baber/WOPTO huggingface dataset:
Patent KR-850001659-B1 (KR)
Title: Cooking apparatus with menu display
Inventor: HIRADA HIDEDOSHI
IPC: F24C7/08
Filed: 1982-01-28
Granted: 1985-11-06
Abstract: A microwave oven has operating keys for selecting a cooking menu.  A display device has a number of display cards which are inscribed with  a cooking menu.  The display cards are swingingly secured along the periphery of a rotatable member.  The display cards are successively turned to change the displayed menu according to the rotation of the rotatable member.  A heating device is operated according to a sequence corresponding to the cooking menu displayed on the display device by the signal from the operating keys.
Patent KR-880001882-B1 (KR)
Title: Dual door type rotary nozzle
Inventor: YOSHIHARA DETSUYA
IPC: B22D37/00
Filed: 1982-02-23
Granted: 1988-09-27
Abstract: A rotary nozzle including a fixed cover (2) and a sliding cover (3) comprises a square cassette (1) having a space (1') to rotatably receive the fixed cover having a brick plate (4) with two nozzle holes.  The fixed cover is hinged to one side of the cassette and has a device (2') to turn the brick plate.  The sliding cover having a driving brick plate (5) and a rotor mechanism (9) is hinged to the other side of the cassette to the fixed cover.  This rotary nozzle can be used for making steel slabs.
Patent KR-860000323-B1 (KR)
Title: Method productor of sinter ore
Inventor: NAM KI-SAM
IPC: C22B1/16
Filed: 1983-09-02
Granted: 1986-04-09
Abstract: The compsn. of bonding particles is regulated to reduce the sintering temp. and amount of coke. The compsn. for bonding particles of 0.5 mm diameter is Fe2O3 (62.0-66.5 wt%); SiO2 (8.0-11.5 wt%); CaO (20.0- 23.0 wt%); Al2O3 (2.8-3.8 wt%); MgO, and some impurities. The bonding particles and CaO from the thermal decompsn. of CaCO3 are fused together and cooled to sintered ore. The compsn. of the product is Fe (56.0-58.0 wt%); SiO2 (5.0-7.0 wt%); CaO (8.0-11.0 wt%); Al2O3 and MgO, below 2.0 wt%, respectively.
Patent KR-910004986-B1 (KR)
Title: 축 밀봉 시스템
IPC: F16J15/16
Filed: 1983-10-19
Granted: 1991-07-20
Abstract: 내용 없음.
Patent KR-930002215-B1 (KR)
Inventor: BURLI MARTIN
IPC: C07C49/665
Filed: 1984-07-11
Granted: 1993-03-27
Abstract: 내용 없음.
Patent KR-910007051-B1 (KR)
Inventor: FREDRICTION TARUSE W
IPC: B25J5/04
Filed: 1984-09-01
Granted: 1991-09-16
Abstract: 내용 없음.
Patent KR-870000531-B1 (KR)
Title: Wettable olefin polymer fibers
Inventor: SAWYER LAWRENCE H
IPC: D03D25/00
Filed: 1985-02-16
Granted: 1987-03-14
Abstract: Wettable fibers or fine filaments are prepd. from a compsn. comprising an olefin polymer, i.e. a linear low density polyethylene(LLOPE) and blends or alloys of LLDPE with other olefin polymers, having an incorporated wetting agent. The wetting agent comprises at least one of ; (a) an alkoxylated alkylphenol(I) in combination with a mixed mono-, di- and/or triglyceride(II), (b) a polyoxyalkylene fatty acid (III), or (c) a combination of (b) and any or all pts. of (a). (I) pref. has the formula(Ia) where R= C1-20 alkyl, n=10-55. (II) pref. has the formula (IIa) where OR1,OR2  and OR3 are, independently, hydroxyl or fatty acid ester gps. (III) pref. has the formula R-(CH2CH2O)n-CH2CH2OH where R=fatty acid ester gp., n=10-55.
Patent KR-870001448-B1 (KR)
Title: Rotary piston type compressor
Inventor: MIYAJIMA HIDENOBU
IPC: F04C29/00
Filed: 1985-03-15
Granted: 1987-08-06
Abstract: The compressor has a housing, with an eccentrically turning rotor, and a rotor shaft, with rotor and balance weight of its rotary and longitudinal axis.  The balance weight (29,33) is located inside the compressor housing(11).  The compressor shaft is formed as a crank shaft, with the rotor (23) supporting itself on its ends, and the balance weight located between its flanks(21).  This consists of a cylinderical weight, and a holder, shaped as a yoke, to form a chamber with the crank shaft surface (17), to accommodate the weight.
Patent KR-890000844-B1 (KR)
Title: Automatic fire prevention with infrared ray responsive type fire detector
Inventor: ODASHIMA TAKASHI
IPC: G01J1/42
Filed: 1985-04-30
Granted: 1989-04-11
Abstract: he fire extinguisher has the detector receiving infrared rays from the flames of a fire in a detecting area at one of an array of light receiving elements which corresponds to the ray's incident angle into an assembly of an infrared ray passing filter and a condenser lens. Variations in the detected output of the detector resulting from flaring of the fire flames are discriminated.  When the output of the fire detector is higher than a predetermined level, an extinguishant tank communicating with the ejection nozzle is opened to discharge towards the flames the extinguishant from the tank.
Patent KR-900000901-B1 (KR)
Title: Sea aquaculture installation
Inventor: BRDANG ANDRE
IPC: A01K61/00
Filed: 1985-05-28
Granted: 1990-02-19
Abstract: The farm consists of at least two floating modules (12,14) which are arranged in a line running at right angles to the average direction of the currents in the surface layer of the sea. THe modules are sufficiently far from one another that waste products from one module do not affect any other module.  The distance between the two modules is approximately equal to the sum of the half widths of the zones of action of the two modules. Each module consists of a floating cage with a minimum horizontal dimension in any direction of 20 meters.
Patent KR-900003566-B1 (KR)
Title: Word processor
Inventor: SHYOJI DAKKAGI
IPC: G06F17/22
Filed: 1985-06-19
Granted: 1990-05-21
Abstract: The word block searching method searches for a specific designed work block (a one-sentence word block). Instead of designating it by a cursor operation from the head position to the tail position of the word block, portions of the head and tail portions are designated. A word block searcher has a CPU for performing head and tail portion search of work block data in a document memory based on partial head and tail position designation. The CPU is also for reading out a word block defined by the found head and tail positions and displaying the readout word block.
Patent KR-880002313-B1 (KR)
Title: Producing method of inoculative materials for leguminous plants
Inventor: MIN TAE-IK
IPC: C12N1/10
Filed: 1986-03-20
Granted: 1988-10-22
Abstract: Root-nodle bacteria inocula for leguminous plants were prepd. Thus, Rhizobium japonicum KLTL 8182p was cultured on the medium contg. 10 mannitol. 1.0 yeast extract, 0.2 MgSO4, 0.2 NaCl, and 0.2g K2HPO4 per liter of water for 3 days at 28↿C. 100 peat, or 100 lignite, or 100 zelite, or 100 g leaf mold was pulverized to > 100 mesh particles, autoclaved for 3 hr at 121↿C,and mixed with the above cultures (40ml), 0.5 g Me, and 5 g B.  The mixt. was packed into a polyethylenevinyl bag, sealed, and incubated for 2 weeks at room temp. to provide inocula availible for 1000m2 soils.
Patent KR-900007044-B1 (KR)
Title: Insulated gate semiconductor device
Inventor: BALIGA BANTVAL J
IPC: H01L29/08
Filed: 1986-04-23
Granted: 1990-09-27
Abstract: An insulated gate semiconductor device includes at least one inherent bipolar transistor, said device comprising in a silicon semiconductor wafer (12): a semiconductor drift region (22) of a first conductivity type; a semiconductor base region (24b) of a second conductivity type opposite to said first conductivity type, said base region adjoining said drift region; a semiconductor emitter region (27b) of said first conductivity type adjoining said base region; and a gate electrode (18a) insulatingly spaced from said base region and conductively coupling said drift region to said emitter region by an inversion layer (24') formed in said base region in response to an appropriate applied bias.
Patent KR-900000528-B1 (KR)
Title: Control circuit for air conditioner
Inventor: KIL YONG-HYUN
IPC: F24F11/02
Filed: 1986-07-07
Granted: 1990-01-31
Abstract: The airconditioner having moisture remover for maintaining constant temperature and humidity inlcudes a controller (1) and a humidity controller (2) operated by the room condition and a function switch unit (10) for selecting the operating function, and relays (RY1-RY4) for controlling a fanmotor (3) and a compressor (4).
Patent KR-930002783-B1 (KR)
Title: Nock for arrows of sports and hunting bows
Inventor: BEITER WERNER
IPC: F42B6/02
Filed: 1986-08-30
Granted: 1993-04-10
Abstract: A nock for arrows is disclosed. This nock is formed so that at all times during spanning of the bow and firing of the arrow, the nock-location section of the bowstring will be received in the nock so that the collar lies evenly against the bottom of the furrow of the nock for accurate firing of the arrow.
Patent KR-920003232-B1 (KR)
Inventor: BUSH JOHN W
IPC: B60C15/028
Filed: 1986-09-02
Granted: 1992-04-25
Abstract: 내용 없음.
Patent KR-960007032-B1 (KR)
Title: Bead ring of pneumatic tire and its manufacturing process
Inventor: LACOUR JEAN-CHARLES
IPC: B29D30/48
Filed: 1987-07-09
Granted: 1996-05-27
Abstract: A bead ring for reinforcing a bead of a pneumatic tire having a carcass ply comprises, on the bead ring surface, ribs made of a material whose secant modulus in extension, measured at 10% elongation and at 160 DEG 0 C., is equal to at least 70 MPa. Pneumatic tires have such a bead ring, the carcass ply being in contact with the ribs.
Patent KR-910006647-B1 (KR)
Inventor: HIROSE KENCHI
IPC: G06F17/30
Filed: 1987-08-28
Granted: 1991-08-30
Abstract: 내용 없음.
Patent KR-910001184-B1 (KR)
Title: Hot-water heater
Inventor: KIM DAE-YOUNG
IPC: F24H1/28
Filed: 1987-09-08
Granted: 1991-02-25
Abstract: The deivce comprises a plurality of heating exhaust pipes (5) being arranged in  hot  water  tank  (1)  with  inner  cylindrical combustion chamber (2); two-stage type  upper  and  lower  stepped parts (3)(3') at the  upper  of  tank  (1);  partition  plate  (4) between the parts  (3)(3');  detachable  lower  cover  (7)  having jointing pipes  (6)  for  connecting  the  pipes  (5),  which  are submerged in the tank (1); at the lower  of  the  tank.  With  the cover  (7)  detached,  the  pipes  (5),(6)  may  be  descaled  for maintenance service of the boiler.
Patent KR-900007509-B1 (KR)
Title: Pad for air bag device
Inventor: SHIRAKI KOJI
IPC: B60R21/20
Filed: 1987-12-03
Granted: 1990-10-11
Abstract: The pad has box-like cushion and insert with soft burstable cover layer. The pad is for use in an air bag assembly enclosing an air bag which inflates in case of an accident. The pad comprises an upper wall (11A) and side walls (11B) extending downward from the fringes of the upper wall. The inset comprises a rectangular tubular base protion made from a synthetic resin and flexible mets disposed on opposite sides of the thin-walled portion.
Patent KR-910001678-B1 (KR)
Title: Multiple calling method by one calling pabx
Inventor: PARK SUN-EUNG
IPC: H04M3/42
Filed: 1988-04-27
Granted: 1991-03-18
Abstract: The method is for forming the telecommunication loop  between a subscriber  group  (without  calling  the  representative  phone number)  but  any  phone  number  belonging  to  the  group.   The telephones  of  the  group  are  given  with  many  phone  numbers representing the group to form the  telecommunication  loop,  then the call can be received even when only one user is in the  group. The method includes a step for finding the dialed phone number  in the look-up table, a step for checking the state of  port  related to the dialed phone number,  a  step  for  transmitting  the  ring signal to the ports and ringback the signal  to  the  transmitter, and a step for forming the loop between  the  receiving  telephone and quitting to provide the ring signal to another telephones.
Patent KR-910005698-B1 (KR)
Inventor: LAI TO-WANG
IPC: E21B43/22
Filed: 1988-06-18
Granted: 1991-08-02
Abstract: 내용 없음.
Patent KR-930005330-B1 (KR)
Title: Method for manufacturing a waterproof paper container
Inventor: JO CHUNG-MUK
IPC: B31C11/04
Filed: 1988-09-13
Granted: 1993-06-17
Abstract: The water proof paper container is manufactured by heat-melt pressing  the hot-melt adhesive (2) on the surface of the outside thick paper tube (1); making paper tube (3) by drawing many of the thick papers (1); and press-coating the heat-melting synthetic resin (4) on the outer surface of the hot-melt adhesive (2) when transfering the paper tube (3). In the process, after the tube (5) coated with the heat-melting synthetic resin (4) is introduced in the cooler to cool only the resin (4), the tube (5) is introduced in the heat oven to stabilize the resin (4); the tube (5) is introduced to a humidifier to humidify the paper tube (3) in the state of satd. humidity; and the tube (5) is cut to obtain the container(A).
Patent KR-920000958-B1 (KR)
Title: Process for the preparation of improvement adhesive
Inventor: CHA CHONG-WON
IPC: C09J4/00
Filed: 1988-10-26
Granted: 1992-01-31
Abstract: The bonding-promoting agent for a heavy fabric is produced by adding 50-150 mole % NaOH  (10%)  to  halogenated  phenol,  adding formalin to the mixt. at 40-80 deg.C for 5-12 hr to obtain a  high purity 2,6-  dihydroxymethyl-4-halophenol  as  an   intermediate, reacting the intermediate with resorcinol at 100-150 deg.C for 4-8 hr to obtain a  phenol-oligomer,  and  adding  an  addive  to  the oligomer. The agent is used in the mfr.  of  a  heavy  fabric  for belts.
Patent KR-930010052-B1 (KR)
Inventor: AWAYA NOBUYOSHI
IPC: C23C16/18
Filed: 1989-05-22
Granted: 1993-10-14
Abstract: 내용 없음.
Patent KR-920003716-B1 (KR)
Title: Tilt control device of monitor
Inventor: KIM DONG-WOOK
IPC: H04N5/64
Filed: 1989-05-24
Granted: 1992-05-09
Abstract: The apparatus is used for variously adjusting the tilt  angle of monitor,  e.g.  lap-top  computer,   word   processor,   panel television, by using a friction force  between  a  bracket  and  a spring. The tilt adjuster comprises a  first  shaft  (1)/a  second shaft (10) having holes (1',10') on the flat face of one end and a screwed part on the other end; a first ring (2)/a second ring (20) fixedly inserted into the two shafts (1,10) respectively; a  first bracket (3)/a second bracket (30) inserted into the two shafts and having holes (3',30') respectively; a first  spring  (4)/a  second spring (40) adhering to the correspondent bracket; a first stopper (5)/a second stopper (50) fixing the correspondent spring.
Patent KR-960007715-B1 (KR)
Inventor: TAKASHIMA HIROAKI
IPC: C10C3/00
Filed: 1989-06-29
Granted: 1996-06-08
Abstract: 내용 없음.
Patent KR-920004388-B1 (KR)
Title: Interlocking circuit of dual system for master and stand-by system
Inventor: YUN TAE-WOOK
IPC: G06F3/00
Filed: 1989-11-10
Granted: 1992-06-04
Abstract: The main and the standby system checks each  other  to  allow the normal system to control the peripheral equippments using  the switching circuit. The switching controller  (14)  receives  heart beat signals (HB1,GB2) transmitted periodically  when  the  master and the standby system is normal to apply life  signals  (LS1,LS2) to the master and the standby system. The master and  the  standby system checks the normality of the opposite system using the  life signals and transmit the switching control  signals  (SC1,SC2)  to the switching controller.
Patent KR-920006135-B1 (KR)
Title: Hands free unit eliminated echo signals in full duplex system
Inventor: PARK CHAN-HYON
IPC: H04B7/26
Filed: 1989-11-30
Granted: 1992-07-31
Abstract: The full duplex type  hand  free  unit  eliminates  the  echo phenomenon. The unit includes a received  audio  signal  amplifier for detecting signal amplified by a speaker amplifier to  generate a first signal, a phase reversing amplifier  for  reversing  audio signal transmitted from a speaker and picked up by a microphone to generate  a  second  signal,  and  a  differential  amplifier  for amplifying  the  first  and  the  second  signal  differently   to eliminate the echo phenomenon.
Patent KR-960012920-B1 (KR)
Title: Afc circuit
Inventor: SO MYUNG-JIN
IPC: H03L7/00
Filed: 1989-12-20
Granted: 1996-09-25
Abstract: a D-flipflop(F/F1) for receiving the horizontal sync. signal(V2) from a horizontal voltage control oscillator as a D-input and the clock pulse (V3) from the oscillator as a clock signal; an inverter(N1) for loading a flyback pulse to inverters(N2,N3) as an input signal; an inverter(N2) for changing its output according to Q_ of a D-flipflop output if the flyback pulse is low; transistors(Q7,Q10) for controlling transistors(Q8,Q9) of the differential amplifier which controls an output voltage(Verror); and a current mirror to get consistent outputs from the AFC circuit.
Patent KR-930004150-B1 (KR)
Title: Process for the preparation of 2,2'-methylene bis phenol derivatives
Inventor: JO NAM-SUN
IPC: C09K15/08
Filed: 1989-12-29
Granted: 1993-05-21
Abstract: A 2,2'-methylene bisphenol deriv. of formula (I) is produced by reacting a phenol deriv. of formula (II) with an aldehyde cpd. of formula (III) in a water solvent in the presence of an acid catalyst (hydrochloric acid or sulfuric acid) for 3-5  hr, neutralizing the reactant with a sodium  hydroxide  (NaOH), precipitating it with 100 % methanol, and reprecipitating it with 70 % methanol. In the formulas, R1 is H,C1-4 alkyl or phenyl; R2 is C1-4 alkyl; R3 is C1-2 alkyl. The phenolic antioxidant is used as an additive to NR,SBR,NBR,PE,PP and latex.
Patent KR-970003291-B1 (KR)
Inventor: ACKERET PETER
IPC: G03B23/02
Filed: 1988-11-21
Granted: 1997-03-17
Abstract: 내용없음.
Patent KR-940000339-B1 (KR)
Inventor: MOLNAR LASZLO
IPC: F02B3/06
Filed: 1989-04-06
Granted: 1994-01-17
Abstract: 내용 없음.
Patent KR-970003457-B1 (KR)
Title: Novel esters of phenylalkanoic acid
Inventor: IGUCHI SADAHIKO
IPC: A61P9/00
Filed: 1990-05-09
Granted: 1997-03-18
Abstract: The esters of phenylalkanoic acid of the formula: <CHEM> wherein R<1> is 4-10 membered, saturated or unsaturated, mono- or bi-cyclic hetero ring containing as hetero atoms:     (i) one or two nitrogen,   (ii) two or three of nitrogen and sulfur in total, or   (iii) one or two sulfur;  R<2> is hydrogen; or R<1> and R<2>, taken together with a nitrogen to which they are attached, form 4-7 membered, saturated or unsaturated, mono-cyclic hetero ring containing as hetero atoms:     (i) one or two nitrogen, or   (ii) two or three of nitrogen and oxygen in total, the aforementioned hetero rings, represented by R<1> or formed by R<1> and R<2>, taken together with a nitrogen to which they are attached, may be substituted by one substituent selected from C1-4 alkyl and C2-5 acyl;  R<3> each, independently, is hydrogen or C1-4 alkyl; R<4> is hydrogen, halogen, trihalomethyl, C1-4 alkyl, C1-4 alkoxyl C2-5 acyl, cyano, nitro or nitroxy; R<5> each, independently, is hydrogen, C1-4 alkyl or phenyl; or the two R<5>'s, taken together with a carbon to which they are attached, form cyclopentane or cyclohexane; and the pharmaceutically acceptable acid addition salts thereof, have beta 1-adrenergic receptor blocking activity, and therefore, are useful for the prevention of and/or in the treatment of cardiovascular diseases such as angina pectoris, myocardial infarction, congestive heart failure, hypertension, arrhythmia, etc.
Patent KR-930007851-B1 (KR)
Inventor: MORI YOSHIO
IPC: C30B15/02
Filed: 1990-07-03
Granted: 1993-08-20
Abstract: 내용 없음.
Patent KR-920009952-B1 (KR)
Title: Forming method for bead preformed articles of tire
Inventor: KIM KYONG-SU
IPC: B29D30/18
Filed: 1990-09-04
Granted: 1992-11-06
Abstract: Method for manufacturing beads for automobile tire  comprises (1) winding a circular wire to give  a  hexagonal  cross-sectional configuration, (2) installing T-type clamp composed of flat member and vertical member on the upper surface of the  wound  wire,  (3) forming bead by winding over again arround the wound wire in which the clamp is installed, and (4) attaching apex onto  the  bead  by using injection molding. The semifinished bead product is used for reinforcing the strength of tire.
Patent KR-950008374-B1 (KR)
Inventor: PELTON JOHN F
IPC: F27D1/00
Filed: 1990-09-11
Granted: 1995-07-28
Abstract: 내용 없음.
Patent KR-940000247-B1 (KR)
Title: Control circuit for excavator-has programmed control for hydraulic swing-motor and boom cylinder
Inventor: LEE JIN-HAN
IPC: E02F9/20
Filed: 1990-10-31
Granted: 1994-01-12
Abstract: The method selectively controls the turning speed of a swing motor related to the lifting speed of a boom according to the condition of work load when lifting of the boom and turning of the swing motor are simultaneously performed. The apparatus comprises a speed ratio control switch (26) for setting a relative operating speed ratio of the boom cylinder related to turning speed of the swing motor when the swing motor and the boom cylinder are simultaneously operated; electronic proportional control blocks (23a,23b) and skew plate angle adjusting valves (20a,20b) for operating the swing motor and cylinder by receiving a controlling current value. When one in respective maneuvering amounts of an operating lever/pedal (22) is not the maximum value, the apparatus outputs controlling current to the valves (20a,20b), the blocks (23a,23b) in order to operate the motor (10), cylinder (16) at a speed according to the maneuvering amount.
Patent KR-930008250-B1 (KR)
Title: Scattering el element
Inventor: HWANG U-HYON
IPC: H05B33/00
Filed: 1990-11-15
Granted: 1993-08-27
Abstract: The  dispersion-type  electroluminescent  displayer   device comprises a back electrode, an insulating layer, a luminous  layer and a front electrode and then the luminous layer  and  the  front electrode consist of the  first  luminescent  layer  containing  a binder, a solvent and ZnS, Cu  luminescent  material,  the  second luminescent conductive layer containing a binder, a solvent,  ZnS, Cu  luminiscent  material,  Indium  oxide  and  tin   oxide.   The insulating layer has the composition of  titanic  acid  barium,  a solvent  and  a  binder  and  the  binder  is   the   mixture   of cyanoethyl-pulluran and cyanoethyl-polyvinyl clcohol.  The  device has a low production cost for not using the  expesive  transparent electrode film.
Patent KR-0158450-B1 (KR)
Inventor: YABE ISAO
IPC: B29L31/32
Filed: 1990-12-27
Granted: 1999-01-15
Abstract: 본 발명에 따른 성형부품은 축선방향 양단에서 안쪽으로 테이퍼지는 관통구멍을 갖는 피가공재와, 상기 관통구멍의 내부에서 몰드성형되고 축방향 관통구멍을 갖는 수지재로 이루어지며, 이 성형부품을 제조하는 성형금형은 하부다이는 모드성형된 피가공부재를 유지하는 피지부재와 몰드성형된 성형부품을 하부다이에서 방출하는 방출핀을 가지며, 상기 피지부재는 무부하상태에서 상부다이 측으로 변위가능한 스트링성을 부여하는 얇은 벽부와 슬릿을 가짐, 상기 성형부품을 유지하는 유지부와 상기 스프링성을 부여하는 결합부를 가지며, 상기 상부다이는 피지부재의 결합부를 누르는 누름부재와 몰드 성형하기 위한 수지를 공급하는 게이트를 갖는다.
Patent KR-0163018-B1 (KR)
Title: Diffraction grating
Inventor: LEE ROBERT ARTHUR
IPC: G07F7/08
Filed: 1989-12-19
Granted: 1999-05-01
Abstract: PCT No. PCT/AU89/00542 Sec. 371 Date Aug. 19, 1991 Sec. 102(e) Date Aug. 19, 1991 PCT Filed Dec. 19, 1989 PCT Pub. No. WO90/07133 PCT Pub. Date Jun. 28, 1990.A diffraction grating of reflective or transmissive lines is formed by a regular matrix of pixels each containing a respective curvilinear portion of one or more of said lines. When the pixels are illuminated, each generates a two-dimensional optical catastrophe image diffraction pattern whereby the total image diffraction pattern of the grating is optically variable but structurally stable. The invention further provides a diffraction grating of reflective or transmissive lines, comprising a multiplicity of diffraction grating regions which are at least partly separated by multiplicity of grating free regions. Each grating free region has a dimension which is at least large enough to be resolved by the human eye, the total grating free areas not exceeding about 20 to 50% of the total area of the grating. The disclosed diffraction grating is useful as a security device for currency or credit cards.