The invention relates to a method of making surface-sized paper/board. The web to be treated in the method is after surface sizing passed to a treatment process for providing a desired drying shrinkage and/or increase of drying stresses to create thereby a desired effect on the flexural strength and/or bulk of paper/board.

1. Field of the Invention
The present invention relates to a method of making surface-sized paper/board.
2. Description of Related Art
In printing paper and board, a high flexural strength/bulk ratio is desirable for adequate runnability and printability. Flexural strength can be increased e.g. by surface sizing, as well as by various gradient structures (multiple structures as well as gradient calendering).
An objective of surface sizing is to improve the strength properties of paper or board, such as internal bond strength (interlaminar strength) and surface strength (picking) Chemicals for use in surface sizing are water-soluble polymers, comprising predominantly starches because of the attractive price thereof. The raw material for starches includes plants, such as corn, wheat, barley, potato, tapioca, etc., the tubers, seeds, etc. thereof being sources of starch. Starch (C6H10O5) consists of straight-chain amylose and branched amylopectin. Other chemicals for use in surface sizing are e.g. various cellulose derivatives (CMC), as well as polyvinyl alcohol (PVA).
Flexural strength is reduced in calendering as the web compresses, resulting in a lower thickness and reduced bulk. Calculated flexural strength increases linearly as a function of thickness according to the following formulae:S1/S2=(E1h13)/(E2h23)E1/E2=h2/h1 h2h13/h1h23=h12/h22
wherein:
S1 and S2 represent flexural strengths of calendered and uncalendered paper, respectively;
h1 and h2 represent thicknesses of calendered and uncalendered paper, respectively; and
E1 and E2 represent elastic moduli of calendered and uncalendered paper, respectively.
The following general description deals with paper and board grades, as well as various calendering and coating processes for use in the manufacture thereof.
Paper and Board Grades
A wide range of various grades of paper and board are in existence and can be divided on the basis of basis weight in two categories: papers with a single ply and a basis weight of 25-300 g/m2 and boards made in multiply technique with a basis weight of 150-600 g/m2. As noted, the dividing line between paper and board is fluctuating, the boards of lowest basis weight being lighter than the heaviest papers. Ordinarily, paper is used for printing and board for packaging.
The following descriptions are examples of presently employed values for fibrous webs and substantial deviations from the given values may occur. The principal source publication for the descriptions is Papermaking Science and Technology, Papermaking Part 3, Finishing, edited by Jokio, M., published by Fapet Oy, Jyväskylä 1999, 361 pages, and Papermaking Science and Technology, Paper and Board grades, edited by Paulapuro, H., published by Fapet Oy, Jyväskylä 2000, 134 pages.
Printing papers made of mechanical pulp, i.e. those with a wood content, include newsprint, uncoated magazine and coated magazine paper.
Newsprint consists either completely of mechanical pulp or may contain some bleached softwood pulp (0-15%), and/or some of the mechanical pulp can be replaced by recycled fiber pulp. General values for newsprint can probably be considered as follows: basis weight 40-48.8 g/m2, ash content (SCAN-P 5:63) 0-20%, PPS s10 roughness (SCAN-P 76-95) 3.0-4.5 μm, Bendtsen roughness (SCAN-P21:67) 100-200 ml/min, density 600-750 kg/m3, brightness (ISO 2470:1999) 57-63%, and opacity (ISO 2470:1998) 90-96%.
Uncoated magazine paper (SC=supercalendered) comprises generally 50-70% of mechanical pulp, 10-25% of bleached softwood pulp, and 15-30% of fillers. Typical values for calendered SC paper (including e.g. SC−C, SC−B, and SC−A/A+) are basis weight of 40-60 g/m2, ash content (SCAN-P 5:63) of 0-35%, Hunter gloss (ISO/DIS 8254/1) of <20-50%, PPS s10 roughness (SCAN-P 76:95) of 1.0-2.5 μm, density of 700-1250 kg/m3, brightness (ISO 2470:1999) of 62-70%, and opacity (ISO 2470:1998) of 90-95%.
Table 1 shows typical values for coatable papers which contain mechanical pulp. (MFC=machine finished coated, FCO=film coated offset, LWC=light weight coated, MWC=medium weight coated, HWC=heavy weight coated)
Table 1
TABLE 1MFCFCOLWCMWCHWCbasis weight,50-7040-7040-7070-90100-135(g/m2)Hunter gloss25-4045-5550-6565-70(ISO/DIS 8254/1), (%)PPS-s102.2-2.81.5-2.00.8-1.50.6-1.0roughness,(offset)(μm) (SCAN-P0.6-1.076/95)(roto)density, (kg/m3)900-9501000-10501100-12501150-1250brightness (ISO70-7570-7570-7570-752470:1999), (%)opacity (ISO91-9591-9589-9489-942470:1998), (%)
Coated magazine paper (LWC=light weight coated) contains 40-60% of mechanical pulp, 25-40% of bleached softwood pulp, and 20-35% of fillers and coatings. HWC (heavy weight coated) can be coated even more than twice.
Woodfree printing papers made of chemical pulp, i.e. fine grade papers, include uncoated and coated printing papers based on chemical pulp, wherein the proportion of mechanical pulp is less than 10%.
Uncoated printing papers based on chemical pulp (WFU) have 55-80% of bleached birchwood pulp, 0-30% of bleached softwood pulp, and 10-30% of fillers. In WFU, the values fluctuate a great deal: basis weight 50-90 g/m2 (up to 240 g/m2), Bendtsen roughness 250-400 ml/min, brightness 86-92%, and opacity 83-98%.
In coated printing papers based on chemical pulp (WFC), the amounts of coating fluctuate a great deal according to requirements and intended application. The following are typical values for once- and twice-coated printing paper based on chemical pulp: once-coated, basis weight 90 g/m2, Hunter gloss 65-80%, PPS s10 roughness 0.75-2.2 μm, brightness 80-88%, and opacity 91-94%, and for twice-coated, basis weight 130 g/m2, Hunter gloss 70-80%, PPS s10 roughness 0.65-0.95 μm, brightness 83-90%, and opacity 95-97%.
Release papers have a basis weight which varies within the range of 25-150 g/m2.
Board making involves the use of chemical pulp, mechanical pulp and/or recycled pulp. Boards can be divided e.g. for the following main categories according to intended application.
Corrugated board provided with a liner and a fluting.
Boxboards for making containers, boxes. Boxboards include e.g. liquid packaging boards (FBB=folding boxboard, LPB=liquid packaging board, WLC=white-lined chipboard, SBS=solid bleached sulfite, SUS=solid unbleached sulfite).
Graphic boards for making e.g. cards, files, folders, casings, covers, etc.
Wallpaper bases.
Calendering
The surface properties and thickness profile of various papers and boards are processed by calendering to meet the requirements of a printing method and further processing. Coated grades are typically precalendered before a coating process and subjected to final calendering after the coating process.
Calenders are grouped in machine calenders, soft calenders, and multi-roll calenders. A machine calender has typically 1-2 nips and both nip-forming rolls are hard rolls. A soft calender has generally 1-4 nips and at least one of the nip-forming rolls is covered with a soft cover. A multi-roll calender has generally 5-11 nips. The roll assembly of a multi-roll calender includes both heated rolls and soft cover rolls.
Special calenders include e.g. a wet stack calender, a breaker stack, and long-nip calenders.
Wet stack calender is more or less identical to a multi-roll machine calender, yet totally different in terms of calendering process. Wet stack calender makes effective use of a moisture gradient, the web arriving at the calender only having a moisture of about 1-2%. Wet stack calender is provided with water boxes for forming a water film on the web surface upstream of a nip, said film being pressed to the web surface in the nip. Thus, the web only becomes wet at the surface, whereby the surface receives more calendering than the overdried interior. Wet stack calender is employed as a precalender for several board grades.
Breaker stack is a machine calender located in the drying section of a paper machine.
Long-nip calenders include a shoe calender, which has a soft belt around a shoe roll and in which the nip length is typically 50-400 mm, as well as belt calenders. The traditional belt calender consists of a soft calender's thermal roll, a belt loop, and a backing roll inside the belt loop, the latter being either a hard roll or a soft roll. The belt runs over the backing roll and guide/tension rolls. A special embodiment of the belt calender is a metal belt calender, wherein the calendering belt comprises a metal belt which travels around guide rolls and establishes, together with a counter-element, typically a roll, a long nip zone having a length of even more than 5000 mm. Inside the belt loop can be further provided a press element, e.g. a deflection-compensated roll, which can be used for establishing a nip point of higher compression load midway across the long nip zone.
Coating Techniques
With coated paper grades and coating as a method becoming more and more popular, the coating processes and equipment are challenged by increasing demands. In coating procedure, more specifically in pigment coating procedure, the surface of paper is formed with a layer of coating color at a coating head, followed by performing the draining of excess water. The forming of a coating color layer can be divided in supplying a coating color onto the surface of paper, i.e. application, as well as in adjusting the final amount of coating. The most important pigment coating method is so-called blade coating, in which the amount of coating is adjusted by means of a so-called doctor blade. The most common types of blade coating heads include a blade coater provided with a applicator roll and a blade coater provided with jet application. The coating process additionally involves the use of a so-called film transfer coater, the use of which has recently become more and more common. Another new technique being introduced involves the use of curtain coaters.
From a practical standpoint, the most essential difference between various coating devices relates to the application process and especially to the penetration occurring therein, i.e. to the penetration of a coating color into the paper.
In the manufacture of high-grade coated printing papers, more and more attention has been lately paid not only to high quality but also to productivity. Quality has likewise become a more important aspect in light coated papers of a bulk product type. Nearly all coaters are under pressure of raising quality, productivity, and running speed.
In applicator-roll application included in blade coating, the application is effected by using a roll rotating in a coating pan for picking up coating color onto the bottom surface of paper carried by a backing roll. The applied amount is normally 200-250 g/m2. In applicator-roll application, the coating color penetrates effectively into base paper. In addition, the fibers of base paper have time to swell prior to doctoring, thus increasing the paper's roughness volume.
In jet application, the coating color is in turn supplied directly onto the web surface by means of a nozzle. An advantage over the applicator-roll application is the absence of a rotating roll and hence improved aptitude to high running speeds. Another advantage is a less powerful pulse of application pressure, resulting in improved runnability. In jet application, the web wetting process is an intermediate between a applicator roll and a short dwell. In jet application, the applied amount is typically 130-220 g/m2.
In short dwell application, the coating color is delivered into an application chamber located immediately behind the doctor blade, one side wall of said chamber being constituted by a moving paper web supported by the backing roll. The moving paper web develops vortices in the application chamber and the coating color has a flowing speed on the paper web's surface which is equal to the paper web's speed. In short dwell application, the wetting of paper is slight as the application zone is subjected to a low pressure and the effective range is short. The swelling of paper fibers occurs partially only downstream of the doctor blade, which roughens the surface smoothed by the blade. Thus, the coating smoothness obtainable by a short dwell coater is inferior to what is achieved by applicator-roll and jet coaters.
The amount of coating remaining on the surface of paper is influenced by a wide range of variables. When such properties of base paper as roughness, porosity, and water absorption, are increasing, the amount of coating will also increase. Likewise, when the dry content and viscosity of a coating color are increasing, the amount of coating will increase. On the other hand, an increase in the water retention capacity of a coating color reduces the amount of coating. When the stress, working angle and blade thickness of a doctor blade are increasing, the amount of coating will in turn be reduced. As for other factors, an increase in running speed, as well as an increase in application pressure, lead to an increase in the amount of coating.
In addition to the above-described blade coaters, the coating and surface treatment can also be implemented by other devices. The following describes a few most commonly employed options. The size press unit consists of two rotating rolls. In this alternative, the coating color to be applied onto the surface of a web is applied to the web in a pond present between the web and the rolls. In addition to surface sizing, the size press can also be used for pigment coating. The amount of coating will be about 1.0-2.0 g/m2/side. A problem in the standard size press has been instability of the application pond at high rates of running speed.
Attempts have been made to eliminate the problem by designing film size presses, wherein a layer of coating or sizing agent desired on the surface of a paper web is first applied to the surface of press rolls, the layers passing therefrom to paper in a nip between the rolls. The employed application devices comprise units like short dwell coaters. Advantages gained by the apparatus include a controlled application even at high running speeds and a possibility of pigment coating (2-6 g/m2/side). Furthermore, the coating color can have its dry content increased with respect to a standard size press. The coating of film coating colors can be carried out either in a one- or two-sided manner. The runnability of a film transfer coating process is usually good with respect to blade coating. Compared to blade coating, the coating layer obtained by film transfer coating usually conforms better to the contour and has more coverage in that sense. It is not possible, however, to achieve high amounts of coating by film transfer coating.
In air brush coating, the application of a coating color is performed either by a single- or a multi-roll blade application apparatus or by means of a nozzle. Adjustment of the amount of coating and smoothing of the surface are in turn performed by means of an air jet. Air brush coating is used almost exclusively in board coating because of an excellent coverage provided thereby. Downsides include a limited running speed of the method and quite low dry contents of the coating color. The coating layer formed by an air brush is of a consistent thickness, conforming to the surface contours of paper.
Accordingly, basic solutions today in terms of coating a paper web are provided by short dwell and applicator-roll coaters, equipment based on jet application, and film size presses. An all-purpose general coater is yet to be designed.
Blade coating in its various forms is and seems to remain also in the future the most common coating method. As running speeds increase and areas for applied coating expand, the applicator roll will probably be replaced almost totally by solutions based on jet application.
One emerging new technique is also a so-called curtain coating technique. Curtain coaters can be divided in slot-fed or slide-fed coaters. In a slide-fed curtain coater, a coating is set flowing along an inclined plane and a curtain develops as the coating trickles over the plane's edge. In slot-fed application beams, a coating is pumped through a distribution chamber to a narrow vertical slot, a curtain developing along its lip and trickling down to the web. A coating can be applied in one or more layers. Compared to blade coating, curtain coating applies a much lesser force on the web and thus results in fewer disruptions caused by breaks in the paper web, thus improving runnability. Curtain coating is not capable of providing a smoothness equal to that achieved by blade coating, but the coverage obtained thereby is better than what is achieved by blade coating. The principal idea has been that the curtain coater would eventually replace the air brush.

Method of making surface-sized paper/board


A crystal growing method for growing a crystal from a raw material melt highly magnetic field is being applied to the raw material melt, the electromagnet for applying the magnetic field being supplied with a direct current having a ripple factor of less than 5% to thereby grow a crystal with good crystallinity properties.

1. Field of the Invention
The present invention relates to a method for growing crystals more particularly semiconductor single crystals such as Si, GaAs, or the like, and more particularly to a method of growing crystals while a magnetic field is being applied to the melt during crystal growth.
2. Description of the Prior Art
Methods of growing a crystal in a magnetic field are industrially important since these methods produce a high quality crystal of Si, GaAs, or the like. One such method is disclosed, for example, in Japanese Patent Publication No. 58-50951. This previously proposed method for growing crystals will be more fully explained in connection with FIG. 1.
In FIG. 1, reference 1 indicates generally a single crystal growing apparatus which is adapted to carry out the above mentioned crystal growing method. Reference 2 refers to a melt of a raw material such as a silicon melt contained in a container 3 consisting, for example, of a crucible made of quartz for accommodating the melt 2. About the outer periphery of the container 3, there is arranged a heating means 4 composed of an electric heater 5 which, for example, takes the form of a zig-zag pattern and forms a cylindrical plane about the outer periphery of the container 3. On the outside of the heating means 4 there is located a jacket 6 which is cooled by means of water or the like. Outside the jacket 6, there is a magnetic field generating means 7 comprising an electromagnet which produces a uniform direct magnetic field and consisting, for example, of a constant conductive electromagnet having an iron core or an electromagnet having a constant conductive solenoid coil. Reference 8 indicates a single crystal seed, and 9 refers to a chuck for pulling the single crystal from the melt as it grows, in keeping with conventional technology.
Pulling the single crystal by use of this apparatus is carried out in the following manner When a direct magnetic field is applied to the melt 2 of raw material in a predetermined direction by the magnetic field generating means 7, the single crystal seed 8 is dipped onto the surface of the raw material melt 2 and pulled while a supporting portion of the single crystal seed 8, specifically, a pulling rotational shaft including the chuck 9 and the crucible 3 are rotated relative to each other whereby a single crystal 10 is grown from the single crystal seed 8.
As described, when a crystal is grown while the direct magnetic field is being applied by the magnetic field generating means 7 to the conductive raw material melt 2, the apparent viscosity of the raw material melt 2 is increased by the magnetofluid effect and consequently the surface tension of the raw material melt 2 is increased and the convection of the raw material melt 2 is decreased. Consequently, variations in temperature and vibrations on the surface of the raw material melt 2 are suppressed. It is therefore possible to obtain a variety of advantages such as growing a single crystal 10 having good crystallinity, the reduction in the amount of materials forming the crucible or container 3, a control of the amount of oxygen to the melt 2, and the like, all of which are accomplished by selecting a suitable intensity of the applied magnetic field.
The aforementioned Japanese Patent Publication discloses that it is important to suppress the ripple of current supplied to the electric heater 5 of the heating means 4 to less than 4% for growing a high quality crystal. However, crystal defects such as a lamination defect or the like may occur in a single crystal grown by the above described method in relatively high density.
It has been found that the occurrence of crystal defects depends on the ripple or pulsation of the current flowing through the electromagnet which generates the magnetic field, and that when the ripple of the current flowing through the electromagnet is large, the intensity of the magnetic field varies with time, and an induced current is generated in the crystal growing apparatus, vibrations occur on the surface of the raw material melt, and consequently crystal defects are produced.
To avoid fluctuations in intensity of the magnetic field caused by the ripple of the direct current flowing through the magnetic field generating means, a battery might be employed as a power supply for the electromagnet. However, a battery is not appropriate as a power supply for the magnetic field which requires an electric power ranging from several kilowatts up to or exceeding 100 kilowatts. Accordingly, a rectifier is used as a direct current power supply source for the magnetic field generating means. The rectifier, for example, may be a silicon rectifier of the three phase, full-wave type, or a six phase, half-wave type, or a double star type with an interphase reactor or the like. Theoretically, the ripple factor or the pulsation ratio can be suppressed but this ripple factor can only be obtained where the rectifier is used in the vicinity of the maxiumum output of the direct power source. If the rectifier is used at a direct current output lower than the value mentioned, the distortion in the output wave form is increased.


The present invention teaches a method for enabling the formation of a high damping, soft polymer gel. The method includes: reacting a poly(alkenyl benzene-co-maleimide) polymer with a maleated polyalkylene and an alkyl diamine under substantially dry conditions sufficient to form a polyalkylene grafted poly(alkenyl benzene-co-maleimide) polymer product; and, dispersing the polyalkylene grafted poly(alkenyl benzene-co-maleimide) polymer product with an extender oil sufficient to form the gel. The present invention also contemplates a polymer gel composition, a polymer composition and an article manufactured from the polymer gel composition.

The polymerization of styrene and maleic anhydride by free radical initiation is well known in the prior art. Similarly, poly(styrene-co-maleic anhydride) polymer is well known. Further, imidization between a maleic anhydride and a primary amine group is a commonly known chemical reaction. Patent publications which have recognized these reactions include: German Patent DE 4241538, assigned to Leuna-Werke A.-G; Japanese Patent JP 94248017, assigned to Monsanto Kasel Kk.; and, Italian Patent EP 322905 A2, assigned to Montedipe S.p.A. Various other non-patent publications have also recognized these reactions. Included among them are: L. E. Colleman, Jr., J. F. Bork, and H. Donn, Jr., J. Org. Chem., 24, 185(1959); A. Matsumoto, Y. Oki, and T. Otsu, Polymer J., 23 (3), 201(1991); L. Haeussler, U. Wienhold, V. Albricht, and S. Zschoche, Themochim. Acta, 277, 14(1966); W. Kim, and K. Seo, Macromol. Rapid Commun., 17, 835(1996); W. Lee, and G. Hwong, J. Appl. Polym. Sci., 59, 599(1996); and, I. Vermeesch and G. Groeninckx, J. Appl. Polym. Sci., 53, 1356(1994).
The synthesis of monofunctional N-alkyl and N-aryl maleimides are also well known in the prior art. They have been extensively used to improve the heat stability of homo- and especially copolymers prepared from vinyl monomers. Typically, the bulk resins comprise ABS (poly(acrylonitrile-co-butadiene-co-styrene)) or a polyblend of poly(acrylonitrile-co-butadiene) and poly(styrene-co-acrylonitrile); PVC (poly(vinyl chloride)); SAN (poly(styrene-co-acrylonitrile)); PMMA (poly-(methyl methacrylate)); and the like. The maleimides can be copolymerized with other monomers such as acrylonitrile, butadiene, styrene, methyl methacrylate, vinyl chloride, vinyl acetate and many other comonomers. A more preferred practice in the industry is to produce copolymers of maleimides with other monomers such as styrene and optionally acrylonitrile and to blend these with ABS and SAN resins. In any event, the polymer compositions are adjusted so that the copolymers are fully compatible with the bulk resins (e.g., ABS and/or SAN) as shown by the presence of a single glass transition point (T(g)) as determined by differential scanning calorimetry (DSC).
It has long been recognized that two or more polymers may be blended together to form a wide variety of random or structured morphologies to obtain products that potentially offer desirable combinations of characteristics. However, it may be difficult or even impossible in practice to achieve many potential combinations through simple blending because of some inherent and fundamental problem. Frequently, the two polymers are thermodynamically immiscible, which precludes generating a truly homogeneous product. This immiscibility may not be a problem since often it is desirable to have a two-phase structure. However, the situation at the interface between these two phases very often does lead to problems. The typical case is one of high interfacial tension and poor adhesion between the two phases. This interfacial tension contributes, along with high viscosities, to the inherent difficulty of imparting the desired degree of dispersion to random mixtures and to their subsequent lack of stability, giving rise to gross separation or stratification during later processing or use. Poor adhesion leads, in part, to the very weak and brittle mechanical behavior often observed in dispersed blends and may render some highly structured morphologies impossible.
It is particularly desirable to prepare a grafted copolymer having the impact strength of polypropylene and the elastomeric properties of a block copolymer. It is also desireable to add an extender or plasticizer to the resultant grafted copolymer in order to obtain a copolymer having a low Shore A hardness.
Accordingly, it is an object of this invention to provide an oil or low molecular weight component extended grafted xe2x80x9ccentipedexe2x80x9d polymer of a maleated polypropylene and a poly(alkenyl benzene-co-maleimide) that is useful in producing high damping and soft materials.
More specifically, it is an object of this invention to provide a grafted centipede polymer formed by reacting maleated polypropylene and a poly(alkenyl benzene-co-maleimide) with a diamine.
Another object of the invention is to provide oil or low molecular weight component extended grafted centipede polymers that exhibit improved properties, including low Shore A hardness less than 35, high damping properties and a service temperature of about 100xc2x0 C.
The present invention is directed to an oil or low molecular weight component extended grafted poly(alkenyl benzene-co-maleimide)-polypropylene polymer soft gel composition having damping properties useful in producing molded products having heat resistance and a high elasticity and damping property.
The present invention is broadly directed to grafted polymer compositions of a maleated polypropylene and a poly(alkenyl benzene-co-maleimide) reacted with a diamine. It is further directed to a process for preparing an oil extended grafted polymer compositions broadly comprising a maleated polypropylene grafted to a functionalized thermoplastic material, namely a poly(alkenyl benzene-co-maleimide), under conditions sufficient to permit grafting of the functionalized polypropylene with the functionalized thermoplastic material. The grafted polymer is a glass-like material that becomes a soft and rubber-like elastomer after being oil-extended.
The extended grafted polymer gels of the present invention contain: 100 parts by weight of a grafted polymer of a poly(alkenyl benzene-co-maleimide) having at least one maleated polypropylene segments grafted thereto through the at least one functional linkage formed by a crosslinking reaction with a diamine grafting agent; and at least 30, preferably 30 to 1000, parts by weight of an extender such as an oil or a low molecular weight component. The poly(alkenyl benzene-co-maleimide) is a xe2x80x9ccentipedexe2x80x9d polymer formed by imidizing a poly(alkenyl benzene-co-maleic anhydride) with a primary amine. The xe2x80x9ccentipedexe2x80x9d polymer has a high molecular weight spine connected with many relatively short side chains formed from the addition of the primary amines. The length of the main chain usually equals or is longer than the entanglement length, which is herein defined theoretically as an order of magnitude of 100 repeating units, while the length of the side chains is much smaller than the entanglement length.
The preferred alkenyl benzenes contributed monomer units of the poly(alkenyl benzene-co-maleimide) xe2x80x9ccentipedexe2x80x9d polymer are either styrene or alpha-methylstyrene. The terms xe2x80x9calkenyl benzenexe2x80x9d and xe2x80x9cvinyl aromaticxe2x80x9d are understood to be interchangeable as used herein.
The poly(alkenyl benzene-co-maleimide) described herein are subsequently graft-reacted through a difunctional linking or grafting agent to a maleated polypropylene to yield a grafted polymer having at least one polypropylene segment grafted thereto through the at least one functional linkages thus formed.
The maleated polypropylene may be any of the conventionally known polypropylene compounds that are subsequently maleated by methods known in the art. The polypropylene grafted segment or segments have molecular weights xe2x80x9cMwxe2x80x9d of about 10,000 up to about 10,000,000, or higher, preferably about 20,000 to about 300,000.
The crystallinity, or tacticity, of the polypropylene may vary from being substantially amorphous to being completely crystalline, that is from about 10-100% crystallinity. Most typically, because of the extensive commercial use of isotactic polypropylene, the grafted polypropylene will be substantially crystalline, e.g., greater than about 90%. Generally, the polypropylene is substantially free of ethylene. However, under certain circumstances small amounts of ethylene, on the order of less than about 10% by weight, may be incorporated. Furthermore, in certain instances the polypropylene contain small amounts of ethylene in copolymers known as xe2x80x9creactor copolymersxe2x80x9d. Thus, it is within the scope of the invention that the grafted polypropylene contain minor amounts of ethylene, both as part of ethylene-propylene segments and as polyethylene segments.
Polymerization conditions for the preparation of polypropylene are well known in the art. Propylene can be polymerized into isotactic polypropylene in the presence of stereo-specific Ziegler-Natta catalyst systems comprising compounds of the transition metals of Groups 4 to 6 and 8 of the Periodic Table of elements, preferably titanium compounds, most preferably titanium halides, and organometallic compounds of elements of groups 1 to 3 of the Periodic Table, especially aluminum alkyls or aluminum alkyl halides. Illustrative examples include titanium trichloride, titanium tetrachloride as catalysts and triethylaluminum and diethyl aluminum chloride as cocatalysts. These transition metal catalyst systems can be non-supported or supported, for example, silica gel, or metal oxides and dihalides, such as MgO, MgCl2, ZnCl2, etc. Such systems can be reacted together and can be complexed with a variety of Lewis-base electron donors.
Molecular weight control is typically achieved by the incorporation of hydrogen via a feed stream into the polymerization reactor. The hydrogen is added at about 0 to 30 mole % based on the total monomer. The polymerization reaction is preferably conducted according to the slurry method employing an inert hydrocarbon diluent or liquid propylene as the vehicle. The polymerization temperature can be in the range of about 50xc2x0 C. to about 100xc2x0 C. and is preferably at a range or about 60xc2x0 C. to about 80xc2x0 C. Polymerization pressure can also vary over a wide range and is not particularly limited. The polymerization pressure can for example be in the range from between atmospheric pressure to 37,000 KPa. Such procedures and components are only illustrative of the knowledge in the art with respect to polypropylene polymerization, any are contemplated as useful within the scope of the invention. For general review of literature and patents in the art see xe2x80x9cOlefin Polymers (Polypropylene)xe2x80x9d in the Kirk-Othiner Encyclopedia of Chemical Technology, 3rd Edition v. 16, 453-469 (J. Wiley and Sons, 1981).
The maleinization of the polypropylene compound to maleated polypropylene is conveniently accomplished by heating a blend of polypropylene and ethylenically unsaturated carboxyl group-containing compounds, e.g., maleic anhydride, within a range of about 150xc2x0 to 400xc2x0 C., often in the presence of free-radical initiators such as organic peroxides that are well-known in the art. Free-radical grafting of the carboxyl group-containing compounds onto the polypropylene readily results. Methods of preparing these grafted polymers are well-known in the art as illustrated, inter alia, in U.S. Pat. Nos. 3,480,580, 3,481,910, 3,577,365, 3,862,265, 4,506,056, and 3,414,551 the disclosures of which are incorporated herein by reference. Such processes are well-known in the art, for example, an independent source of the description of the process is found in Y. Minoura, M. Ueda, S. Mizinuma and M. Oba, 3. Applied Polymer Sci. 1625 (1969). The use of heat and/or physical shearing optionally with the free-radical initiators, in such equipment as extruders, masticators, and the like, to simultaneously accomplish controlled degradation in molecular weight of the polypropylene along with the free-radical grafting of the maleic anhydride, as is known in the art, will be useful in accordance with this invention.
In particular, it is preferable to conduct the maleinization with such amounts of maleic anhydride and free-radical initiators, and under conditions of temperature and shearing such that free-radical sites on the polypropylene are formed substantially at the time of scission of the polypropylene chains and are formed at the point of such scission. The maleic anhydride is then grafted onto the scissioned end of one side of such broken chains. In this manner the anhydride groups are located principally at the ends of the maleated polypropylene chains, and the substantial majority of such maleated polypropylene chains contain one site of maleinization. This procedure permits grafting of the maleated polypropylene at its maleated end to the maleated block copolymer though the use of a difunctional linking or grafting agents having two functional groups each functional group being reactive with a maleate group on the polypropylene and block copolymer. Multiple sites of maleinization can lead to grafting of the maleated polypropylene to more than one maleated block copolymer polymer chain or at more than one site of one or more maleated block copolymer. The same substantial chemistry applies to the centipede polymers of the present invention.
In accordance with the above, the free-radical initiator is preferably used and will typically be utilized in an amount of from about 0.01 to 1.0 wt. %, preferably from about 0.02 to 0.5 wt. %, and most preferably from about 0.04 to 0.3 wt. % of the total polypropylene, and solvent if used, and will be added first. The mixture is then heated to a temperature at or about the known decomposition temperature of the selected free-radical initiator, concurrently with any optional mechanical shearing. The maleic anhydride is subsequently added in an amount typically from about 0.01 to 10.0 wt. %, preferably from about 0.1 to 5 wt. %, and most preferably about 0.75 to 2 wt. % of the total polypropylene.
The maleated polypropylene of this invention contain from about 0.01 wt. % incorporated maleic anhydride, based upon the weight of the maleated polypropylene, up to about 5 wt. %. Preferably the maleic anhydride content will be from about 0.01 to about 2 wt. %, most preferably about 0.03 to about 0.2 wt. %. As will be apparent, unreacted polypropylene will also be present in the reaction mix as will minor amounts of reaction by-products, such as decomposed free-radical initiator compounds and low molecular weight free-radical products. These by-products are substantially removed, by methods known in the art, e.g., sparging with nitrogen or washing with water. Maleic anhydride may not be left in substantial amounts in the polymer without detrimental affects on the subsequent reaction of the poly(maleimide-co-alkenyl benzene) with the maleated polypropylene.
The poly(alkenyl benzene-co-maleimide) of the present invention is formed by reacting a poly[alkenylbenzene-(co)-(maleic anhydride)] at from about 100xc2x0 C. to about 250xc2x0 C. and from about slightly above vacuum to about 20 atmospheres, under substantially dry conditions in the presence of a primary amine. The present invention is preferably directed to a polymer compositions of a poly(styrene-co-maleimide) formed by reacting a poly(styrene-co-maleic anhydride) with a primary amine.
For the purposes of this invention, poly(alkenyl benzene-co-maleimide) and poly(alkyl benzene-co-maleic anhydride) are defined to encompass random and stereo-specific copolymers, including copolymers having alternating alkenyl benzene and maleimide or maleic anhydride contributed monomer units along the polymer backbone. Such alternating structure are typically described as poly(alkenyl benzene-alt-maleimide) and poly(alkyl benzene-alt-maleic anhydride); however, these polymers are encompassed herein within the descriptions poly(alkenyl benzene-co-maleimide) and poly(alkyl benzene-co-maleic anhydride).
Processes for forming poly(alkyl benzene-co-maleic anhydride) polymers are well known to those skilled in the art. The preparation of the copolymers from electron donor monomers, such as styrene, and electron acceptor monomers, such as maleic anhydride, as a result of complexation of the electron acceptor monomers may be carried out in the absence as well as in the presence of an organic free radical initiator in bulk, or in an inert hydrocarbon or halogenated hydrocarbon solvent such as benzene, toluene, hexane, carbon tetrachloride, chloroform, etc. (N. G. Gaylord and H. Antropiusova, Journal of Polymer Science, Part B, 7, 145 (1969) and Macromolecules, 2, 442 (1969); A. Takahashi and N. G. Gaylord, Journal of Macromolecular Science (Chemistry), A4, 127 (1970).
Poly(alkyl benzene-co-maleic anhydride) polymers are prepared by reacting monomers of alkenylbenzene with maleic anhydride. The preferred alkenyl benzene monomers used for forming the poly(alkyl benzene-co-maleic anhydride) polymer are styrene or xcex1-methylstyrene. Suitable, but less preferred substitutes are: p-methylstyrene, 4-phenylstyrene, m-methylstyrene, o-methylstyrene, p-tert-butylstyrene, dimethylstyrene, and combinations thereof.
The poly(alkyl benzene-co-maleic anhydride) for use in the present invention is a polymer containing from about 5 to 99 mole percent of maleic anhydride monomer with the remainder being alkyl benzene monomer. The preferred poly(alkyl benzene-co-maleic anhydride) contains from 20 to 50 mole percent of maleic anhydride monomer. The most preferred poly(alkyl benzene-co-maleic anhydride) for use in the present invention is poly(styrene-co-maleic anhydride) containing 50 mole percent of maleic anhydride monomer and 50 mole percent of styrene monomer. The comonomers, maleic anhydride and alkenyl benzene, can be randomly or alternatingly distributed in the chain, however, it is preferred to have these comonomers alternating along the polymer backbone chain.
The poly(alkenyl benzene-co-maleic anhydride) has a molecular weight range between about 1,000 and up to about 500,000 or higher, more typically between about 10,000 and 500,000, and even more typically between about 150,000 and 450,000, where the molecular weight is weight-average (xe2x80x9cMwxe2x80x9d).
The poly(alkenyl benzene-co-maleimide) of the present invention is formed by reacting a poly(alkyl benzene-co-maleic anhydride) in the presence of a mono-primary amine at a temperature from about 100xc2x0 C. to about 300xc2x0 C. and at a pressure from about slightly above vacuum to about 20 atmospheres, under substantially dry conditions. The reactants are preferably dry mixed in the absence of solvents in a suitable mixing apparatus such as a Brabender mixer. It is preferable to purge the mixer with nitrogen prior to the charging of the reactants. The primary amine may be added in a singular charge or in sequential partial charges into the mixer containing a charge of poly(alkyl benzene-co-maleic anhydride). Preferably the primary amine is charged in ratio between 0.8 to 1.0 of moles of amine per monomer contributed units of maleic anhydride in the poly(alkyl benzene-co-maleic anhydride).
Suitable primary amine include but are not limited to: alkyl amines; alkyl benzyl amines; alkyl phenyl amines; alkoxybenzyl amines; alkyl aminobenzoates; alkoxy aniline; and other linear primary amines containing from 1 to 50 carbon atoms, preferably 6 to 30 carbon atoms, in the alkyl and alkoxy substituents in these primary amines. It is understood that the alkyl and alkoxy substituents on the above discussed primary amines can be linear or branched, preferably linear, and saturated or unsaturated, preferably saturated. Exemplary, but not exclusive of such amines are: hexylamine, octylamine, dodecylamine and the like.
The poly(alkenyl benzene-co-maleimide), prior to grafting with maleated polypropylene, preferably has a molecular weight range between about 1,000 and up to about 500,000 or higher, more typically between about 10,000 and 500,000, and even more typically between about 150,000 and 450,000, where the molecular weight is weight-average (xe2x80x9cMwxe2x80x9d).
The centipede polymer of the present invention may be prepared by any means well known in the art for combining such ingredients, such as blending, milling or internal batch mixing. A rapid and convenient method of preparation comprises heating a mixture of the components to a temperature of about 50xc2x0 C. to about 290xc2x0 C.
The centipede polymers of this invention are preferably manufactured by mixing and dynamically heat-treating the components described above, namely, by melt-mixing. As for the mixing equipment, any conventional, generally known equipment such as an open-type mixing roll, closed-type Banbury mixer, closed type Brabender mixer, extruding machine, kneader, continuous mixer, etc., is acceptable. The closed-type Brabender mixer is preferable, and mixing in an inactive gas environment, such as nitrogen or carbon dioxide, is also preferable.
Grafting of maleated polypropylene and poly(alkenyl benzene-co-maleimide) is performed by addition of a grafting agent such as a polyamine, preferably an organic diamine, to a blend of maleated polypropylene and poly(alkenyl benzene-co-maleimide) to partially cross-link the polypropylene to the poly(alkenyl benzene-co-maleimide) through the maleate functional groups.
Suitable organic diamines or diamine mixtures containing two aliphatically or cycloaliphatically bound primary amino groups are used as grafting agents for the process according to the present invention. Such diamines include, for example, aliphatic or cycloaliphatic diamines corresponding to the following general formula: R1(NH2)2 wherein R1 represents an aliphatic hydrocarbon group having from 2 to 20 carbon atoms, a cycloaliphatic hydrocarbon group having from 4 to 20 carbon atoms, or an aromatic hydrocarbon group having from 6 to 20 carbon atoms or R1 represents an N-heterocyclic ring having from 4 to 20 carbon atoms, e.g., ethylene diamine; 1,2- and 1,3-propylene diamine; 1,4-diaminobutane; 2,2-dimethyl-1,3-diaminopropane; 1,6-diaminohexane; 2,5-dimethyl-2,5-diaminohexane; 1,6-diamino-2,2,4-trimethyldiaminohexane; 1,8-diaminooctane; 1,10-diaminodecane; 1,11-diaminoundecane; 1,12-diaminododecane; 1-methyl4-(aminoisopropyl)-cyclohexylamine; 3-aminomethyl-3,5,5-trimethyl-cyclohexylamine; 1,2-bis-(aminomethyl)-cyclobutane; 1,2-diamino-3,6 dimethylbenzene; 1,2- and 1,4-diaminocyclohexane; 1,2-; 1,4-; 1,5- and 1,8-diaminodecalin; 1-methyl-4-aminoisopropyl-cyclohexylamine; 4,4xe2x80x2-diamino-dicyclohexyl; 4,4xe2x80x2-diamino-dicyclohexyl methane; 2,2xe2x80x2-(bis-4-amino-cyclohexyl)-propane; 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diamino-dicyclohexyl methane; 1,2-bis-(4-aminocyclohexyl)-ethane; 3,3xe2x80x2,5,5xe2x80x2-tetramethyl-bis-(4-aminocyclohexyl)-methane and -propane; 1,4-bis-(2-aminoethyl)-benzene; benzidine; 4,4xe2x80x2-thiodianiline, 3,3xe2x80x2-dimethoxybenzidine; 2,4-diaminotoluene, diaminoditolylsulfone; 2,6-diaminopyridine; 4-methoxy-6-methyl-m-phenylenediamine; diaminodiphenyl ether, 4,4xe2x80x2-bis(o-toluidine); o-phenylenediarnine; o-phenylenediamine, methylenebis(o-chloroaniline); bis(3,4-diaminophenyl)sulfone; diaminodiphenylsulfone; 4-chloro-o-phenylenediamine; o-amino-benzylamine; m-phenylenediamine; 4,4xe2x80x2-C1-C6-dianiline such as 4,4xe2x80x2-methylenedianiline; aniline-formaldehyde resin; and trimethylene glycol di-p-aminobenzoate. Mixtures of these diamines may also be used.
Other suitable polyamines for use as grafting agents in the process according to the present invention include bis-(aminoalkyl)-amines, preferably those having a total of from 4 to 12 carbon atoms, e.g., bis-(2-aminoethyl)-amine, bis-(3-aminopropyl)-amine, bis-(4-aminobutyl)-amine and bis-(6-aminohexyl)-amine, and isomeric mixtures of dipropylene triamine and dibutylene triamine. Hexamethylene diamine, tetramethylene diamine, and especially 1,12-diaminododecane are preferably used.
Thus in the preferred embodiment the process for preparing the grafted polymer of this invention comprises the steps of:
(A) combining a commercially available poly[alkenylbenzene-(co)-(maleic anhydride)] and a primary amine under substantially dry conditions sufficient to react substantially most of the acid anhydride moieties to form the poly(alkenyl benzeneco-maleimide); and,
(B) mixing a commercially available maleated polypropylene with the mass of step (A) under substantially dry conditions of elevated temperature;
(C) adding a diamine to the reaction mass of step (B), under a condition of agitation sufficient to form the grafted polymer of the present invention and cooling; and,
(D) adding an extender oil to the final polymer of step (C) under conditions of agitation.
In broadest terms the process for preparing the grafted polymer of this invention comprises combining the poly(alkenyl benzene-co-maleimide) with the maleated polypropylene and the grafting agent under conditions sufficient to permit grafting of at least a minor portion of the poly(alkenyl benzene-co-maleimide) onto the polypropylene. Thus the grafted centipede polymer composition of this invention will comprise the reaction product of the above described, the poly(alkenyl benzene-co-maleimide) grafting agent and the maleated polypropylene. The grafting reaction is accomplished by contacting the grafting agent and the poly(alkenyl benzene-co-maleimide) with the maleated polypropylene whereupon interaction and cross linking take place. Apparently the primary amino groups of the grafting agent react to form covalent chemical bonds (imide bonds) with the maleic moieties of the maleated polypropylene and the poly(alkenyl benzene-co-maleimide). The polypropylene is thus grafted to the poly(alkenyl benzene-co-maleimide) through covalent chemical functional linkages.
For best results, a proportion of approximately one-half molar equivalent of grafting agent per molar equivalent of maleic moiety can be employed due to the difunctionality of the grafting agent. The contacting can be accomplished by combining solutions of the polymeric reactants in suitable solvents, such as benzene, toluene, and other inert organic and inorganic solvents, in a suitable reaction vessel under substantially anhydrous conditions. Heating will accelerate the reaction and is generally preferred. More preferably commercially, the contacting can-be accomplished by premixing preformed pellets of the neat functionalized polymers and adding the grafting agent and melt processing in a physical blender or mixer, such as a Brabender mixer or an extruder, at temperatures of from about ambient to about 350xc2x0 C., preferably about 75xc2x0 to about 300xc2x0 C., and most preferably 120xc2x0 C. to about 250xc2x0 C. It is important that essentially all moisture or water be removed by drying prior to contacting the polymer reactants in order to avoid hydrolysis reactions which will compete with the sought cross linking and reduce the yield of the grafted copolymer composition of this invention.
The amounts of poly(alkenyl benzene-co-maleimide) and maleated polypropylene reacted into the grafted compositions of the invention may vary somewhat depending upon the properties desired in the finished composition. In general, the amounts of maleated polypropylene included in the grafted composition may range from about 1 to about 50 percent by weight based on total weight of composition. Preferred amounts of maleated polypropylene are from 1 to 30 percent by weight with a particularly preferred amount being from 10 to 25 percent by weight. The amounts of poly(alkenyl benzene-co-maleimide) centipede polymer included in the grafted composition may range from about 99 to about 50 percent by weight based on total weight of composition. Preferred amounts of the centipede polymer are from 99 to 70 percent by weight with a particularly preferred amount being from 90 to 75 percent by weight.
The centipede polymer gels of the present invention have an extender added to the prepared grafted copolymers during final processing. Suitable extenders include extender oils and low molecular weight compounds or components. Suitable extender oils include those well known in the art such as naphthenic, aromatic and paraffinic petroleum oils and silicone oils.
Examples of low molecular weight organic compounds or components useful as extenders in the compositions of the present invention are low molecular weight organic materials having a number-average molecular weight of less than 20,000, preferable less than 10,000, and most preferably less than 5,000. Although there is no particular limitation to the material which may be employed, the following is a list of examples of appropriate materials:
(1) Softening agents, namely aromatic naphthenic and paraffinic softening agents for rubbers or resins;
(2) Plasticizers, namely plasticizers composed of esters including phthalic, mixed phthalic, aliphatic dibasic acid, glycol, fatty acid, phosphoric and stearic esters, epoxy plasticizers, other plasticizers for plastics, and phthalate, adipate, sebacate, phosphate, polyether and polyester plasticizers for NBR;
(3) Tackifiers, namely coumarone resins, coumarone-indene resins, terpene phenol resins, petroleum hydrocarbons and rosin derivative;
(4) Oligomers, namely crown ether, flourine-containing oligomers, polybutenes, xylene resins, chlorinated rubber, polyethylene wax, petroleum resins, rosin ester rubber, polyalkylene glycol diacrylate, liquid rubber (polybutadiene, styrenetbutadiene rubber, butadiene-acrylonitrile rubber, polychloroprene, etc.), silicone oligomers, and poly-xcex1-olefins;
(5) Lubricants, namely hydrocarbon lubricants such as paraffin and wax, fatty acid lubricants such as higher fatty acid and hydroxy-fatty acid, fatty acid amide lubricants such as fatty acid amide and alkylene-bis-fatty acid amide, ester lubricants such as fatty acid-lower alcohol ester, fatty acid-polyhydric alcohol ester and fatty acid-polyglycol ester, alcoholic lubricants such as fatty alcohol, polyhydric alcohol, polyglycol and polyglycerol, metallic soaps, and mixed lubricants; and,
(6) Petroleum hydrocarbons, namely synthetic terpene resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic or alicyclic petroleum resins, aliphatic or aromatic petroleum resins, polymers of unsaturated hydrocarbons, and hydrogenated hydrocarbon resins.
Other appropriate low-molecular weight organic materials include latexes, emulsions, liquid crystals, bituminous compositions, and phosphazenes. One or more of these materials may be used as extenders.
In accordance with the present invention, the grafted polymer containing gel composition of the present invention may have added thereto at least about 1, preferably 30 to 1,000, parts by weight of extender per 100 parts by weight of the grafted copolymers. Most preferred amounts of added extender include from about 50 to about 500 parts of oil per 100 parts of grafted copolymer and ideally about 80 to about 300 parts of extender per 100 parts of grafted copolymer. The weight percent ratio of the polyalkylene grafted poly(alkenyl benzene-co-maleimide) to the extender is from about 100:1 to about 1:100, preferably 5:1 to about 1:5.
The polymer gels produced according to the present invention generally have high damping properties having a tan xcex4 in the range of about 0.1 to about 1.0, preferably higher than 0.3 over the temperature range of 30xc2x0 C. to 100xc2x0 C., and a Shore A hardness ranging from 0 to about 50, preferably about 0 to about 30, most preferably about 5 to 20 at about 20xc2x0 C. to 25xc2x0 C. or at room temperature. The service temperature of the gels of the present invention is less than or equal to 100xc2x0 C. for most of the polymers of the present invention, e.g., 100xc2x0 C. compression set of the gel is about 50. Some of the extended polymers of the present invention have a potential use up to 140xc2x0 C.
It is frequently desirable to include other additives well known in the rubber art to the compositions of the present application. Stabilizers, antioxidants, conventional fillers, reinforcing agents, reinforcing resins, pigments, fragrances and the like are examples of some such additives. Specific examples of useful antioxidants and stabilizers include 2-(2xe2x80x2-hydroxy-5xe2x80x2-methylphenyl) benzotriazole, nickel dibutyldithiocarbamate, zinc dibutyl dithiocarbamate, tris(nonylphenyl) phosphite, 2,6-di-t-butyl-4-methylphenol and the like. Exemplary conventional fillers and pigments include silica, carbon black, titanium dioxide, iron oxide and the like. These compounding ingredients are incorporated in suitable amounts depending upon the contemplated use of the product, preferably in the range of 1 to 350 parts of additives or compounding ingredients per 100 parts of grafted copolymer.
A reinforcement may be defined as the material that is added to a resinous matrix to improve the strength of the polymer. Most of these reinforcing materials are inorganic or organic products of high molecular weight. Various examples include glass fibers, asbestos, boron fibers, carbon and graphite fibers, whiskers, quartz and silica fibers, ceramic fibers, metal fibers, natural organic fibers, and synthetic organic fibers. Other elastomers and resins are also useful to enhance specific properties like damping properties, adhesion and processability. Examples of other elastomers and resins include adhesive-like products including Reostomer (produced by Riken- Vinyl Inc.), hydrogenated polystyrene-(medium or high 3,4) polyisoprene-polystyrene block copolymers such as Hybler (produced by Kurare Inc.), polynorbornenes such as Norsorex (produced by Nippon Zeon Inc.) and the like. In this case the foregoing materials are equally applicable to the present centipede polymer compositions.
The gels containing oil or low molecular weight component extended and polypropylene compositions of the present invention may be prepared by any means well known in the art for combining such ingredients, such as solution blending, milling, internal batch mixing, or continuous extrusion of a solid form of the centipede polymer and polypropylene compositions and the other ingredients. A rapid and convenient method of preparation comprises heating a mixture of the components to a temperature of about 50xc2x0 C. to about 290xc2x0 C.
The gels containing oil extended grafted poly(alkenyl benzene-co-maleimide)-polypropylene compositions of the present invention can be manufactured by mixing and dynamically heat-treating the components described above, namely, by melt-mixing. As for the mixing equipment, any conventional, generally known equipment such as an open-type mixing roll, closed-type Banbury mixer, extruding machine, kneader, continuous mixer, etc., is acceptable. The closed-type is preferable, and mixing in an inactive gas environment, such as nitrogen or argon, is also preferable.
The composition obtained using the manufacturing method of this invention can be molded with equipment conventionally used for molding thermoplastics. It is suitable for extrusion molding, calendar molding, and particularly injection molding.
The composition of the present invention can be mixed in any conventional mixer such as a Banbury mixer or roll mill or extruder normally conducted within the temperature range of about 120xc2x0 C. to about 300xc2x0 C., preferably maintaining the composition above its melting point for a few minutes up to several hours, preferably 10 to 40 minutes. A particularly useful technique is to add any fillers in the beginning of the mixing cycle in order to take maximum advantage of heating time and to prevent surface bleeding and overheating when forming the molded articles.
The resultant gel composition may be molded in appropriate press ovens and the like to form products in the form of extruded pellets, cut dices, preferably as small as possible since smaller pellets provide short heating times and better flow when utilized in flow molding. Ground pellets may also be utilized.
The extended grafted centipede polymers of the present invention can be used in high temperature applications including uses in injection molding or in any other compositions typically used for elastomeric properties.
In summary, the molded polymers produced from the gels containing extended grafted poly(alkenyl benzene-co-maleimide) and polypropylene compositions of the present invention retain elastomeric characteristics and are useful in high temperature applications and/or high damping applications.
Damping is the absorption of mechanical energy by a material in contact with the source of that energy. It is desirable to damp or mitigate the transmission of mechanical energy from, e.g., a motor, engine, or power source, to its surroundings. Elastomeric materials are often used for this purpose. It is desirable that such materials be highly effective in converting this mechanical energy into heat rather than transmitting it to the surroundings. It is further desirable that this damping or conversion is effective over a wide range of temperatures and frequencies commonly found near motors, automobiles, trucks, trains, planes, and the like.
A convenient measurement of damping is the determination of a parameter called tan xcex4. A forced oscillation is applied to a material at frequency f and the transmitted force and phase shift are measured. The phase shift angle delta is recorded. The value of tan xcex4 is proportional to the ratio of (energy dissipated)/(energy stored). The measurement can be made by any of several commercial testing devices, and may be made by a sweep of frequencies at a fixed temperature, then repeating that sweep at several other temperatures, followed by the development of a master curve of tan xcex4 vs. frequency by curve alignment. An alternate method is to measure tan xcex4 at constant frequency (such as at 10 hz) over a temperature range. We have defined a thermoplastic unfilled material as useful for damping when tan xcex4 greater than xcx9c0.3 over at least a 4 decade range, preferably a 6 decade range of frequency.
It is further important that this high degree of absorption of energy be accompanied by good mechanical and thermal stability, as the part prepared from the subject polymers will be cycled through various environments and repeatedly such to various forces of compression, tension, bending, and the like.
The compositions of the present invention are favorably used in the manufacturing of any product in which the following properties are advantageous: a high degree of softness, heat resistance, decent mechanical properties, elasticity and/or high damping. The compositions of the present invention can be used in all industry fields, in particular, in the fabrication of automotive parts, tire tread rubbers, household electrical appliances, industrial machinery, precision instruments, transport machinery, constructions, engineering, and medical instruments.
Representative examples of the use of the extended graft polymers of the present invention are in the fabrication of damping materials and vibration restraining materials. These uses involve connecting materials such as sealing materials, packing, gaskets and grommets, supporting materials such as mounts, holders and insulators, and cushion materials such as stoppers, cushions, and bumpers. These materials are also used in equipment producing vibration or noise and household electrical appliances, such as in air-conditioners, laundry machines, refrigerators, electric fans, vacuums, driers, printers and ventilator fans. Further, these materials are also suitable for impact absorbing materials in audio equipment and electronic or electrical equipment, sporting goods and shoes. Further, as super low hardness rubbers, these materials are applicable for use in appliances, damping rubbers, and as low hardness plastics, and it is preferable for molding materials. Further, because the present compositions can be used to control the release of internal low molecular weight materials out from the compositions, it is useful as a release support to emit materials such as fragrance materials, medical materials and other functional materials. The compositions of the present invention also possess utility in applications of use in liquid crystals, adhesive materials and coating materials.
Specific examples of uses of the compositions of the present invention as damping materials are as follows:
in audio equipment, such as in insulators for a portable CD or a CD mounted on a vehicle, mike holders for home video cassette recorder, radio cassette recorder, karaoke or handy mike, etc., an edge cone of a speaker, a tape holder of a radio cassette, a holder of a portable mini-disk player, an optical disk holder of a digital video disk, etc.;
in information relating equipment, such as in insulators for a hard disk, insulators for motors such as a spindle motor for HHD and stepping motor, insulators for floppy disk drive, insulators for CD-ROM of personal computer, and a holder for optical disk;
in communication equipment, such as in a holder for compact high performance mike or speaker of a portable telephone, a pocket bell or PHS, a mike holder for a wireless equipment, and a disk holder for portable note type electronic equipment;
in home electronics equipment, such as in insulators for CD-ROM of home TV game, insulators for cassette holder or CD-ROM of cassette holder or game machine, a holder of high performance mike, and cone edge of speaker; and
in other applications, such as in damping materials for printer head of a wordprocessor, printer of personal computer, small or middle handy type printer, or name printers, and insulators for CD-ROM used for measure equipment.
In the following, the present invention will be described in more detail with reference to non-limitative examples. The following examples and tables are presented for purposes of illustration only and are not to be construed in a limiting sense.

Gels derived from extending grafted centipede polymers and polypropylene


A moisture drying mattress comprised of at least one cushion that has opposite top and bottom surfaces and a plurality of apertures that extend through the cushion from the bottom surface to the top surface. An air channel mat is positioned below the cushion. The air channel mat is adapted and dimensioned to fit beneath the cushion and support the cushion bottom surface in a spaced relation above a bottom base of the mat to thereby form an air flow space between the cushion and mat through which air can flow. A vapor permeable, liquid impermeable cover encases the air channel mat and the cushion defining a vapor evaporation area under the cover. The air channel mat defines a moisture drying zone within the vapor evaporation area. An air pump is provided for selectively supplying a flow of air to the air channel mat. A controller is provided to control the flow of air to the air channel mat to evaporate the vapor in the vapor evaporation area. In an alternative embodiment, the air channel mat is positioned above the cushion.

(i) Field of the Invention
The present invention relates in general to cushioning devices, in particular to a mattress comprised of an air cell mattress with a plurality of apertures extending through the air cell mattress, a plurality of air channel mats residing beneath the air cell mattress, a top and bottom cover, and an air pump with a controller. The air pump communicates with the air channel mats to provide a flow of air to the bottom of the air cell mattress which flows upwardly through the plurality of apertures to remove moisture vapor which has accumulated below the cover. These mattresses typically are used in a hospital setting for users that are severely disabled or debilitated and readily cannot move.
(ii) Description of the Related Art
Over the years various mattresses for use in therapeutic care and the prevention of pressure ulcers on the user of the mattress have been developed. Pressure ulcers are red areas or open sores on the skin, often accompanied by indications that the skin and surrounding tissue is in the process of dying and decomposing. Pressure ulcers are caused by damage to the body""s soft tissue in areas where bone is close to the skin. Pressure ulcers, also known as bed sores, can occur over any boney part of the body such as the heels, hips and back. Users who are severely disabled or debilitated and cannot move are ideal candidates for developing pressure ulcers. These users are apt to lie or sit motionless in one position for long periods of time (hours). The major causes of pressure ulcers include (1) oxygen and nutrient starvation of the soft tissue; (2) pressure; (3) friction and skin shear; (4) excess moisture or moisture build-up at the skin; and (5) heat build-up in the tissue. Pressure at the user-mattress interface can constrict capillary blood flow and starve body tissue of oxygen and nutrients. The starvation of the tissue causes the tissue to began to die and decompose, causing the formation of a pressure ulcer.
While the interface pressure is very important, other factors also contribute to developing pressure ulcers. Friction and skin shear forces intensify the damaging effects of interface pressure. Friction results in abrasion damage to the skin surface. Skin shear is the horizontal force between the user and the mattress surface that produces tearing forces within deeper tissues. Skin shear can occur when a user is positioned or slides on a bed surface, stretching and damaging skin, connective-tissue, muscle and blood vessels. Excess moisture or moisture build-up at the user-mattress interface can be absorbed through the skin and possibly result in over-hydration of the skin. Over-hydration of the skin dramatically reduces soft tissue strength and increases the potential for friction/shear damage. Excess moisture on the mattress also raises the drag friction of the user-mattress interface due to liquid surface tension and can greatly increase friction and shear damage. Another factor contributing to the development of pressure ulcers is heat build-up in the tissue. Elevated tissue temperatures increase cellular metabolism and the subsequent need for oxygen and nutrients. Typically, the prior art mattresses designed to prevent pressure ulcers employ some type of air cell mattress wherein the individual air cells communicate with one another so as to evenly distribute the supporting force over the body of the user of the mattress. While the use of mattresses that provide a uniform supporting force reduces the possibility of developing pressure ulcers, other factors need to be addressed in order to further diminish the possibility of a user developing pressure ulcers.
For example, excess moisture or moisture build-up at the user-mattress interface can result in over-hydration of the skin along with an increase in the friction and skin shear forces experienced by the user, which greatly enhance the potential for developing pressure ulcers. To overcome the excess moisture build-up, prior art mattresses have employed methods of providing a flow of air through the mattress and along the user-mattress interface to remove any built-up moisture and minimize the potential for moisture to build-up. These mattresses included the use of an air pump to supply a flow of air to an air distribution member residing beneath the mattress which flows between the air distribution member and an inflatable mattress and then upwardly through the mattress to the user-mattress interface. These prior art mattresses use a single air distribution member to provide the flow of air to the mattress. However, these mattresses had a drawback in that, the use of a single air distribution member does not provide the flexibility to custom tailor the flow of air to different parts of the mattress to provide different levels of comfort and moisture removal for the user of the mattress.
Typical prior art mattresses also employ a single air pump to supply air to both the inflatable mattress and the air distribution member. The use of a single pump to provide air to the the inflatable mattress and to provide a flow of air to the mattress air distribution member to remove moisture increases the complexity and cost of the air supply system and prevents the use of other manufacturer""s mattresses. The complexity of the air supply system for both the mattress air cells and the air distribution member may also be difficult for a user to understand and control.
Some prior art mattresses utilize air from the air cells to provide a flow of air from the mattress to remove moisture. A typical mattress of this type uses low air loss air cells wherein the air cells are constantly venting a small amount of air out of the air cells as new air is being continuously pumped into the air cells. The air venting from the air cells provides the air flow to the mattress to remove the moisture. Additionally, other mattresses systematically inflate and deflate some of the air cells of the air cell mattress in order to relieve pressure on the user of the mattress. The deflation of the air cells provides an exhaust flow of air that is routed from the mattress to remove moisture therefrom.
Some prior art mattresses also utilize drainage holes in the mattress to remove large amounts of liquid that may be excreted by a user of the mattress, such as urine. While this aids in the removal of the liquid moisture, it does not remove moisture vapor and allows for a potentially unsanitary and non-hygenic mattress. The use of this type of mattress requires the mattress to be cleaned and disinfected after having been contaminated.
The present invention overcomes shortcomings of prior art mattresses by providing a cushion that provides a uniform supporting force over a large area, a cover that provides a smooth surface for the user to lay on that is vapor permeable and liquid impermeable, and an air channel mat for supplying air to the cushion to evaporate and remove moisture vapor from between the cover and the cushion. Furthermore, the present invention provides for a plurality of air channel mats that are supplied with a flow of air from an air pump that can selectively control which parts of the mattress are supplied with a flow of air to evaporate and moisture.
An effective therapeutic mattress that minimizes the possibility of pressure ulcers will (1) distribute pressure as evenly as possible along a user""s body; (2) have a low friction user-mattress interface that minimizes the skin shear forces; and (3) actively removes excess user-mattress moisture vapor.
The moisture drying mattress of the invention is comprised of at least one cushion that has opposite top and bottom surfaces and a plurality of apertures that extend through the cushion from the bottom surface to the top surface. An air channel mat is positioned below the cushion. The air channel mat is adapted and dimensioned to fit beneath the cushion and support the cushion bottom surface in a spaced relation above a bottom base of the mat to thereby form an air channel between the cushion and mat through which air can flow. An air pump is provided for selectively supplying a flow of air to the air channel mat. A controller is provided to control the flow of air to the air channel mat. A cover encases the air channel mat and the cushion.
In one exemplary embodiment, the cushion is an inflatable air cell mattress comprised of a plurality of air cells. The air cells are interconnected to permit air flow between the air cells and are preferably cubic in shape with a domed top. The inflated air cell mattress provides a uniform supporting force for the user of the mattress to minimize the pressure concentrations on the user. The distribution of the supporting force helps to prevent the occurrence of pressure ulcers. A plurality of apertures are provided in the cushion that extend through the base sheet and top sheet of the air cell mattress but do not communicate with the air cells. The apertures provide a path through which air can flow from the air channel mat upwardly through the apertures and between the air cells and to an area between the mattress and cover to remove moisture.
In the exemplary embodiment, the air channel mat is a plurality of air channel mats that are each dimensioned and adapted to fit beneath a portion of the cushion and support the cushion bottom surface in a spaced relation above the base of the air channel mat. The air channel mats each have a peripheral edge separating opposite top and bottom surfaces of the base. An air supply connector is associated with each air channel mat along its peripheral edge. Air supply connector can be part of the air channel mat or can be in the cover. A plurality of projections extend upwardly from the base top surface of each air channel mat and engage with the cushion bottom surface to support the cushion bottom surface in a spaced relation above the base top surface and create a channel into which air can flow between the air channel mat base and the cushion bottom surface. In another exemplary embodiment, the air channel mat is comprised of a three dimensional, resilient and air permeable support fabric.
In one exemplary embodiment, each air channel mat is also provided with a skirt that extends along a portion of the air channel mat peripheral edge. The skirt extends over the air supply connector and along a portion of the peripheral edge on both sides of the air supply connector. The skirt extends inwardly from the peripheral edge to cover a portion of the top surface of the base and the projections that extend upwardly from the base. The skirt serves to secure the air supply connector to the air channel mat and prevents the flow of air to the air channel mat from escaping along the portion of the peripheral edge with the skirt. In another embodiment, the air channel mat is without a skirt and the air connector is associated with the bottom cover.
In the exemplary embodiment, the air pump has a plurality of air outlets, with each outlet being controlled by a valve that is selectively positionable between opened and closed positions. The outlets are connected with the air supply connectors of the air channel mats, with each outlet being associated with one air channel mat and providing a flow of air from the air pump to the associated air channel mat when in the opened position. When the valves are in the closed position they prevent a flow of air from the air pump outlets to their associated air channel mats. The valves thereby allow a user to selectively choose which air channel mats receive a flow of air from the air pump.
In the exemplary embodiment, the air pump includes an air supply controller that controls the valves and the air pump and has a plurality of selectively adjustable inputs, the inputs controlling the opening and closing of the valves and the operation of the air pump. The inputs control a cyclic opening and closing of the valves for predetermined periods of time. The selectively adjustable inputs thereby enable a user to custom tailor the air flow to the mattress and the subsequent moisture removal.
In the exemplary embodiment, the cover is dimensioned and adapted to enclose the cushion and the air channel mats. The cover has a top sheet with a peripheral edge and a bottom sheet with a peripheral edge. The top and bottom sheets are connected together along portions of their peripheral edges, leaving an opening between the peripheral edges that provides access to an interior of the cover between the top sheet and bottom sheet.
Preferably, the bottom sheet has opposite top and bottom surfaces. The bottom sheet top surface has a plurality of pockets dimensioned and adapted to receive the air channel mats. The pockets are comprised of a U-shaped frame having an outer peripheral edge, an inner peripheral edge, and a margin extending between the outer and inner peripheral edges. The outer peripheral edge is secured to the bottom sheet top surface and the frame margin of the pocket overlaps a portion of the top of the air channel mat, thereby holding the air channel mat in the pocket. A portion of the air channel mat beneath the frame opening is exposed to the cushion bottom surface so that the mat projections engage with the cushion bottom surface to support the cushion bottom surface in a spaced relation above the air channel mat base.
Preferably, each pocket separates each of the air channel mats and forms a seal between the pocket and the cushion bottom surface. The seal directs the flow of air from the air pump through the air channel mat and then upwardly through the apertures in the portion of the cushion that is above the air channel mat, enabling the flow of air to be directed to the desired portion of the cushion.
In the exemplary embodiment, the top sheet of the cover has a top surface, upon which the user will interface with the mattress, that is both vapor permeable and liquid impermeable. The top sheet is comprised of a nylon sheet laminated to a urethane sheet. The nylon sheet is above the urethane sheet so that a user of the mattress will interface with the nylon sheet and the urethane sheet is positioned between the nylon sheet and the cushion top surface. The laminated top sheet allows moisture vapor to permeate into the cover and prevents liquid on the top surface of the cover from entering the mattress and contaminating the cushion and air channel mats. The moisture vapor is trapped between the cover and the mattress.
The use of a nylon sheet as the interface between the mattress and the user reduces the friction between the cover and the user and thereby minimizes the possibility of the user developing pressure ulcers from friction or skin shear. Additionally, by utilizing a flow of air to remove the moisture vapor from between the cover and the mattress, more moisture vapor will be removed from the mattress-user interface. The user""s skin is less likely to over-hydrate and as a result the soft tissue is strong enough to reduce the potential for friction and/or skin shear damage.
In another exemplary embodiment the vapor drying mattress includes at least one cushion, a cover over the cushion having a top and a bottom, with the top including an outer layer and an inner layer laminated to said top layer. The cover is impermeable to fluid but permeable to moisture vapor. The cover includes at least on pocket at the bottom layer of the cover top with a light weight, flexible air diffuser positioned in pocket. The pocket and air diffuser define a moisture drying zone below said cover. An air pump operatively connected to the pocket selectively supplyies an air flow to the air diffuser. The air flow supplied to the air diffuser flows through the air diffuser, generally downward toward the moisture drying zone to remove moisture vapor by a flow of air in the moisture drying zone.
The moisture drying mattress of the present invention overcomes the disadvantages of the prior art. The use of a plurality of air channel mats that can be selectively supplied with a flow of air from an air pump allows the user to selectively choose which portions of the mattress receive the vapor drying air flow. The use of a cover having a top surface upon which the user will interface that is made of a nylon sheet laminated to a urethane sheet keeps liquids out of the mattress while allowing the moisture vapor to pass through the cover and contact air flow around the mattress to remove the moisture vapor. The nylon surface provides a smooth, low friction surface upon which the user interfaces with the mattress and reduces the risk of damage to a user""s skin. The use of an air mattress that distributes a supporting force over the entire portion of the user""s body that is in contact with the mattress further reduces the possibility of developing pressure ulcers.

Moisture drying mattress with separate zone controls


A method of filling gaps on a semiconductor wafer with a dielectric material employs a plasma enhanced chemical vapor deposition (PECVD) process with a temperature in the range of 500 to 700xc2x0 C. As a result of the deposition process, gaps resulting from e.g. shallow trench isolation or premetal dielectric techniques are filled homogeneously without any voids. The deposition may be improved by applying two radio frequency signals with different frequencies.

The invention relates to a method of filling gaps on a semiconductor wafer with a dielectric material using a CVD (chemical vapor deposition) processing apparatus for performing a CVD-process under plasma and vacuum conditions at elevated temperatures.
When manufacturing integrated semiconductor circuits, certain process technologies require the filling of gaps on the surface of the semiconductor wafer. The wafer incorporates a plurality of integrated circuit elements after certain processing steps are executed. The requirement to fill gaps applies especially when manufacturing integrated circuit elements on semiconductor wafers that have been produced in accordance with sub 0.25 micron layout rules. The gaps may be located between transistors for isolation purposes according to the shallow trench isolation technique (STI) or may be located between polysilicon signal wires that precede the metalization process steps (premetal dielectric, PMD). The dielectric material to fill the gaps may be any known dielectric material as for example SiO2, BPSG, PSG, BSG, SiN, etc.
In known processes for the manufacturing of ICs rather complex or ineffective CVD-deposition processes for filling gaps were used. For example a High Density Plasma-(HDP)-CVD-reactor based on a silane/argon gas mixture at around 350 to 400xc2x0 C. is used employing simultaneous oxide deposition and sputtering. Also, a HDP-CVD-process based on a silane-helium mixture at 600xc2x0 C. is used for gap filling. However, helium is a very light ion and its sputter efficiency is almost zero. This leads to a bottom up fill of the gap.
Another process uses post deposition reflow, e.g. deposition of a glass on basis of boron phosphorous silane (BPSG) or tetra ethyl ortho silicate (TEOS) and a subsequent annealing at 850xc2x0 C. Further, another process uses in situ reflow above the glass transition temperature which is greater than 750xc2x0 C., e.g. in a Low Pressure-(LP)-CVD-reactor; the glass itself flows. Below the glass transition temperature at about 400 to 600xc2x0 C. a Sub Atmospheric Pressure-(SA)-CVD-reactor is used. A SACVD reactor commonly operates at pressures in the range from 2.66xc3x97103 Pa to 8.0xc3x97104 Pa (20 to 600 Torr).
HDP-CVD-reactors operate at a very low pressure, typically in the range of 0.133 Pa to 3.33 Pa (1 to 25 mTorr). The reaction chamber is rather expensive. SACVD-reactors use aggressive ozone molecules. The turnaround time for wafers is rather low so that a number of SACVD-reactors have to be operated in parallel. Thus, HDP-CVD-based processes or SACVD-based processes are quite expensive.
U.S. Pat. No. 5,643,640 discloses a fluorine doped phosphosilicate glass process (FPSG) using a Plasma Enhanced-(PE)-CVD-deposition for filling gaps or voids. The gaps may have a high aspect ratio. The process is carried out at a temperature between 400 to 500xc2x0 C. Using fluorine, however, has the drawback that the gate oxide may be contaminated, damaged or the fluorine may further be oxidized. Fluorine doped deposition materials are not desired in the lower front end of line levels of subquarter micron process technology.
U.S. Pat. No. 5,204,138 discloses a plasma enhanced CVD process for fluorinated silicon nitride films. The process runs at about 267 Pa to 1.33xc3x97103 Pa (2 to 10 Torr) at a temperature between 300xc2x0 to 600xc2x0 C. The fluorinated nitride film shows a high conformality over silicon trench structures.
International Publication No. WO 97/24761 discloses a void-free trench-fill process, which fills a trench in a two-step approach. The first step involves the deposition of a protection layer of silicon dioxide over the wafer into the trench. The second step involves forming a trench-fill layer of silicon dioxide over the protection layer. The two steps employ different RF bias levels to the wafer. During trench-fill the temperature of the wafer is kept in a range of about 200xc2x0 to about 700xc2x0 C.
In U.S. Pat. No. 5,356,722 the RF power for a PECVD TEOS deposition can be employed at a frequency of 13.56 MHz or at lower frequencies in the range between 100 to 450 kHz.
It is accordingly an object of the invention to provide a method of filling gaps on a semiconductor wafer which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which provides a good void-free filling of a gap with a dielectric material at moderate costs.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of filling gaps on a semiconductor wafer with a dielectric material, the method including the steps of:
inserting a semiconductor wafer into a reaction chamber of a plasma enhanced chemical vapor deposition processing apparatus;
providing a reaction gas including nitrogen and being free of an element selected from the group consisting of a halogen component and ozone;
performing a chemical vapor deposition (CVD) under plasma conditions and under vacuum conditions to deposit a dielectric material on the semiconductor wafer by using the reaction gas;
performing the chemical vapor deposition at a temperature above 500xc2x0 C.; and
providing a reaction gas pressure between 13.3 Pa and 1.33xc3x97103 Pa (100 mTorr to 10 Torr) in the reaction chamber of the plasma enhanced chemical vapor deposition processing apparatus.
In other words, the method of the invention uses a plasma enhanced-(PE)-CVD-deposition apparatus at an elevated temperature above 500xc2x0 C. Particularly the temperature is in the range of 500 to 700xc2x0 C. In such a PECVD-process there is no need for using halogen ions or radicals. The PECVD-deposition process according to the invention is applicable to any common dielectric material, e.g. SiO2, BPSG, PSG, BSG, SiN, and provides a conformal filling of the gap. A PECVD-reaction chamber operates at reasonable temperatures and vacuum pressures so that the costs of the reactor are below that of a HDP-CVD-apparatus. The throughput of a PECVD-reactor is higher than for a SACVD-reactor. Practically, a PECVD-chamber according to the invention will cost approximately half of a HDP-CVD-chamber and will have approximately double the throughput of a SACVD-chamber.
The reaction temperature, which lies preferably between 500 and 700xc2x0 C. is caused by a ceramic heating element located under the receptor carrying the semiconductor wafer. The vacuum is generated by a vacuum pump. The pressure is between 13.3 Pa and 1.33xc3x97103 Pa (100 mTorr and 10 Torr).
The plasma gas in the chamber is generated by a radio frequency signal. The signal has a frequency of more than 10 MHz, preferably 13.5 MHz. The radio frequency signal is coupled into the chamber opposite the front side of the wafer. According to a preferred embodiment of the invention a second radio frequency signal is coupled into the chamber, too. The second radio frequency signal has a frequency of less than 100 kHz, preferably about 10 kHz. This means that the two frequencies of the radio frequency signals differ by at least two orders of magnitude. The first radio frequency signal has a power of several hundreds of Watts. The second radio frequency signal is applied with lower power. Both signals are applied through different coupling devices into the chamber or through the same coupling devices.
The reaction gas composition in the chamber may be of any known type. Due to the high temperature an addition of halogen components or radical components as is ozone will not be necessary. The reaction gas or precursor gas composition includes one of the following compositions:
Dielectric Material to be Depositedxe2x80x94Precursor
SiO2xe2x80x94TEOS, O2, N2 or SiH4, N2O, N2
SiNxe2x80x94SiH4, N2O, NH3, N2
BSGxe2x80x94TEOS, TEB, O2, N2 or SiH4, B2H6, N2O, N2
PSGxe2x80x94TEOS, TEPO, O2, N2 or SiH4, PH3, N2O, N2
BPSGxe2x80x94TEOS, TEB, TEPO, O2, N2 or SiH4, PH3, B2H6, N2O, N2
BSG/PSG/BPSG: Boro-/phosphorsilicate-/borophosphorsilicate-glass
TEB: Tri ethyl borate
TEPO: Tri ethyl phosphate
The semiconductor wafers to be processed by the method according to the invention have gaps on the surface of the semiconductor wafer to be filled. The gaps may be shallow trenches that had been etched into the silicon substrate, e.g. by any dry etching technique. The trenches serve to separate and isolate transistors of the same type from each other. This layout structure is commonly called shallow trench isolation (STI).
Another area of application of the invention is to fill the gaps established by the polysilicon wiring structure. A multilayer structure composed of polysilicon, tungsten silicide and nitride is deposited on top of the wafer during the respective process steps. After patterning in order to generate local connections such as gate electrode connections and trench capacitor connections for DRAMs (dynamic random access memories), gaps are left between the multilevel polysilicon wiring structure. The gaps are to be filled with dielectric material according to the PECVD-process of the invention. The gaps in the polysilicon structure have high aspect ratios of up to 17. On the filled planar polysilicon-dielectric surface there is further deposited a metal layer for wiring. The above mentioned dielectric, therefore, is known as pre-metal dielectric (PMD).
Thus according to a preferred mode of the invention, gaps formed between transistors on the semiconductor wafer are filled with the dielectric material and according to another mode of the invention gaps formed between portions of a metalization layer on top of the semiconductor wafer are filled with the dielectric material.
Under the conditions of the PECVD-deposition process according to the invention, the reactive molecules have a high enough mobility due to the elevated temperature so that they reach the bottom of the gap to be deposited there. The corner effect, i.e. the phenomenon that molecules are primarily deposited at the upper edge of the gap, is reduced by the higher mobility of the molecules due to the elevated temperature. The second radio frequency coupled into the reaction chamber causes a sputter effect at the upper edge of the gap, i.e. molecules tending to be deposited at that location are loosened again by the application of the second radio frequency signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of filling gaps on a semiconductor wafer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Method of filling gaps on a semiconductor wafer