500 to about 5000 and preferably from about 700 to about 2500. Commercially available polyethylene glycols are typically designated as polyethylene glycol 600, polyethylene glycol 1500, and polyethylene glycol 4000.
High molecular weight thermoplastic polyurethanes are produced by reacting together preferably in a one-shot process the ethylene ether oligomer glycol intermediate, an aromatic or aliphatic non-hindered diisocyanate, and an extender glycol. On a mole basis, the amount of extender glycol for each mole of oligomer glycol intermediate is from about 0.1 to about 3.0 moles, desirably from about 0.2 to about 2.1 moles, and preferably from about 0.5 to about 1.5 moles. On a mole basis, the high molecular weight polyurethane polymer comprises from about 0.97 to about 1.02 moles, and preferably about 1.0 moles of non-hindered diisocyanate for every 1.0 total moles of both the extender glycol and the oligomer glycol (i.e. extender glycol+oligomer glycol-1.0).
Useful non-hindered diisocyanates comprise aromatic non-hindered diisocyanates and include, for example, 1,4-diisocyanatobenzene (PPDI), 4,4xe2x80x2-methylene-bis(phenyl isocyanate) MDI), 1,5-naphthalene diisocyanate (NDI), m-xylene diisocyanate (XDI), as well as non-hindered, cyclic aliphatic diisocyanates such as 1,4-cyclohexyl diisocyanate (CHDI), and H12 MDI. The most preferred diisocyanate is MDI. Suitable extender glycols (i.e. chain extenders) are aliphatic short chain glycols having two to six carbon atoms and containing only primary alcohol groups. Preferred glycols include diethylene glycol, 1,3-propane diol, 1,4-butane diol, 1,5-pentane diol, 1,4-cyclohexane-dimethanol, hydroquinone di(hydroxyethyl)ether, and 1,6-hexane diol with the most preferred glycol being 1,4-butane diol.
The hydroxyl terminated ethylene ether oligomer intermediate, the non-hindered diisocyanate, and the aliphatic extender glycol are co-reacted simultaneously in a one-shot polymerization process at a temperature above about 100xc2x0 C. and usually about 120xc2x0 C., whereupon the reaction is exothermic and the reaction temperature is increased to about 200xc2x0 C. to above 250xc2x0 C.
An effective amount of a salt, salt complex or salt compound formed by the union of a metal ion with a non-metallic ion or molecule is added during the one-shot polymerization process. While the exact mechanism of attachment and/or attraction of the salt to the ESD polymer reaction product is not completely understood, the salt unexpectedly improves the surface and volume resistivities of the resulting polymer without the presence of unacceptably high levels of extractable anions. Moreover, the static decay times remain in an acceptable range, that is, the times are not too fast or too slow. Examples of salts useful in the subject invention include: LiClO4, LiN(CF3SO2)2, LiPF6, LiAsF6, LiI, LiBr, LiSCN, LiSO3 CF3, LiNO3, LiC(SO2 CF3)3, Li2 S, and LiMR4 where M is Al or B, and R is a halogen, alkyl or aryl group. The preferred salt is Li N(CF3SO2)2, which is commonly referred to as lithium trifluoromethane sulfonimide. The effective amount of the selected salt added to the one-shot polymerization is at least about 0.10 parts based on 100 parts of the polymer, desirably at least about 0.25 parts and preferably at least about 0.75 parts.
It has been discovered that the amount of salt utilized can be unexpectedly lowered when the salt is added in conjunction with an effective amount of a co-solvent. Examples of co-solvents suitable for this purpose include ethylene carbonate, propylene carbonate, dimethyl sulfoxide, tetramethylene sulfone, tri- and tetra ethylene glycol dimethyl ether, gamma butyrolactone, and N-methyl-2-pyrrolidone. Ethylene carbonate is preferred. Although the addition of one of the co-solvents is optional, in some applications lower amounts of the salt may be desirable. The effective amount of co-solvent required to achieve the desired result of lower salt usage while still attaining the desired properties in the ESD polymer, is at least about 0.10 parts based on 100 parts of the polymer, preferably at least about 0.50 parts, and most preferably at least about 1.0 parts. Thus, it is unexpectedly found that addition of the co-solvent together with a lowered amount of the salt synergistically lowers the surface and volume resistivities of the ESD polymer, without adversely affecting the presence of only relatively low amounts of extractable anions, in a manner similar to that which is observed when slightly higher amounts of the salt alone are added to the polymerization.
Other suitable static dissipative agents include, but are not limited to, antistats and the like. Examples of antistatic agents include quaternary ammonium salts, ethoxylated quaternary ammonium salts, propoxylated and ethoxylated fatty amines and/or amides, amine salts, polyamines, glycerol stearates, alkyl sulphonates, alkylbenzene sulfonates, and phosphonium salts.
In order to render the overlayer compatible with the core layer, preferably the host polymer used in the overlayer is the same as the host polymer used in the core layer. For example, if HIPS is utilized as a core polymer, the host polymer is the same. Accordingly, if an amorphous polyester is utilized in the core layer, the host polymer is also an amorphous polyester, and so forth.
The amount of the host polymer present in the overlayer is generally in a range from about 50% to about 90% by weight, and preferably from about 70% to about 85% by weight based upon the total weight of polymer in the overylayer, i.e. one or more host polymers and one or more dissipating polymers. The difference, that is from about 10% to about 50% by weight and preferably from about 15% to about 30% by weight, naturally, is the dissipating polymer.
In order to assure good adherence of the overlayer to the core polymer layer as when these layers are incompatible, a tie layer comprising adhesion promoting additives optionally can be utilized between the overlayer(s) and the core layer. Suitable tie layers include block copolymers of styrene-butadiene-styrene such as Kraton(copyright) FG 1901X made by Shell Chemical Company. Other adhesion promoting agents include EVA and Acrylic Copolymers. The tie layer thickness is generally very thin such as from about 1 to about 3 mils.
Alternatively, adhesion promoting additives can be utilized directly in the overlayer or core layer. The amount of such adhesive promoting agents generally ranges from about 0.1 to about 20 parts and desirably from about 1 to about 5 parts by weight for every 100 parts by weight of polymer in the overlayer or core layer.
The surface resistivity of the overlayer is generally from about 1.0xc3x97105 to about 1.0xc3x971012, and preferably from about 1.0xc3x97107 to about 1.0xc3x971010 OHM/Sq., and the volume resistivity is generally from about 1.0xc3x97105 to about 1.0xc3x971012 and preferably from about 1.0xc3x97107 to about 1.0xc3x971010 Ohm-cm.
The overlayer can be applied to the core layer in any conventional manner such as by extrusion followed by lamination, co-extrusion and the like. Preferably, by co-extrusion of multi-layers using two or more extruders in tandum to produce an AB laminate, an ABA laminate or an ABC laminate or an ACBCA laminate etc., wherein A is an overlayer, B is a core layer, and C is a tie layer. Co-extrusion of the multi-layer is commonly known technology utilizing two or more extruders connected by a specific distribution-block structure to a multi-manifold extrusion die head to produce the above noted laminates.
The end result is a laminate or a multi-layer sheet article containing the above-described core layer and preferably an overlayer on each side of the core layer. The surface resisitivity of the multi-layer article or laminate is generally from about 1.0xc3x97105 to about 1.0xc3x971012 and preferably from about 1.0xc3x97107 to about 1.0xc3x971010 OHM/Sq., and the volume resistivity of a multi-layer article or laminate is generally from about 1.0xc3x97105 to about 1.0 xc3x971012 and preferably from about 1.0xc3x97107 to about 1.0xc3x971010 Ohm-cm. With these laminates, static decay is desirably within 1 second and preferably 0.1 second or less.
Tribocharge is desirably less than 20V and preferably less than 10V.
Inasmuch as the overlayer has no carbon black therein, the laminate of the present invention is essentially free of particulation so that carbon black particles emitted are negligible. That is, the amount of particulation is generally far less than 15,000, 10,000, or 5,000 counts and desirably less than 1500 counts by LPC (Liquid-borne Particle Counter).
The carbon black free overlayer also results in a laminate generally free of sloughing. This term defines the propensity of a polymer blend filled with carbon black to impart dark prints on contact surfaces such as work benches, etc. Moreover, overlayers free of carbon black do not contaminate packaged components or interfere with subsequent soldering operations. Accordingly, laminates of the present invention generally have a sloughing rate of 2 or less, desirably 1 or less, and preferably 0, when rated on the scale of 0(No sloughing/No Mark at all) to 5(dark like a pencil mark).
The electrical advantages of the current invention are 1) a static dissipative surface providing a controlled release of electrical potential from a charged object that comes into contact with it, 2) a surface free from xe2x80x9chot spotsxe2x80x9d due to the uniform morphology of the inherently dissipative polymer alloy used as the overlayer, 3) a conductive core that enhances charge decay compared to an inherently dissipative polymer alloy monolayer.
Advantage one is important because a conductive surface, such as that of a carbon black filled HIPS, will rapidly release electrical potential from charged objects that it comes into contact with. Sensitive electronic devices that have become charged can be damaged if they rapidly release potential to a ground. The invention has a static dissipative surface that will release potential at a rate that does not damage devices.
Advantage two is important because materials filled to practical levels with conductive particulates such as carbon black often have microscopic domains that are electrically insulative. This is particularly true after secondary processing such as thermoforming. These domains, often referred to as xe2x80x9chot spots,xe2x80x9d can trap or retain charge. This retained charge can damage ESD sensitive devices that come into contact or proximity to the surface. The invention provides a surface that is free from xe2x80x9chot spots.xe2x80x9d
Advantage three is important because it provides enhanced protection to sensitive devices. Path of lowest resistance will be away from the surface and packaged components since the conductive core has lower resistance than the static dissipative surface. Inherently dissipative polymer alloy monolayers do not offer this advantage.
The electrostatic dissipating polymeric laminates of the present invention are thus ideally suited for various packaging applications such as shipping and handling trays for the electronic field, for example chips, GMR heads, printed circuit boards, and the like in order to reduce the susceptibility of static charge buildup.
The laminates of the present invention provide rapid but controlled decay of electrical potential. As stated hereinabove, the core layer of the present invention preferably is more conductive or dissipative than the overlayer and tie layer. Accordingly, preference for charge transfer is in the more conductive core layer rather than the surface layers and thus away from the packaged material such as a sensitive electrical component thus protecting the same.
Depending upon the particular end use, the layer thickness of the laminate can vary considerably. The thickness of the core layer can generally range from about 5 to about 200 mils, and desirably from about 10 to about 80 mils. The thickness of each overlayer is from about 0.1 to about 20 mils and desirably from about 1 to about 3 mils.
Advantageously, the laminate sheets of the present invention can be thermoformed as known in the art into a desired shape, wherein the laminate is heated to a molten state and formed via vacuum or pressure against a mold.
The foregoing invention will be better understood by reference of the following examples which serve to illustrate, but not to limit the present invention.

Electrostatic dissipating polymeric multi-layer article or laminate


A method and apparatus for acquiring scanning cone beam projection data along a three dimensional scanning trajectory is disclosed. The technique ensures acquisition of a substantially uniform distribution of Radon data that is sufficiently complete for exact image reconstruction of an object irradiated by a scanning cone beam source. By choosing a scanning trajectory whose planar projection onto a plurality of coaxial planes, when taken together, forms a continuous, convex, closed curve about a corresponding projection of the object being scanned; the Radon information obtained therefrom is complete and information coverage is uniform over the region of support of the object. Accordingly, this condition provides a practical, easy to implement, visual method for evaluating candidate three dimensional scanning trajectories.

The present invention relates generally to three dimensional (3D) computerized tomography (CT) and more specifically to a method and apparatus for acquiring cone beam data along a three dimensional scanning trajectory to obtain a substantially uniform distribution of Radon data that is sufficiently dense to ensure the acquisition of a complete set of Radon data for exact image reconstruction of an object irradiated by a cone beam source.
Conventional CT employs a technique for obtaining cross sectional slices of an object from planar parallel or fan beam irradiation of an object. The technique is primarily utilized in medical and industrial diagnostics. Traditional image reconstruction techniques have been predominantly two dimensional. In three dimensions, an undistorted image of an object can be mathematically reconstructed in an exact manner by back projecting a parallel beam which has been attenuated after passing through the object using an inverse transform based on the Fourier Slice Theorem. The use of a parallel beam source and a flat two dimensional detector geometrically simplifies reconstruction but complicates practical considerations having to do with speed and ease of data collection.
Back projections can be mathematically accomplished for a 3D cone beam source by inverse Radon transforming suitable planar integrals. The planar integrals are computed from detector integrals which utilize measured cone beam projection data i.e. the detected attenuated intensity representative of the density distributions of the irradiated object. The use of a 3D cone beam source expedites data acquisition, but complicates geometrical considerations when used with a flat array detector.
In two dimensions, the analog of a cone beam source geometry is illustrated by fan beam geometry. For the case of two dimensional fan beam geometry, the detector integrals are equivalent to the Radon transform of the object. Unlike the two dimensional case, a direct Radon inversion of three dimensional cone beam data from a cone beam source is not possible. Before the inverse Radon transform can be undertaken in three dimensions, the cone beam detector integrals must be reconfigured into planar integrals suitable for inverse Radon transformation. Due to the limitations of direct inversion, three dimensional CT imaging has traditionally involved stacking slices representative of the density distribution through the object obtained from various parallel or fan beam attenuation projections. Each projection is associated with a particular view angle or configuration of source and detector relative to the object. A data set is generally acquired by either rotating a source and detector, fixed relative to each other, around an object taking projections as the object is scanned; or alternatively, rotating the object between the fixed source and detector.
The three dimensional Radon inversion problem was addressed in two commonly assigned patent applications: U.S. patent application Ser. No. 07/631,815 filed Dec. 18, 1990 by Kwok C. Tam, now U.S. Pat. No. 5,257,183, entitled METHOD AND APPARATUS FOR CONVERTING CONE BEAM X-RAY PROJECTION DATA TO PLANAR INTEGRALS AND RECONSTRUCTING A THREE-DIMENSIONAL COMPUTERIZED TOMOGRAPHY (CT) IMAGE OF AN OBJECT discloses method and apparatus for converting cone beam data to values representing planar integrals on any arbitrary set of planes in Radon space for 3D image reconstruction through inverse Radon transformation. A related U.S. patent application Ser. No. 07/631,818 filed on Dec. 21, 1990 by Kwok C. Tam, now abandoned, entitled PARALLEL PROCESSING METHOD AND APPARATUS FOR RECONSTRUCTING THREE-DIMENSIONAL COMPUTERIZED TOMOGRAPHY (CT) IMAGE OF AN OBJECT FROM CONE BEAM PROJECTION DATA OR FROM PLANAR INTEGRALS discloses a two step approach for performing an inverse Radon transform from planar integrals obtained on a plurality of coaxial planes. The first step involves calculating from the planar integrals a two dimensional projection image of the object on each of a plurality of coaxial planes; while the second step involves defining normal slices through these coaxial planes from which a two dimensional reconstruction of each slice is obtained. In this slice by slice way, the reconstruction algorithms operate on the plurality of planar integrals to produce a three dimensional image of the object.
It is further essential to note that the acquired data set is complete only if it provides sufficient Radon data at every necessary point in Radon space, i.e. Radon space must be sufficiently filled with data over the region of support in Radon space which corresponds to that region in object space occupied by the object. Radon data is generally acquired by exposing an object within the field of view of a source and scanning about the object using a source fixed with respect to a corresponding detector to obtain measurements. Sufficient filling of Radon space by a candidate scanning trajectory is necessary for exact image reconstruction. Furthermore, if the detector integral space is filled over the region of support for the object, the Radon data set is complete. Bruce D. Smith in an article entitled "Image Reconstruction from Cone-Beam Projections: Necessary and Sufficient Conditions and Reconstruction Methods," IEEE Trans. Med. Imag., MI-4 (1985) 14, has shown that a cone beam data set is complete if each plane passing through the object cuts the scanning trajectory in at least one point. This criterion assumes that the detector is fixed relative to the source and that the entire object can be scanned in a continuous manner within the field of view of the source. Depending on the scanning configuration employed to obtain the cone beam projection data, the data set in Radon space may or may not be complete. Furthermore, the method of acquiring cone beam data along a suitable scanning trajectory determines whether Radon space is filled completely. The necessary volume of Radon space must be filled in a sufficiently dense as well as uniform manner to reflect consistency in the inversion process. Underfilling results in incomplete data, while overfilling results in redundant data. Clearly both the density of Radon data and the distribution of this density contribute to the accuracy and efficiency of image reconstruction. Utilizing an incomplete and/or non-uniform data set for image reconstruction by Radon inversion introduces artifacts which compromise image quality and may render the image inadequate for medical or industrial diagnostic use.
The scanning trajectory chosen for data acquisition significantly impacts the quality of data obtained. A scanning configuration comprising two circular trajectories whose axes of rotation are normal with respect to one another is suggested by Gerald N. Minerbo in "Convolutional Reconstruction from Cone-Beam Projection Data" IEEE Trans Nucl. Sci., Vol. NS-26, No. 2, pp. 2682-2684 (April 1979); and Heang K. Tuy in "An Inversion Formula for Cone-Beam Reconstruction" SIAM J Math , Vol. 43, No. 3, pp 546-552 (June 1983). Smith points out in his 1985 article that this trajectory satisfies the completeness criterion. Although complete, this scanning configuration is not practical as it is mechanically difficult to implement. A much easier to implement complete scanning trajectory has been disclosed in commonly assigned U.S. patent application Ser. No. 07/572,651, filed Aug. 27, 1990, by Eberhard et al, now U.S. Pat. No. 5,073,910, entitled "SQUARE WAVE CONE BEAM SCANNING TRAJECTORY FOR DATA COMPLETENESS IN THREE-DIMENSIONAL COMPUTERIZED TOMOGRAPHY". However, the scanning geometry most commonly adopted is the simple circular scanning trajectory which engulfs the object in the field of view of the source. Although easily implemented, a circular scanning trajectory acquires incomplete data. A scanning configuration which minimizes data incompleteness obtained from dual circular scans is disclosed in commonly-assigned U.S. patent application Ser. No. 07/572,590, filed Aug. 27, 1990, by Eberhard, now U.S. Pat. No. 5,068,882, entitled "DUAL PARALLEL CONE BEAM CIRCULAR SCANNING TRAJECTORIES FOR REDUCED DATA INCOMPLETENESS IN THREE DIMENSIONAL COMPUTERIZED TOMOGRAPHY".
Commonly assigned U.S. patent application Ser. No. 07/572,590 discloses an apriori approach to reducing the effects of incompleteness on three dimensional cone beam reconstruction by correcting two dimensional projection images obtained on each of a plurality of coaxial planes in Radon space using optically obtained object boundary information. From this, a three dimensional image is reconstructed on slices normal to the common axis in a slice by slice manner using two dimensional reconstruction on each slice. There is generally no a priori method to account for missing Radon data. Only proper data acquisition ensures a complete data set having sufficiently dense information to accurately reconstruct the image in a uniform manner by employing sampling consistent with a uniform data density distribution.
Generally a difficult to implement method for assessing whether a source scanning trajectory satisfies both the completeness criterion and a uniformity criterion has been disclosed for accommodating efficient exact image reconstruction in three dimensions. Three dimensional exact image reconstruction is by its very nature computationally intensive; therefore, ensuring that data is collected in a manner that sufficiently fills the necessary volume of Radon space in a uniformly distributed efficient manner without unduly escalating the complexity of practical data acquisition provides a significant improvement over the existing art.
A typical scanning and data acquisition configuration employing cone beam geometry is depicted in FIG. 1. An object 20 is positioned within the field of view between a cone beam point source 22 and a typical two dimensional detector array 24, which provides cone beam projection data. An axis of rotation 26 passes through the field of view and the object 20. For purpose of analysis, a midplane 28 is defined normal to the axis of rotation 26 which contains the cone beam point source 22. By convention, the axis of rotation 26 is generally taken to be the z axis, having its origin at its intersection with the midplane. The object centered (x,y,z) coordinate system is fixed relative to the source 22 and detector 24. In scanning the object 20 at a plurality of angular positions, the source 22 moves relative to the object and the field of view typically rotates along a preferrably circular scanning trajectory 30 lying in the midplane 28, while the detector 24 remains fixed with respect to the source 22 (or alternatively the object 20 can be rotated while the source 22 and detector 24 remain stationary). Data is acquired at a plurality of source positions during the scan. Data collected at detector 24 represent line integrals through the object 20. The approach to reconstruction then embodies calculating planar integrals on a corresponding set of coaxial planes from various line integrals through the object, then performing an inverse Radon transform on these planar integrals to reconstruct a three dimensional image of the object.
It has already been noted that data collected using a commonly adopted single circular scan is incomplete and artifacts may accordingly be introduced into the reconstructed image. Dual parallel circular scanning trajectories have been shown to reduce data set incompleteness. A circular square wave scanning trajectory, on the other hand, as well as, dual mutually perpendicular circular scanning trajectories provide sufficient Radon data for exact image reconstruction by satisfying the completeness criterion. More recently, Bruce D. Smith in an article entitled "Cone-beam Tomography: Recent Advances and a Tutorial Review", Optical Engineering, Vol. 29, No. 5, pp. 524-534, May 1990, mentions several complete scanning trajectories. Applicant has articulated a practical to implement, easy to visualize statement of the completeness criterion evaluating several examples of complete three dimensional scanning trajectories in co-pending U.S. patent application Ser. No. 07/737,117. However, no such easy to utilize criterion for ensuring the uniform density of complete data so obtained has been disclosed.

Method and apparatus for acquiring a uniform distribution of radon data sufficiently dense to constitute a complete set for exact image reconstruction of an object irradiated by a cone beam source